It's been a busy few weeks again. I finished one new mix (listen here) but mostly did some quick edits and tinkered (with a relatively low success) with some mastering gizmos on some recordings. In addition, our project band has got some new spark on recording our next song. Not to mention the home-front with all the undone stuff piling up. Therefore I decided to start a series of Short'n Snappy tutorialish snippets on all things mixing. These shouldn't take too much time and I'm sure that I will learn a lot, as I try squeeze my limited knowledge on a Short'n Snappy format. And who knows, maybe someone else can get something out if it too.
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| Short'n Snappy Compression |
So onwards to the Short'n Snappy road to understanding Compression. Read why you would want to compress things, what compression does, what are the basic controls concerning compression and check out a bonus example of CLA-3A compressor on action. Welcome!
What is compression?
In a coconut shell, compression refers to the pushing down the high volume peaks of a track, as if pushing the waveform down to make it more flat - hence the name compression. This flattening effect is usually combined with an overall volume lift to raise the general volume-level back to the desired level. This basically means that the high volume parts are turned quieter, and the more silent parts are turned up, which creates a more stabile overall volume level for the track, reducing its dynamics.
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| Compress that! |
Why would I want to compress anything?
Everybody does it, don't they? You don't really want to use peer pressure compression, meaning that all and everything is super-compressed because compressing is something everybody does. Compression should be applied only when situation calls for it. Here are a few thoughts.
When mixing tracks, the main objective is to find the right balance so all the tracks work nicely together. If one finds a track with an anxious fader (when listening to the song you constantly feel the need to change the tracks volume), compression might be a solution. Compression stabilizes the track by shortening the volumic distance between the loud and softer parts of the track.
Sometimes an instrument is so dynamic, that without compression you can't really hear the quieter parts. Vocals are a good example of this, with their soft whispers and head splitting screams. Compression for the win!
Compression can also be used to prevent the standard stuff at the background fattening the mix, from popping out too much. For example background vocals might be heavily compressed to keep them on a constant volume behind the main performing vocal.
A little compression can also go a long way to "glue" multiple tracks together. By compressing the summed output, the tracks can sound more like they naturally belong together. But this might also be a bit psycho-acoustic phenomenon, at least in my case.
When mixing tracks, the main objective is to find the right balance so all the tracks work nicely together. If one finds a track with an anxious fader (when listening to the song you constantly feel the need to change the tracks volume), compression might be a solution. Compression stabilizes the track by shortening the volumic distance between the loud and softer parts of the track.
Sometimes an instrument is so dynamic, that without compression you can't really hear the quieter parts. Vocals are a good example of this, with their soft whispers and head splitting screams. Compression for the win!
Compression can also be used to prevent the standard stuff at the background fattening the mix, from popping out too much. For example background vocals might be heavily compressed to keep them on a constant volume behind the main performing vocal.
A little compression can also go a long way to "glue" multiple tracks together. By compressing the summed output, the tracks can sound more like they naturally belong together. But this might also be a bit psycho-acoustic phenomenon, at least in my case.
Basic controls for compression
Compressors come in all sizes and shapes. They tend to have a familiar set of controls though, and once you familiarize yourself with one, you'll be quite comfy with the rest.
Threshold
This little knobby sets the volume level after which the compressor starts to reduce the signal volume. High threshold can be used to just shave off some nasty peaks, and a low threshold setting can be used to reduce the overall dynamics of the track. Using an imaginary scale, say that you set your threshold to 7. A signal with a volume of 6 wont be affected by the compressor at all, but a signal with a volume of 9 will be grabbed by the compressor. The first 7 units of the signal will not be modified. The signal volume of 9 subtracted by the threshold of 7 leaves 2 units of volume that will be adjusted by the compressors other settings.
Ratio
This fellow will adjust how strong the compression will be after the threshold is passed. A ratio of 1:2 will halve affected peak and similarly a ratio of 1:20 will cause heavy compressing by reducing the part of the signal passing the threshold to a miniscule one twentieth part of its original strength. Taking the previous example with a threshold of 7 and peak of 9 with a ratio of 1:2, we will have an overall signal of 8 coming out at the peak. 7 untouched units plus 1 from the compressed peak (half of two). Take that you math wizards!
Gain
Simple control simply adjusts the volume of the whole track after compression (output gain). The overall volume will be lowered naturally after compression, so this can be used to compensate for that. Compressors can also use input gain, which can be used to raise the track volume to have the signal cross a fixed threshold. But output gain is the standard, i think.
