Getting StartedIn most situations common for smaller bands, you'll be in a club with a less than stellar PA system. That's not to say you won't find a club that'll surprise you. In this article, we're going to be taking a look at mixing live sound from the angle of an aspiring engineer, not necessarily a band who's bringing their own PA system with them.
When you're faced with mixing sound, the first thing to take into account is the room itself. It's easy to overdo it; you really need to only reinforce what isn't easily heard in the room. When you're in a small room, amplifiers and drums are very easily heard naturally, especially in a very small space. Putting them through the PA will do nothing but make it sound messy in the room. One of the best pieces of advice I can give you is to keep it simple.
Mixing VocalsThe vocals are the most important part of any small-room mix. Making sure that they're loud and able to be heard clearly throughout the room is of utmost importance because they're no competition for loud guitar amps and drums. The biggest factor you're going to have to compete against is monitor feedback. Check out the guide to mixing monitors for information on killing feedback before it starts.
One technique I prefer to use is subgrouping. On a lot of boards, you'll have the option to group channels together to one fader, with the ability to insert a compressor across the whole group. This way, you can compress the vocals all at once (saving you valuable compressor room if you're limited in the number of comps you've got), and you can also double-bus - meaning, put the vocal in the subgroup as well as the channel itself - to get some extra gain.
DrumsDrums are a difficult thing to mix live. In order to deliver the best-sounding mix, you need to take stock of what you can hear in th room naturally, without amplification. Most drum kits, in a small room, won't need any amplification past the kick drum.
For a good small room, I prefer to mic the kick drum, as well as the snare. Toms generally don't need any amplification, as they're generally not played enough to warrant dedicated channels. If you're in a club that holds, say, between 250 and 500 people, you may need to mic them. If you're low on microphones, you can put one microphone for every two toms, placing them in between. Depending on the quality of the kit, you'll need to compress.
Overheads and cymbal microphones are of low priority. Even some small clubs that hold less than 1,000 people may not need amplification on the overheads. Sometimes, I'll mic the high-hat in a small room if the drummer plays it softly, but generally, it's not necessary.
I prefer to compress the kick drum separately, and EQ with a boost in the mid frequencies. I also, as usual with most channels, cut out everything below 80Hz.
Here's another tip: if you've got a loud snare, but still want to add reverb to it, you can switch the reverb send on that channel to pre-fader instead of post-fader. That way you can still send the snare signal to the reverb unit while not actually putting any in the house!
Bass & GuitarsQuite simply, in most small rooms, you won't need to mics the guitar amps and bass cabinets. In fact, I'm almost always finding myself having to ask the players to turn them down because they're too loud in the house. Sometimes you'll find you need more definition in the bass guitar, or your drummer will want more in their monitors. In this case, I'll put a DI box between the guitar itself and the amplifier. That way, you're in total control of the tone, and the amplifier on stage can still do its job as the player wishes.
Acoustic guitars are a different matter. Sometimes, you'll find players with an acoustic amp, but those generally don't cut through the mix well. Putting a DI box out for the acoustic is the best way to get the best sound; you'll need to carefully EQ it to avoid feedback. I always keep a Feedback Buster - a specially-designed round disk of rubber sold in most music stores - to lend to guitarists who don't have one. These block the majority of the frequencies from entering the guitar's soundhole, which prevents the major feedback problems you usually get.