Compression Basics

Today we will take a look at the basics of compression. What is it and what can you do with it? Also, we will take a look at an example piece of bass guitar, in which you can clearly hear the effect. Let’s quickly take a look at compression!

In this case, we are talking about dynamic compression, not data compression. Data compression means reducing the disk size of, for example, a WAV audio file. This way it does not take up much space on your disk. This is something we will talk about at a later point. With dynamic compression I mean the sound technique used a lot in music production. Applying compression on a sound signal means automatically changing the volume when it reached a certain volume level. If the volume is reduced this way, you can in turn increase the volume of the whole signal, effectively making the difference between the lowest and loudest sound of the signal smaller. You bring up the loudness of the signal (but not the volume).

Compression is used a lot in the music industry. For example: it is used to make signals more consistent or more clear. But it is also being used to make a signal that dies quickly, die less quickly. This is what I’ve used for a piece of bass guitar. The strike of the string generates a lot of signal, but reduces quickly after the strike as well. With compression, you can reduce how quick the signal decayes and make it last longer.

There are several parameters required and changable for compresison. We will stay at the basics, so I will go through the most important ones: Threshold, Ration, Attack & Release.
Threshold is the level in dB, which any signal above this level will be affected by compression. If you set the threshold at -10 dB, all signal levels above -10 dB will be compressed.
Ratio is the amount of compression in input/output ration that is applied on the signal. A 4:1 ratio reduces the output signal to 1 dB for every 4 dB of input signal.
Attack is the time used to make the compressor do it’s work. If the signal is above the threshold, the attack decides how long it will take for the signal to be reduced to the desired level.
Release is the counterpart of attack, which sets the time the compressor takes to increase the signal back to (let go of) the desired level when it is under the threshold level.

For This Is Living, I’ve recorded a piece of bass guitar to use as the bass tones in the song. The original probably uses something else (a synthesizer), but I have a bass guitar and thought: why not? It is far from perfect yet and requires more mixing, but here is a piece of bass guitar without compression.
Compression (Image Source: WikiPedia)

And now with compression turned on.

You should be able to clearly hear the difference between the two. The bass guitar sounds louder and stays longer with compression than without. Hopefully this gives you a clearer image of compression!

Stay in tune!

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