# Oscilloscope and DSP



## aykhan (Oct 22, 2015)

I have a 3 amp system active system. A 4 channels feeds the tweets and midranges,a 2 channel feeds 2 midbass' and a single feeds two subs wired at 1 ohm. I need to set up amplifier gains. I was thinking about using the SMD DD1 but enough people have said that they're not sure if it's accurate enough and I haven't read any head to head comparison with an oscilloscope. So my question is: which is the best oscilloscope I can buy within the 100-150 buck range? My second question is that in an active system run through a DSP, do I do the tuning in the DSP before setting gains or after or does it not matter? Appreciate all the advice I can get.


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## aykhan (Oct 22, 2015)

Also has anyone looked into these smartphone oscilloscope apps??? Are they any good?


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## Weigel21 (Sep 8, 2014)

Buying an O-Scopes to set gains is "for many" a waste of money, as is the DD-1. The DD-1 detects 1%THD, the same point in which most scopes will begin to show deformation of the wave and the point in which the vast majority of people can hear distortion when playing test tones. 

"I" myself picked up a lower cost DSO201 and proved to myself that my ears could in fact detect 1%THD when playing test tones. Still, setting gains by ear with the aid of test tones is not for everyone, but even so, I'd not invest too much in an O-Scope. The DSO201 I bought was merely $57 back when I bought it and it will work perfectly fine for setting gains. I wouldn't even consider a smart phone app for setting gains. 

Just remember, setting gains using a 0dB test tone will often result in lackluster output. Most recommend using anything from -3dB to -10dB tones to set sub amp gains, but in the end, one will usually do fine adjustments by ear to blend the system together.


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## aykhan (Oct 22, 2015)

Is there a tutorial somewhere as to how to use this device. I'm totally lost. Do I plug the single probe into the positive of the speaker output in the amp and play the required frequency (1000Hz for the component amps and 40Hz for the sub amp)?


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## fcarpio (Apr 29, 2008)

I've used a cheap O-Scope to set gains. Works for me. But as mentioned before, using 0db test tones is going to give you very low output. I usually do -10db for subs and -5db for everything else and take it from there.


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## aykhan (Oct 22, 2015)

Excuse my ignorance. By setting the test tone are we talking about the volume of the head unit?


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## gijoe (Mar 25, 2008)

O-scopes are a waste of money for most people in car audio. I certainly wouldn't buy one simply for gain setting. You system can sound equally as good by setting your gains by ear, or with a DMM. Gains simply need to be set somewhere within a range that allows you to turn up the music to satisfactory levels, and prevent damage/excess distortion from your speakers. This isn't a singular point on the gain knob. Simply changing songs can take you from optimal to non-optimal gain settings, meaning, no single gain setting will be "perfect" for every song you play due to the differences in recording levels. 


O-scopes are great tools, don't get me wrong, but they are unnecessary for setting gains. The money that you would spend on an o-scope could be put towards a very nice DMM, which would be much more useful for car audio (and any other electrical) projects. The only time I would use an o-scope to set gains would be if the amps were drastically underpowered, and I needed to get every single watt from them, and avoid clipping. Besides that, any modestly powered amp will produce enough clean power for very decent listening levels, and a scope won't do anything to improve the sound.


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## aykhan (Oct 22, 2015)

This makes very good sense. Any tutorial for a DMM gain setting method? Also should I do the tuning in tMy DSP before setting gains or leave everything at flat?


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## fcarpio (Apr 29, 2008)

aykhan said:


> This makes very good sense. Any tutorial for a DMM gain setting method? Also should I do the tuning in tMy DSP before setting gains or leave everything at flat?


I am interested in this as well.

EDIT: Here is a tutorial on how to set gains using a DMM.

https://www.youtube.com/watch?v=bRzn1KCX2sQ


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## Proboscis (Mar 15, 2016)

Nice Thanks for the link


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## Weigel21 (Sep 8, 2014)

Unless your amplifiers are capable of producing the power you are wanting to set the output for and your car's electrical system can maintain proper voltage to those three amps, the DMM method isn't a method "I'd" recommend, as it has no way to inform the user if the output it's measuring is clipped or clean power. I don't like to recommend the DMM method for setting gains when maximum clean output is the end goal. They can work well for setting gains to limit output to a safer level for the driver being used (again, if one is completely sure the amplifier and electrical system allow for said port to be produced cleanly).


