# Sticky  The RTA Walkthrough and Usage thread. With Video.



## ErinH

This is a spin off of my discussion in my build log here:
http://www.diymobileaudio.com/forum...edan-v-my-full-disclosure-build-tune-log.html



This is intended to lay out the basics of measuring your car audio system using Room EQ Wizard, which can be found here:
http://www.hometheatershack.com/roomeq/


Here goes...




As mentioned above, I use REW for my testing. It's free and pretty easy to use _once you figure out how to use it_. :blush:
I've used every bit of software under the sun. At this point, I've just grown to like REW more than I used to so I've gone back to it for my tuning measurements. For those wanting to see how I'm using REW, here's some info.

*RTA vs Impulse Response Measurement Method:*
One thing to note is there are different meanings of the term, at least how we use it:

RTA - Real Time Analyzer: 
This is simply a real time measurement of what the mic hears. Birds chirping, subs playing... whatever. It records it. 
RTAs are typically used to record pink noise.

Impulse Response:*** 
This can be a form of RTA, depending on how you look at it. An impulse is used typically to measure something before a reflection because you can gate the response. In other words, let's say I want to measure Speaker A. I know that the walls and floors create reflections occurring after 3 milliseconds (ms) that will 'tarnish' the speaker's response as measured by the mic if I let it. To keep this from happening, I look at the impulse response, tell the software to ignore everything after 3ms. Bammo... no more reflections in the measurement. Just Speaker A. 
The impulse response is measured by sweeping a sine wave and capturing the response.


*** I have severely watered down my explanations here and there are caveats; especially when you get in to different window type methods. But for the sake of this post, it's fine. 

The bottom line: In a car, you don't care about impulse gating. You can't really achieve a reflection free zone so there's not much point in trying. -- If you care to disagree please see discussion and reply here (link) so I don't get this one junked up). -- Therefore, we just disregard the whole gating process. That leaves us with a very long impulse response that matches what an RTA would show you, if the signal were the same (ie: pink noise). *IOW, using a very long impulse window (100's of milliseconds) in the car will yield an RTA measurement.*

Why use this impulse method if it essentially nets you the same thing as an RTA measurement? Because RTA measurement only gives you RTA data; SPL vs frequency. You can't get Decay or some of the other things I am looking to get. More data. That's all. I get in to it more below. 



*Cliffs**:*

When measuring a car, there are a couple ways to do it. 
RTA and Impulse are not the same. They each have their own use. However, when the impulse is used without filtering or gating it, it nets you the same result as an RTA.
The benefit of using impulse measurements are you get more data such as decay, group delay, etc.
Like a standard RTA measurement, multiple impulse responses should be taken and averaged together if you want to tune to a car.


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## ErinH

*Re: 8th Gen Honda Civic Sedan v.∞: My full disclosure build and tune log*

I'll discuss how to use either of the two methods listed above. But first off, let's discuss the equipment you need and why you need it.



If doing *RTA only* measurements all you really need is:
A CD with pink noise 
A mic to capture the sound.

If doing *impulse measurements* you need two things:
A way to use the software's signal generator and send that signal to your audio system. This can be done by using a soundcard output and run it in to your audio system auxiliary input. 
A mic is used to capture the sound.


If you are looking to achieve a target curve of any sort you MUST USE A CALIBRATION FILE with the mic.



-------------------------------------


For impulse measurements, this is the gear I'm using. It's pretty simple:

M-Audio Transit. This sends the signal from REW software via a 3.5mm male/female cable to my P99's auxiliary input. I use this because I don't have on-board audio.
Dayton Omnimic USB microphone. It comes with a cal file.


You don't have to use what I have. In fact, you can save a good deal of money by simply using:

Your laptop's built-in headphone output
This Dayton mic (click link here). There are numerous other mic alternatives. This is just an easy one with one USB cable. Plug and chug. And it comes with cal files.


------------------------------------------


You know what you have to have. Why do you have to have it?

The soundcard output is used to send the signal to your auxiliary source. Every headunit should now have one of these. This is how I do my testing most of the time. If it doesn't, you may be limited to using the pure RTA method only.
The mic records the system output. Simple as that.



-----------------------------------------


Here's some pictures of my gear:


M-Audio Transit, using the output via a 3.5mm headphone extension cable.






















Dayton Omnimic USB mic (it has electrical tape because I broke the tip; these things are pretty fragile and I made a goof):














Mic in the headrest:























3.5mm aux cable plugged in to my headunit's aux input on the face panel:


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## ErinH

Woke up early before the little one did to make this video so forgive me if I sound half dead and my video has the shakes. 

This covers only the RTA aspect of using REW. I'll post another video soon showing how to use the impulse measurement method since I feel it's a bit more complete depending on what you want to do and given I'll be posting results from that kind of measurement. 

Let me know if you have questions. 










- Erin


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## ErinH

I'll pick this back up with more discussion of using REW impulse measurements for further capability (such as decay plots for targeting modal issues with Parametric EQ, Time Alignment, etc).


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## ErinH

holder for impulse measurement tutorial


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## Woosey

Subbed!! Thanks! 

Looking forward to read the stuff that's coming..


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## james2266

Woah, so subbed here. I have used REW before but have settled on Tru-RTA lately. After your awesome video, I am thinking I will go back and try REW once again. It's so much easier to take readings and average things than Tru-RTA is. I am really looking forward to learning more about how to use it for the other features which I pretty much have no clue about really. I am especially interested in learning more on how to deal with modal issues as I think I have a nasty one that runs car width right at the front passenger head position at 60-70 Hz. At least I think that is the cause of the dive there from my sub. I am really hoping my new 9 inch midbasses will play that frequency better than my current 6. 8 more days and I should know on that front.


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## james2266

On a more personal note, does anyone know if there is an auxillary in on the Pioneer Z110BT nav system? Or, Erin, you have any idea on how to get it connected to my Mobile PreUSB preamp? I am using this and a Behinger ECM 8000 with xlr cables. I assume this will suffice to do the impulse measurements?


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## ErinH

there's an A/V input on the rear harness, iirc.


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## james2266

bikinpunk said:


> there's an A/V input on the rear harness, iirc.


Hmm, thanks. I will have to look into that one. Have to pull the damned deck again to get at it tho. Sounds like a nice weekend project at some point


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## ErinH

Every time I install a deck with rear AV input, I go ahead and run a cable out to the glovebox. That way I have easy access to it in the future.


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## acidbass303

Great post!


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## Ray21

Very nice walkthrough so far!


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## eddieg

Hi Erin (I hope I am spelling your name correctly :worried: ) 

First of all THANKS for a lovely walk through with the REW soft. 

I've just downloaded beta version 5 build 13 from their forum and I am about to use it with the new MIC from MiniDSP the UMK-1 

UMIK-1 | miniDSP

Up so far I was using True-RTA in conjunction with a RadioShack SPL meter which is actually a standard Phillips MIC (just use the standard calibration file) 

I really wanted a better MIC so this is why I am ordering the UMK-1 and I liked the way you used the average calculation, I also tend to balance left and right and take separate measurements of each side and as well each element on its own tone by tone and then at the end run a pink noise test. 

Of course - I have a bit 1 so I do not go beyond 1/3 octave but as well, for a car, I do not see a need to go beyond that, right? :surprised:

Any way - I would like to know, be tipped by you as for how to use RTA measurements and understand from it if I have any phase or time alinement issues -> I would tend to believe that such issues would be easier to debug/troubleshoot using a scope no?

Thank you very much!

Eddie (please forgive my englaize - I am not a native speaker of this language)


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## Sonus

Thank you!

I'll give REW a shot before I potentially shell out for True RTA.


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## 07azhhr

Thank you Erin for posting this. This should be a big help. I am looking forward to part 2.

A few questions. I noticed your mic was not at what I would think would be ear level so is it just a matter of getting close? Also does the direction matter for example yours is horizontal. Will there be a difference if the mic is angled up say at 30-45 degrees? 

I am also wondering about the mic cal. I have a DBX mic but I do not have a cal file for it. But when I play tones via REW into my hu the response is perfectly matched. For example if I play a 3000hz tone it shows the response at 3000hz. I have tried this at various frequencies and it is always correct but I have not tried all frequencies. If a cal is needed are ther places that I can send it to to get a cal file made?


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## GavGT

Sub'd! I'm especially looking forward to you showing how to get time alignment spot on using impulse response. Cheers


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## ErinH

Lots of good questions. Give me a day or so and I'll try to answer them all. Been working 16 hour shifts lately to get stuff out the door so have only been posting from the phone.


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## Woosey

07azhhr said:


> I am also wondering about the mic cal. I have a DBX mic but I do not have a cal file for it. But when I play tones via REW into my hu the response is perfectly matched. For example if I play a 3000hz tone it shows the response at 3000hz. I have tried this at various frequencies and it is always correct but I have not tried all frequencies. If a cal is needed are ther places that I can send it to to get a cal file made?


I believe the DBX mic's are corrected in the hardware of DBX like the driverack or such.. So the mic should be calibrated for correct FR measuring

If the played freq. is visual on your screen it means is "hears" the correct freq., the calibration is to adjust the sensitivity of the mic so it shows the "actual relative" level


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## charliekwin

This is a great thread Erin. I use REW as well and have a good handle on how to use the software, but the posts you put on the build log have helped to "connect the dots" with respect to what I'm actually _doing_ with it. Great work, and I thank you for it.

One question, though: I noticed in the video that all your measurement snapshots are instantaneous. I don't have it in front of me, so this is going by memory, but there's also an option to do multiple samples (4, 8, 16, etc.) for each measurement. Is there any benefit (or detriment) to doing so?


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## 07azhhr

Woosey said:


> I believe the DBX mic's are corrected in the hardware of DBX like the driverack or such.. So the mic should be calibrated for correct FR measuring
> 
> If the played freq. is visual on your screen it means is "hears" the correct freq., the calibration is to adjust the sensitivity of the mic so it shows the "actual relative" level


Thank you Woosey. I kinda figured the cal was good since it matches on the screen. I just figured I would ask since Erin made sure to emphasize the need for a cal file if going for a target curve. 