Attack
Crafty little knob adjusts the reaction time of your compressor. Using a fast attack, you can really catch the fast peaks. Fast attack might be needed to effectively compress percussive instruments such as drums, guitar and sneezes. That is of course if you want to flatten the transient hits from those. In most cases though, a slow attack might be preferable to really catch the nature of the percussive instrument by letting the hit peaks come through. This is most surely an 'adjust and listen' kind of knobby.
Release
This mysterious control is still a bit out of my regular use. It controls how fast your compressor stops compressing after the signal drops under the threshold. Just like attack, this is most definitely an 'adjust and listen' style control.
But enough jabbering. Lets get down to business!
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| Compressors of all sizes and shapes |
Threshold
This little knobby sets the volume level after which the compressor starts to reduce the signal volume. High threshold can be used to just shave off some nasty peaks, and a low threshold setting can be used to reduce the overall dynamics of the track. Using an imaginary scale, say that you set your threshold to 7. A signal with a volume of 6 wont be affected by the compressor at all, but a signal with a volume of 9 will be grabbed by the compressor. The first 7 units of the signal will not be modified. The signal volume of 9 subtracted by the threshold of 7 leaves 2 units of volume that will be adjusted by the compressors other settings.
Ratio
This fellow will adjust how strong the compression will be after the threshold is passed. A ratio of 1:2 will halve affected peak and similarly a ratio of 1:20 will cause heavy compressing by reducing the part of the signal passing the threshold to a miniscule one twentieth part of its original strength. Taking the previous example with a threshold of 7 and peak of 9 with a ratio of 1:2, we will have an overall signal of 8 coming out at the peak. 7 untouched units plus 1 from the compressed peak (half of two). Take that you math wizards!
Gain
Simple control simply adjusts the volume of the whole track after compression (output gain). The overall volume will be lowered naturally after compression, so this can be used to compensate for that. Compressors can also use input gain, which can be used to raise the track volume to have the signal cross a fixed threshold. But output gain is the standard, i think.
Attack
Crafty little knob adjusts the reaction time of your compressor. Using a fast attack, you can really catch the fast peaks. Fast attack might be needed to effectively compress percussive instruments such as drums, guitar and sneezes. That is of course if you want to flatten the transient hits from those. In most cases though, a slow attack might be preferable to really catch the nature of the percussive instrument by letting the hit peaks come through. This is most surely an 'adjust and listen' kind of knobby.
Release
This mysterious control is still a bit out of my regular use. It controls how fast your compressor stops compressing after the signal drops under the threshold. Just like attack, this is most definitely an 'adjust and listen' style control.
But enough jabbering. Lets get down to business!
CLA-3A in action
Some compressors have even more simple controls. I tested the Waves CLA-3A compressors effect on the track waveform, adjusting the amount of compression on multiple tracks. The test was mainly for my entertainment, but the results were a bit surprising for me, revealing some insight on the inner workings of this compressor. Quite a nice eye opener. The CLA-3A emulates the classic LA-3A compressor and only has two main knobs to fiddle with - Gain and Peak reduction. I left the gain untouched and increased the peak reduction on a short electric guitar riff. CLA-3A started to have an effect with a compression value starting from four. Below you can see the results.
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| CLA-3A effect on waveform. Compression increased from the top to bottom using values 4.5, 5, 5.5, 6.5 and 7. |
Now, on a hindsight, it would have been better to adjust the gain to better match the tracks for their shape comparison. Now the natural tendency of compression to lower the volume, makes spotting change in shape a bit more difficult. The compression effect can now be seen best from the angles at the waveforms. Increasing the compression lessens the angle, which would mean, that increasing the gain would result in the softer parts to grow in volume and the loudest parts to lose a bit volume.
Now the interesting part can be seen from the box marked as the 'fast transient'. CLA-3A did not, at least in my eye, touch those peaks at all. I was under the impression that the CLA-3A would be a fast compressor, but this would indicate otherwise. I guess that's just a mental note for me if I try to tame fast dynamics. If this doesn't seem to work, I will try something with an adjustable attack.
Now the interesting part can be seen from the box marked as the 'fast transient'. CLA-3A did not, at least in my eye, touch those peaks at all. I was under the impression that the CLA-3A would be a fast compressor, but this would indicate otherwise. I guess that's just a mental note for me if I try to tame fast dynamics. If this doesn't seem to work, I will try something with an adjustable attack.
Final words
Go ahead and experiment. But keep in mind that louder generally sounds better to the human ear. So when testing compressing try to keep the signal output volume fairly constant, so you can really estimate the effects of the actual compression. I know I have fallen into this trap quite a few times just listening to that screaming signal and feeling it getting apparently better, when in fact the compression really trashed the signal. Compress away but buyer beware!Please leave a comment, Maybe suggest the next stop for the Short'n Snappy train?
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