Gain Structure
This page was originally written by Jorn Nettingsmeier.
Poor audio quality, both in terms of distortion and noise, often occurs due to improper gain handling. First, bear in mind that every amplifier has a range in which signal-to-noise ratio is optimal. This is usually not all-the-way-up! also, remember some amplifiers sound better than others.
When connecting a mixer (or any other device) to your soundcard, there is a mixer output amp and the soundcard input amp. It is safe to assume the soundcard amp is generally the worst in the studio. :) so in order to obtain maximum quality, let the mixer do the work and keep the soundcard input (often termed record gain) down. With my card, I can set it to zero, meaning that the amplifier will not amplify at all, but let the signal through as it is. Watch out, though: other cards will mute the input at zero. Anyway, keep it as low as possible and crank up the mixer output as much as soundcard can handle.
This has another advantage: the signal that flows through the cable will be louder than with low mixer out and high soundcard in. Thus, the noise from random electro-magnetic garbage that creeps into the cable will be (relatively) lower.
Generally, try to find those parts of the signal chain that are likely to pick up noise, usually long cable runs or everything inside the computer :( , and keep the signal as loud as possible there. watch for distortion, though. Your mileage may vary.
Try to provide as high a level to the card's converters as it can stand, i.e. without the slightest distortion. Remember: a shiny 20bit adc fed with too weak a signal will sound like an old 8bit. "Hello, my name is Linus Torvalds, and I pronouce linux as lee-nucks". We certainly don't want that type of sound. No sacrilege intended.
Same rules apply to the output. As far as I know, most soundcard mixers work in the digital domain. If you turn it down to 1/3 of maximum level, you will again cripple your 20-bit DAC to 8 bits. So leave the output way up and control the volume at your monitor amplifier. You will gain considerably more detail at low level."
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