What Is Gain Structure?
Well, let's think if of it this way. Gain structure is how you set levels throughout your recording chain. All of us set our levels right after the microphone with the preamp. After that, we may send the signal from the preamp into hardware compressor. From there we send it to a our analog to digital converter (which may be built into your computer interface / sound card). From there, we alter the level of the signal in our digital recording software channel strip. Of course, various plugins may be inserted before the signal goes to the stereo out (or “2 bus” as I like to call it) where we can effect the gain even more.
At any one of these points, we may be pushing way too aggressively or not aggressively enough in terms of level intensity. In order to maximize the clean level (without noise or clipping) in a system, we need to properly balance the load between the various components. Turn a preamp all the way up (especially a cheaper preamp) and you will greatly increase your chances of hearing noise. (My expensive preamps do not get audibly noisy at any level, though). Use too high of gain on a loud signal and you'll distort the output of the preamp and the input of the converter.
Poor Gain Structure
The classic example of poor gain structure is seen on live sound mixers where the trim knob is cranked up to oblivion but the master fader is down by 30dB or more. In this particular case, the preamps are being pushed really, really hard. While they are probably not going to blow up, they are going to complain when they asked to amplify the signal more thany they want to. This complaining is in the form of “hiss”.
There is another form of complaining, which is a little more “violent” sounding. It's called “clipping”. It's when you cram more signal into a preamp or mixer than it can stand. In other words, you are boosting the signal way too much. This creates distortion (the same kind of distortion on your guitar, just not nearly as pleasing to the ear).
The lesson here is to keep all the levels balanced and start them all out at zero. There is no need to use 30dB of boost on a preamp just to knock it right back down with the master volume (2 bus) fader. In this case, we could have left the 2bus at 0 (not boosting or cutting) and then left the preamp 30dB lower than it is now.
A Few More Examples Of Poor Gain Structure
I see a lot of guys who have problems with noise in their acoustic guitar tracks. This is usually caused by cranking up the gain on an inexpensive preamp to the point that noise is introduced. This is fairly common because acoustics guitars are one of the most quiet instruments you will record on a regular basis.
A lot of tail chasers will tell you that analog to digital converters sound better when you give them a hot signal. . However, they don't factor in that you may be sending a ton of noise into your tracks. If the preamp is the cause of the noise, TURN IT DOWN!! The whole point to setting proper gain structure is not to push any one component to the point where it's complaining.
In the modern digital recording era, it's extremely easy to give a volume boost digitally in the software. This digital volume boost may not be as great as using a $2,500 preamp that has no noise, but the average ear will never know that you boosted the signal digitally (in your software). However, they will know if they are hearing noise and hiss.
Going along this same theme, if the acoustic guitar is not a prominent instrument in the mix, there is absolutely no reason to boost it really high with the preamp anyway. I don't care if a magazine said that you should try to hit -6dB on your converter. The point is null and void when, after boosting the crap out of the acoustic guitar, you end up reducing it 20dB in your recording software. You would have been better off just leaving the track low in the mix.
I've read of several guys who try to set their gain structure so that they don't have to even adjust the level at all in the mix. They say that any manipulation of the signal is going to distort the track in some way.
Good Gain Structure
Ideal gain structure is present when all components work together to deliver a strong, clean signal to the analog to digital converter and throughout the software as well. With ideal gain structure, your preamp will be boosting as much as needed and not a dB more. Your compressors, plugins, etc will not have to boost or cut too much. No one part of the chain should be pushed harder than any other part of the chain. You can always see if a certain part of the chain is being pushed because it will begin to start complaining somewhere.
While not the most exciting part of home recording...(in fact, this may be the most boring article I've ever written) a strong understanding of the fundamentals of gain structure are required to make great recordings. It makes sense not to push any one component too hard.