that won't work. If the drums are quieter than the intended source, then there's no way at all to utilize a
comp. If they're louder, they'll take down the source with them when the signal compresses and while you've lowered the drums, it's moot since the intended signal is lowered equally.
The options in this area are A) if the drums are coming up in others microphones, but at a lower
level than the source, use a
gate. This will turn off the signal whenever the
level drops below a
threshold you set. Now the quiet drums only come through when say the choir is singing, which doesn't matter since the choir will hopefully overpower that quiet drum signal.
B) If the drums are overpowering signals into other mics, use a
limiter on the
channel. This way, you'll still get drums, but those loud hits can be brought down to the loudest
level of the intended source.
Of course, the real thing to look at is keeping the drums from ever reaching a
microphone they shouldn't be or at least lowering them to a
point where a
gate remedies the problem.
First off, I suspect that with so many choir mics, you're loosing a lot of available
gain before
feedback. Lessen the number of mics and things will most likely sound cleaner and LOUDER!
So here's the rundown as far as mics go as I see it.
no more than 5 mics on drums. And that's really on the high end. You could really go with 3 or 4, which I certainly recommend if you aren't too experienced.
2 mics on the piano. give good attention to placement.
DI the
bass and a mic on the guitar.
As far as the choir goes, use 2 microphones. Andy is spot on in saying that you should let the choir mix themselves. That's the whole
point of a choir. Ideally they should go unamplified. Or at least that's sort of the indended setting. So really you aren't mixing the parts, you're amplifying the whole. Think of it as a sort of submix in the air you're picking up.
As far as soloists go, I guess that's show specific, but given a choir of 30 on the high end, I don't see the need for more than two soloist microphones. Again, though, you really shouldn't need them. It's the singer's job to mix themselves in and come above the group for a solo. Also the groups job to lower their own voices. I realize this isn't likely in high school, and soloists need help. The best bet is to setup mics SL and SR and have singers go to them, but this might not work for you and handheld, passed around mics may be all you can do.
So, you really should only need 10-12 board channels. Let's go crazy and give you 4 soloist mics and 5 drum mics and even another choir mic and you're just at 16. You certainly don't need a new board. I'm really amazed that without drum mics, you're pushing the limit. That can only mean you're wayyyy over micing the choir. If the money's there, burning a hole in your pocket, maybe look at high quality microphones for the choir and of course a drum
baffle.