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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.

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  • Just to be sure: are we talking about dynamic compression (e.g. via a VST plugin or a Compressor module) or about an audio compression algorithm (e.g. MP3 or DTS)
    – Pelle ten Cate
    Dec 7, 2010 at 20:24
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    Based on the description of "live" in the question title, I think it's probably about "dynamic" compression, i.e., a built-in, or outboard audio processing for PA applications.
    – Clint Miller
    Dec 7, 2010 at 20:27
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    Pelle ten Cate, 99% percent of the time compression will be mentioned on this site, it will refer to dynamic range compression. The only exceptions I can think of will be around the words MP3, data, and mixdown.
    – Vortico
    Dec 7, 2010 at 20:28
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    Could you define limited budget? 8 channels of compression can be costly if you going the hardware route. However if using VST's in a live scenario , you could have latency issues.
    – Jeffroe
    Dec 7, 2010 at 20:43
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    @Vortico, I know, I just stated the comment to get rid of the ambiguity. We need this integrity in the private beta. :)
    – Pelle ten Cate
    Dec 9, 2010 at 9:06

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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.

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    I've never been aware of compression controlling feedback - it raises the level of lower signals, making them more likely to feed back.
    – Skilldrick
    Dec 7, 2010 at 21:03
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    It depends on how you use the compression. If you compress the transients without raising the entire signal level afterwards then you may effectively guarantee no transients will trigger a feed back. If, on the other hand you raise the level after compression, your point will be valid and there will likely be far more events close the maximum level.
    – Kim Burgaard
    Dec 7, 2010 at 21:10
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    @Skilldrick That's only true if you raise the level after compression. Some compressors do this automatically, which may be what you're thinking of.
    – Warrior Bob
    Dec 8, 2010 at 17:13
  • That sounds more like limiting than compression then...
    – Skilldrick
    Dec 15, 2010 at 11:31
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    @Skilldrick: correct me if I'm wrong, limiting just moves the clip limit (everything above a level is cut to that level). A compressor in its compression area has variation in output level, depending on the input level. In other words: in a out vs. in graph, the limiter in limiting area is flat. The compressor has a slope.
    – Gauthier
    Sep 29, 2011 at 11:52
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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.
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    Regarding monitors, I've found that inexperienced vocalists often get confused and uncomfortable if their vocals are compressed; since they don't hear themselves getting louder, they will often just push harder. Explaining what's going on can help. Of course, if you don't have a seperate monitor board, there's not a lot of choice anyway.
    – Rich Bruchal
    Dec 7, 2010 at 23:32
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    @Rich : in my experience all vocalists hate it when their voice is compressed in their monitor. Possible solution: Y split the signal to 2 channels, compress 1 and send the other exclusively to the monitor.
    – jan
    Dec 8, 2010 at 1:17
  • Nice idea. I'll have to try that at some point. Requires spare channels though, which I don't always have - but probably worth it
    – Rich Bruchal
    Dec 8, 2010 at 1:50
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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.

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Compression is definitely great for live audio work. Used correctly in the mix, it can bring you lots of control for highly variable audio content.

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I love using compression for my live audio!!!

I use it for individual mics and for the main & monitor mixes.

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Absolutely, but you have to pay attention to your group. You can over-compress a more classical group that actually plays with dynamics. On the other hand, you are dealing amplification. That means that your dynamic differences are going to be exaggerated. Compression helps mitigate that exaggeration. I have a choir, orchestra, and front vocalists. The choir and orchestra use the dynamics they rehearsed. I use very little compression with them. The front vocalists are used to singing into microphones and don't entirely practice good dynamics. In fact some of them don't even have very good microphone discipline. They are up front because they sing really well and have good stage presence, not because they are better than anyone else at being disciplined. The move their mics back and forth from their faces. Some of them have weird spikes. Guitarists are bad about stepping away to play and stepping up to sing, and not exactly being up the mic before they start singing or backing away before their done. Some of them sing louder the higher they sing and softer the lower they sing rather than having dynamics that work with everyone else. So I typically use heavy compression on the front vocalists to tame their bad practices and make them fit with everyone else.

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