Compression has become an integral ingredient of most music these days. At the same time it remains somewhat a secret science – a commonly misunderstood one. It’s a great pleasure to have the mastering engineer Barry Gardner from SafeandSound online mastering services to talk to us about how to learn compression. During his long career in music Barry has worked with people such as Terry Callier, Ronnie Wood, Craig David, Kano, Chick Corea and many others. Needless to say he knows his stuff. Time to pay attention.
Compression can be used in both technical and creative ways and is a much misunderstood process in audio production. Hopefully this article will help you learn what compression is capable of and introduce ways of understanding it based on a goal, rather than trial and error.
The best way to understand compression is to deconstruct it and then reconstruct it with a goal, be it technical or creative.
The Common Controls of a Compressor
Let the deconstruction begin. It is good to have in mind that job of a compressor is an automated level control which has and initial downward action – much like pulling down a fader. However there are certain controls which fix the response of the compressor. In this case what goes down must come up! We shall start with each control found on a basic compressor. We could go into great depth about the variations you can find, but for this article we will only be concerned about the controls that are relevant to all audio compressors.
- Threshold: level at which compression starts to take place.
- Ratio: amount of compression applied when the threshold has been exceeded.
- Attack: Speed at which level is reduced (a time constant) practically expressed in milliseconds.
- Release: Speed at which unity gain is restored (second time constant) also practically expressed in milliseconds.
- Make-up gain: A post compression gain control allowing the gain to be restored to that similar as the pre compression level (remember compression reduces the level of sound peaks).
Uses for Compressors and the Importance of a Sonic Goal
For a compression novice there will be significant online producer peer pressure to use compression whether you understand it or not. Make no mistake, compressors can make your music sound worse quite easily if you do not understand them. Do not rush here if you are starting out. A much better way to learn compression is to understand some basics and then apply.
In technical context a compressor can even out the levels between the naturally occurring peaks and troughs in a piece of audio. For example in a voice recording, the voice will naturally be softer and louder at times and it can be good to even this level out for the purposes of intelligibility – for example against a music back ground. This is a good technical use of a compressor.
A creative use of a compressor could be to adjust the tone of an instrument. This can be achieved by enhancing the micro dynamics of for example a snare drum. It is possible to bring out some extra snap in the drum attack when the stick hits the skin and maybe some extra body from the decay of the sound.
Initially it will be difficult to practice a goal driven need for compression. When you first start using a compressor at degrees where it would commonly be used it requires significant listening skill to determine the subtle changes. So some fairly extreme settings should be used at first so the audible changes are more dramatic. This can be backed off when you improve your ear to hand coordination skill set.
For the following practice I recommend a good pair of headphones so you can focus on the sound changes with less disturbance from room acoustics and/or other room noises.
The human voice is a good sound source to practice on. The human ear is very sensitive to any unnatural artifacts introduced into this important human sound.
I suggest setting up a track with some speech or singing on it and applying a compressor with these settings (compressors are employed in the insert point of a track most commonly). Ensure the loud peaks in the voice are peaking at -8dBFS and set the compressor as follows:
- Threshold -16dBFS
- Ratio to 10:1
- Attack to 5ms
- Release 200ms
When you play the voice track you should see activity on the gain reduction meter (amount of compression being applied). You should also be able to hear the voice level drop in synchronization with the meters activity. The main practical use of this meter serves to provide an indication of how much make-up gain to add in order to match the original signal level.
Make-up Gain Is Very Important When Learning Compression
I cannot stress this enough, the make-up gain is the control which allows you hear compression action as opposed to level difference. We know the level will drop when compression is applied. But we want to hear the improvement or detrimental effects of the action of compression and not the volume change. If the predominant change is level drop, it will be difficult to judge if the action is positive or negative. Once the input and output levels are matched, you can then use the bypass button to listen to pre and post compression sound.
The next step is to start gently adjusting the attack time and listening to what audible effect this has on the action of the compressor. As the attack time becomes longer you should hear a little more punch coming from the somewhat muted (at 5ms) snare attack. Then try adjusting the release time and considering what happens audibly. When adjusting the attack and release, always consider the make up gain control and A/B the input signal versus the volume matched compressed version.
Ok – so you might feel that was a lot to take in! Well it is, and learning how to effectively use compressors usually takes most producers and engineers a few years to become competent. This is made more complex by the fact that most compressors have different sonic signatures. Some are smoother and some are more aggressive and so on.
Learning how to use compressors is an iterative process as opposed to a smooth learning curve. The reason being is you will try a compressor on a new sound source and it will probably not respond the same as on any other source. The frequency content and dynamics of that particular instrument are different. Try another compressor and again it sounds quite different at the same settings. So be prepared that there is a lot of practice to be had before you will master it.
Suggested Second Practice
I recommend getting a drum loop playing and peak it at -8dBFS. It is best this is a sparse drum pattern. A kick, snare and hihat is ideal. Set the compressor controls as before. Listen to what happens to the attack of your drums when compression is applied and make-up gain is matched. A/B the input signal and listen carefully to what you hear. Then you can start adjusting the attack and release times and considering the sonic results.
Listen to the following aspects:
- Punch/snap (or lack thereof) of kick and snare drum.
- Room ambience/acoustics in between sounds.
- The pressure of the sound as a character of sound.
- The tone of the sound and lose or gain of highs.
Lots of subtle changes can be identified and this is why these tools are coveted by sound engineers.
How to Learn Compression – Summary
To learn how to use a compressor will take time and practice and progress will be somewhat dependent on grasping the fundamentals and your ability to hear the subtle changes. As one progresses you can use less extreme settings ( i.e. lower ratio, say 3:1 or longer attack times with shorter release) and continue to listen to the changes as you do.
Eventually you will slowly be able to discern all of the changes the compressor invokes. So put some time aside for some daily practice to learn compression and in the not too distant future you will be a competent controller of dynamic range in your tracks.