First let me differentiate between audio level compression, which we’re talking about today, and data compression– both of which can apply to audio.

Data compression is the removal of extraneous data by encoding a data file, generally resulting in a smaller file. Like compressing your audio into MP3 or compressing your video to MPEG2.

What we’ll be talking about today is compression in the sense of using an audio level compressor. Compression is a vital part of your audio chain, whether you’re doing a podcast, recording music, or working with audio for video. A compressor manipulates the dynamic range of an audio signal.

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The dynamic range can be describes as the relationship between the loudest and softest parts of the signal. The compressor reduces the dynamic range if it passes over a set threshold.

In compressor plugins or on an outboard compressor, you might have seen a ratio setting, like 2:1, 3:1, 4:1. If you have your compressor set to 4:1 and your threshold set to -12 db, if the audio signal goes over the threshold by 4dB, it will be reduced so it only goes over by 1 db. This is called attenuation.

A compressor will also have attack and release settings. Attack is how quickly the compressor starts compressing, usually measured in milliseconds, and release is how quickly the compressor stops compressing.

Many compressors offer a setting called Make Up Gain. Because we’re attenuating the signal– making it quieter — this setting will raise the overall level to make up what you’ve compressed.

So why use a compressor? Many people like to “compress to tape” — which I’ve put in quotes because we don’t use tape much anymore — but we still use this phrase a lot to describe using a compressor on the incoming signal to compress the dynamic range — lower the loud parts, bring up the quiet parts, and then raise the overall level to get the best level we can for recording. And then you can compress after you’ve recorded with a plugin to further control your dynamic range.

Compression is incredibly useful and important– it should be a part of everyone’s audio chain. But use your ears! Jumping into compression without really learning how it works can be detrimental. Of course, that’s why we’re here at the Mac MediaCast, to get you going in the right direction.

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