As a follow up to last week’s tip about gain structure between mixers, processors, and power amps (see inSync 3/29/01) one astute reader pointed out a significant potential problem for engineers mixing with gain controls.
“I found your concept of mixing with the preamp gains interesting. One thing you neglected to caution against was that if you are also providing a monitor mix for the band with that same mixer, twiddling the preamp gains will affect your monitor sends (read “levels”) and that will really piss a band off [Ed. – not to mention the risk of feedback and damage to speakers]. You also run the risk of overdriving a preamp and unlike a guitar tube preamp, that does not sound pretty.”
A very valid point, however, most engineers who are skilled enough to actually mix with gain controls wouldn’t be surprised by these factors. Nevertheless the point that this technique only applies when there is a separate monitor mix is important. As for preamps overloading, that is conceptually addressed in last week’s tip. This is just a general gain structure issue. If preamps are out of headroom then obviously any additional level must come from something downstream.
This raises another issue. Many engineers set the preamps just below clipping on mixers. While this works fine most of the time you can get in to trouble. If you are close to clipping, and the guitarist makes a volume adjustment to his rig on stage (this never happens, right?), then that channel is going to begin clipping. An attentive engineer can usually catch this before it becomes noticeable to the audience, but if you leave yourself some headroom (3 to 6 dB or so) at that first gain stage you’ll reduce the risk of something potentially ugly happening.