Compression is a necessary aspect in a good mix. In subtle amounts, it adds punch, depth, and even ‘feel’ to a mix. When overused, you can end up with a stale, lifeless, squashy mix. Here I’m going to run through the basics of compression, using a lovely Tama snare track as our waveform. Compression has four main parameters.

So, what’s Attack/Release/Threshold/Ratio? I had talked about this in my previous post on Mixing drums.

But now, let’s look at it visually.

Here’s the original waveform. A beautiful transient at the start, and fades out nice and clean. Ahhhh. Click to enlarge.

Uncompressed Tama Snare Waveform

Now, let’s compress it. Here’s how it looks after using the following settings, with a threshold low enough to trigger the compressor right at the start. The white line shows the moment when the compressor starts (estimated attack), and the red line shows when the compressor ‘releases’, which means it stops acting on the waveform.

Attack: 100ms (white line) Release: 500ms (red line), Ratio 2:1

Now, let’s try different settings.

Attack: 50ms (white line) Release: 1ms (red line), Ratio 2:1

Notice how the red lines kick in almost immediately after the white lines ‘attack’ the waveform. This is because the release is set at a very low setting of 1ms. What does this mean to the audio? It means that the compression takes place almost throughout the whole waveform after the first attack since as soon as the compressor ‘releases’, the audio is ‘attacked’ immediately. Of course, threshold will determine when the compressor will stop attacking, based on the shape of the waveform.

Next example.

Attack: 1ms (white line) Release: 500ms (red line), Ratio 2:1

Makes sense now? Compare this to the original waveform and notice how the shapes are different.

Attack: 1ms (white line) Release: 1ms (red line), Ratio 2:1

Straightforward again?

Ok, now you have a better grasp of how compressors work. But, how does it affect the sound of the waveform? Let’s take the snare drum as the example.

As is obvious, the snare waveform consists of two major parts – The initial hit of the snare, and then the decay of the snare. When you have a very small attack setting, of about 1ms, the compressor acts on the initial ‘hit’ of the snare, and affects the dB based on your ratio.

What does it do to the sound again? You get a ‘crack’ sound. Yet, it sounds tiny. Why? This is because the initial transient or hit of the snare is important in giving the snare some beef as well as snap. Now, slowly increase the attack to 5ms and gradually to 15ms. You will notice more and more of the snare’s initial transient goes through uncompressed, which inturn makes the snare more present in the mix. I leave it to you to experiment with the release settings and figure out how that affects the sound.

Happy compressing!

- Sridhar