I am not sure what you mean by the mic's hardware or driverack. It is just a black version of that Dayton in Erin's video (well atleast it has the same shape but in black lol) ran thru a micmate then on to the laptop.


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## req

awesome stuff erin. i about about to go to tintbox's this weekend to play around and ill snag REW and play around haha.


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## ErinH

eddieg said:


> Hi Erin (I hope I am spelling your name correctly :worried: )
> 
> First of all THANKS for a lovely walk through with the REW soft.
> 
> I've just downloaded beta version 5 build 13 from their forum and I am about to use it with the new MIC from MiniDSP the UMK-1
> 
> UMIK-1 | miniDSP
> 
> Up so far I was using True-RTA in conjunction with a RadioShack SPL meter which is actually a standard Phillips MIC (just use the standard calibration file)
> 
> I really wanted a better MIC so this is why I am ordering the UMK-1 and I liked the way you used the average calculation, I also tend to balance left and right and take separate measurements of each side and as well each element on its own tone by tone and then at the end run a pink noise test.
> 
> Of course - I have a bit 1 so I do not go beyond 1/3 octave but as well, for a car, I do not see a need to go beyond that, right? :surprised:
> 
> Any way - I would like to know, be tipped by you as for how to use RTA measurements and understand from it if I have any phase or time alinement issues -> I would tend to believe that such issues would be easier to debug/troubleshoot using a scope no?
> 
> Thank you very much!
> 
> Eddie (please forgive my englaize - I am not a native speaker of this language)



Use whatever mic you want. ecm8000 works well and you can get them calibrated by Herb @ Cross Spectrum Labs. The Dayton mic I linked will work as will the MiniDSP mic you linked. There are likely numerous others I don't know of or haven't seen. As long as you have the means to use it (ie: you don't need special equipment) and a calibration file is provided, get what you can afford and call it a day. 


As for phase/ta, I'm not really sure how you would use a scope to determine the acoustic alignment at your seated position, relative to each speaker.


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## ErinH

charliekwin said:


> One question, though: I noticed in the video that all your measurement snapshots are instantaneous. I don't have it in front of me, so this is going by memory, but there's also an option to do multiple samples (4, 8, 16, etc.) for each measurement. Is there any benefit (or detriment) to doing so?


Yep. I actually thought of that after I posted the video (on my way to work). I'll have to check this out again. When I used TrueRTA, I use averaging to essentially slow down the response (keep it from jumping so wildly). That number was usually '50'. But, I'll need to go back and see how REW is set up for this. I really don't use it's RTA feature. I only use the impulse function because, frankly, it's easier as odd as it may sound. I don't have to worry about pausing the CD when I am not measuring. I like using the built in generator from the impulse method. (trueRTA has a built in generator for all sorts of samples)


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## ErinH

07azhhr said:


> Thank you Erin for posting this. This should be a big help. I am looking forward to part 2.
> 
> A few questions. I noticed your mic was not at what I would think would be ear level so is it just a matter of getting close? Also does the direction matter for example yours is horizontal. Will there be a difference if the mic is angled up say at 30-45 degrees?
> 
> I am also wondering about the mic cal. I have a DBX mic but I do not have a cal file for it. But when I play tones via REW into my hu the response is perfectly matched. For example if I play a 3000hz tone it shows the response at 3000hz. I have tried this at various frequencies and it is always correct but I have not tried all frequencies. If a cal is needed are ther places that I can send it to to get a cal file made?





Woosey said:


> I believe the DBX mic's are corrected in the hardware of DBX like the driverack or such.. So the mic should be calibrated for correct FR measuring
> 
> If the played freq. is visual on your screen it means is "hears" the correct freq., the calibration is to adjust the sensitivity of the mic so it shows the "actual relative" level





07azhhr said:


> Thank you Woosey. I kinda figured the cal was good since it matches on the screen. I just figured I would ask since Erin made sure to emphasize the need for a cal file if going for a target curve.
> 
> I am not sure what you mean by the mic's hardware or driverack. It is just a black version of that Dayton in Erin's video (well atleast it has the same shape but in black lol) ran thru a micmate then on to the laptop.



Woosey is right.

Think of a calibration file as not one that calibrates the frequency but the _SPL_ measured at a given frequency.

You need this ability if you want to target a curve of any sort. Otherwise, you won't be guaranteed any accuracy.

For example:
Let's say your mic has a natural rise in response above 5khz (most do). If you don't have a calibration file to compensate for this and flatten this out, then this rise will show up in every measurement. In a fictional world, let's say your car measured flat. If your mic has a rise above 5khz, you'd measure an apparent rise above 5khz and you'd start cutting it to flatten it (or whatever you'd do to target X curve). You'd be cutting something that's caused by the mic; not by the car. 

Make sense?


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## 07azhhr

bikinpunk said:


> Woosey is right.
> 
> Think of a calibration file as not one that calibrates the frequency but the _SPL_ measured at a given frequency.
> 
> You need this ability if you want to target a curve of any sort. Otherwise, you won't be guaranteed any accuracy.
> 
> For example:
> Let's say your mic has a natural rise in response above 5khz (most do). If you don't have a calibration file to compensate for this and flatten this out, then this rise will show up in every measurement. In a fictional world, let's say your car measured flat. If your mic has a rise above 5khz, you'd measure an apparent rise above 5khz and you'd start cutting it to flatten it (or whatever you'd do to target X curve). You'd be cutting something that's caused by the mic; not by the car.
> 
> Make sense?


So where do I get it cal'd at? I don't use any driverack or other device with this mic. Also what about the mic placement/direction questions.


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## ErinH

07azhhr said:


> So where do I get it cal'd at? I don't use any driverack or other device with this mic. Also what about the mic placement/direction questions.


it's late (to me) so forgive me for slacking... 


you'd have to send it somewhere. Herb @ Cross Spectrum could probably do it. Personally, for the price of a cal + shipping, I'd just pick up the Dayton USB mic and call it a day.

Placement should be near the head area. The video I posted was an 'on the whim' video. I didn't necessarily pay attention to putting the mic exactly where I would if I were measuring and tuning. I plan to cover the nitty gritty with later posts. For now I just wanted to focus on getting people up and running with REW's RTA feature.

Direction will alter the measurement some but consider the environment. It has a more detrimental affect and really overrides the issue of pointing. I've read about pointing the mic up in a diffuse environment but I've not found it to be extremely helpful either way. However, microphones are like speakers, in that they are directional. So, there is some plausibility in placing and pointing the mic for higher frequency content. That said, at the end of the day, it's kind of a wash. A good head space average will yield good results. 

When tuning via RTA you have to realize that the target curve may or may not result in the best sound you've ever heard. It really depends on a lot of things. But, if you go with this standard method of measurement, you at least get close... and up through about 5khz, you get a really good response. Above 5khz is typically where I have to do the most final shaping by ear to tailor things to my seated position. RTA'ing it gets you at least 70% there (obviously a made up number but you understand what I mean). And once you get experienced and better understand the correlation between measurement and subjective likes/dislikes, you'll get better at closing the gap from 70% to 90%. I still believe a well trained in will always be able to fix flaws a mic cannot, simply due to the environment you're measuring in.


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## ErinH

To anyone who has watched the video, be honest... 

Did it help?
Would you like me to do anything different?


I ask because I can shoot those videos on my iPhone in minutes and upload them from there. It's incredibly easy on me. I do have a Canon pro-sumer GF10 that is flat out stunning in resolution but if I use that, it requires more effort on the back end and takes longer to get the videos published on youtube. In short, it's just a lot more work. If there isn't an advantage from the viewers' point, then I won't bother doing that. If, however, you guys would like better PQ and a more legitimate video set, then I'll go that route.




Secondly, as we go, let's really try to make this a group effort. Post up your own response curves and methods. Videos, too. I'd like to make this a means to help others learn about the use of measurements and possibly walk people through the basics of tuning. Let's make this an interactive tuning thread. Again, I'm not saying you should lean on measurements but I can guarantee that once you get the basics down and we get a couple more posts on here, you'll be using the RTA to garner some really impressive and quick results. And who doesn't like efficiency?


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## charliekwin

bikinpunk said:


> To anyone who has watched the video, be honest...
> 
> Did it help?
> Would you like me to do anything different?
> 
> <snip>
> 
> Secondly, as we go, let's really try to make this a group effort. Post up your own response curves and methods. Videos, too. I'd like to make this a means to help others learn about the use of measurements and possibly walk people through the basics of tuning. Let's make this an interactive tuning thread.


Being honest, it didn't really help *me,* but that probably should come with a caveat that I'm a web developer and am in front of a computer for 10+ hours a day, so I was up and running with REW in just a couple of minutes after some clicking around. For others, though, I can definitely see the benefit and I'm sure it was quite helpful.

That said, I am by no means particularly knowledgeable about tuning. I've been fumbling through it as I go and feel like while I'm doing *okay,* I'm probably leaving 25% of the "essqueues" on the table, so to speak. A tuning thread is something I'd definitely subscribe to. Seeing how other people are going about getting their results would be interesting -- at least I'd get a better idea if I'm doing it the "right" way myself.


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## soul786

Looking forward to following along with this. I'm hoping my install will begin next week so in due time this will be quite useful


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## Oliver

Erin has multiple videos on youtube, 21 of em, I think at this time.

I've enjoyed several.



> I.E. - Mosconi DSP 6to8 Testing
> Mosconi DSP 6to8 Testing Part 2


Nice job Erin !


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## Woosey

bikinpunk said:


> To anyone who has watched the video, be honest...
> 
> Did it help?
> Would you like me to do anything different?
> 
> 
> I ask because I can shoot those videos on my iPhone in minutes and upload them from there. It's incredibly easy on me. I do have a Canon pro-sumer GF10 that is flat out stunning in resolution but if I use that, it requires more effort on the back end and takes longer to get the videos published on youtube. In short, it's just a lot more work. If there isn't an advantage from the viewers' point, then I won't bother doing that. If, however, you guys would like better PQ and a more legitimate video set, then I'll go that route.
> 
> 
> 
> 
> Secondly, as we go, let's really try to make this a group effort. Post up your own response curves and methods. Videos, too. I'd like to make this a means to help others learn about the use of measurements and possibly walk people through the basics of tuning. Let's make this an interactive tuning thread. Again, I'm not saying you should lean on measurements but I can guarantee that once you get the basics down and we get a couple more posts on here, you'll be using the RTA to garner some really impressive and quick results. And who doesn't like efficiency?


