Hey Conrad,
When using two mic's in close proximity to one another like the snare drum example, what happens is something called "phase cancelation" - The wave produced by the snare drum is entering both mic's at the same time and at the same volume or amplitude. Unfortunately, one wave signal is positive the other is negative. (sorta brings us back to the unbalanced vs balanced stuff
). So 1 plus -1 is 0 I suppose, but only at certain periods throughout the recording. Some mixers have a button that reverses the phase of the signal as it enters the mixer. This may reduce the cancelation effect. On a snare drum this is fine, it is a short duration signal, and the resulting waveform is not quite as complicated (or long) as say, a piano.
You want to avoid this phase cancelation because you will end up with a thin, phazy kind of sound when using two mic's in close proximity. There is something called the 3:1 rule, which states that if your micing instrument A at a distance of one foot, no other mic should be within 3 feet of A. This is a good rule to follow as it will reduce the chances of this inherent electrical phenomenom.
In most editing type of software there is usually a function for reversing the phase of the waveform (sorry, I don't have soundforge or wavelab installed at the moment, I don't know the precise instructions but it is in there).
Great question, hope I answered part of it.
Emeric
[This message has been edited by Emeric (edited 07-01-1999).]