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COMPRESSION

"P.S.K What does it all mean" - Schoolly D

 

COMPRESSION 

Compression can be a real pain in the ass if you understand what a compressor does. It can seriously can lead to depression. It took me a long time to understand what the compressor does and when to apply. 

 

So to use the compressor you first have to know what it does. Since Ableton Live is my weapon of choice i will use the audio effect compressor of Ableton to give you an idea. Although this can be applied to almost any compressor. So a simple and short explanation: 

 

COMPRESSION EXPLAINED

 

The function of a compressor is to compress or ‘squash’ the amplitude of an audio track so that it is more consistent. Still confused? This picture demonstrates it pretty well:

 

 

 

 

 

As demonstrated by the above image, compressing audio also means that as a whole, your audio can be louder (without any peaking occurring). You might also notice that compression takes away some of the dynamics of the audio – so, if you over compress something it will sound very ‘flat’ dynamically, even though it may sound louder.

 

TRESHOLD & OUTPUT

 

These form the basics of how the compressor works.

 

  • Threshold; anything above the threshold volume wil be reduced in amplitude

  • Output; increases/decreases the entire volume of the audio

In the picture below, everything above -15,8 dB is going to be squased a little. Use the threshold to control how much audiois compressed and then use the output to bring up the volme as far as you can without the audio peaking.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ATTACK AND RELEASE

 

  • Attack; how soon the compression "kicks" in once the threshold level is reached

  • Release; how the compression continues after sound drops below the threshold level

 

In the image below, the compression will start 1millisecond after the threshold level is reached. 20 milliseconds after the volume drops below the threshold level the compression will stop. Attack & release are neccessary for the compression to sound smooth, without them, compression would start and stop too quickly

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PEAK/RMS/OPTO

 

  • Peak – this measures the volume by taking the highest possible point of the audio wave.

  • RMS (or root mean square) – this measures the average volume over a short space of time. Because it’s an average, some peaks may still sneak through without much alteration from the compressor.

  • Opto (optical compression) – this is slightly different again. It emulates a form of analog compression, and in doing so can sound slightly more natural.

 

RATIO & KNEE

 

  • Ratio – when the compressor kicks in, it squashes audio by a certain amount, and this amount is determined by the ratio. Let’s say the ratio is 2 – any sound over the threshold level will be reduced to half the original volume.

  • Knee – the graph shown earlier is great for seeing what this does. Instead of a single ‘kink’ in the graph at the threshold volume, a high knee value will smooth the kink out (try it and see for yourself!). Think of it as a way of applying a gradual threshold.

 

 

 

Acknowledgement: http://www.everythingableton.com/2011/01/understanding-abletons-compressor/

 

 

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