Recording 101/5 Hail! The Compressor

May 24, 2010 by Neps

Well, let me 1st say "rock on 2009!" It was a crazy 2008 and for some of us (that would be me) it was a time to re-evaluate why I do what I do.. After mixing 3 Music Productions for TV I really got to hate some of the SA pop music. But this is not the reason for writing today's thread on Recording.

After pondering for a while, whilst walking on the golf course and breaking my 9-iron I suddenly realized.. What the world needs is more compressors. But before you can actually use the thing, how does it work..?

On a very basic level a compressor can be seen as a piece of equipment that 'compresses' the level of any signal being passed through it. hahaha, just had to write it that way. Compressors was one of the 1st things to see the light when radio broadcasting saw the light. To stop signals from overpowering the stations broadcasting equipment and antenna, they developed Compressors/Limiters.. They were quite crude designs, and didn't have all the control features you see today on most comp's. They worked according to the amount of input signal and then you just had a control for the output and if you were lucky, a Ratio control..

As time progressed these pieces of essential gear became more sophisticated. And today you have quite a lot of control over what your compressor will be doing. Today we find the following controls on most hardware comp's and plug-ins

- Input
- output (make up gain)
- threshold
- knee
- attack
- release
- ratio

So what does all these buttons do..?

INPUT
Well, as the name states, this is the incoming level of the signal. Normally you cant make it louder coming in, but some plugins do allow that.. I've personally never used the Input knob in my life on a comp

OUTPUT (Make up gain)
This is the output of your signal when it's passed through the comp. There are some schools of thought about using this. Some say 'leave it, thats why you've got faders!', others say that you should use it to boost your gain going out of the comp, to match what you're compressing. e.g.. If your gain reduction is -6-dB's then you'll make your output +6-dB's and so forth. I've not taken hold of any one of these, seeing that I work in a totally digital domain and I can do what I want to whatever signal. So it's just 'how I feel today' that will get me to use one of the 2 options.

If, however, I was working on Tape on an analog desk, I'd use the Make up gain theory.

THRESHOLD
This is where you control how much of your signal you want to compress.. Say you have a kick drum thats peaking to about -9-dB's, and you want to compress just 3-dB's, you'd set the Threshold to -12-dB's. As easy as that. But as we all are muso's, we mostly just take the threshold knob and turn it till we're happy..! RULZ were made to be broken!!

KNEE
This is the option that selects how 'hard' the compressor will kick in when the signal reaches the threshold. So say you choose hard knee, it really just means, when the signal reaches the threshold the full Ratio that you selected will be applied.. Soft knee means the opposite. A quick illustration that I always remembered in the beginning was 'If you hit you knee into someone groin hard, he folds down quickly, If you do it softer, he goes down slower!'

ATTACK
This is just the option to tell the comp how quickly it should kick in when the proper threshold is reached.. So if you select 17 ms it'll take the comp 17 ms to react with the applied ratio and the proper knee setting.

RELEASE
This is to tell the comp how much time it has before it 'releases' the signal after it ducks below the threshold. So if you choose 167 ms it'll take that full 167 ms before the comp releases the signal.

RATIO
Here you set how much you want to compress the signal after it hits the threshold. An easy way to think of it is to look at when you pump up a tire. When There is not resistance the air goes in easily, as soon as you reach a certain pressure it gets more difficult to get air into the the tire. Thats because the tyre has an inbuilt 'ratio' of air it can take, and so the closer you get to its maximum the more effort it takes to pump.

Compressors are very handy tools to use, not just for keeping a handle on dynamics, but also to create effects. You get to have a lot of control over various instruments and also to place them better in a mix. But be warned, they can also make a good mix VERY bad. The only way to really get to grips with comps is to experiment, try using the Factory Presets on plugins and adjusting the threshold for that particular preset.

An example is the bass preset on the ProTools DynIII plugin

Knee : 18dB
Ratio : 2.5:1
Attack : 7 ms
Release : 600 ms

Now all you have to do is play around with the Threshold setting and Voila!! you have compressed you bass signal with a quite common bass Comp setting!
As always.. Use your ears, Enjoy, Laugh at yourself and remember "DRUMMERS are AWESOME!"

Have a Rocking 2009!

p.s I'm going to try and post some audio clips regarding comps and settings at some stage.. Lets just hope I don't get eaten alive by some Evil Reverb Machine!!