Compression: Bringing up the background

I usually use my compressor to keep VO levels a bit more even across the range. Compressors are great for that, a gentle touch and it can really help you keep it all together. But forget that gentle garbage! We’re doing sound design baby!

The nasty truth about compressors is that they bring down the level of sounds in the “foreground” so to speak, and they bring up sounds in the “background.” Generally, this really sucks, so you want to keep your compression to a minimum. Why? Because normally the background is noise. You don’t want to bring down your vocals or instrument levels so that everyone can listen to your air conditioning, (really it should be off while you’re recording mic’d up sources) or traffic, (oh how I wish I could switch traffic off) or whatever internal noise exists in your system (compression will help you appreciate low self-noise mics, preamps, mixers, etc).

But sometimes, this can be good. I decided to dust off the old compressor today, throw Elements into mono output, and SQUEEEEEEEZE the life out of my output. I mean I crushed it. Absolutely decimated it… and it was beautiful. Why? because sometimes we have some really beautiful sounds in the background, such as reverbs, delays, and all kinds of other sorts of other little sonic pleasures, just lingering behind the scenes.  And when we bring the pain to the foreground sounds, we give these guys in the background a chance to shine.

So, every now and then, throw a compressor in line, do a bit of *transient decimation and see if you have any beauties lingering behind the scenes, that need to be brought center stage.

The basics of how this works is:

  1. We set a threshold on our compressor (the level above which transients are annihilated)
  2. We set a compression ratio (the amount of annihilation we wish to dish out)
  3. We set an attack time (how much of a chance we want to give a transient to sneak into the recording before the annihilation begins).
  4. We set a release time (how long will the annihilation continue after the transient is pulverized, and put in its place [below the threshold]).
  5. We set the make up gain (after all that annihilation things can sound pretty quiet, so we need to bring our levels back up to something proper).

By doing all this, we generally make the loud parts quieter (compression above a threshold) and the quiet parts (below the threshold) louder (make up gain). But there are certain approaches to compression which can help us minimize or maximize this effect. Today, we want to maximize our background sound.

When focusing on bringing up the background of your sound, here are a few keys:

  1. Set the threshold so the quieter parts are safely below it. Be sure they have a few dB to breathe.
  2. Set the attack and release times quite fast. The compressor will grab the loud parts, but let go almost as soon as they go below the threshold. This way the quiet parts remain relatively untouched.
  3. Give it some make-up gain. The loud parts have been brought down, the quiet bits are safe, and now we bring it all back up to a good level, and we can really hear those background sounds brought forward.

This track is a single-channel recording of Elements. Light modulation by Tides, and run through a compressor:

Threshold: 0dB
Compression Ratio: 10:1
Attack: 250 micro seconds
Release: .5 milliseconds
Make Up Gain: 11dB

This setup really hammered the sound of each strike on elements, but also really brought out this sort of ghostly hum from the background. I switched the compression in and out through the recording. As it begins, the compressor is bypassed, the sound is a bit hollow. But when the compressor is switched in the sound of each strike is tamed and these background tones really shine through.


* In acoustics and audio, a transient is a high amplitude, short-duration sound at the beginning of a waveform that occurs in phenomena such as musical sounds, noises or speech. ~Wikipedia

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