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Is there any more frustrating saying in the English language than, "You have to learn to walk before you can run"? There is a corollary to this that states, "If your bicycle isn't going fast enough, you'll fall off into the dirt." But what would-be advice giver is ever going to say that?
So I am faced with a dilemma. Should I give a newcomer to live sound the correct advice, which is not to use a compressor at all until you can make a really great sound without it? Or should I face the reality that they are going to do it anyway, despite anything I say?
There is however one pretty much universal truth of audio... A compressor can't make things better until your work is already very good.
So if you are unhappy with your mixes, either live or in the studio, plugging in a compressor isn't going to help. You're unhappy because you haven't built up sufficient skill in balancing levels, EQs and pans, which in essence is what mixing is.
The plus point however is that if you are unhappy with your mix, then at least you can hear that it isn't right. You are halfway up the ladder already!
But suppose that your basic mixing skills are good already, and you feel you are ready for the compressor. What should your settings be?
Well I would imagine that anyone's reason for using a compressor live would be to achieve the 'studio sound' in front of an audience. Let's continue with that in mind...
One thing you can do in the studio that you can't do live is set the compressor any way you like. Nothing matters in the studio other than getting a pleasing sound (and getting paid by the client of course!)
But in live sound the other issue is avoiding feedback (howlround). And if there is one tool that is bad news on this front it is the compressor.
A compressor works by lowering peak levels. And since the average level of the signal is now lower than it was previously, you will use make-up gain to compensate. Do this all you want in the studio, but in live sound it will reduce your margin before feedback.
Let's suppose you are working in a small club and feedback is a problem that lurks just around the corner for you. Clearly you will do all you can in terms of loudspeaker and microphone positioning, taking monitors into account too. You will probably use a graphic equalizer to take out some of the most problematical feedback frequencies.
Now let's say that you can set the level of the lead vocal mic so that the singer sits nicely above the band and is clearly audible through the PA. However, you know from the sound check that if you raise the vocal fader by 6 dB, you will start to hear 'ringing', which is the precursor to feedback.
Now let's say that you insert a compressor into the vocal channel and set it in such a way that the gain reduction meter shows 6 dB on peaks. Since the level of the peaks is now lower, then you make a setting of +6 dB on the gain make-up control (or do the same but using the fader).
Oops, you have now reduced your margin before feedback to zero. Not nice.
But maybe your reason for using compression was to control a 'peaky' vocalist. In this case you don't need to use the gain makeup, so you are as safe feedback-wise as you were before.
What I am saying therefore is that you can use compression on live sound - if you know what you are doing. And in my opinion, no-one knows what they are doing sufficiently well to use compression to any benefit unless they can already craft an audience-pleasing mix without it.
In other words, you do have to be able to walk with confidence and grace before you can run.
Regarding the settings - lowering the threshold and increasing the ratio are both likely to lead to you wanting to increase the gain make-up setting. These are the three key areas to look out for (plus the gain reduction meter) when seeking to avoid feedback in live sound.
In the studio, you might have ten tracks in a mix that benefit from compression, and your mix sounds better for it. In live sound that would be ten compressors to set, ten more things to handle when there's enough going on anyway, and ten more things to go wrong!
P.S. We would welcome your comments on how you have used compression successfully in live sound. Go on... give us all a few of your best and most secret tips!