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Putting The Squeeze On Live Sound

Keeping things under control with compression and limiting.

Editor’s Note: This article first appeared on the original Live Sound International website in the late 1990s, and provides a lot of information that’s still relevant today.

The first time I mixed a band—wow—it was like riding the musical equivalent of a mechanical bull, stuck on 10!

There just seemed to be no way to keep everything under control. I just couldn’t keep the levels loud without them running away from me.

Things would be alternately too loud or soft, but by the time I’d moved the appropriate fader, the situation would change. I despaired of ever getting it together—the sound was all over the place.

At the end of the night I felt relieved that it was over, and also a bit cheated. Whatever happened to the other guys that I’d watched mixing, casually tweaking a level here and adjusting EQ there?

Still, from this inauspicious start I learned two things: 1) I had a lot of learning to do, and 2) I had to find a way to keep things more under control.

There was only one answer—I had to learn about compressors, and pretty quick! Because, the fact is, that if you want to mix any music loud and up front, compressor(s) are a must. So with a fair amount of practice, and a couple of borrowed compressors I discovered I could let them (the compressors) handle the housekeeping while I looked after the window dressing—setting up delays, reverb, stereo panning, solos, looking cool, that type of thing.

Let’s face it, you might be able to work a 12-channel console without dynamics control, but even then you’d be working flat out to control levels. And the sonic consistency would inevitably suffer. And on 40 channels? Forget it! “Keep that kick drum up—whoops, too loud, bring it down. Where are those vocals? Whoa that’s too much—now they’ve disappeared again. What’s that singer doing?” and so on. If you’ve ever mixed, you get my drift.

What’s What & What’s Not?

Basic compressor controls are Threshold, which sets the level at which compression begins; Ratio, a measure of how hard things get squeezed when they hit the Threshold; and Output, where you can adjust the output level of the compressor.

Where and how to set these controls is critical. Compressor operations are not necessarily user-friendly. In particular, the Output control deserves your respect. Don’t run more than a couple of dB past 0 dB (unity) unless you are positive that your room EQ is perfect.

What happens is simple; when the music is happily bopping away, there’s no problem. When it stops, there’s nothing to compress, so all that extra gain is just sitting there waiting to feed back. And it usually doesn’t wait very long! If you’re just using one compressor over the console main output, you can usually catch things in time. Four or more channels though, and your fingers will be doing more than walking!

Kick drum and bass guitar are particular culprits. If your compressor has controls for attack and release, set them on medium! Compressors that don’t have attack and release controls have those kind of decisions made internally, automatically, depending on the signal characteristics. Personally I prefer to let the machine make that kind of decision, because on a constantly changing signal like live music, frankly, most of them do it better. More importantly, they do it faster!

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Keyboards, in particular, are a problem because the volume levels of different synth patches can vary enormously. Where one just sits happily in your mix, a sudden switch to another can really bend the needles, usually just when you’re busy reprogramming a digital delay! Plus, any keyboard player with his own volume pedal, can effectively take control of the sound away from you. Not good! To counteract this problem use a harder compression ratio, say 8:1, so that sudden volume changes are managed until you have a chance to attenuate the level.

Another major control issue is deciding where to set the limiter threshold. Because of its brick wall nature, a mismanaged limiter threshold will make the sound appear unpleasantly squashed. In general, limiting thresholds should be employed as a last line of defense to save the PA components and systems from being overloaded and/or damaged.

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