I am running sound on a very limited budget and am wondering if adding some compression to our vocals and/or guitars will help our sound much. I am thinking I would only need 8 channels of compression and this might be a big improvement over our current sound.
Yes, definitely. Especially if your vocalists are not trained in microphone technique.
Dialing in some compression to take off the worst of the transients will help your live mix in exactly the same way it helps a mix of recorded music. It can also help you control feed back, because it will reduce the loud transient sounds that can trigger a feed back signal.
For live rock show, 4-7 piece bands, I've had good success with the following guidelines. As with anything else, remember that these are just guidelines - every room, every gig, every setup is different, and what works for one combination may not work for another.
- Drums - usually, I'll compress the entire submix for the drums. Very little compression, and I rarely had a problem if it wasn't compressed. Be careful if you're also using gates, you can trigger some strange sounding artifacts if you have the compression dialed up too high.
- one subgroup for keyboards. I usually run a fairly high compression on this, especially if I'd dealing with touch sensitive keys, and if you have a keyboard player that likes to mess around with settings, you may end up with some sounds much louder than others. You can also get a lot of low energy from a keyboard, and compression can help to keep that under control.
- rarely will I compress guitars
- on the other hand, for live sound, I almost always compress the bass. Depending on the playing style, you may get away with mild compression, but someone who goes from finger picking to slapping is going to need to have the compression turned way up.
- backing vocals will usually get grouped & compressed, if possible, but you can get away without it. It's more important if the backup singers are doing a lot of harmonies it seems - keeps the levels nice & consistent.
- lead vocal(s) - there are a lot of variables that go into deciding what & how much. Some singer hate it, some don't care, but if you have a singer who isn't consistent in how close they are to the mic, it can really help. Using a lot of compression can lead to feedback, so be careful. Depending on whether you're doing monitors from the same board, or have a separate monitor mix, you may have to adjust to allow the monitors to punch a bit more.
- horns are another good candidate for compressing the entire submix - a bit of compression can make the mix much more managable. I may compress an individual horn if needed, expecially if the instrument is being mic'd from a stand, and the player likes to move around a lot.
- effects: You can do some interesting things by running effects into a compressed mix, but you can also destroy some subtle effects by forcing them up too much.
Like anything else, you should use it if the situation warrants it.
Do you have issues with dynamic range? I once had a gospel style vocalist with a very big voice and a lot of range - when she hit the loud parts, it pushed the levels to somewhat uncomfortable levels. A bit of compression helped to take the edge off those parts without altering the rest. But if you don't have issues like like that you may not need compression.
Are you going for a specific compressed "sound"? If so then of course it makes sense to use it. Also, if you have issues keeping the vocal above everything else, compression can help keep you at the (high) levels you need without getting too loud. Although if that's the case, you might want to explore ways to get the instruments down, rather than pushing the vocal up.
As for feedback, you still have to be careful. Any make-up gain you use in the compressed channel can potentially push you into feedback territory when there's no signal getting through, even though it may not be there when there's signal present and the compressor is reducing the gain.
In other words, use it if there's something specific you need it to do. Simpler is better.