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## aykhan (Oct 22, 2015)

My subwoofer amp can churn out 2300 watts at 1 ohm and I have 2 Morel Ultimo Ti subs wired at 1 ohm each 1000 RMS, the midbass' have a separate 2 channel amp and the tweeters and midranges have a 4 channel amp and all Focal Utopia Be 7 active components are well supplied. These amps are capable Audison Thesis. All wiring is 0 guage OFC and I am in the process of upgrading my alternator to 320 amperes. I think a DMM might be fine for setting gains?


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## 14642 (May 19, 2008)

Turn the volume control of your radio up to about 3/4. Turn the gain of your high frequency amp (nothing else should be playing) up until you begin to hear some distortion. Stop. Turn the volume of your radio all the way down. Listen for high frequency hiss from your tweeters. If you don't hear any, set the levels of the other amps according to what sounds best. If you do hear hiss, turn the gain of your high frequency amp down until it goes away. Then, set the levels of everything else so it sounds good. 

Done. 

The O-scope method is useful when you have several signal processors in the chain and each one has gain controls and some kind of a preamp. This was common 25 years ago when crossovers, equalizers and amplifiers were all in separate boxes and nothing had differential inputs. Noise of all kinds was a hassle and having one of the processors clip before the others sounded bad. 

These days, we often have a radio and some amplifiers or the same with an additional DSP. All of this fretting over gain settings is outdated.


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## jdunk54nl (Apr 25, 2015)

You will want to set gains before you do any eq'ing in your dsp. Otherwise you will spend all that time getting everything level matched and go to set your gains and mess up all of your levels. This will also give you the max volume of all of your speakers to level match off of. There will be a speaker that is the quietest out of the bunch, usually farthest away from you, when everything is set max gain and nothing done in your dsp that you will then use as your reference speaker for setting the levels of your other speakers.

Have fun!


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## aykhan (Oct 22, 2015)

I'm going to try and summarize what I've learnt here so far. Do let me know if I missed anything.

So I need to go back into my DSP (Helix DSP Pro) and set everything back to flat? Does that apply to the Time Alignment also?

After that's done I unplug the speakers wires from all the 3 amps. 

Use the Ohms Law to calculate the desired voltage out off each amplifier making sure it's not above the RMS of my componet speakers or subwoofer. My subwoofer amp gives 2300 watts while my subs total 2000 so I use Ohms Law to calculate for 2000 watts. (My amps can be set to class A or AB or High Current and at each setting they pump out different wattage. It's summer how and they heat up so I am using class AB for the component amps and Hi Current for the subs amp)

Turn the head unit volume to 3/4 of max

Play a high frequency 1000Hz sine wave file to adjust the gains of the 4 channel amp supplying the tweets and midranges. Use same 1000Hz file to set gains for the 2 channel amp for the midbass'. Then play a 40 or 60Hz sine wave file to set gains of the subwoofer amp. When this is done the gains are set and likely there will be no clipping. Does it make sense to probably set a volt or two lower than the calculation to make sure I'm avoiding clipping???

Now go back into the DSP and do the EQ


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## bugsplat (Nov 7, 2014)

Used an oscilloscope all today fixing levels I thought were right. That little scope sees everything wrong in my setup. I will never build a system without one. Got the dso200 and it worked great. Best $50 I've ever spent


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## aykhan (Oct 22, 2015)

Although the SMD DD1 is simple and probably close to accurate, the DMM approach also likely works and is dirt cheap but it is true that what you see from a Oscope is actually VISUAL. The question remains that if the amps have enough power for the speakers do we really need to be that accurate? Is it not OK to use a cheap DMM and maybe set the gain a little lower to be safe? For example my subs are 2000 watts RMS total and amp can give 2300 watts so why don't I just calculate for 1900 watts and set gains accordingly? There really isn't an SQ compromise here unless you really want to crank up the system all the way up, correct me if I'm wrong.

Why not consider buying a decent Oscope and then selling it on eBay after use. Once the gains are set I don't think they ever need to be changed for that amp? Check out this one, it's seems quite simple to use compared to the dso nano 201 202 or 203

http://m.ebay.com/itm/TEST-PRODUCTS...loscope-True-RMS-DMM-/281616461409?nav=SEARCH


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## Weigel21 (Sep 8, 2014)

The DSO-201 isn't difficult to use, heck, it has an auto mode if one doesn't want/know how to make adjustments on it. 

Meade used that same True RMS/O-Scope in some videos when setting gains and showing the DD-1 working. IMO, it didn't appear to have a very nice easy to see display (poor resolution), but perhaps there are adjustments that can be made to improve it or it was just poor camera work. 

If a person has use of a True RMS DMM as well, then it's not a bad tool, but it is 5 times as much as the DSO201.