Still working with HOLM, but i hope this weekend I have my measuring "cart" ready ( basically a tool cart where i'm building a pc in an a lcd tv on top with mic and soundcard in the drawers haha... ) and then I will try using this software..


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## voyagerx

bikinpunk said:


> To anyone who has watched the video, be honest...
> 
> Did it help?
> Would you like me to do anything different?
> 
> 
> I ask because I can shoot those videos on my iPhone in minutes and upload them from there. It's incredibly easy on me. I do have a Canon pro-sumer GF10 that is flat out stunning in resolution but if I use that, it requires more effort on the back end and takes longer to get the videos published on youtube. In short, it's just a lot more work. If there isn't an advantage from the viewers' point, then I won't bother doing that. If, however, you guys would like better PQ and a more legitimate video set, then I'll go that route.
> 
> 
> 
> 
> Secondly, as we go, let's really try to make this a group effort. Post up your own response curves and methods. Videos, too. I'd like to make this a means to help others learn about the use of measurements and possibly walk people through the basics of tuning. Let's make this an interactive tuning thread. Again, I'm not saying you should lean on measurements but I can guarantee that once you get the basics down and we get a couple more posts on here, you'll be using the RTA to garner some really impressive and quick results. And who doesn't like efficiency?


It helped me a little, as I have never used REW, and have played a little with TrueRTA. What would help me the most is a discussion on what to look for and what to change, as well as things that can't be changed.

I've used TrueRTA in the past to get a relative flat curve and it sounded horrible. I also found areas that I could not EQ, even with different speakers, installation techniques, etc. I'd imagine this was vehicle specific, etc. I think a video/discussion of you thinking out loud and tuning as you use REW, and come across things like this would be extremely helpful.

What you have posted is great and will help many people get started with the software and the use of an RTA to tune their car. What would be incredibly helpful to me would be now that I have it running, what do I look for? What do I do? I realize this is mainly subjective, but your opinion (based obviously on your expertise), would be greatly appreciated.

And finally....thanks for taking the time to do this!


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## DJTrevLuv

The video was a big help for me. I bought the “$100 RTA” a couple years ago but didn’t really use it as much as I thought I would because I didn’t really understand how the program worked. I look forward to trying REW.

Keep the videos coming and thanks for sharing all of your audio knowledge!

Trevor


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## acidbass303

bikinpunk said:


> To anyone who has watched the video, be honest...
> 
> Did it help?
> Would you like me to do anything different?



Definitely helped me and I am sure many many others like me would benefit a lot from it. MOAR please


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## Wesayso

Can you do an impulse response in the car? just curious.


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## goodstuff

This helped. Thanks. I've had the omni mic system for a while now and not done anything with it/ This should motivate me. 

What are your thoughts on sitting in the seat while you measure?
How would it change the results vs not being in the car?


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## ErinH

Wesayso said:


> Can you do an impulse response in the car? just curious.


yes. but your question has multiple meanings. So, can you be more precise as to what you're asking?



goodstuff said:


> This helped. Thanks. I've had the omni mic system for a while now and not done anything with it/ This should motivate me.
> 
> What are your thoughts on sitting in the seat while you measure?
> How would it change the results vs not being in the car?


I've measured in the car and out of the car. This is the kind of thing that really needs to be experimented with by the user to see how it works. See my response above regarding mic placement/direction.


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## ErinH

voyagerx said:


> It helped me a little, as I have never used REW, and have played a little with TrueRTA. What would help me the most is a discussion on what to look for and what to change, as well as things that can't be changed.
> 
> I've used TrueRTA in the past to get a relative flat curve and it sounded horrible. I also found areas that I could not EQ, even with different speakers, installation techniques, etc. I'd imagine this was vehicle specific, etc. I think a video/discussion of you thinking out loud and tuning as you use REW, and come across things like this would be extremely helpful.
> 
> What you have posted is great and will help many people get started with the software and the use of an RTA to tune their car.  What would be incredibly helpful to me would be now that I have it running, what do I look for? What do I do? I realize this is mainly subjective, but your opinion (based obviously on your expertise), would be greatly appreciated.
> 
> And finally....thanks for taking the time to do this!



Yes. At some point this thread will start to get in to more of the explanation of what you're seeing and ways to attack it. I fully intend to film my process at some point with the caveat that it's not a one size fits all. But I need to try to get everyone who might be interested in that up to speed with knowing how to measure first. 

I'd like to have a friend film this for me sometime but that may not be feasible if time is of the essence.


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## Justin Zazzi

I've used REW a bit before seeing this thread and did not know about the averaging method you used with constant pink noise playing. I have instead used the sweep method by pressing the "measure" button, and the program (I believe) will average how ever many sweeps I choose to do.

Do you know if there is a benefit to your method vs using the built-in "measure" method? I do not think your method can view the more detailed time-domain information like impulse response and waterfall graphs, right? Can your method make use of the auto EQ functions or not? From what I remember reading, it relies heavily on time-domain information for making the best suggestions.

-J


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## Wesayso

bikinpunk said:


> yes. but your question has multiple meanings. So, can you be more precise as to what you're asking?


While I asked about impulse response, what I wanted to know is impulse and step response. Just trying to figure out if John Dunlavy had a point with his opinion on impulse and step response. See: Loudspeaker designer John Dunlavy: By the Numbers... Page 2 | Stereophile.com



Dunlavy said:


> I think a lot of people, especially those who don't listen to live music a great deal of the time, are not really concerned with whether the music they're reproducing matches the live performance. They're after more of an effect. And so the accuracy of their systems doesn't need to meet the same criteria that would have to be met if one wanted to make a loudspeaker where you couldn't hear the difference between it and the original performance. And that's what we're into. Certainly there's plenty of room in the marketplace for what might be called "good-sounding" speakers, "sweet-sounding" speakers, "nice-sounding" speakers, "pretty-sounding" speakers—everybody hears differently. On the other hand, there are a lot of people who regularly attend live concerts who want accurate reproduction.
> 
> Designing with higher-order crossover networks greatly simplifies the blending task between drivers. But what most people don't realize is that one of the really great difficulties in designing with higher-order crossovers is that they store energy. That's very visible when you look at the impulse response of a speaker that has a second-, third-, or fourth-order network. And the step response also looks terrible.
> 
> Of all of the measurements that we take that come more close to predicting, or most close to predicting how a speaker is going to emulate a properly recorded live performance, it's step response. Everything is implicit if you know how to interpret a step response...if my life depended upon my describing what I thought a speaker was going to sound like, all other factors being equal, I would choose step response. And feel very confident that I would be spot-on.


There's also a paper from Dunlavy going further into what he thought is important in speaker design. I'm just trying to connect the dots between your power response case, backed up by views from Linkwitz, Geddes and Tool etc. and the views from Dunlavy, Vandersteen, Thiel... what if you get both power response and timing right? Would that work even better? Is it possible?

Here's Dunlavy's digest take on power response:


Atkinson and Dunlavy said:


> Atkinson: You talk about accuracy, but so far you've just defined that in terms of the impulse or step response on the speaker's intended listening axis. What about the speaker's power output into the room? That surely has as much effect on the perceived balance as the on-axis performance?
> 
> Dunlavy: That's certainly true. We pay an awful lot of attention to the power response of the speaker into the room. Because that's one of the things that permits us to determine whether we're listening to a live instrument, let's say with our eyes closed, in a typical room. We hear two things. We hear the direct sound of the instrument, but we also hear all of the reflected sound, the reflections off of all of the boundaries of the room. And the ratio between that direct sound as a function of frequency and the reflected sound determines to our ears whether we perceive it as being realistic or not.
> 
> We spent a lot of time and money, over 20 years ago, doing measurements in an anechoic chamber of the three-dimensional response patterns of 17 different musical instruments, including drums, string bass, cello—we measured a bassoon, a clarinet, a violin. If a loudspeaker's directivity pattern is incapable of emulating the aggregate, the average of the patterns of all of these musical instruments, it will never sound "accurate."
> 
> Most musical instruments are almost omnidirectional at low frequencies, as are most loudspeakers, so it doesn't pose a problem. But as you go higher in frequency, to between 100Hz and 300Hz, if you don't get the beam-width of the speaker correct in this range—and by "correct" I mean that it simulates most live instruments—it will add warmth, unnatural warmth, to the sound of voices and musical instruments. It'll make the average male voice sound too chesty, very unnatural. As you go up higher in frequency, if you have a tweeter that radiates too broad a pattern...it's going to produce shrieky sounds, it's going to sound too zippy. I think everyone's experienced that, especially from inexpensive speakers that have a rising high end.
> 
> So a good designer certainly knows that he has to pay a lot of attention to the polar response of a loudspeaker.


What does the step response look like now with 12 dB slopes and what does it look like if you used 6 dB slopes. (obviously louder volumes would be dangerous for the tweeter).

Just trying to learn, no hidden agenda here. I can relate to both theories, just trying to figure out what works. Speakers like Magico get rave reviews and they use eliptical slopes, kinda like brick walls. So who is right, or is there even such a thing as beeing right? What theory comes closer to the real thing, that beeing the music that was recorded? I know it all sounds different compared to each other. Or am I not able to hear that? I was intregued by your test with 4th order and second order networks. If this is not the place for this question I understand. But if we can test the impulse response and step response we might get closer to our goals. I wouldn't know where and how to start, what software to use etc. but I'm sure that can be found somewhere. It's much to cold over here to do it myself in my Garage at this time but I thought it might fit in and make us learn something.

I looked at a lot of speaker reviews on stereophile to see their power response and the subjective opinion on them, just to learn. There were quite a few with good power response that showed a step response that was way different from the ideal step response Dunlavy descibes. I also focussed on resonances from the box itself, trying to figure out what combination would give us the best compromise. That last point is something Magico has high on their list of priorities. And that is something we deal with in the car as well. The things Highly did with his sub construction to decouple it from the car comes to mind.
I decoupled my sealed sub from the car the best I could and noticed improved low bass that seems to float giving more depth. It caused less resonances that way.


