Compressors – The theory

aircompressorNo matter what music you compose, you’ll eventually have to deal with compressors. There is just no escaping. Compressors are what you apply to make music better. That’s right. They help you make your music beyond studio quality. You’re one plug-in away from stardom!

All the glamour aside, compressors are one of the studio workhorses that are applied to achieve anything from subtle smoothing to downright squashing. It does help to know how the tools you use work though, and I’m hopefully going to provide you with just that. Let’s go from knob fiddling to consistent predictable results! Follow the link for an easy FREE introductory promotional kit (order the full 3 x video tape kit NOW and receive an instant $3.00 rebate!)

I’m a visual person. I learn better and faster when there are graphs and diagrams to look at. Some people just need a really easy to understand explanation. Some don’t want to learn at all. The video of the female Star Wars theme trumpet performer might be a better choice. If you’re like that I don’t like you. Sorry. People who don’t want to learn anything suck. For the rest, I’ll try my best to affect all your senses throughout this enriching learning experience. Ok, we’re not going to lick or touch anything here. Or are weeee? ;)

Now, compressors. What do they do? What are they for? What’s the use in them? Are they compatible with Excel? In a nutshell, a compressor is used to even out the “sound bumps”. Typical example – a vocalist performs a song in the studio. During the verses she is singing at normal levels, but as the chorus starts she begins to practically yell the lyrics out (think screaming 90’s house diva’s). Assuming everything got recorded without clipping and she hasn’t lost her voice altogether in the process, you will have a bit of a problem: if you try to set the levels for the vocal track now using the verse as a reference, when it comes time for the chorus the vocalist’s voice will ride on top of absolutely everything in the mix. Ride on time!


Okay, not a biggie. We do have automation available to us right? Give yourself an extra point for thinking inside the box. But what if our singer was changing the amplitude of her voice much faster than that, say up and down on every beat? Apart from sounding completely hilarious, it would call for some tedious automating. That’s where we pull out our mean looking compressor guns. Let’s go over the controls.

In simple terms, a compressor is used for automatic volume controlling. It looks at the signal you feed into it, and when that signal peaks beyond a certain level you set, called a threshold, the compressor brings the levels down. Just how much quieter the compressor will make the signal is determined by the ratio. A 4:1 ratio will tell the compressor to make the peaking signal 4 times quieter than the original. Hence, for slight variations in volume you would use a smaller ratio, whereas when your singer goes from whispering to yelling at the top of her lungs you would probably want to crank the ratio up.

At which point, you would be limiting. What is a limiter? Nothing but a compressor with an insane ratio. 10:1 and up usually. Most compressors are also limiters. Don’t know why they had to come up with a different name for it. I guess it’s like chips and fries. No one’s entirely clear on either. Is one French??

Now, there are a few more controls to cover. Firstly, attack and release. Those are easy. They basically control how drunk the compressor is. If you crank up the attack, the compressor will take longer to react to changes in volume. A 0ms attack time will mean that the compressor will kick in the instant a change in amplitude occurs (sober) whereas a 100ms attack time will slow the compressors reaction down by the set amount of time (wasted). The opposite applies to release – a longer release time will mean the compressor will take a while to get back to its normal state whereas a snappy release will get it back into the default state quicker.

The last one and the easiest is gain – it should be fairly clear that if the compressor reduces the volume of the peaks, the overall volume of the signal will then be lower. Hence it makes sense that we now need to boost the resulting out coming out of the compressor to bring it up to an acceptable level. Gain does just that. Crank up responsibly.

And that’s that! Hopefully that helped out a bit. I have a small demo project in the works which in the next post I will use to illustrate all the theory. Get ready for some funky disco beats!


7 Responses to “Compressors – The theory”

  1. 1 dave December 26, 2007 at 1:57 am

    i was just reading your back posts and came across one where you were selling a fostex e16. wondering if this is still available. i just bought one off ebay but it was busted during shipping, so i’m looking to send it back and hopefully get another. i know that post was quite a while ago, but here’s hoping…

    dave fell.

  2. 2 chrisrenne January 8, 2008 at 5:55 am

    i personally like limiters better for the most part with a compressor thrown in here and there. but that’s just me.

  3. 3 Laurent February 4, 2008 at 5:11 pm

    Here is the difference between compressors and limiters:

    Compressors usually have an attack time and they compute the gain reduction regarding an weighted value of the signal power.

    Limiters have a instant attack time (zero) and determine the gain reduction regarding the instantaneous signal level.

    A compressor won’t work the same manner as a limiter even if both are set with the same release time and the same ratio.

    That was my two cents.


  4. 4 September 25, 2013 at 3:58 pm

    You are so awesome! I don’t suppose I’ve read through
    something like this before. So great to find somebody with a few genuine thoughts on this topic.

    Really.. many thanks for starting this up.
    This website is onee thing tha is needed on the internet, someone with some

  5. 5 Full Article December 1, 2014 at 4:55 am

    Great information. Lucky me I discovered your blog by accident (stumbleupon).
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  1. 1 Muzyka » Blog Archive » Compressors - The Theory Trackback on April 28, 2008 at 12:10 pm
  2. 2 Compressors – The Theory » The Chip Collection – Synthesizers, Sound Downloads, & Reason Trackback on July 10, 2012 at 11:46 am

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