funny results setting gains with DMM

[capitolj80]

Sooo.. The two times that I went ahead and used a dmm set the amp gains in a car (mine and my bro's), I used my phone to play a 60hz sine tone as I don't have one on a cd (nothing currently to burn it with). I turned the phone's player volume all the way up cuz I figured I was supposed to be sending the head unit the full signal. I was very suprised by how low the gains on both amps were at the proper voltage. I'm talking MAYBE 1/8 of the way up on his, barely over 1/4 on mine. Both our head units put out 4v. In his car, when I put a cd on, the voltage was bouncing between 13 and 20 (target was 28.2). In my car on a cd, it was between 31 and 40 (target is 49). Was using the phone's player a mistake? Or is this just the nature of using a tone to set gains?

[ttocs]

yes using a seperate source, of probably very poor signal quality, to tune your stereo would be like tuning your cars motor to honda standard even though you drive a ford.

In general though tuning a system with a meter is like trying to to fine wood carvings with a flat head screw driver and a 15 lb sledge or do fine painting with a 4" wide brush. Sure it will get you close but its just not the right tool for the job and there is a reason you will have a hard time finding any professional installer that will say he tunes systems with meters and it isn't because they don't have a meter.....

[capitolj80]

what would be the correct tool? oscilliscope (dont have one)? my ears (have two)?

[ttocs]

yes and yes. if your ears are the final judge of what sounds good/bad then why would you not trust them? People have been doing it like that for decades, its not rocket surgery and it makes you a better informed listener in the long run...

[ajaye]

Using your phone's 1/8" output (headphone jack) is essentially adding another gain stage to your signal path. You certainly don't want the volume at its max. Ideally you want to bypass the amplification if possible, for instance using an iphone's docking cable output with an adapter vs the 1/8" jack.

I'm no expert in car audio tuning specifically, but my ears have served me well enough in most home and work situations. I prefer to sacrifice spl for the best sound quality possible though, which has gotten me into many arguments about gain settings in clubs, especially when any of my equipment is involved (the modern day club DJ mantra seems to be "red vu meter = PARTY TIME!"). Just remember to account for equalization adjustments too and readjust gains down the signal path accordingly, low frequency boosts and multiple band boosts especially. When in doubt, cut vs boost.

[trickyricky]

what would be the correct tool? oscilliscope (dont have one)? my ears (have two)?

Wow, I dont want to sound like a jerk or know it all....but a lot of people can't hear clipping so they set their gains where the output signal is clipping.

Long term or even short term clipping can damage your speakers and/or your amplifier. Right now am removing all caps and op amps due to some idiot that drove the amplifier into clipping all the time (it also cause the four filter caps to leak-almost damaged the circuit trace/board).


With a scope you can determine when your input and output signal starts to clip. Input signal being that from your HU (I notice on mine the signal clips at 33 out of 35 so pretty good) and your output signal being that from your speaker terminals (you match this with your head units signal and get the most out of it without clipping or damaging anything).

You know that steve maede (or what ever his name is) gain setting "thing" cost around 150.00 for one, you can get a used Tek scope for the same price or a bit more (200.00) and get better results and use it for other things besides SETTING GAIN's lol.

[ttocs]

I keep hearing this theory that "alot of people can't hear clipping" - what prevents them from hearing it? Is it just something in their DNA that prevents it or is it just that they hear this theory and want to take the easy way out? Maybe its true but if it is and they continue to tune their crap via meter then they will never be able to hear it and due to nothing but their own actions. Again, listen to your music, don't let your meter tell you what to do they are all disco fans.........

you can buy a portable o-scope on the bay for $80 so not sure why you would buy anything else made to do it for more then 2x as much.

[ajaye]

I keep hearing this theory that "alot of people can't hear clipping" - what prevents them from hearing it? Is it just something in their DNA that prevents it or is it just that they hear this theory and want to take the easy way out? Maybe its true but if it is and they continue to tune their crap via meter then they will never be able to hear it and due to nothing but their own actions. Again, listen to your music, don't let your meter tell you what to do they are all disco fans.........

you can buy a portable o-scope on the bay for $80 so not sure why you would buy anything else made to do it for more then 2x as much.

I wondered the same thing. It is seriously not a hard concept to grasp, I still have to laugh at "clipping" being like the end all voodoo no no word in car audio, when it still seems like so many people don't know what the fuck they are talking about.

If you "can't hear" a signal clipped to the extent that its going to be damaging to your system, you may want to reconsider spending big money on audio gear. It is completely possible, and these days very feesible with internet downloads from blogs and the like, that your source material may contain a clipped signal. No amount of gain tweaking with scopes and test tones can help you when that happens.

I'll be happy to provide some examples of what clipping sounds like with some pictures to help illustrate what it is you are supposed to be hearing being "clipped" if anyone is unsure of what we are talking about or wants to know what to listen for.

[trickyricky]

Its a pretty common thing among teens and bass heads. They think the gain pot is really a volume control and "why the hell am I going to set my volume at half way when I can set it full blast and get all more power!!"- atleast thats what they think.

I never said "EVERYONE" cannot hear clipping, just those that are real young and dumb or just straight idiots that are into SPL. Nothing against SPL, but most people dont understand or hear clipping --- well atleast all the people I ran into, lol.


