''Progressive All The Way''

Tutorial How to Use a Compressor
For a long time the compressor was a complete mystery to me. All I knew was that is was something that everyone said I should use, so I did. I threw it on my VST's and to me everything sounded just the same as before. Is a compressor an essential tool for electronic music? Hell yes, and or anyone who doesn't quite get what a compressor does like I once did read on and I'll shed some light on this dark art!


What Is a Compressor?

A Compressor is one of those effects that unless you know what to listen for you really can't expect to hear what it is doing. It's not like a phaser, or flanger that you can throw on and turn the knobs until you hear something you like. It can also be very intimidating if you are only guessing what it is doing. Those knobs, Thresholds and Outputs can be plain confusing.

It will probably come a lot of you as a surprise, but what the compressor does is really really simple, and as soon as you hear this things will start to make a lot more sense. When you put any audio into a compressor, all it really does is make the loud parts softer. That's it! That's all it does!


So Why Would I Want to Use a Compressor?

I heard a great analogy of a compressor once and I like to think of it this way now.

A compressor is like a little man who sits there with a remote control for the volume. Every time he hears the sound is too loud he turns the volume down until it's quieter and then he turns it back up.

What this is going to do is reduce the fluctuation on the volume when it is loud so it doesn't spike into the red and distort your sound, so that you can turn the volume of the audio up and get a much louder overall sound. With the correct settings, a compressor can really help to bring out some of the sounds hiding away in your tracks, and without compression your tracks can sound dull and lifeless compared to other tracks.

There is a drawback however, over compression can lead to a noticeable loss in your audio's dynamic range. There are times when you want to have your piano or guitar play notes quieter to have more feeling.


Types of Compression

There are some effect units that are called something else but really are just a type of compression these are:

1.Limiter
A limiter adjusts the audio signal with a higher compression ratio to attempt to keep the audio within the limits set by the user. A Brickwall limiter is a much stricter type of limiter which will not let any audio at all past the limits. It does this by using a very high ratio, usually 50:1 or above.

2.Maximiser
A maximiser makes the mixes sound louder with the punch and is so often required in contemporary productions.

3.Dynamics Processor
This is a kind of compressor used a lot with synths or with vocalists. Sometimes called a multi band compressor. It enables you to not only make the loud bits quieter but also specify what frequency to start working. If a singer makes a terrible shhhhh sound every time they say an "S" you can tell the compressor to make the higher frequencies that make up the "S" sound to be really quiet.


How to use a compressor

Ok, so lets get into what the knobs and switches to on a compressor. If the compressor you are using doesn't have these features don't fret, at the end of the day anything other then a threshold and a ratio are not absolutely essential. They will however make your life a lot easier.

Before you start to play with the controls of the compressor, first have a brief think about how loud you want the sound coming out to at its loudest point and its quietest point. For things like heavy ripping basses you would probably want it be fairly compressed, but for acoustic guitar parts you might only want a slight compression to keep the dynamics of the acoustic strings.


Ratio

The ratio setting tells the compressor how much balls you want to give it. When you set it to 1:1 (it's absolute lowest setting) it wont do anything. When you set it to its maximum (varies, but can be infinite) it will squash the entire audio so it never gets past your threshold in the slightest even for a millisecond.


The Threshold

The Threshold control is on all types of compressors, and it simply sets the volume level that the compressor will start to work at. Anything louder or above the level you set is when the compressor start turning things down. If you set the threshold to the maximum the compressor won't do anything at all because the level coming though is quieter then the level you want it to turn on at.


Gain/Output

So far the controls have only really turned the sound down. The gain/output is used to turn the overall compressed sound back up to a level you choose. Some compressors have a nifty switch called an Auto Gain switch with does the same thing


Attack/Release

When you use a compressor you can sometimes hear a distinct pumping sound. This is the compressor turning on and turning off very quickly. For some styles of music you might want this (think Eric Prydz) but for other styles you might want something a little smoother. Setting the attack higher simply tells the compressor take slowly start to work, to slowly move the volume down and not jerk it down like a mad pumping DJ. The same for release, only in reverse, it tells the compressor to return to normal slowly.