----------



## ErinH

Jazzi said:


> I've used REW a bit before seeing this thread and did not know about the averaging method you used with constant pink noise playing. I have instead used the sweep method by pressing the "measure" button, and the program (I believe) will average how ever many sweeps I choose to do.
> 
> Do you know if there is a benefit to your method vs using the built-in "measure" method? I do not think your method can view the more detailed time-domain information like impulse response and waterfall graphs, right? Can your method make use of the auto EQ functions or not? From what I remember reading, it relies heavily on time-domain information for making the best suggestions.
> 
> -J


Please see my first and second posts. I discuss there the two main methods of measurement which should answer your questions. Bottom line: the RTA method isn't as powerful as the impulse method which I will focus on the most. This is what you're talking about, I'm pretty sure.


----------



## ErinH

Wesayso said:


> While I asked about impulse response, what I wanted to know is impulse and step response. Just trying to figure out if John Dunlavy had a point with his opinion on impulse and step response. See: [
> 
> Snipped/.




This question is much better suited outside of this particular thread where we can discuss it in more detail. I think it's a really good topic but probably too in depth for here and I don't want to bog this thread down. Seriously, I want to discuss it so feel free to start a new thread.


----------



## Wesayso

bikinpunk said:


> This question is much better suited outside of this particular thread where we can discuss it in more detail. I think it's a really good topic but probably too in depth for here and I don't want to bog this thread down. Seriously, I want to discuss it so feel free to start a new thread.


I agree, here it is: http://www.diymobileaudio.com/forum/technical-advanced-car-audio-discussion/144532-what-key-elements-reproducing-audio-power-responce-time-coherence.html


----------



## charliekwin

I hope Erin was serious about making this an interactive thread, because I'm volunteering to contribute. As I said earlier, before installing this system, I'd never done any kind of active tuning. I think I'm getting it, but am fully prepared to embarrass myself here!

Erin's new build log helped illuminate some of the finer points of the RTA for me a little bit and I also came across frequency response graphs for the Virtus 603s. After seeing both, I decided to bust open the DSP this weekend and redo some things.

I started by changing the crossover points. Without getting too longwinded, the midranges were previously bandpassed at ~600 and 5000. They're now at ~500 and 3000. I also removed all the EQ and re-ran the RTA to see what needed attention. There were a few particularly egregious peaks that I pulled down, but equalization is rather minimal. At least, I think it is. I had a lot more going on before, but don't have anything else to compare to. I hope that's the point of the thread 

Here are the results from REW. The average of 4 measurements of 16 samples. This is stereo...forgot to save the individual L&R graphs. Here's the 1/3 octave smoothing. Not a bad start?









Here's 1/12, which reveals some of the trouble spots.









I have a few peaks that definitely need to be knocked down. 110, 750 and 1700 are probably up first. The woofer as a whole might need to be backed down a bit as well.

I also threw in the IASCA tools disc and gave that a listen and a couple of the spectral tests jumped out as problem areas. I noted those and, happily, they mostly matched up with the uglier RTA sections. So that was instructive.

Here's shots of each driver setting in the P-DSP:

























































I'll leave it alone for a couple days and then try a bit more tweaking. If there's any suggestions out there from people who actually know what they're doing (instead of just faking it like me!), I'd love to hear them.


----------



## ErinH

awesome feedback and contribution! this is the kind of stuff I want this thread to contain. even if it's something that didn't work, the 'journal' of sorts really helps others out.

thanks,
Erin


----------



## Justin Zazzi

bikinpunk said:


> Please see my first and second posts. I discuss there the two main methods of measurement which should answer your questions. Bottom line: the RTA method isn't as powerful as the impulse method which I will focus on the most. This is what you're talking about, I'm pretty sure.


I think we're talking about the same thing. I was mostly confused why you went through the effort of pointing out how the impulse method is more powerful, but then spent all your effort discussing the rta method.

Either way, I look forward to the discussion here!

-J


----------



## ErinH

I didn't spend "all my effort" on the RTA method. 
I just wanted to highlight it for those who can't do the impulse method (ie: don't have an aux input to input signal in to their system).

I'll cover the impulse stuff soon. I've just got other stuff on my plate to finish up.


----------



## Hanatsu

This is a great feature as well:



















These two show the same thing a little differently. They can be used to observe modes and energy storage (for example). As you can see around 40Hz there some weird stuff happening, the SPL are not decaying with time as it does at other frequencies.


----------



## ErinH

Hanatsu said:


> This is a great feature as well:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> These two show the same thing a little differently. They can be used to observe modes and energy storage (for example). As you can see around 40Hz there some weird stuff happening, the SPL are not decaying with time as it does at other frequencies.


I've got a pretty good example of this in my build log and plan to go further with it once I get my new DSP installed (it has PEQ). This is the good stuff that I mentioned in my OP and can only be measured via impulse method.


----------



## james2266

I can't possibly be the only one with this potentially stupid question but... How does such a decay plot tell me where I need to do some work with sound deadening?


----------



## ErinH

This is from my build log. It's a good example of how the impulse method gives you more insight in to your system. 

Again, I'll document how to do this via video at some point soon. I'm just trying to get through some other stuff first. 



bikinpunk said:


> After doing that, it's time to get back to the driver's seat and start measuring response from there.
> 
> One might choose to measure the system response as a whole and use the RTA that way, but it's a bit more conclusive to study each individual side's response (left and right side response). This is easy to do: just pan the balance to one extreme or the other and measure. When you do, you'll have the left side stereo contribution vs the right side stereo contribution.
> 
> So, here we have just that. Panned left is Green. Panned right is Purple. No EQ. 1/12 octave (to show the crappy little modal stuff that 1/3 doesn't get).
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> What this really shows me is that both the left and right side stereo contributions have their own problems. Notice that slight dip around 85hz at the driver's seat? Everyone has that problem to some degree because of their proximity to the speaker. Bottom line, that dip is a cancellation mode. There's nothing I can do to fix it, either. I can EQ it up but what will happen is I'll just keep applying more power to the driver's side midbass, causing distortion to ramp up and likely audible issues due to it. And while it may raise the response there, it'll also make resonant modes more problematic. The potential to damage the driver certainly exists. There's just not a whole lot you can do here. Some EQ will help but if you try to flatten it out by adding 4-5dB of EQ you'll alter the response curve in a negative way and create other issues. The only way to really fix a problem like this is to move from the boundary causing the null or move your driver(s). So, I just ignore this. Truth be told, it's not a real big issue when listening. And this is just one more example of why you should not rely entirely on the RTA. You should always use your own ears to accompany what you've measured. If you have a narrow dip it's not as audible as a broad dip; the same goes for a bump in response.
> 
> So, yea... I'm not going to sweat that dip at 85hz measured at the driver's seat. It's a lost cause and serious waste of time to try to flatten it. I just want to smooth it so a bit of EQ here and there will help that.
> 
> 
> Now, look at the rest of the curves. That dip around 85hz on the left side is exacerbated by the rise in response around 125hz. After looking at the decay plot, measured by REW, I see why...
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> This is a plot of response over time, laid out in 2-D. The highest levels are closer to the initial response time. As the graphs change color below one another, you're seeing 'slices' of the response in time. Look at the legend. It shows time in milliseconds (ms). Each color corresponds to a time slice/section. Ideally want to see is each slice dying out quickly and contributing less and less to the results. However, what you actually get is modal issues showing up... these are the ones that linger around and don't taper off smoothly. Looking at these plots is pretty subjective and really should be used with some subjective listening as well. But, I'll give some thoughts on how I look at it...
> 
> The 125hz issue showing up in the left side FR plot... now look at the decay plot around that frequency. See how the darker blue looks pretty mountainous here with a dominant spike at about 125hz? Notice how the shade of blue just before this has the same spike? This is an indication of a modal issue. Luckily, I have an EQ band right here... I can cut it some. The problem, however, is cutting here also affects the tonality in other ways. With a parametric EQ, I can set a narrow Q and cut accordingly. But, I don't have that, so I have to cut here with the 31 band EQ. Here is the result when I use the EQ to cut 125hz by 3dB:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Not surprisingly, there was no miraculous alteration of the issue. It cut the problem by 3dB as it should but it didn't make the ringing issue go away. It did lessen the effect some. This is where subjective listening will tell you if it helped. The drawback here is you also changed the tonality of the system because the Q (bandwidth) of the 1/3 octave equalizer is so wide; it doesn't just change a single frequency.
> 
> This site is a great reference for what frequencies influence what you hear and can help you understand the tradeoffs you deal with when changing EQ bands to fix problem areas:
> Interactive Frequency Chart - Independent Recording Network
> 
> 
> 
> There are other frequencies that do the same thing. 100hz definitely lingers. 83hz lingers as well. Remember earlier my bit about bumping up 80hz to fill in that hole caused by the left side response? What do you think happens when you do that regarding the modal issues? It's a nasty problem. What you really need is a way to target specific modes without negatively affecting the other areas you want to fix with standard EQ methods. This would be a really good intro in to why parametric EQs are so good. So, I'll stop here and pick up there when I have the chance.
> 
> Keep in mind I've only really discussed one component of the system response here. The right side response has it's own problems as well.
> 
> 
> *Cliffs:*
> 
> Room modes suck. They muddy up system response as a whole.
> When the midbass is muddy it overshadows everything good about the rest of the system.
> All cars have modal issues smack in the midbass area.
> Standard EQ can only go so far. But when properly used, EQ can help tame some of the modes which results in a much more tonally pleasing car stereo and much better blending with sub on the low end and midrange on the high end.
> 
> /
> 
> 
> 
> Hope this stuff helps you guys out!
> 
> 
> - Erin


----------



## mooch91

Hey Erin,

Some thoughts and questions on video #1 (basic RTA).

Your technique for obtaining a smoothed and averaged plot is to take multiple individual measurements at the full spectrum, smooth them to an octave width, and then average them together over a few separate steps.

I've always had the software (True RTA or REW) do the smoothing and averaging _while taking the data_. Basically, I've set the mode in REW to measure directly in 1/3 octaves and set the averages to a high number. Then, while the pink noise is playing, I move the mic slowly around the headrest to get a continuous average until the curve stabilizes (30-60 seconds). I've found it to be very reproducible.

