# RTA-REW individual speaker tuning correlated vs uncorrelated Pink Noise



## tjk_bail (Feb 2, 2012)

When doing individual speaker tuning, I know you're supposed to use correlated(mono) PN Pink noise, but is it a good practice to use uncorrelated Pink noise when tuning L&R speaker pairs?

I'm asking this question because of the newest HELIX Software version as it includes some tuning .wav files. Its got a Time alignment.wav file, INPUT Signal Analyzer correlated pink noise .wav file, and has a RTA uncorrelated .wav file. Got me thinking why would they supply just the uncorrelated(stereo) pink noise for RTA......


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## Ge0 (Jul 23, 2007)

What do the manuals say? I'm curious.

Ge0


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## opekone (Mar 24, 2020)

pink noise, correlated vs uncorrelated


i know one is stereo, the autosound 2000 disc says to find an in between my rta's are different, should i lean towards one or the other, thanks




www.diymobileaudio.com


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## tjk_bail (Feb 2, 2012)

Thank you for the link opekone. I'm still a little fuzzy on weather or not I should use uncorrelated pink noise when tuning L&R together. Correlated or uncorrelated pink noise can be used for a single speaker. The link you posted is from 2008, and they were using correlated pink noise mainly for time alignment, and using uncorrelated pink noise to tune a single speaker at a time, but nobody mentions anything about EQ'ing L&R together using uncorrelated.

Audio Frogs USB microphone comes with a tuning CD and tuning instructions. In the tuning instructions, it explains that track 1 on the CD is 15 minutes of correlated (mono) pink noise, and the objective is to use the mono pink noise to tune the left side of your stereo, then tune the right side of your stereo, then match your left side to the right side. But mentions nothing about tuning (EQ'ing) L&R together.

The info in that threat suggest using uncorrelated to tune a single speaker, Audio Frog uses correlated for the whole system,,,, and well now I'm confused.

So, the link you posted sortra implies to use uncorrelated for L&R but is not clear, and the Audio Frog tuning guide uses correlated. Most current tuning practices today suggest to, tune a left speaker, then tune a right speaker, then tune L&R together. 

I'm guessing that I should use correlated to tune each speaker individually, then use uncorrelated when tuning L&R together, but I'm just guessing, and would like to know what truly is the best way.


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## SkizeR (Apr 19, 2011)

If you understand the difference between the two, it should be pretty obvious.. When doing one speaker at a time, or even one side at a time, correlated vs uncorrelated is irrelevant. Stick with mono (correlated) though. It shows how the sides interact and will show phase anomalies. Stereo (uncorrelated) is used for certain situations, but its rare. 

Sent from my SM-G975U using Tapatalk


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## jtrosky (Jul 19, 2019)

Why are they refered to as "correlated" and "uncorrelated" instead of just "Mono" and "Stereo" to begin with? Just causes more confusion as you have to remember which one equates to "Mono" and which one equates to "Stereo". Everyone is already familiar with "Mono" and "Strereo" - why not just stick with those names? 

Is there a reason why they just don't use "Mono" and "Stereo"?


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## tjk_bail (Feb 2, 2012)

I understand the difference between them. When tuning a single speaker or a entire side, I totally understand it doesn't matter if mono or stereo is used, and I totally understand mono is a good tool to show phase anomalies, I get that.

But after I have fixed my phase probs and tuned each side (or speaker) with mono, I then focus on whole system Overall tonality and Frequency Response (tuning to my Overall House Curve), wouldn't it make sense to use stereo pink noise at this point ??


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## tjk_bail (Feb 2, 2012)

jtrosky said:


> Why are they refered to as "correlated" and "uncorrelated" instead of just "Mono" and "Stereo" to begin with? Just causes more confusion as you have to remember which one equates to "Mono" and which one equates to "Stereo". Everyone is already familiar with "Mono" and "Strereo" - why not just stick with those names?
> 
> Is there a reason why they just don't use "Mono" and "Stereo"?



I don't know why.... but from now on going forward, i'll use the mono/stereo terms....


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## opekone (Mar 24, 2020)

jtrosky said:


> Why are they refered to as "correlated" and "uncorrelated" instead of just "Mono" and "Stereo" to begin with? Just causes more confusion as you have to remember which one equates to "Mono" and which one equates to "Stereo". Everyone is already familiar with "Mono" and "Strereo" - why not just stick with those names?
> 
> Is there a reason why they just don't use "Mono" and "Stereo"?


Because that's not what they mean


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## jtrosky (Jul 19, 2019)

tjk_bail said:


> I don't know why.... but from now on going forward, i'll use the mono/stereo terms....


