theloopbox.com

Compressors

Compressors are dynamic processors that will help you control the level of an audio track, or during a recording. Wheather you should use compression while recording or not is quite an often asked question, and there is not one correct answer to that issue. Some sources may benefit from a bit of compression, but bear in mind that once compression has been applied it´s hard to remove. So if you decide to use compression while recording use very subtle settings. You can always compress more at a later point.

Used in the traditional way compression should be as transparent as possible; almost inaudible. If used as an effect a more pumping sound can be achieved when driving a compressor hard.

Basically there are 5 important parameters to know when using a compressor:

Threshold, Ratio, Attack, Release and Gain.

The compressor section of the Focusrite ISA220 Channelstrip

Waves Renaissance Compressor plug-in

Threshold: Here you define at which level the compressor should "kick in" and do it´s wonders. You set the level in dB. If you set the Threshold at -20 dB the compressor will begin to process as soon as the level of the audio signal reaches this level.

Tip: Try to imagine the Threshold as the "ceiling". How much room is there before the ceiling is reached?

Ratio: This parameter adjusts how hard the processor will treat the audio material. A low ratio (e.g. 1:1.5) will be more subtle and transparent than a high ratio setting (e.g. 1:10). Some Compressors even have an "Infinte" ratio which actually makes it a brick-wall limiter.

Tip: Try to imagine the Ratio as the material of which the ceiling is made. If it´s a low ratio the ceiling may consist of soft cotton or similar. The higher the ratio the more solid the material. With these tips in mind it could be easier to understand what happens when you tweak the buttons on your compressor.

Attack: This parameter adjusts how fast (or how slow) the compressor kicks in. Some compressors (as the ISA220) simply lets you turn the knob from F (fast) to S (slow), and others will use ms (milliseconds) as value.

Release: This parameter determins for how long the compressor should keep processing. The longer the release time the longer it keeps processing. Most compressors use ms and seconds as the release value parameter.

Gain: Naturally a compressor will lower the overall signal, so the last step in the chain offers a chance to make up for the lost signal. Often this parameter is called "Gain", "Make Up Gain" or as on the ISA220 simply "Makeup".

However there are a few interesting products for everyone who don´t care too much about having complete control over every single parameter.

A true classic hardware unit is the UREI 1176 limiting amplifier. It is a very simple unit with just a few buttons and knobs but it sounds fantastic. Unfortunately these units are rather hard to find these days, and if you do it´s probably not going to be cheap.

That´s why Universal Audio started a reproduction of these units a few years ago. The UA 1176LN has already become a modern classic which sounds very very nice.

Another great classic reproduced by Universal Audio is the Teletronix LA-2A unit, also a no-nonsense machine with a very simple user interface.

Basically these units will let you control Input and Output. The harder you drive them the more they process the incoming audio. Because of this simple structure it´s quite easy to get a great sound right away. Of course, this is the simple explanation as there are other adjustable parameters, and you can read all about it at Universal Audio.

Another great Universal Audio product (we don´t own any UA stocks! We just like their stuff) is the DSP card "UAD-1". Here you can have many classic units as plugins, and at much lower prices too. They don´t sound excactly as the originals, but they come pretty close, and most important: they sound great!

There´s 1176LN, LA-2A and even a software version of the legendary Fairchild compressor.

A nice virtual compressor rack !

The idea of a simple user interface has been adapted by other plugin companies. For instance Waves has made special verisons of their Renaissance compressor. Both the Renaissance Vox and the Renaissance Axx are simple compressors with just a few adjustable parameters, optimized for vocals and guitar respectively. However they can be used on almost any material with good results.

Waves Renaissance Vox Waves Renaissance Axx

Links to compression related articles:

Advanced Compression Techniques, Part 1 (Sound on Sound, December 2000)

Advanced Compression Techniques, Part 2 (Sound on Sound, January 2001)

Understanding Compressors (MIX Magazine / www.barryrudolph.com)

All About Compressors (www.tweakheadz.com)