Does the more manual method you've described offer any advantage to this? I've always liked my approach because I can get my output in one step versus multiple steps otherwise. When I'm tweaking the EQ for small changes, I can see my results relatively quickly this way without having to do a lot of software manipulation.

Thanks and great vid! I'm looking forward to part 2 because I think I've reached my limits with basic RTA. I've gotten a pretty good output with it, but there are just some things I cannot fix with the data I've got.


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## ErinH

They're similar, if not all but the same. 

I honestly forgot to use the averaging method here. I typically set averages to high and measure multiple instances. The reason I do this outside the car method is simply that I haven't found an appreciable difference worth cramming myself in to the back seat. Additionally, I'd have to use my NetBook to be in the car. I can't do the sweeping average method with the PC simply because I'd have to get back out. 

I will say I have measured all sorts if ways. I used to use omnimic with me sitting in the car. I still do sometimes. I really wanted the videos to be simplistic in nature. At least up through the point where people who are new get a handle on it. I don't want to scare folks always with all the crazy ways you can do it. Not yet.


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## ErinH

If the null is truly a cancellation null then I won't worry about it. I'll tackle that when I get there. 

Boosts will be attacked via PEQ if they are too large to treat by other methods. Which, they most likely are. It would take a good deal of space consumption for mechanical bass absorption (ie: bass trap, or helmholtz absorber).



cajunner said:


> Now you are able to correlate your subjective opinion with an objective graph, is this what you mean by full disclosure in your build thread?


Yes. That's exactly what I meant. I'll try to document everything I can. I'll also post it here, if it fits.


----------



## charliekwin

After playing around yesterday, I had the feeling I was getting closer. Kid's upstairs taking a nap (valuable time!), so I figured I'd see what I could do.

First up, the left and right channels individually (no sub), before making any changes today:










And the stereo plot:









There were a couple areas I knew I wanted to tackle in particular, so I started going nuts with the EQ.

By the time the laptop battery died and the kidlet woke up, I got the plots to look like this:

















Which is better, but the whole range between 160-500 especially is too loud and after listening for a while, I wasn't convinced I made much (if any) improvement.

One thing I've wondered about for a while is EQ. You don't see people post their settings, and there are a lot of comments out there that imply that with good equipment installed well, there shouldn't be a need for "much" (whatever that means) equalization. Then there's also the fact that when you only have a hammer, everything looks like a nail.

By the time I finished, my woofer and midrange EQs looked like this:

















I'm honestly not sure if that's a lot, a little, or just average. I thought (and think) it's more towards the high end. The muddied up sound also made me think I was just making things worse by screwing with the EQ too much.


Fast forward a couple hours, and I go give it one more shot, focusing especially on the mid-bass. Even _more_ futzing with the EQ (nail, meet hammer...) and I get the RTA plots to this:

















And I'm proud-ish of myself for that, but the DSP settings look even wonkier, so I have low hopes for this round of changes:

















Sweet baby Jesus on toast! What. a. difference. Everything is better. Everything. It's like those Claritin commercials when they do the wipe effect and everything's clear and colorful. _Finally_ I made some real progress. I still don't know if I'm doing any of this right or not, but damn am I ready for a celebration beer!


----------



## Hanatsu

Looks good


----------



## astrochex

subscribed.

This is an excellent thread.


----------



## Sonus

Hmm... had some time to lay with REW today after my Dayton UMM6 USB mic arrived.

However I can't seem to get rid of spikes at 1000Hz from 2kHz and up?

The noise measured is only background noise, but it is the same with different background noise

I've downloaded the cal file from daytonaudio.com and loaded it into REW.

EDIT: measured my Bose Quietcomfort15 headset with pink noise


----------



## Hanatsu

Sonus said:


> Hmm... had some time to lay with REW today after my Dayton UMM6 USB mic arrived.
> 
> However I can't seem to get rid of spikes at 1000Hz from 2kHz and up?
> 
> The noise measured is only background noise, but it is the same with different background noise
> 
> I've downloaded the cal file from daytonaudio.com and loaded it into REW.
> 
> EDIT: measured my Bose Quietcomfort15 headset with pink noise


First picture looks like soundcard feedback issues. Run REW in loopback first and check your soundcard. If you got a Creative card, you might have issues in Win7 with the flexijack ****.


----------



## Sonus

I'm using a Samsung NP530U3B laptop runnning W7. However it hasn't got a seperat line out or mic in, but a combined jack with in and out on the same jack 

So I'd need to make up a "shorting jack" to loop the line out into the mic in to calibrate the "sound card"?


----------



## Hanatsu

Sonus said:


> I'm using a Samsung NP530U3B laptop runnning W7. However it hasn't got a seperat line out or mic in, but a combined jack with in and out on the same jack
> 
> So I'd need to make up a "shorting jack" to loop the line out into the mic in to calibrate the "sound card"?


Uuh.. hate those combo jacks.

You should measure some speaker with a known frequency response in nearfield. And see if you get a reasonable flat response, otherwise you might have issues. Make sure the "listen on the device" is deactivated in the mic settings within the sound manager in Win7.


----------



## Sonus

I've got an old Bose Quiet Comfort 15 lead with mic that is broken. I might modify that so that the left and right line out is looped back into the mic line in. Just hope the wires are large enough to work with 

That should make it possible to calibrate the sound card I guess?


----------



## Hanatsu

Sonus said:


> I've got an old Bose Quiet Comfort 15 lead with mic that is broken. I might modify that so that the left and right line out is looped back into the mic line in. Just hope the wires are large enough to work with
> 
> That should make it possible to calibrate the sound card I guess?


Output on left channel and input on right channel (or vice versa). Should be possible, yes.


----------



## mooch91

Erin,
Uncorrelated (stereo) or correlated (mono) pink noise? I always notice some dramatic differences at frequencies in the upper midbass, lower midrange region depending on which I use. Never knew which result was "right".
Thanks again.


----------



## eddieg

charliekwin said:


> After playing around yesterday, I had the feeling I was getting closer. Kid's upstairs taking a nap (valuable time!), so I figured I'd see what I could do.
> 
> First up, the left and right channels individually (no sub), before making any changes today:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> And the stereo plot:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> There were a couple areas I knew I wanted to tackle in particular, so I started going nuts with the EQ.
> 
> By the time the laptop battery died and the kidlet woke up, I got the plots to look like this:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Which is better, but the whole range between 160-500 especially is too loud and after listening for a while, I wasn't convinced I made much (if any) improvement.
> 
> One thing I've wondered about for a while is EQ. You don't see people post their settings, and there are a lot of comments out there that imply that with good equipment installed well, there shouldn't be a need for "much" (whatever that means) equalization. Then there's also the fact that when you only have a hammer, everything looks like a nail.
> 
> By the time I finished, my woofer and midrange EQs looked like this:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> I'm honestly not sure if that's a lot, a little, or just average. I thought (and think) it's more towards the high end. The muddied up sound also made me think I was just making things worse by screwing with the EQ too much.
> 
> 
> Fast forward a couple hours, and I go give it one more shot, focusing especially on the mid-bass. Even _more_ futzing with the EQ (nail, meet hammer...) and I get the RTA plots to this:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> And I'm proud-ish of myself for that, but the DSP settings look even wonkier, so I have low hopes for this round of changes:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Sweet baby Jesus on toast! What. a. difference. Everything is better. Everything. It's like those Claritin commercials when they do the wipe effect and everything's clear and colorful. _Finally_ I made some real progress. I still don't know if I'm doing any of this right or not, but damn am I ready for a celebration beer!


Hey Charli, 

I liked this part of your message: "One thing I've wondered about for a while is EQ. You don't see people post their settings, and there are a lot of comments out there that imply that with good equipment installed well, there shouldn't be a need for "much" (whatever that means) equalization. Then there's also the fact that when you only have a hammer, everything looks like a nail." 

The reason for buying high end equipment - at least in my point of view - is that you buy a product in which the manufactur spent a lot of time for R&D and it gets you the results with the smallest ammount of efforts to get it sound right.

Today for HU's and Amplifiers - I don't see the need to spend so much money as most HU's today, even the most simple and cheap ones (for example 2din multimedia untis that are carpc based - excellent RCA signal, very clean) and as well you can get extreemly strong amps with very low disturtion at a funny cost comparing to good few years behind.

BUT! when it comes to speakers and install -> this is where it all goes CRAP 

And this is exactly where high-end speakers would be better sounding on basic installs and basic tune up. 

At this point the DSP with all its features - especially the equalizer comes in to picture and does its "magic" - if you have cheap speakers which are detailed enough and percise, with a good work done on your install and DSP (eq) you can get amazing results, most probably, with high end speaker - you will have much easier work getting there.

These are my 0.5NIS :laugh:


----------



## Hanatsu

mooch91 said:


> Erin,
> Uncorrelated (stereo) or correlated (mono) pink noise? I always notice some dramatic differences at frequencies in the upper midbass, lower midrange region depending on which I use. Never knew which result was "right".
> Thanks again.


Use uncorrelated (stereo) for FR measurements.

Sent from my Samsung Galaxy 3 via Tapatalk.


----------



## req

eddieg said:


> quoted stuff


please dont quote images like that. it really clutters up threads.




i should have taken some shots of what i did with tintworx's sutff. it took a while to get use to the quirks in the mosconi 6to8... im not a huge fan of the software. backing out and going back into the other menus to mute and what not is really annoying after a while... but it is powerful. the fact that there are different eq types for each pair of channels kind of sucks though.

this is all i took with his car










the video was helpful because the menus are kind of located in wonky spots - so yea. i would say get a tripod or something to mount your iphone to in order to make it less weird - or just download some screen-cap video software and do it that way.

once i get moved into my house and i can put my car in the garage and do that sort of thing i should be able to be more involved in this thread though


----------



## Hanatsu

Anyone know if it's possible to set T/A with RoomEQ somehow? (Impulse response always end up at "0" ms.) Need to see the relative time.

Haven't figured it out. Quite easy to do with HOLMimpulse or ARTA.