My comment wasn't directed at you - I was just curious why some people use "correlated/uncorrelated" and others use "mono/stereo". I see it constantly and it constantly causes confusion for those that aren't familiar with the correlated/uncorrelated names. In the end, someone always ends up having to cross-reference them to mono/stereo anyway.  Even @SkizeR x-references them above as well.

A lot of times you'll see "Stereo" and "Mono" in parenthesis after uncorrelated and correlated (or vice-versa). Whether or not they technically mean the exact same thing, people eventually have to cross-reference them at some point - so I was just curious why the two different ways are used to identify the same thing - or if there was some technical reason why - that's all.


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## tjk_bail (Feb 2, 2012)

Optimal RTA curve "template"


Thanks Han. I was looking at MiniDSP, but I don't have a laptop and don't want to get one just to tume the stereo. I picked up the AC DQ-61 - which is all manual knobs for EQ and T/A. Not the most adjustable or smallest of steps, but it actually does a really nice job. I have a couple 25ft RCA...




www.diymobileaudio.com






Welp, I found the answer I was looking for. Hanatsu posted this on post #153 in the above thread. >>

"Uncorrelated noise for full system frequency response measurements.

Correlated noise to tune T/A and L/R EQ by ear. 

Using MLS or Swept Sine (Avilable in ARTA and RoomEQ/REW) you can get much more data than using noise / pink noise. You can even T/A by looking at the impulse response. "


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## tjk_bail (Feb 2, 2012)

tjk_bail said:


> Optimal RTA curve "template"
> 
> 
> Thanks Han. I was looking at MiniDSP, but I don't have a laptop and don't want to get one just to tume the stereo. I picked up the AC DQ-61 - which is all manual knobs for EQ and T/A. Not the most adjustable or smallest of steps, but it actually does a really nice job. I have a couple 25ft RCA...
> ...



and this post is for jtrosky>>

"STEREO noise for full system frequency response measurements.

MONO noise to tune T/A and L/R EQ by ear.

Using MLS or Swept Sine (Avilable in ARTA and RoomEQ/REW) you can get much more data than using noise / pink noise. You can even T/A by looking at the impulse response. "


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## RockitFX (Aug 22, 2018)

opekone said:


> Because that's not what they mean


How is that not what they mean? In practice it's exactly what they mean.


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## opekone (Mar 24, 2020)

The pink noise is either phase aligned or phase random, it's either correlated or uncorrelated. How you route that signal is up to you. Don't you think it's confusing to play a stereo file mono or play a mono file stereo?


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## RockitFX (Aug 22, 2018)

opekone said:


> The pink noise is either phase aligned or phase random, it's either correlated or uncorrelated. How you route that signal is up to you. Don't you think it's confusing to play a stereo file mono or play a mono file stereo?


It's either 1 channel or 2; so it is mono or stereo.


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## opekone (Mar 24, 2020)

Uncorrelated and Correlated noise files are both stereo. The interesting distinction is that in one case the two channels are in phase and in the other they are both in a random state. If the only thing that means to you is mono and stereo then sure, great.


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## tjk_bail (Feb 2, 2012)

If you play a phase random file through 1 channel, its mono. If you play a phase random file through 2 channels (L&R) its stereo.
If you play a phase aligned file through 1 channel, its mono. If you play a phase aligned file through 2 channels (L&R) its mono.


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## RockitFX (Aug 22, 2018)

opekone said:


> Uncorrelated and Correlated noise files are both stereo. In one case the two channels are in phase and in the other they are both in a random state. If the only thing that means to you is mono and stereo then sure. Great.


So in the case where they are in phase, there are different signals being sent to left & right? Or they are the same signal, of which there are 2 channels?


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## opekone (Mar 24, 2020)

You can answer that yourself. They are labeled to describe the significant and interesting difference between them. If the best way you can describe that is with stereo and mono, then run with it brother.


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## jtrosky (Jul 19, 2019)

tjk_bail said:


> and this post is for jtrosky>>
> 
> "STEREO noise for full system frequency response measurements.
> 
> ...


Honestly, I don't use different pink noise files for tuning different parts of the system. I use the same pink noise file for everything - single speaker, speaker pairs, whole sides and overall system EQ measurements - I use the Kicker "20 min Lab Grade Pink Noise" file that is hosted on the Kicker site (https://www.kicker.com/files/test_tones/Lab_Grade_Pink_Noise_20_minutes.wav) - they only offer one type of pink noise file - it's 2-channel, but the left and right channels are exactly the same - which I'd consider mono pink noise. I've been using that same .wav file since I first started tuning and it works well for me. It _does_ show phase issues when measuring multiple speakers together.