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## aykhan (Oct 22, 2015)

I read some review about crappy software in dso 20- which needs to be upgraded to make the unit worthwhile.


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## aykhan (Oct 22, 2015)

Will the dso nano 201 be able to handle the output from my amplifier? My 2 subs wired at 1 ohm are 1000 watts RMS each i.e. total 2000 watts RMS and the amp can supply 2300 watts. That's something like 44 volts per Ohms law if I were to check with a DMM as I went up on the gain. Will I need to get some other probe or will the stock probes suffice?


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## nineball76 (Mar 13, 2010)

Use the right tool for the job. a dmm can never fully replace a scope. And honestly the 3/4 volume method is crap these days. Granted it will make sure you never clip out of your head unit, but if your head unit is anything like a Kenwood Excelon, 3/4 will be low voltage. The Excelon is very clean at full volume 35/35 (5v). But it takes 26v to even reach 1v. And about 1/2v each click after that. So on that head unit, 3/4 volume will only be about 1.5v. 

This is the one I have and love. Add a bnc to rca adapter to easily fit rca ends to the unit. 
VELLEMAN HPS140I HANDHELD POCKET SCOPE 40MS/s (probe included) https://www.amazon.com/dp/B004KKTUV6/ref=cm_sw_r_other_awd_PpQ7wb1BKAQTJ


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## Weigel21 (Sep 8, 2014)

The software that came on the one I got was fine, but since I too had heard all the rumors that the software needed to be upgraded, I did just that. Honestly, I liked the original software better. The only issue with it (IMO) was that there was always a purple wave in the background upon poweing it up that one had to either deal with or go into the menu to turn off every time. A little annoying I guess, but othe than that, I didn't have any issues with the original software. I ASSuME many of the complaints came from people who got a unit with even older software or just flat out refused to learn even the basics about an O-Scope. "IF" you do get one and want to update the software, I could potentially help with that. It was a bit of a ***** to upgrade. There are many different updated software files one can put on the unit, but not all will work. I went through three before the SO201 was even usable again (wouldn't actually power up with "incompatible" software), then I had to learn how to make adjustments with the new software. Again, I'd have just left it alone had I known what would have become with updating the software, I mean the purple sound wave wasn't that big of a deal to me. 

And 44VAC shouldn't be an issue, it's got a 1X/10X probe. Granted, if you set to 1X, it'd probably go off scale to where you can't see the full wave, but I don't think that'd be high enough voltage to do any damage to it. Setting the probe to 10x should allow it to be just fine. 

Again, an O-scope, nor a DMM are dire in setting gains successfully. 


It's been said before and it's been mentioned again, one should find their HU's maximum clean volume level when setting gains, 3/4 volume can be a crap shot at best. If one is using the internal amp for anything, 3/4 could result in the internal amp clipping. And if one is using more budget minded gear, 3/4 could result in clipping in the preamp. Then with higher quality gear, 3/4 is well below maximum clean volume and as it's been said before, the output of a HU is not linear.


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## bugsplat (Nov 7, 2014)

Weigel21 said:


> The software that came on the one I got was fine, but since I too had heard all the rumors that the software needed to be upgraded, I did just that. Honestly, I liked the original software better. The only issue with it (IMO) was that there was always a purple wave in the background upon poweing it up that one had to either deal with or go into the menu to turn off every time. A little annoying I guess, but othe than that, I didn't have any issues with the original software. I ASSuME many of the complaints came from people who got a unit with even older software or just flat out refused to learn even the basics about an O-Scope. "IF" you do get one and want to update the software, I could potentially help with that. It was a bit of a ***** to upgrade. There are many different updated software files one can put on the unit, but not all will work. I went through three before the SO201 was even usable again (wouldn't actually power up with "incompatible" software), then I had to learn how to make adjustments with the new software. Again, I'd have just left it alone had I known what would have become with updating the software, I mean the purple sound wave wasn't that big of a deal to me.
> 
> And 44VAC shouldn't be an issue, it's got a 1X/10X probe. Granted, if you set to 1X, it'd probably go off scale to where you can't see the full wave, but I don't think that'd be high enough voltage to do any damage to it. Setting the probe to 10x should allow it to be just fine.
> 
> ...


Agree 100%. Upgraded mine and It seemed no better, just no purple line. Ended up reflashing and going back. Even this basic scope has everything you could need just sit down for a few hours and study all the options. I played the whole DMM game for years. People are kidding themselves if they thank it is as good as a scope. Spend the $50 guys, just buy one


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