Wednesday, April 20, 2011

Compression and how it works

So I mentioned in a previous post about compressors and their use with vocals. I thought I'd write a post explaining compression a bit more thouroughly for you all since it is a huge asset for most recordings.

So basically there's two different types of compression. Hardware and software. Hardware compressors can be extremely expensive but if you have the budget they are definately a worthwhile purchase. Hardware compressors can give a much more natural sound than software. That said though, software compression is at a very high quality and you can definately get away with it. Or you can use both for varied results.

The main thing to remember is that both hardware and software compressors essentially work the same. I'm not going to go into the various compression settings for mixing as I will cover it in a seperate post but for now I just want to explain exactly what compression does and basic controls.

So what does a compressor do?

When it comes to recording vocals, there is normally a very large dynamic range to them. This means that parts of the vocals will be very loud and parts will be very quiet. Volume fluctuations are very hard to avoid when recording and vocals tend to be hugely varied.

What a compressor does is try and balance it out. It will bring the loud sections (peaks) to a lower level and it will push the quiet sections to a higher level to give a more uniform sound.

That's the basics behind a compressors function but it can get more involved than that. You must know how to work your compressor because using it at its fullest will leave sounds sitting dull or sounding very unnatural.

So what are the various functions a compressor has?

Ok, now most compressors have the same basic knobs or controls and I will explain them for you. Some compressors may have different controls or be multi band compressors (meaning you compress the low, mid and hi ends of the EQ seperately) but the basics remain the same across the board.

So on most compressors you can expect to see the following controls. Threshold, Ratio, Attack, Release and Gain.


Threshold basically tells the compressor how loud you want the volume of the recording to be before it gets compressed. Think of it like your ceiling. If you set your threshold at a certain volume level, anything under that threshold won't be compressed. If you keep your threshold low, then more of your signal will be compressed and it will have a much larger effect.


This will control how much you want to compress the audio that is outside of the threshold. You will notice on compressors when changing the ratio it will be numbers such as 2:1. This number means that for every 2dB increase that goes over the threshold will be reduced back to 1dB. If you heighten your ratio, the more it will flatten out your peaks. Anything within the threshold though will not be adjusted with the ratio.


This controls how quickly the compressor will come into effect for each section. For instance, if you set your attack to be slow (or long) it will mean that once a peak above the threshold is put through, it will let through a certain amount of audio before the compressor kicks in and bring it back down.


This is basically the exact same principle as attack but instead of telling the compressor when to kick in at the beginning of each signal input, it tells it how quickly to turn off the compression for the end of each section.

If it helps, think of Attack and Release like the accelorator and brake of a car. Attack controls how fast your car speeds up, Release controls how fast you want to slow down.


This is very simple. After using compression you will find that the overall volume will be less than it started. Gain is used to simply boost it back up. The higher the gain the higher the volume.

With these basics you will now understand how to control a compressor so feel free to start playing around with various settings and see what works. There is no universal 'good' setting for vocals as different voices and different sections of tracks will require different settings. With a basic understanding of how each setting works though you will be able to at least play with the controls and understand what exactly they are doing.


  1. Compressors have always confused me ! Thanks for the post , sets it out very simply

  2. Thanks about this, I'll show this to my friend - he's hiphop producer

  3. Good post, tho I don't have any use for a compressor.

  4. I must be getting dumber in my old age, I had to read it twice and I'm not quite sure if I completely understand all of this yet!

  5. Good to know the next time I use the compressor

  6. this is great info! and well organized, great job!

  7. Thanks, this will help me a lot!

  8. Interesting, never knew much about it!