I've never used true Stereo pink noise (2 channels with different content in each channel) for any tuning (right or wrong).

I think it's safe to say that when someone says "Mono Pink Noise", they are referring to correlated pink noise and when someone says "Stereo Pink Noise", they are referring to "Uncorrelated Pink Noise"....


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## RockitFX (Aug 22, 2018)

What's wrong with using the built in pink noise generator provided by REW?


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## tjk_bail (Feb 2, 2012)

RockitFX said:


> So in the case where they are in phase, there are different signals being sent to left & right? Or they are the same signal, of which there are 2 channels?


If you play a _*phase random*_(Uncorrelated-Stereo)) file through 1 channel, its *mono*. If you play a* phase random*(Uncorrelated-Stereo) file through 2 channels (L&R) its *stereo*. So if you play the Stereo pink noise on only 1 speaker at a time, regardless if it is a left or right channel, it will play mono. But when you play Stereo pink noise through 2 speakers that are Left and Right channels, then its stereo. If you play Stereo pink noise through mulitple left side speakers or only right side speakers, its still *mono*. It only becomes *stereo* when playing Left and Right Speakers together.

If you play a _*phase aligned*_(Correlated-Mono) file through 1 channel, its *mono*. If you play a _*phase aligned*_(Correlated-Mono) file through 2 channels (L&R) its *mono*. So, even playing on Left and Right channels at the same time... it is MONO.


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## Petererc (Dec 28, 2016)

RockitFX said:


> What's wrong with using the built in pink noise generator provided by REW?


Now ya did it, REW, Pink PN, periodic pink noise? Someone got some xplaining to do.


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## RockitFX (Aug 22, 2018)

Petererc said:


> Now ya did it, REW, Pink PN, periodic pink noise? Someone got some xplaining to do.


I'm still trying to figure out the difference between Pink Noise & Pink PN.


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## Petererc (Dec 28, 2016)

I was just looking it up, PN has a lower crest factor and should be smoother. I read that off the internet, so ....


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## tjk_bail (Feb 2, 2012)

Jazzi's tuning companion for room eq wizard


Note: See the link in my signature to download the latest version of this tool. This spreadsheet has been a lot of fun to make! My goal is to take as much guesswork out of the tuning and installation process as possible. With this tool, you can calculate a safe high-pass crossover point for...




www.diymobileaudio.com





I think Jazzi explains it somewhere in his thread...


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## Petererc (Dec 28, 2016)

This is what I was reading








REW Confused on proper measuring Car Audio


It seems in reading different threads everyone has different ways they measure with REW. Some use the RTA some use the Spectrum mode. Some use uncorrelated pink noise and some use correlated pink noise. What is the proper method with using REW? All I have at my disposal is uncorrelated pink...




www.hometheatershack.com


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## jtrosky (Jul 19, 2019)

RockitFX said:


> What's wrong with using the built in pink noise generator provided by REW?


Nothing wrong with it. In my case, I just already have the Kicker-sourced pink noise file on my head-unit thumb drive, so I use it (had it since before I even started using REW). But you could save the REW periodic pink noise to a file and use it as well (or use it through the headphone out jack on the laptop, but I get crappy sound quality though my aux-in jack, so I don't use it for anything). 

Like anything in tuning, always more than one way to accomplish the same thing.


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## tjk_bail (Feb 2, 2012)

Petererc said:


> This is what I was reading
> 
> 
> 
> ...



Man oh man...wish you would have posted this link yesterday.. would have saved me a few hours searching forums in regards to my original question in this thread....


Here is just one little small quote I took from the above link....

"Uncorrelated pink noise is a necessity for FR measurements with multiple channels at once, vs channel balancing with correlated noise. "

Hey, Thanks for posting that link !


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## Petererc (Dec 28, 2016)

Yea man, when I get off work gonna find some time to give that a thorough read.


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## jtrosky (Jul 19, 2019)

My understanding is that you'd want to use correlated (mono) pink noise when measuring more than one speaker so that you can see where there are phase cancelations. Both Nick (@SkizeR) above and Andy from AudioFrog (in his tuning guide) say to use mono pink noise for measuring both single and multiple speakers. I would think that is the correct way to do it.

You don't want to "hide" phase issues when multiple speakers are playing together, which I think using stereo pink noise would do. You want to see them so that you can fix them.


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## RockitFX (Aug 22, 2018)

A little off topic but related, where can a person find a house curve to download? I don't have excel on my windows machine, so using Jazzi's spreadsheet is out of the question.


