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Author Topic: "gain structure"  (Read 4192 times)

bellulah

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"gain structure"
« on: May 14, 2004, 04:29:04 AM »

hello everyone!

so i need help understanding something.  a friend of mine was telling me about a sound guy he was talking to, and the guy told him that "people just aren't taught about gain structure anymore."

so that is my question - what is gain structure?  i've been recording for a little over three years now, and i have a good idea of what's going on.  i know about mic level vs. line level, and using gain to compensate.  is that what he's talking about?  contextually i was led to believe that he was speaking in terms of just mixing.  

any help understanding the beast known as gain structure would be greatly appreciated.

thanks!!

josh dennison
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saxist

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Re: "gain structure"
« Reply #1 on: May 14, 2004, 09:14:31 AM »

I just did a web search through Yahoo! for "gain structure."  It took about 15 seconds, and the top 12 hits were:

1. Advanced Gain Structure
www.community.chester.pa.us/technote/gainadvd.html

2. Gain Structure
www.thenoizeworks.co.uk/tech2.html

3. ProSoundWeb.com | Study Hall Featured Site (PDF)
www.prosoundweb.com/studyhall/studyjump.php?pdf=gain
 
4. live_audioStudyHall-Gain Structure
www.live-audio.com/studyhall/gain.html

5. [same as #3]

6. Basic Gain Structure
www.community.chester.pa.us/technote/gainbasc.html

7. Gain Structure
www.stressfreestudios.com/learn/topics/gain_structure.html
 
8. Prefect's Pages.. Publications .. MQP .. Gain Structure Diagram
www.gweep.net/~prefect/pubs/mqp/node46.html

9. Gain Structure
www.padj.org/memonly/2001/gainstructure.html
 
10. Gain Structure - 1
www.mmproductions.co.uk/gain1.html

11. Levels and Gain Structure
www.donlisms.com/html/gainstruc.html
 
12. Tip #31 Gain Structure Part 2
www.geocities.com/tcsound_1999/Tip31GainStructurePart2.htm

Use of an internet search engine will often get answers to question like this a lot faster than posting on a professional forum.... (also note that one of the hits above leads to the study hall on this website)

Eric Honour
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bellulah

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Re: "gain structure"
« Reply #2 on: May 14, 2004, 11:43:54 AM »

okay...

look, i apologize in advance here.  i never say things like this, but i just have to for the sake of people at the same stages of their career as me.  

people beginning to understand the subtle nuances of this art get to a point where everything is a blur.  you get to a threshold where you totally get how to capture sounds, mix, just be good at what you are doing.  then you start to wonder about those other possibilities. like what makes things tick.  

so you stumble on a forum such as this.  amazing in and of itself - a whole mass of like minded people seemingly willing to help out one and all.  and some will.  there was a post not too long ago about impedence.  did he get flamed for asking about the apparently general curiosity question?  i have pre's with impedence buttons, and my instruction manual tells me what it does.  big whooop.  but it can't tell me what posting in a forum like this can - practical situations, applications, examples... just real people telling about real experiences.  lamen's terms, as that poster put it.  

the same thing applies to my question about gain structure.  i'm not an imbecile (even though i can't spell so hot sometimes) - i did my homework.  yes, i saw thsoe websites.  that's all fine and good if i had an osciliscope, or seven things in a signal chain, or every mic an amp with a pad like the examples given.  

but i'm a dude with some mikes who records folk music.  the sound is all in the mic, right?  how do i benefit from gain structure?  i can read definitions till monday but that won't help.  sound guy that i mentioned - he was using the pre's on the board - mic to board to PA.  that was his signal path.  how does gain structure help him.  

i came here to ask that question hoping to get some real life 'here's what happened to me' or 'i was a sound guy and here's what he meant in a simple path like that...'  and sure, i'll take partial blame.   maybe i should've suspected that i could get flamed by a 'professional,' and provided every last detail (such as his signal path).  and i didn't - my bad!  

but hey, its cool.  to each his own.  again, sorry my first post seemed ignorant, and sorry about this rant here that might not do me too well, either.  but to every other person like me out there who reads this, who wants to practical advice from people who have lived it for 20 years, and who wants that personal touch to their learning experience,  don't let this stop you from posting!!  that's the reason this board is here!!  

lord knows this won't stop me.  i'll post more questions, i'm sure.  and i definately will come here to learn from the tons of professionals that here, as well as the people like me who just stumble across things as they go.

thanks/sorry
josh dennison
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Peter Simonsen

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Re: "gain structure"
« Reply #3 on: May 14, 2004, 01:56:51 PM »

josh,

Look I really don't think that Eric Honour was trying to put you down in any way..at least thats not how I read his post. He was merely to the best of my understanding trying to help you, and must have used a fair amount of time doing the "copy&paste" thingy. I have read/scanned quickly the first of the links he did for you, and it pretty much explain the subject for you...I don't know abut the rest, but I would expect that you would find merely different ways of looking at the topic at hand.

This is a quote from the first link..pretty much sums it up..

Quote:

Realistically, audio signals at or near the noise floor of a system are not useful because the signal will not be significantly louder than the noise. Therefore, some minimum usable level must be assumed below which the electronic noise is considered objectionable. A signal to noise ratio of 20 dB is considered minimally acceptable for good intelligibility. For a high quality system 30 dB would be a better figure to use. Using this value, the range from this minimum signal level (30 dB above the noise floor) to the clipping level is the usable signal range window for the system (also called the dynamic range in my way of thinking).


Anyway I do think people here are trying to help.. Smile  

Kind regards

Peter



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david gregORIO

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Re: "gain structure"
« Reply #4 on: May 14, 2004, 02:44:25 PM »

 I'm a relative newbie to recording and pro-sound in general myself, I generally lurk because I've had my hands full just reading the info that's already out there.