Hand held scopes are neat only because their portable. Can you please please name me one that has a clean display such as a Tek scope, thats still under 200.00? I've seen the display on those hand-held scopes and trust me you can't tell if your signal is all that good, because of the "crappy old-display" look, the sine waves look weird (almost like trying to draw curved lines on a windows95 or older paint program).

[capitolj80]

OMG I STARTED A PHORUM PHIGHT!! LOL I'm gonna go ahead and set it by ear and then maybe put on a test tone CD to confirm my accuracy.

[Eric D]

I can't hear clipping and I have been in car audio for several years now. Any time I set gains by ear, when I go back and look at them on my o-scope, they are clipped. It is not a ton of clipping, but when your goal is no clipping, any amount is no good.

[ttocs]

Its a pretty common thing among teens and bass heads. They think the gain pot is really a volume control and "why the hell am I going to set my volume at half way when I can set it full blast and get all more power!!"- atleast thats what they think.

agreed

I never said "EVERYONE" cannot hear clipping, just those that are real young and dumb or just straight idiots that are into SPL. Nothing against SPL, but most people dont understand or hear clipping --- well atleast all the people I ran into, lol.).

well I too never said everyone, and I think even most is streching a bit. I think people have an idea of what sounds good or as like he said above, you might reconsider getting good gear...

Hand held scopes are neat only because their portable. Can you please please name me one that has a clean display such as a Tek scope, thats still under 200.00? I've seen the display on those hand-held scopes and trust me you can't tell if your signal is all that good, because of the "crappy old-display" look, the sine waves look weird (almost like trying to draw curved lines on a windows95 or older paint program).

http://www.ebay.com/itm/ARM-DSO201-Port ... 1c25e59029

That scope was recomended to me by an industry pro and used by alot of other in the biz of installing fulltime, I love mine. Not sure what you mean by a clean display if you are using scopes you can't read, well you minus well use your phone as your source and your meter, or even just hire a tarrot card reader to tell you higher/lower(hope the death card doesn't come up).

Eric while you say you can't hear clipping you can't tell me in your years of experience when you walked either into a club or was heard a cars system and though,"Fuck that thing is clipping!!!". I am sure your ears are as good as anyones and yes it is possible to set it by ear and put it into clipping, but I think its more likely to happen to an uneducated listener that used his meter and thinks it has to be good the meter said so.... Those people would be more likely to just crank it up and ignor the obvious sounds of clipping, while still complaining that they can't hear it. Yes there is only one way that you will get to know what clipping sounds like and every listener should know what it sounds like to be able to turn it down when its needed.

[ajaye]

I can't hear clipping and I have been in car audio for several years now. Any time I set gains by ear, when I go back and look at them on my o-scope, they are clipped. It is not a ton of clipping, but when your goal is no clipping, any amount is no good.

*disclaimer, I have entirely too much time on my hands.
OK, here's where it starts to get tricky, especially in car audio and I'll try to explain why. Recorded music is not a perfect thing. It used to be a lot closer to being at least somewhat standardized; the mastering houses had the source material and they knew they could only fit so much information on a record physically, so the RIAA standards were used to take out a certain eq curve to save space on the record, and usually everything under 80 hz would be cut mono vs stereo since its non directional anyway. When you plug a turntable into the "phono" input on your receiver, there is a preamp that is reinstating that standardized eq curve before the music is amplified and played through your speakers. If you've ever tried to play a record through a regular line-level input, you heard how shitty it sounded, and that is why.

Now, with the rise of the internet download, the amount of "information" if you will that can be contained in a song to create the actual sound is essentially limitless with regard to distribution medium (ok bandwith yeah yeah, you know what I'm saying). I can show you many many examples of newer songs that are label releases, post production and mastering has been completed, and they are actually clipping. Would you ever hear it? Doubtful, the only reason I notice it is because I use different software that plots out the waveform and can tell me its clipped.

What's my point? Every single cd, cassette, mp3, wav, flac, whatever is different. If you look at any professional sound reproduction tool (ie DJ mixer, mixing console, etc) the gains are set each time the source material is changed prior to every pushing the signal further down the line. So without changing anything else throughout the entire signal path except the record/cd that is playing, one gain setting for the first record may be peaking at about 0dB, but the next one may actually be clipping at the same gain settings.

In car audio, your gain adjustments are not easily accessible in most cases. You would probably end up with a very conservative sounding system if you have your gain set to never, ever clip regardless of source material. You (and I) probably have a rough time hearing when a hot source comparatively speaking has some hi hats barely peaking above clipping (0dB). Its really not a big deal for it occasionally. We are talking about serious fucking disregard for both your ears begging for mercy before that's going to do some damage.

So without either seriously missing out on some of your systems abilities, or constantly popping your trunk and making adjustments when you change cds, you will probably have some amount of clipping happen at some point. What you need to be able to recognized is a severely over amplified signal, which in almost any case, is going to be audibly noticeable to even most novice listeners. This does not mean high volume. So one way you can sometimes help yourself recognize it is when something still sounds off even when your volume is at a moderate level. Again, I have to agree with ttocs, trust your ears, and the more you do, the more you are going to be able to decipher what it is they are telling you.

[ttocs]

that pretty well covers the way I feel exactly. Well said.

[Mr. Wild]

Moral of story: Use sufficiently powerful amps with headroom to spare. Then you are less likely to clip your shit.

In other words use Phoenix God amps and bridge 'em.