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## tjk_bail (Feb 2, 2012)

jtrosky said:


> My understanding is that you'd want to use correlated (mono) pink noise when measuring more than one speaker so that you can see where there are phase cancelations. Both Nick (@SkizeR) above and Andy from AudioFrog (in his tuning guide) say to use mono pink noise for measuring both single and multiple speakers. I would think that is the correct way to do it.
> 
> You don't want to "hide" phase issues when multiple speakers are playing together, which I think using stereo pink noise would do. You want to see them so that you can fix them.


I agree, it is good to use if your going to use the Left .vs. Right type of tuning, as in the Audio Frog method. Its just my preference, but I like to use the "Tune the Left Tweet, Tune the Right Tweet, then tune the Pair of Tweets. Using Mono pink noise to tune both Tweets at the same time (or any pair) from what I have been reading is NOT best practice. And I agree that Mono is useful to help point out phase problems, then you fix them and move on to Stereo pink noise. Most if not all phase problems can be fixed by tweaking the XO's, slope or timing. Most of the time, EQ adjustments are not used to fix phase issues except for the APF (All Pass Filters)

I've read over and over these past few days, and a bunch of posts from the old Timers, those from years back, who no longer linger here, but were very deep into the profession and had years of experience and winning Competition events. Their general consensus was tuning using Stereo pink noise .... there are 30 plus threads were peeps are asking the ol 'correlated .vs. uncorrelated' question, and most of the responses were to use uncorrelated pink noise for Frequency Response measurements, and overall system tonality, and use Mono for Timing, setting levels and Frequency amplitude by ear EQ adjustments. I did not find where somebody actually pinned one of them down to state "Yes Uncorrelated when EQ'ing a Pair of L&R speakers", as that was the response I was hoping for when I started this thread.

I'm starting to ramble on here, so sorry about that, almost done. I bought the Audio Frog tuning Gear a few years ago, and used that method quite a few times, but never really like the results. So changed my method to what I explained above, and all time I was using the Audio Frog Pink Noise from the CD, and still never really liked the results. I know now that my method will not work using Mono Pink noise for Frequency Response, System Tonality AND Left with Right tuning. As the Mono method is really only good for Left .vs. Right tuning.

This whole started with me when I downloaded the newest Helix DSP software version, and within that new software they included a Uncorrelated pink noise wav file to be used in there RTA platform...I noticed they did not include correlated wav for the RTA function, probably because they included a new speaker timing method and timing wav file in the new software.


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## tjk_bail (Feb 2, 2012)

RockitFX said:


> A little off topic but related, where can a person find a house curve to download? I don't have excel on my windows machine, so using Jazzi's spreadsheet is out of the question.


copy/paste this into notepad.

20 10.5
25 9
31 7.2
40 5.8
50 4.5
63 3.2
80 3
100 2.2
125 1.5
160 0.8
200 0
250 0
315 0
400 0
500 0
630 0
800 0
1000 0
1200 0
1600 0
2000 -1.5
2500 -3
3100 -3
4000 -1.5
5000 0
6300 0
8000 0
10000 0
12000 0
16000 0
20000 0

Change the number to the right of the frequency to whatever you want to use, then Import into REW. This will give you a overall house curve..... It will not work for individual speaker curves... you would need the excel for that....


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## SkizeR (Apr 19, 2011)

Mono for your front speakers in a 1 seat tune.

/thread

Sent from my SM-G975U using Tapatalk


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## RockitFX (Aug 22, 2018)

SkizeR said:


> Mono for your front speakers in a 1 seat tune.
> 
> /thread
> 
> Sent from my SM-G975U using Tapatalk


Where can I find info on a 2 seat tune, or tuning when there is a center channel? 

Thanks Nick!


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## SkizeR (Apr 19, 2011)

RockitFX said:


> Where can I find info on a 2 seat tune, or tuning when there is a center channel?
> 
> Thanks Nick!


There are many different methods. If this is specifically regarding your car, email me and ill give you a list 

Sent from my SM-G975U using Tapatalk


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## RockitFX (Aug 22, 2018)

SkizeR said:


> There are many different methods. If this is specifically regarding your car, email me and ill give you a list
> 
> Sent from my SM-G975U using Tapatalk


Give me 10 minutes... thanks!


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## tjk_bail (Feb 2, 2012)

SkizeR said:


> Mono for your front speakers in a 1 seat tune.
> 
> /thread
> 
> Sent from my SM-G975U using Tapatalk



Are you saying "Yes Correlated when EQ'ing a Pair of L&R speakers", don't use Uncorrelated for speaker pairs".