I think I understand your delema, basically most of the info available on the term "Gain Structure" is targeted towards understanding and achieving proper gain structure,
 the goal of which is to make sure that every piece of a signal path is used within it's optimal range to eliminate unwanted distortion of the signal.

Everything you include between the sound source and the recording medium is going to affect this. Keep in mind that unity gain and negative gain (loss) counts as far as "gain structure" is concerned.

I don't think I've ever heard or read anyone specifically talk about "using gain structure" to whatever purpose. Technically when someone is using gain structure to effect their recordings they are actually purposely using improper gain structure (ie distortion pedals, running compressors hot or pre's hot etc.) to achieve a desired sound.  This happens all the time, but it's hardly ever referred to in the context of "gain structure".

More often you'll see/hear people talking about a certain piece introducing pleasant harmonics or distortion (especially tube equipment) when overdriven, or things like tape compression etc.

Unfortunatly it's difficult to really discuss it any further as you have to hear it, but there are plenty of sales associates who will blab on about it in depth.

Since you heard this from a live sound guy I should also mention that proper gain structure is also important in preventing feedback in SR settings, and optimal mic pre trims may vary between FOH, Monitors and recording environments.

Finally, make use of the RecPit archives. Alot of these issues have been discussed ad-nausium and it's alot more fun to read someone else getting smacked down! (+ you still benefit from the discussions). Most people here are very helpfull, but the longer you hang here the more you'll understand how annoying the same questions over and over can be. Don't take it personally.
dg
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ted nightshade

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Re: "gain structure"
« Reply #5 on: May 14, 2004, 03:25:16 PM »

Another way of looking at it- every piece of gear has it's sweet spot, where it sounds best- often way better than it does in a perfectly competent setting without real noise or distortion issues. But find that sweet spot, and things sound like they won't sound anywhere else.

I learned a lot about such things working with a Manley Dual Mono mic preamp- it is most nonlinear, with a input transformer and optional output transformer. Just how hard you hit the input transformer has everything to do with how this box sounds. There are very few controls, and there are really no correct settings- you have to wonder if the attenuator is way down there and you at 45 or 50 dB overall gain before the attenuator, instead of the minimum of 40, but hey, what sounds best sounds best, and a little noise and that may not really matter. So you have some knobs to twiddle, and then the very amorphous business of hitting that input transformer at a nice level- the way the instrument is played, how close it's mic'ed, how hot the mic is, all play into it. But you can get wonderful, wonderful sounds by doing things not much differently than you would to get just good sounds. The sweet spot. Some folks much prefer very linear systems to work with, so as not to need to chase all that so much, but there are reasons folks like to work the other way too.

So, when every piece in the chain is in it's sweet spot, you're beyond just healthy gain structure- but it's very much a matter of gain structure to find those sweet spots and exploit them.
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Extreme Mixing

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Re: "gain structure"
« Reply #6 on: May 14, 2004, 04:38:55 PM »

Another point on gain structure is to avoid turning things up just to have to pad them down later, or vice versa.

Example:  Don't use a 20db pad on the mic and then use 50db of gain on the mic pre.  It's better to forget the pad and just add 30 db of gain.

Sometimes you wind up reducing gain at the compressor (1176 come to mind ?) when it was really the mic pre that was too hot and causing the distortion in the first place.  Because you didn't understand the gain structure, you turned down the wrong thing.

In digital recording the problem is usually people printing things too hot in a failed attempt to squeeze out higher resolution.  Why print a wind chime at full scale only to turn it down 30 db in the mix?

The mic preamp is the most important gain stage in the recording chain.  Where else are you going to add 60 db of gain to a signal?  Think how accurate that amp has to be to add so much gain without changing the frequency response of the signal.  Color is when it changes the response and we like it.  Distortion is when we don't.

In the "olden days" we always made sure the input fader was near unity gain so that the tape or bus meter would give an accurate representation of what the mic pre was doing.  Most meters were RMS, so Hats and Tamb were recorded with the meters at about -10.  Guitars and basses peaked at 0 or so.  Vocals from -3 to 0 VU.  To get more level to tape, we aligned the tape recorder to +3 or +5 or with the newer tapes up to +9.  That meant a signal that was RECORDING at +9 (meters pinned) would show up on the meters at 0VU.  That way you could tell what you were printing on tape.  Lets face it once the meter pins, you don't really know if you are printing +9 or +30!

Do some of the reading, then make sure you are watching the proper gain stage when you make changes as you record.

And don't trip on it too much.  The main thing is to listen and make sure you like what you are hearing.

Steve

saxist

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Re: "gain structure"
« Reply #7 on: May 14, 2004, 05:41:23 PM »

I didn't tell you not to post.  I also didn't flame you.  I gave you some links to sites that answer your question -- which, you may note, asked for general information on gain structure, not personal anecdotes -- and pointed out that you could find the same links very quickly through an Internet search.  Since your post seemed to be seeking very general information, and since you mentioned little about research you'd already done on the topic, my answer seemed to me to be charitable.  And, as Peter pointed out, it took me a little while to put together.  And, of course, since then several other people have decided to spend their time answering your question even further.

I agree with several other posts above: the point of proper gain structure is to avoid losing headroom and/or adding noise to your signal through inappropriate gain or attenuation at any step along the path.  It's entirely possible to have very poor gain structure on a mixer (i.e. not boosting enough at the pre, boosting more to make up for it at the fader, cutting the signal down a lot at a submaster, and then boosting the master fader to make up for that, not to mention issues with EQ, aux. sends/returns, etc.).  Just try to keep good levels throughout the signal path and you'll be fine.

Best of luck,
Eric Honour  Smile
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