Soft Knee

Some compressors have a few extra controls to make life easier. Sometimes too quiet or way too loud and a normal compressor doesn't quite take the edge off them. The soft knee allows you to set the ratio a lot higher, and then takes it's time (a time set by you) at reaching the maximum ratio level. So in effect it slows down the time the ratio moves into gear. This works like saying, I want the ratio at 2:1 but if the sound gets really loud, I want you to compress it to 5:1


Peak/RMS/Automatic

Sometimes you might see a switch marked as either Peak, RMS or Automatic. Sounds impressive but all it really does is attempts to manage your attack and release for you as best as the programmer/circuit designer has coded/built it to do. When you have this turned on, your attack and release switches do nothing at all.


In/Out

This is a very under appreciated switch that turns the compressor off. Use it to hear the difference you are making as you tweak!


SideChain

Most analogue compressors will have a Side-chain somewhere on them. The compressor works by listening to the input and turning the volume down. What you do with the SideChain is actually tell the compressor to listen to the kick drums, but to turn down the bass channel. This is some producers get really pumping bass sounds, and let the kick come through the bass without sacrificing either of them.

Sidechain also lets you insert other effects like graphic equalisers immediately before the compressors control system. You wont' really hear the effect as it is not in the main audio path and doesn't affect the sound. It just changes the way the compressor responds. This system lets you over emphasise a certain frequency that you want the compressor to listen out for.


Real World Examples


Using Compression to Add Bite to a Sound

This is a great tip for bass or percussions. Sometimes when you are mixing down your channels the bass or the percussion sounds just don't break through the mix, and just don't leave an impact. This might be a time where you could employ a compressor. We all now know that what a compressor is really doing is turning the volume down when the audio gets too loud, or peaks but by using this you can actually make your entire percussions have more bite!

What you want to do to bring out the punch of an audio track is to let some of the loud sounds gain volume slightly so they peak where they didn't peak before. To do this, set your ratio really high, if not the maximum and start with your attack and release set to a fairly slow speed (which is really a high setting on the dials), and turn off any soft knee settings.

Turn the threshold down slowly. You will hear everything get quieter, but if you listen really carefully you will notice that everything is starting to peak at the simular levels. When you happy with the levels, crank up the Output control on your compressor and you will have some crispy crunchy audio with bite. Now play with attack and release until you get a pumping sensation you are happy with, and play with the threshold over some of the quieter parts of the track to make sure you happy.


Compressing The Mixdown

One of the things that I do when finalising a track is to mix down groups of audio together. I will mixdown all the drums and FX together and compress them. Then mix that with the bass and bassy synths and compress that etc. I do this so that my final mixdown sounds clean and crisp, punchy and loud. I should also note though that on the very final mix, compression is a bad idea if you are going to pay for someone to master your track. Let them do that!

When I am trying to achieve a good final mixdown I would use a plugin generally geared as a mastering compressor, or a limiter. See the end of the tute for a list of great compressors to use.

Start with the Automatic/PEAK/RMS switched turned on. What we are doing here is instructing the compressor to listen ahead to our music and judge wether or not to turn on fast or slow (it automates the attack and release remember!).

For now, set the threshold to the highest so we can slowly bring it down later. For mixdown compression we want to be subtle, so a ratio of around 3:1 is a good start. I wouldn't go much more then that, this really is just for cleaning up and if the compressor doesn't help that then you have much bigger issues with your mix then a compressor will help with.

Now turn the threshold down, and adjust the output as you do this until you are happy with the punchyness of the mix.


De-Esser

Sometimes when you mix a particular vocalist with a particular mic, or words you end up recording really harsh sounding ‘SH' or ‘Te' sounds whenever they sing a word with S or T in it. Don't worry, this is a common problem and is easily fixed with a compressor. Use a fast Attack and a Fast release and about a 3:1 ratio. Please an Equalizer in the side chain and get rid of the bottom end, and the mid section and boost the highs (anything above 3-6 Khz).

Now the Threshold will control the volume of your S or T sounds. Congratulations you have now built yourself a cheap De-Esser.

While this is a great technique, you are probably better off purchasing an actual compressor unit focused on De-Essing but this is the theory behind it.




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CompressorX

good post