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## jtrosky (Jul 19, 2019)

tjk_bail said:


> copy/paste this into notepad.
> 
> 20 10.5
> 25 9
> ...


FYI - If you use a "full" house curve in REW (like the one you provided here), you don't need separate house curves for individual speakers - REW can generate those for you "on the fly" from the full house curve. To do that, using a midbass speaker as an example:

1. Open the EQ tab for the midbass speaker response
2. In the "Target Settings" area on the right, select "Speaker Driver" (the "Speaker Driver" selection allows _you_ to specify the HP and LP crossover types and slopes, whereas the other selections assume butterworth, if I remember correctly)
3. Set your acoustic high and low-pass frequencies and types (use LR4 for Linkwitz-Riley 24dB slopes)
4. REW will automatically create the "Target" curve for that individual speaker from the full house curve specified in the REW preferences.
5. Adjust the Target curve level with the "Target Level (dB):" field.
6. Use the "EQ FIlters" window to tune that speakers response to the per-speaker house curve that REW generated on the fly.

You can use this for any individual speaker - REW just uses the "Speaker Driver" target settings to create the appropriate per-speaker house curve on-the-fly. If you want to do a tweeter, for example, just set the "Crossover LP type" to "None", since you don't need a LP filter for a tweeter. 

Hope that helps! REW is an amazingly powerful app - it just takes some time to fully learn it's ins-and-outs. I absolutely love the "Overlays" window as well, since it will show you the "Predicted" response of multiple speakers at the same time - so you can see how well your "predicted" left and right midbass speakers responses line up, for example - as well as seeing how the crossover for your "predicted" tweeter and mid responses line up with each other with your new EQ settings (before even taking a measurement). It's not 100% accurate, but it's pretty damn close!


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## tjk_bail (Feb 2, 2012)

Thats some good info jtrosky, thanks for the post !!


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## RockitFX (Aug 22, 2018)

I FINALLY made some progress with the REW EQ function & Helix. It's not perfect, but I forgot to turn my AC off when measuring, so there's room for improvement (once the sun goes down):


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## tjk_bail (Feb 2, 2012)

Hey. looks good !... flatten down the peak at 1200k, and your well on your way to a good tune!


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## RockitFX (Aug 22, 2018)

tjk_bail said:


> Hey. looks good !... flatten down the peak at 1200k, and your well on your way to a good tune!


Thanks! It only took me a month to wrap my brain around the process! And I've barely scratched the surface. 😳😁


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## opekone (Mar 24, 2020)

Looking good. Most of the graphs you see have the scale on the left in 5db increments. Or smaller if you've got some god car.


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## jtrosky (Jul 19, 2019)

Yeah, the "standard" on the forum is 5dB for the dB increments and I'd also recommend taking measurements with the 1/48th RTA setting (you can always smooth it down when viewing, but you want to capture the most detail you can, just in case you do need it). Sometimes, 1/3rd and 1/6th scaling can "hide" some serious peaks/dips that are much more visible at higher detail levels.

Glad to see that you are well on your way though!


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## RockitFX (Aug 22, 2018)

jtrosky said:


> Yeah, the "standard" on the forum is 5dB for the dB increments and I'd also recommend taking measurements with the 1/48th RTA setting (you can always smooth it down when viewing, but you want to capture the most detail you can, just in case you do need it). Sometimes, 1/3rd and 1/6th scaling can "hide" some serious peaks/dips that are much more visible at higher detail levels.
> 
> Glad to see that you are well on your way though!


I used 1/6th, and honestly I think it's hiding some peaks&dips. I'll do it again tonight with 1/48th once the temps dip below 90.


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## RockitFX (Aug 22, 2018)

jtrosky said:


> Yeah, the "standard" on the forum is 5dB for the dB increments



How do I change the scaling? I looked around and couldn't find an option to change it.Thanks!


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## jtrosky (Jul 19, 2019)

RockitFX said:


> How do I change the scaling? I looked around and couldn't find an option to change it.Thanks!


On the screens that shows the graphs (All SPL, Predicted SPL, etc), there are little + and - icons in the upper-left-hand corner (above the "SPL" dropdown box). Those icons will change the SPL increments on the left-hand side.


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## RockitFX (Aug 22, 2018)

Got it! Thanks


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## 156546 (Feb 10, 2017)

No. No No No. 


"Correlated" means that both channels are the same."Uncorrelated" means that both channels are not the same. 

There's no use for uncorrelated in tuning a stereo system. Everyone who is telling you to use it when tuning left and right together are wrong. 

Here's why.