----------



## Woosey

Hanatsu said:


> Anyone know if it's possible to set T/A with RoomEQ somehow? (Impulse response always end up at "0" ms.) Need to see the relative time.
> 
> Haven't figured it out. Quite easy to do with HOLMimpulse or ARTA.


Not sure, but isn't this possible with a reference measurement at the same time? Ref comes first hardwired from pre-out or amp or pc and marks the 0.0ms, then the acoustical measurement comes later.

I know holm is inaccurate sometimes as you set to zero so a measurement with hardwired reference is most accurate in my opinion.

If you just mean with a click on a button : I don't know


----------



## dmazyn

Well I did my first RTA using REW on the new system. I just got everything installed and running last weekend so have had no time to do any tuning but wanted to see what the response was from the initial setup of the 3sixty.3.


----------



## charliekwin

Hanatsu said:


> Anyone know if it's possible to set T/A with RoomEQ somehow? (Impulse response always end up at "0" ms.) Need to see the relative time.
> 
> Haven't figured it out. Quite easy to do with HOLMimpulse or ARTA.


Any chance of posting a how-to on doing it with ARTA? I tried it, but I always got an identical delay for every driver. Figured it was an issue with the hardware and/or how I set it up and couldn't find much help online. Went with a tape measure instead.


----------



## masswork

Hanatsu said:


> Anyone know if it's possible to set T/A with RoomEQ somehow? (Impulse response always end up at "0" ms.) Need to see the relative time.
> 
> Haven't figured it out. Quite easy to do with HOLMimpulse or ARTA.


Try this:
preferences -> analysis -> uncheck set t=0 at IR peak.

Agree, ARTA is easier 
Love the grid in ARTA.


----------



## masswork

charliekwin said:


> Any chance of posting a how-to on doing it with ARTA? I tried it, but I always got an identical delay for every driver. Figured it was an issue with the hardware and/or how I set it up and couldn't find much help online. Went with a tape measure instead.


If you see the same peak at around 5-6ms for all measurements, look for another peak after that one. Usually after 8ms or more. That's the signal from speaker.

See the pic:


----------



## ErinH

You may also need to make sure you're doing a loopback measurement so your soundcard can reference the signal going out in time vs when it's actually sent out of the soundcard. This tells the system the internal delay.


----------



## mojozoom

Erin,

I'm going to play the straight man here -

Is there a clear way to identify the frequencies that we shouldn't be trying to boost, using the tools provided in REW?

This would be under the assumption that the measurements are taken one channel at a time, so any dips seen in the response aren't due to phase cancellation from the other channel.

Thanks!


----------



## eddieg

I've downloaded ARTA - it is nice that they let you work on demo mode as much as you want.

I simply take snapshots instead of save - I think I understood how to tune the time correction using this tool. 

Very very nice! THANKS!

For what that I see I need to calculate the "gate" and remove from it the internal feedback time than find the differences between each speaker left and right and each speaker on same side to the other ones and then the difference between the sub result to the avarage calculation of both midbasses. 

That is on one leg and I am not sure yet if it is correct but I do believe I am on the correct road?

Thank you again!

Eddie


----------



## Justin Zazzi

mojozoom said:


> Erin,
> 
> I'm going to play the straight man here -
> 
> Is there a clear way to identify the frequencies that we shouldn't be trying to boost, using the tools provided in REW?
> 
> This would be under the assumption that the measurements are taken one channel at a time, so any dips seen in the response aren't due to phase cancellation from the other channel.
> 
> Thanks!


Minimum Phase (article from the author of REW)

I admit I had to read through this a few times to understand what is going on. The thing that was not immediately obvious is there are TWO examples on that page.

This method cannot be done using Erin's method in the video. You want to instead make a measurement using the "measure" function within REW where it generates and records a swept sine wave. Then on the _Group Delay_ (GD) graph page, click on _Controls_, then click on _Generate Minimum Phase_. A new plot will be generated labeled _Excess Group Delay_.

Based on my understanding of the article I linked above, whenever the excess group delay is significantly above zero, the affected range of frequencies is no longer in a "minimum phase" relationship and will not respond to a boost from EQ like normal.

-J


----------



## Justin Zazzi

http://www.diymobileaudio.com/forum...sion/92336-up-front-bass-just-illusion-5.html

For time alignment, I find the above thread to be very insightful (lycan and Andy's posts in particular from about post #100 onwards). Using time alignment to match the relative distance between drivers usually gives good results. But as demonstrated in the thread above and also by the very popular thread http://www.diymobileaudio.com/forum...5069-better-technique-ear-time-alignment.html using time alignment to precisely match phase between drivers _at the crossover frequency_ can be much more pleasing. There is some mention of this as well in the thread http://www.diymobileaudio.com/forum...-discussion/144111-up-front-bass-new-way.html .

I found this thread on home theater shack a while ago detailing how to precisely align a subwoofer in a home theater setup and I didn't understand it at the time. It is still a good read if you want to learn about impulse response and how to use some of the more advanced features of REQ.

Case Study: Sub Alignment using REW v5 - Home Theater Forum and Systems - HomeTheaterShack.com

For a more simple method, I play two channels at a time with one out of phase relative to the other (sub and left midbass for example). Then I watch on TrueRTA in real time while playing pink noise. Because one channel is out of phase with the other, I adjust the time delay of one speaker to get the most interference _at the crossover frequency_ (the deepest valley). Then flip the phase of that one channel back to normal, and done.

-J


----------



## Wesayso

Jazzi said:


> For a more simple method, I play two channels at a time with one out of phase relative to the other (sub and left midbass for example). Then I watch on TrueRTA in real time while playing pink noise. Because one channel is out of phase with the other, I adjust the time delay of one speaker to get the most interference _at the crossover frequency_ (the deepest valley). Then flip the phase of that one channel back to normal, and done.
> 
> -J


Tried a few different methods of TA and this one I can repeat when trying different things and always sounds good to me! 
I feel like proper TA adjustment makes you nod your head and tap your feet, it just clicks into place.


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## aj1735

Subscribed 

I have lots of learning and experimenting to do. I will post questions when I get doing it.


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## evangojason

Hey Erin, just wanted to say thanks for all the info you've provided to this site. A year ago I would skim over your articles and reviews but didn't really "get it". I've learned a lot over the last year on this site and really enjoy the science part of car audio now. Your video in this thread was extremely helpful and really simplified the process. It convinced me to order a laptop, DSP, and mic this week for the build I'm working on. Looking forward to the rest of this thread and think video is definitely easier to learn from. Thanks again.


----------



## bertholomey

I realized I haven't posted here - just sub'd through tools. 

Once I get back from this trip to Charleston, I may post up a couple graphs for you all to shoot holes through


----------



## Hanatsu

I can announce that setting T/A with RoomEQ is possible. Works awesome in fact. Can observe the peak differences on the X-axis in overlays tab. To get it to work you need left microphone --> left speaker output in loopback mode and right channels for normal operation. After that go into the preferences/soundcard and set the "timing reference I/O" to the left channels. On my computer the the timing box only shows up after using the soundcard in ASIO mode. After this is done, go into the 'Analysis' tab. Click the 'Use loopback for timing reference' box and you're set.

I had problems with the Creative ASIO driver but it works after an update now. 

Calculate the time differences with this calculator if you're lazy 

Conversion of time difference and sound path distance or length millimeters time of arrival milliseconds calculate calculation delay line noise sound wave in air calculator - sengpielaudio Sengpiel Berlin


----------



## Hanatsu

Here's a screenshot on the overlayed impulse peaks. Calculate the time difference and you'll get;

0=1.54ms (reference)

1,703-1,54ms = 0,163ms = 2.201142" 
1,857-1,54ms = 0,317ms = 4.280748"

This was exactly how much I moved the mic each time in this example.


----------



## masswork

Hanatsu said:


> Here's a screenshot on the overlayed impulse peaks. Calculate the time difference and you'll get;
> 
> 0=1.54ms (reference)
> 
> 1,703-1,54ms = 0,163ms = 2.201142"
> 1,857-1,54ms = 0,317ms = 4.280748"
> 
> This was exactly how much I moved the mic each time in this example.


Are you sure that's correct?
How can the impulse is - in time? It should be after 0ms or 0 if set t=0 at peak.

Also, it's better to change the graph into %FS rather than dbFs so we can also check the polarity.


----------



## Hanatsu

masswork said:


> Are you sure that's correct?
> How can the impulse is - in time? It should be after 0ms or 0 if set t=0 at peak.
> 
> Also, it's better to change the graph into %FS rather than dbFs so we can also check the polarity.


You could see the same thing around 0ms but it was harder to see up there. The further away I moved the mic the more negative in time the IR peak got. Dunno why really, it was consistant and accurate (in relation to eachother) as far as I can tell. I haven't thought about the %Fs view mode, thanks for the tip!

Btw... perhaps the negative time happened because the input was inverted? Idk...

Sent from my Samsung Galaxy 3 via Tapatalk.


----------



## Benja

How much decay is attributed to just the cone movement after the frequency is cut? None?


----------



## mojozoom

Hanatsu,

I did some research and messed with this a bit, and found really nice results by switching to %FS (in the upper left corner), and by limiting the width of the sweep SIGNIFICANTLY.

For a sub to mid test, you can set your sweep up for about 5 Hz on either side of the crossover frequency. So for an 80 hz crossover, sweep from 75 to 85 hz. 

That should get you some clean impulses that are directly comparable.


----------



## Hanatsu

mojozoom said:


> Hanatsu,
> 
> I did some research and messed with this a bit, and found really nice results by switching to %FS (in the upper left corner), and by limiting the width of the sweep SIGNIFICANTLY.
> 
> For a sub to mid test, you can set your sweep up for about 5 Hz on either side of the crossover frequency. So for an 80 hz crossover, sweep from 75 to 85 hz.
> 
> That should get you some clean impulses that are directly comparable.


Great tip! I'll try it out. Never thought about limiting the sweep /stupid <--


----------



## mojozoom

Here's a link to the HT Shack post where they outline this method. It's got some really good info:

Case Study: Sub Alignment using REW v5 - Home Theater Forum and Systems - HomeTheaterShack.com


----------



## Dillyyo

bikinpunk said:


> You may also need to make sure you're doing a loopback measurement so your soundcard can reference the signal going out in time vs when it's actually sent out of the soundcard. This tells the system the internal delay.