Stereo systems (2-channel systems) are designed, along with stereo (2-channel) recordings to reproduce left, right and everything in between. When something happens in the left channel only, then the same thing doesn't happen in the right channel. When something happens in the right channel only, then the same thing doesn't happen in the left channel.

The idea is that the left and the right channel should match and should also have the appropriate frequency response--I'm not going to get into target curves here because that's another quagmire. 

If the lefty and the right channels match in frequency response and the phase is matched at the listening position, then things that happen in BOTH channels will appear in between the two speakers. If the sound is recorded EXACTLY the same in the left and the right channels, then it appears in the center. If it's the same but 6dB louder in the right, then it appears halfway between the center of the image and the right speaker. If it's recorded 6dB louder in the left than the right, then it appears halfway between the center and the left speaker. 

So, using correlated (mono) pink noise gives you the frequency response of the system AND the center image and everything in between when you turn on both sides. If you use uncorrelated pink noise for this, then you are just ****ing up what you've already done when you've tuned both sides individually. This condition doesn't exist in music. When the two are different, then we don't care about the sum. The only reason to even look at the response with both sides are playing at the same time is to make sure that the sum is correct. If your delay is wrong, that will show up. You may also want to use that measurement to set the level of the bass. 

But you should NOT do a bunch of additional EQ with both channels playing. 

The only use for uncorrelated pink noise is to make all the speakers in a system with an upmixer EXCEPT FOR THE CENTER play. I'm pretty sure that's not what you guys are doing here. 

Don't use uncorrelated noise for anything when you're tuning a stereo system.


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## RockitFX (Aug 22, 2018)

So you know all of those fireworks you guys think you're hearing at night? That's really just the sound of my head exploding, over and over....


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## 156546 (Feb 10, 2017)

And, I have yet to talk to one of these "old school competitors" who knows what the hell he's talking about. 

There are so many bad practices left over from that era that it's ridiculous. The other one is to center the image using 31 sine waves. This is really stupid.


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## opekone (Mar 24, 2020)

GotFrogs said:


> So, using correlated (mono) pink noise gives you the frequency response of the system AND the center image and everything in between when you turn on both sides...
> 
> But you should NOT do a bunch of additional EQ with both channels playing.


And then you are trying to EQ phase interactions with boosts and cuts. Is your method common, it's not one I've seen discussed in any medium (cars, professional audio, or home theater - though my experience is limited). The second sentiment makes the most sense to me unless you are specifically targeting phase alignment.


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## jtrosky (Jul 19, 2019)

GotFrogs said:


> And, I have yet to talk to one of these "old school competitors" who knows what the hell he's talking about.
> 
> There are so many bad practices left over from that era that it's ridiculous. The other one is to center the image using 31 sine waves. This is really stupid.


That's why I always refer people to your tuning guide (which is awesome, by the way!). People may get sick of me referring to it, but it is a gold mine of information. Not only does it explain what to do, but it also explains _why_ you do it, which is the best part. 

Thank you for that great guide!


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## 156546 (Feb 10, 2017)

opekone said:


> And then you are trying to EQ phase interactions with boosts and cuts. Is your method common, it's not one I've seen discussed in any medium (cars, professional audio, or home theater - though my experience is limited). The second sentiment makes the most sense to me unless you are specifically targeting phase alignment.


This is precisely why you shouldn't "re equalize" when both channels are playing.

If there were other common methods that worked well enough, I wouldn't have spent all the time I spent writing a process and developing a mic kit and a CD that could be sold for a reasonable price and that makes this more predictable and makes it possible for people to do this successfully. That's kind of like asking in the early 1930s, "I've never heard of penecillin before. Is it commonly used? Can't we just attach leeches to the patient's forehead?"


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## opekone (Mar 24, 2020)

GotFrogs said:


> This is precisely why you shouldn't "re equalize" when both channels are playing.
> 
> If there were other common methods that worked well enough, I wouldn't have spent all the time I spent writing a process and developing a mic kit and a CD that could be sold for a reasonable price and that makes this more predictable and makes it possible for people to do this successfully. That's kind of like asking in the early 1930s, "I've never heard of penecillin before. Is it commonly used? Can't we just attach leeches to the patient's forehead?"


I mean, I guess. But professional audio isn't really full of snake oil like end user audio is, and really that's where all this information and theory comes from. You figure the industry is a little bit more advanced than leeches, no?


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## 156546 (Feb 10, 2017)

opekone said:


> I mean, I guess. But professional audio isn't really full of snake oil like end user audio is, and really that's where all this information and theory comes from. You figure the industry is a little bit more advanced than leeches, no?


This is one of the biggest problems in car audio. Developing a home speaker or tuning a 50 element line array system in MSG are NOT REMOTELY similar to what we do in cars. Simply moving those processes to a tiny reflective space in which the speaker system is literally part of the space and in which the speaker systems cannot be separately optimized before being placed in the listening space is unique to car audio. This misunderstanding is what contributes to preposterous ideas about what's really important. Things like the supposed necessity of delay increments in hundredths of inches, the use of 1/48 octave analysis for equalziing, sitting in the car and collecting thousands of averages around each ear for use with a target curve that supposes no one in the car and no high frequency masking from one's head, the use of 1st order "phase coherent" crossovers, systems with no tweeters, thinking that aiming a speaker on axis eliminates reflections and the list goes on and on and on and on--and it's all because basic acoustics isn't applied to the application--the assumption is that the applications are the same.

There isn't anywhere one can go for formal training and there isn't a lot of specific information about this outside some AES papers written by engineers who build OEM systems. Very few real experts make youtube videos because there are more useful ways for experts to provide the benefit of what they know to people who will be able to make use of the information. 

And that's why I provide the info I've provided and the tuning kit that I provide.


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## RockitFX (Aug 22, 2018)

GotFrogs said:


> Things like the supposed necessity of delay increments in hundredths of inches, the use of 1/48 octave analysis for equalziing, sitting in the car and collecting thousands of averages around each ear for use with a target curve that supposes no one in the car and no high frequency masking from one's head,


I wish I would have had this info yesterday, it would have saved a lot of sweating in my car! :-D

But seriously though, if not 1/48th octave, what should we be using? (I'm sure it's in one of your tuning guides, but my brain is only so big and that info was forced out weeks ago to make room for something else). Thanks


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## 156546 (Feb 10, 2017)

Use 1/3 above 1k and look at 1/6 when you feel like you need more info. Us 1/6 below and look at 1/12 if you feel like you need more info. Too much "precision" will land you squarely in the weeds.


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## RockitFX (Aug 22, 2018)

GotFrogs said:


> Too much "precision" will land you squarely in the weeds.


😂😂😂😂😂😂😂😂😂😂😂😂


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## tjk_bail (Feb 2, 2012)

GotFrogs said:


> No. No No No.
> 
> 
> "Correlated" means that both channels are the same."Uncorrelated" means that both channels are not the same.
> ...


I really want to get a full understanding about this in regards to using Correlated vs Uncorrelated pink noise, so I'm gong to pose this to you.

I think everything you said is totally correct ...IF... the tuning method is using a single microphone placement (not sweeping the mic), and performing a Left .vs. Right equal frequency response system, then use Correlated noise.

But, if you are the type who measures using the sweep method (moving mic left to right in front of face) and are performing a Left with Right response system, then use Uncorrelated noise.

Am I way off on this, or is it just hands down, only use Mono regardless of measurement technique.


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## 156546 (Feb 10, 2017)

No. No need for uncorrelated noise. And you shouldn't equalize with both channels playing unless it's a general or global target curve adjustment--like more bass. Sitting in the car and waving the mic around doesn't change the appropriate stimulus, but it does change the target curve a lot. Who provides a target curve that includes all of this? No one that I know of.
So, if you're doing this and using any of the published targets, chances are you have to go back and add some high frequency output--probably by ear.


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## jtrosky (Jul 19, 2019)

tjk_bail said:


> I really want to get a full understanding about this in regards to using Correlated vs Uncorrelated pink noise, so I'm gong to pose this to you.
> 
> I think everything you said is totally correct ...IF... the tuning method is using a single microphone placement (not sweeping the mic), and performing a Left .vs. Right equal frequency response system, then use Correlated noise.
> 
> ...


Keep in mind that the L+R combined response should be the same as the left and right individual responses - just a few dB higher due to summation. If the combined L+R response doesn't look just like the individual L and R responses (only higher), then something is wrong (time alignment error or phase-related issue causing cancellation, for example).

Before I realized the power and usefulness of Allpass filters, I would do what you are talking about (with mono pink noise though) - I would adjust the individual left and right responses however I had to in order to make the L+R combined response match my target curve (even though the individual responses would no longer match the curve). However, as I continued to learn, I realized that the L+R combined response should mirror the individual responses, just a little higher due to summation - and if it didn't match the individual left and right responses, then I needed to figure out why and fix it. This way, you never need to "tune" L+R combined response - it just falls into place based on the individual left and right responses - and matches the overall "shape" of the individual responses. I ended up having to use a few allpass filters to get the L+R combined response to match the individual responses - without using any EQ.