Erin....can you go over how to accomplish this with my laptop. Lenovo T500 with input and output jacks (only 1 of each) and windows 7. I cannot seem to find in Windows & where I can alter anything about the soundcard and the signals.


----------



## preston

Can you explain how you approach L vs R tuning ? 

Do you RTA the right side, then the left side, and then RTA them together ?
or is it best to just RTA as a system as you've shown ? 

And how would this play into the "windshield ate my soundstage" approach of centering test tones via EQ ? or is that even considered a valid approach ?


----------



## 07azhhr

mojozoom said:


> Hanatsu,
> 
> I did some research and messed with this a bit, and found really nice results by switching to %FS (in the upper left corner), and by limiting the width of the sweep SIGNIFICANTLY.
> 
> For a sub to mid test, you can set your sweep up for about 5 Hz on either side of the crossover frequency. So for an 80 hz crossover, sweep from 75 to 85 hz.
> 
> That should get you some clean impulses that are directly comparable.





Hanatsu said:


> Great tip! I'll try it out. Never thought about limiting the sweep /stupid <--


I used the sweeps band limited too. I extended out atleast half an octave past the xo points so I could eq out there if neccessary. 

I also used the sweeps to help pick my xo points for my 3's and tweets by playing the sweeps across each drivers safe range. Since there were bad spots near the outside limits I picked xo points inside them. I forget where these were but both driver types had some bad spots that I was able to eliminate via the xo. This eliminated some potental eq needs.


----------



## 07azhhr

preston said:


> Can you explain how you approach L vs R tuning ?
> 
> Do you RTA the right side, then the left side, and then RTA them together ?
> or is it best to just RTA as a system as you've shown ?


 
For me I have seperate 10 band parametric eq's for each driver along with 16 fixed bands for each side in the HU so I rta'd each driver seperately first. I built my eq bands in the para taking into account what bands I had in the HU that would effect "ONLY" that specific driver. If I had spots that would effect the next driver up or down I would turn that driver back on and do a sweep again. Once all drivers were done seperately I rta'd each side as a whole and did some more adjusting where neccessary. After that I checked the whole system to see if there was more to adjust.


----------



## CaptainMorgan

I'm so glad this thread happened. There is such a wealth of information for me to dissect but it's exactly the topic that I'm loaded with questions about.

I need to do some final tweaking to my install before I'm ready to get good tuning results (loose connection on an amp from a stripped screw causing some noise, need to secure front door pods directly to the metal of the door).

I'm a bit fortunate for my tuning needs because my source unit is the computer that will be running rew. I'm already connected directly into my system. I have all the tools to get to work, just need to learn what to do with them.

I'll gladly post all my results and experiences to contribute to this thread. I can't wait to dive head first into it. I'll probably start some time next week.


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## Sonus

I'm trying to calibrate my soundcard on my laptop, however it hasn't got a seperate line in and line out, but a combined jack like Iphone ear buds.

Luckily I've got a spare jack that I can modify to make a loop from the line out portion into them mic line in.

However I am not sure how to connect it.

Would the latch in the attached picture do the trick?


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## bigbubba

Post marked


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## therapture

I just got my UMM-6 mic today, and I read a bit to learn how to take some measurements. That part is easy actually.

Now, learning how to interpret the readings, and WHAT to DO...that's another whole ballgame. This thing sure is fun, in a geekish kind of way. 

I'll be right back to post a couple pics of what I got. It looks CRAZY jagged. And NOTHING like what I am seeing from some of you guys here. I am wondering if I have something setup wrong.


----------



## therapture

Well, here ya go. First is obviously the averaged plots, taken from the headrest at center, right, and left.










And the plots overlaid with the average.










Looks like I have ALOT of EQ work ahead. What I DON'T know, is how the curve should look?! And I love the way my car sounds at this point, I think I have done a good job of level balancing from left to right, but the peaks and valleys, what to make of them? I tried a couple EQ cuts and boosts, and while my ears hear them, they really did not seem to show up as much different after I did a second RTA run through. For instance, at 4500k, I cut 3db off on both sides, and it showed almost zero difference in the plots from session 1 to session 2. I also boosted 7k 3db and still showed practically no difference, what did I do wrong?


----------



## evangojason

therapture said:


> Well, here ya go. First is obviously the averaged plots, taken from the headrest at center, right, and left.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> And the plots overlaid with the average.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Looks like I have ALOT of EQ work ahead. What I DON'T know, is how the curve should look?! And I love the way my car sounds at this point, I think I have done a good job of level balancing from left to right, but the peaks and valleys, what to make of them? I tried a couple EQ cuts and boosts, and while my ears hear them, they really did not seem to show up as much different after I did a second RTA run through. For instance, at 4500k, I cut 3db off on both sides, and it showed almost zero difference in the plots from session 1 to session 2. I also boosted 7k 3db and still showed practically no difference, what did I do wrong?


Here is another really good thread to go along with this one.

http://www.diymobileaudio.com/forum...44455-quick-tip-using-auto-eq-roomeq-rew.html

Using housecurves makes it really easy to balance right and left. I like to do left side plus sub, then right side plus sub. Using the sub as a reference point for both sides. Try out some of the housecurves posted and make some of your own.


----------



## eddieg

therapture said:


> Well, here ya go. First is obviously the averaged plots, taken from the headrest at center, right, and left.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> And the plots overlaid with the average.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Looks like I have ALOT of EQ work ahead. What I DON'T know, is how the curve should look?! And I love the way my car sounds at this point, I think I have done a good job of level balancing from left to right, but the peaks and valleys, what to make of them? I tried a couple EQ cuts and boosts, and while my ears hear them, they really did not seem to show up as much different after I did a second RTA run through. For instance, at 4500k, I cut 3db off on both sides, and it showed almost zero difference in the plots from session 1 to session 2. I also boosted 7k 3db and still showed practically no difference, what did I do wrong?


Most probably your DSP has a 1/3 octave EQ so the best tip the way I see it would be to set the REW - RTA resolution (under the settings) to 1/3 octave so you will see the curve on the very same resolution your EQ works. 

You will find it much easier to tune that way. 

Usually most people like the whole bass area to be up to 6db stronger than the rest of the spectrum and the rest as flat as possible until somewhere around the 12KHz and then start a graduate rolloff to about -3db up to -9db until you reach the 20hz area depending on your liking (taste in sound) 

Note that in most musical recording after 16KHz or so there is hardly any "information" so trying to level the 16KHz to 20KHZ based on music would be a BAD IDEA. 

I use pink noise to tune the curve and brown noise to tune the bass area.

I do it once per left side and once per right side and then I compare the avg of all of it.

Before I even do EQ, I compare that both sides - each element to each element are playing at the same level, then first TC settings and only then I do the EQ.

after that is done, listen to your refernce music and fix the pix or areas you did not like how they sound and you are good to go.


----------



## therapture

eddieg said:


> *Most probably your DSP has a 1/3 octave EQ so the best tip the way I see it would be to set the REW - RTA resolution (under the settings) to 1/3 octave so you will see the curve on the very same resolution your EQ works. *
> 
> You will find it much easier to tune that way.
> 
> Usually most people like the whole bass area to be up to 6db stronger than the rest of the spectrum and the rest as flat as possible until somewhere around the 12KHz and then start a graduate rolloff to about -3db up to -9db until you reach the 20hz area depending on your liking (taste in sound)


Well, on my 363 I can also manually enter whatever frequency I want and then adjust that, or does that not work in practice? And that crazy spike at 4500k...and the dip at 45hz...

It just seems that plot is very jagged, or is it because I chose the 1/12 resolution and am seeing small things that really are not as big as they look?


edit: So on the chart/plot...is that 5db gap using the marked lines, REALLY a 5db gap in the actual sound? (don't laugh, I am new to this, utterly)  ...meaning if I have a 3db dip at say, 500hz, I boost my EQ 3db there, I should see a 3db rise in the response on the plot?


----------



## eddieg

therapture said:


> Well, on my 363 I can also manually enter whatever frequency I want and then adjust that, or does that not work in practice? And that crazy spike at 4500k...and the dip at 45hz...
> 
> It just seems that plot is very jagged, or is it because I chose the 1/12 resolution and am seeing small things that really are not as big as they look?
> 
> 
> edit: So on the chart/plot...is that 5db gap using the marked lines, REALLY a 5db gap in the actual sound? (don't laugh, I am new to this, utterly)  ...meaning if I have a 3db dip at say, 500hz, I boost my EQ 3db there, I should see a 3db rise in the response on the plot?


Even if you can peak a specific carrier frequency - you should set the REW to work at a resolution as close as possible to your EQ resolution, you will then see that you have a better tuning ability as you are comairing apples to apples instead of apples to grapes - I hope it makes the picture in a better light.


----------



## fcarpio

Awesome thread, subbed.


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## therapture

I'll be drinking a couple beers while I play with the mic again tonight  that sounds bad.


----------



## mojozoom

I'd love to see what you have going on, and help give some ideas on things to try. Could you test and post the following, in 1/3 octave smothing and 5 db (or ms) graph resolution:

Right mid sweep, then excess group delay at 1/6 smoothing
Right tweet sweep
Combined right sweep

Left mid sweep, then excess group delay at 1/6 smoothing
Left tweet sweep
Combined left sweep

Combined L&R sweep

Sub sweep

You should be able to show most of those clearly together on one plot, and maybe make a separate one for the combined L&R with the sub (that's how we're going to see what your crossover frequency really is). This'll give us alot to talk about.


----------



## therapture

Just saw this post mojo....I will run those sweeps tomorrow and get to them. I made some changes tonight that I think I like better. 

I need to get into one thread or the other, this one or this one http://www.diymobileaudio.com/forum...081-how-eq-rew-measured-response-curve-2.html

Which would be better thread to continue in? I was thinking the technical forum one, since it stays up top as we add to it.