At least that is how I now understand it - I'm certainly no expert!


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## tjk_bail (Feb 2, 2012)

Okay, got it. Thank You !!

You asked who provides a target curve that includes all of this....... Audiotech-fisher, they supply a Uncorrelated pink noise file to use with their DSP RTA platform, and a global target curve... and they do not supply a Correlated pink noise for RTA....I'm not all that familiar with their RTA, but I think its meant to be used, to tune the entire system all at one time, so maybe thats way they supply Uncorrelated....

Its just kinda frustrating.... the TOP guys in this field like yourself, and other Top guys have completely different opinions about this subject....I'll try both, and just go with sounds best to me.....


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## tjk_bail (Feb 2, 2012)

jtrosky said:


> I realized that the L+R combined response should mirror the individual responses, just a little higher due to summation - and if it didn't match the individual left and right responses, then I needed to figure out why and fix it. This way, you never need to "tune" L+R combined response - it just falls into place based on the individual left and right responses - and matches the overall "shape" of the individual responses. I ended up having to use a few allpass filters to get the L+R combined response to match the individual responses - without using any EQ.
> 
> At least that is how I now understand it - I'm certainly no expert!


 okay... I follow what you are saying here...Thanks for that explanation.. Make the tweeks to the Left or the Right to get the combined Left&Right together to follow the curve... actually I think I knew that... .I've just been overthinking everything lately.....


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## jtrosky (Jul 19, 2019)

tjk_bail said:


> okay... I follow what you are saying here...Thanks for that explanation.. Make the tweeks to the Left or the Right to get the combined Left&Right together to follow the curve... actually I think I knew that... .I've just been overthinking everything lately.....


Kind of... BUT.... You really shouldn't need to tweak the left and right responses to get the combined response to match the curve. If the individual responses match the curve, then the combined response should also match the curve automatically. If the individual responses match the curve and the combined response does not, then you have some sort of issue - whether it be a time-alignment issue, a phase-related issue (cancellation, for example) or some other issue (they are the only two I can think of that would cause the combined response to not match the individual responses). 

I have some examples in another thread of what a phase issue looks like - basically a big dip in the combined response that doesn't exist in the individual responses. I now use allpass filters to fix those issues - so that, in the end, the combined response matches the individual responses pretty much exactly (there will be very minor differences, but).

Here is a for example of my current tune (the combined response is the same "shape" as the individual responses):










Here is an example of an earlier version of the tune where I had some obvious phase-related issues - which you can see by the dips in the combined response that don't really exist in the individual responses) - the combined response almost reaches down as low as the individual responses in those areas - I ended up using allpass filters to "fix" those:









Hope that helps show what I meant. If you just use EQ to get the combined response where you want it, then the individual responses wouldn't match the curve anymore. The goal is really to get the individual AND combined responses to match the curve. 


Disclaimer: Again, I am still learning as I go here - so this is the way that I understand things - and what's worked for me (my current tune is the best my system has ever sounded). Just wanted to mention that before someone came along to tell me how wrong i am.


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## tjk_bail (Feb 2, 2012)

Thanks man.... You nailed it for me this time. I have seen that above example before, but I think it really hit home this time. Thanks again for taking the time to help me understand and for taking the time for a really good response !!


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## tjk_bail (Feb 2, 2012)

jtrosky said:


>



I really like your Overall house curve... can you post the the info.... I'd like to use those numbers. Freq/db's


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## jtrosky (Jul 19, 2019)

tjk_bail said:


> I really like your Overall house curve... can you post the the info.... I'd like to use those numbers. Freq/db's


I really don't have one in a typical house curve format as this just kept evolving along the way, but here is an export of my current overall response from REW - it can still be uses as house curve in REW - it just won't be perfectly smooth because it's an actual measured response instead of a "perfect" target response. However, you can use it in the REW house curve field as a starting point and then evolve it as you need to for your setup/preferences. For example, I only have an under-seat sub, so my sub bass falls off quickly at 35hz, whereas those with a real sub can go lower. You'll also probably need to adjust the treble areas for your setup/preferences as well. My tune is also a little bass-heavy when sitting still, but I found that extra bass makes things sound better while actually driving, which is what I'm most concerned with.

But like I said, it's a start....

JTCurve-CDT24.txt

Like I said, I'm still learning all of this crap myself - and I was changing speakers very often before, so I had to keep re-tuning because of that. Really happy with my current speaker setup though, so hopefully, I'll leave things be for a while (might still make a few tonality-related changes, but they would be minor at this point).

Good luck - would love to see what you end up with!


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