----------



## Fetus

Sonus said:


> Hmm... had some time to lay with REW today after my Dayton UMM6 USB mic arrived.
> 
> However I can't seem to get rid of spikes at 1000Hz from 2kHz and up?:


Were you able to correct this, Sonus? I am having the same spikes. Seems strange to be a soundcard calibration issue, considering I don't have the soundcard selected as an input or output device in the preferences menu...


----------



## rich20730

Sonus said:


> Hmm... had some time to lay with REW today after my Dayton UMM6 USB mic arrived.
> 
> However I can't seem to get rid of spikes at 1000Hz from 2kHz and up?
> 
> The noise measured is only background noise, but it is the same with different background noise
> 
> I've downloaded the cal file from daytonaudio.com and loaded it into REW.
> 
> EDIT: measured my Bose Quietcomfort15 headset with pink noise





Fetus said:


> Were you able to correct this, Sonus? I am having the same spikes. Seems strange to be a soundcard calibration issue, considering I don't have the soundcard selected as an input or output device in the preferences menu...


This is an issue with the UMM-6, the UMIK-1, and probably most of the other USB microphones available. I have the UMM-6 and it confused the hell out of me when I first started using it to take measurements. I initially thought that the giant spikes at 1khz were due to the impedance peaks of my tweeters, but when none of my EQ/crossover adjustments made any difference, I checked the response without any input signal and the spikes were still there.

Measurements I took in a silent part of my house:










The EMM-6 is running through my Art Dual Pre, which seems to have the same USB-related noise spikes.

Here's a link to a discussion about this issue on the AVS forums:

http://www.avsforum.com/t/1449924/s...t-techniques-and-how-to-interpret-graphs/1170

Possible explanation: 

"The 1Khz distortion and its harmonics are clearly present as stated. Likely the cause is the USB frame sync which has a time of 1 msec or frequency of 1000 Hz. The device simply does not have proper isolation between its digital and analog sections (common problem when components are packed together this close and not enough attention is paid to such an issue."

The spikes shouldn't affect your measurements as long as you take your measurements at a level that is sufficiently above the noise floor (~ 70dB or higher). Also, since the spikes are so narrow, you can pretty much negate their effect by applying some smoothing:

No smoothing:










1/12 Octave Smoothing:










1/3 Octave Smoothing:


----------



## Alextaastrup

Do not rely on generic calibration files, which could be easily founded at a lot of sites. My ECM8000 has a raise of up till 9 dB at higher frequences and no generic calibrations were able to match my mic. Do calibration by yourself or let professionals to do it. Be careful with corrections at low frequences. Very often they say more about room acoustics than the microfon itself.
My point - individual calibration of mic is must for correct measurements.


----------



## DonutHands

so, yea, what happened to the rest of this?

will there ever be impulse measurements? time delay? waterfall?

is there a different tutorial somewhere on how to set up and use REW? The RTA part was super helpful but not what im looking for.


----------



## exhumed4u

I know that this is an old thread, so don't be at me up too bad. But when you were referring to moving the mix around to different spots at different heights, would I need to adjust the angle as well? So 45 to the right and left maybe even 90. The reason I am asking is because I am using LARSA through Audio Tools and it gives me the a ability to file save and average up to eight impulse responses.


----------



## Elgrosso

Damned, still so many good readings on this site, we need a "thanks" button!
Or does it exist?


----------



## ninetysix

Thanks to the OP, great to have an easy to follow step by step guide like this - some guides seem to really start at the deep end and only go deeper.

I'll apologise in advance if my question doesn't belong here, but I've searched Google and here with no luck.

I've got a cheap RE audio 12" in a ported box about 1.5cuft tuned about 38hz (from memory, what ever the manufacturer specs recommended for SQ) in the trunk of a small sedan facing the rear up against the back seat. If I use REW with a UMIK-1 in the listening position for a "measurement" (sine sweep right?) from say 10-200hz no eq no xover it shows a ~25dB dip around 40 hz, only about 3-4hz wide but otherwise pretty flat between 30-80hz. With the trunk open the response is very flat, but about 25dB lower, ie all other frequencies drop to the level of the dip with the trunk closed. Face the sub up, sideways or forwards no difference. Back seats down still the same. During the sweep you can really hear the dip as if it's muted at 40hz.

But fire up the RTA with pink noise (using REWs generator on sub cal and the RTA set to take 16 sample average with either 1/3 or 1/6 smoothing) as per the OPs YouTube video and its only about 10dB down though a bit wider. Auto EQ with REW to my minidsp and it's looking perfect, sounds pretty good but the measurement sine sweep still sees a dirty big 15dB dip, though it's a lot harder to hear now.

Which one should I go by?


Thanks


----------



## ninetysix

One more question, is it considered poor form to use pink noise and an RTA to fine tune time alignment?

Everything I've read says it's not that simple. First I got it close to what sounded right, but on the RTA I could see a slight dip either slightly before or slightly after the xover point between sub and 8" mids. Adjust delay in real time by 0.1ms increments until it's basically right on the xover point which also really smooths out the frequencies above and below, sounds great too. I haven't worked on the dip much yet, but it seems to match the curve of the drivers when measured one at a time.

It's not supposed to be that easy is it?


----------



## ultimatemj

So, I'm trying to take some simple RTA measurements using a Dayton Umm6, their provided calibration file, and uncorrelated (stereo) pink noise.

My measurements are coming up with more slant than my ears hear. Comparing it to the Andy housecurve you'd think it was super bass heavy (+30db above vocals) and dull up high (-15db from 4k up).








So, I found a quiet place in my house and turned on the RTA to see what the mic picked up....and it seems "slanted"...sorry forgot to smooth it, but you can see 20Hz is about +30db!








Did I miss a step in my setup? Or a preference? Or?

Thanks in advance for any insights!


----------



## ultimatemj

For anyone else running into this, I got my answer over on HomeTheaterShack (home base for REW)



> You have the RTA in spectrum mode, select an RTA mode for an RTA-style display. Use these settings:


Now onto tuning :thumbsup:


----------



## lizardking

Huge difference


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## lizardking

I also noticed you have the "Adjust RTA Levels" checked. Any reason as to why?


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## ultimatemj

Just because it was that way in the settings image JohnM from HTS recommended. I haven't read up on what it does...


Sent from my iPhone using Tapatalk


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## lizardking

I've always used Spectrum at 1/6 up to 1/24 smoothing. You got me wondering now to try the RTA Mode. Post link to your discussion...love to read it.


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## lizardking

RTA mode....what a difference. Glad you posted that. Spent the last couple hours playing around.


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## lizardking

The difference between spectrum and RTA modes is how the information is presented. 

In spectrum mode the frequency content of the signal is split up into bins that are all the same width in Hz. For example, with a 64k FFT length and 48 kHz sample rate the bins are 0.732 Hz wide. The plot shows the energy in each of those bins. 

In RTA mode the bin widths are an octave fraction, so their width in Hz varies with the frequency. For example, a 1 octave RTA plot has bins that are 70.7 Hz wide at 100 Hz and 707 Hz wide at 1 kHz. The plot shows the combined energy at each frequency within each bin. This is closer to how our ears perceive sound. 

The different presentations mean signals with a spread of frequency content will look different on the plot. The best known examples are white noise and pink noise. 

White noise has the same energy at each frequency. On a spectrum plot, which shows the energy at each frequency, the white noise plots as a horizontal line. On an RTA plot it appears as a line that rises with increasing frequency, as each RTA bin gets wider it covers more frequencies and so has more energy, the bin widths double with each doubling of frequency so the energy also doubles, which adds 3 dB on the logarithmic plots we use to show level. White noise sounds quite 'hissy', we perceive it as having more energy at higher frequencies. 

Pink noise has energy that falls 3 dB with each doubling of frequency. On a spectrum plot it is a line that falls at that 3 dB per octave rate, on an RTA plot it is a horizontal line as the energy in the signal is falling at the same rate as the bins are widening. We perceive pink noise as having a uniform distribution of energy. 

Single tones are a special case, they will appear at the same level on either style of plot as their energy is all at one frequency, so on a spectrum plot they show as a vertical line, on an RTA plot they show (typically) as a bar of the width of the bin width at their frequency, but the height of the bar is the same as the height of the line on the spectrum as all the energy is at that one frequency.

Read more: Need some help figuring out what happened - Home Theater Forum and Systems - HomeTheaterShack.com


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## ultimatemj

Further interpreting JohnM's feedback over on HTS, 

Note his comments about random (uncorrelated) pink noise...


> over any short period its spectrum can deviate significantly from the ideal especially at low frequencies





> Random pink noise typically has a crest factor of around 12 dB
> That means to get a reasonably accurate (to within a few dB) view of the response at a single position you would need to leave the mic stationary there for about 30s, with the RTA averaging all the while.





> *Random pink noise is pretty useless for measuring responses./B]*


*

1.5sec of Random (uncorrelated) Pink Noise









Compare the 20-200Hz range when averaged for 30sec!










When I have been taking RTA measurements (at 6 mic positions and then averaging) I'm fairly sure I'm capturing "milliseconds" and getting random snapshots (Avergaing was set to "none") that (in the lower frequencies) vary up to 12db from the PN alone!

I haven't used periodic PN yet, but I did try the RTA Average settings on 32 averages and it definitely improved the the "resolution", which will keep me from tweaking the EQ 1db here 2 db there when it was only a snapshot of PN variation...and not representative of what I hear.








Now I've got to figure out which of these dips/combs I can actually do anything about with EQ  Insights welcomed! 






*


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## thornygravy

I wanna watch the video.


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## ErinH

Did I take it down? I don't recall. 


Probably for the best. I've learned since then. If anything, I should make a new video.


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## thornygravy

My bad. I'm getting this "ERROR" message on a lot of imbedded videos lately. I guess it's just me. I was able to get the link by inspecting in chrome.

We do need more tuning videos though! So by all means lol.


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## itte

What are the right settings for measuring car audio with rew rta? Video does not work anymore.


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## Lou Frasier2

itte said:


> What are the right settings for measuring car audio with rew rta? Video does not work anymore.


erin has a pretty awesome YouTube channel, im pretty sure you can find it there bro,


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## Lou Frasier2

its called Erins audio corner


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## itte

Cant find it anymore.


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## itte

Here is picture from the srceen?


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