Compression remains a mystery to many, but it really doesn’t have to be that complicated…
Essentially, compression and limiting deals with dynamic control over the incoming signal, pushing down the peaks and smoothening out the dynamics.
So, why would I want that? I can control the dynamics with my fingers. I am that good! Well, that might be true, and compression is in no way a must. But it can actually come in handy in some situations, and you may also want to use it for more deliberate tone-shaping purposes.
On many compressors used in recording and mixing studios, you would find five basic parameters. While pedals are often different, let’s start by taking a brief look at these five parameters.
The threshold defines when (at which level) the compression is kicking in.
The ratio defines how hard the compression is kicking in.
The attack defines how fast the compression is kicking in.
The release defines for how long the compression is kicking in.
The gain compensates for the level that you loose due to compression kicking in.
To me, the most complicated parameters to grasp were the threshold and ratio – and not least how they interact with each other in the processing. You may adjust the ratio heavily, but if you have set the threshold so high that the compressor never kicks in, it doesn’t matter at all. And vice versa, if you have se the ratio too low, you can lower the threshold all you want and still nothing happens…
It helped me to think about the threshold and ratio parameters and the relationship between the two as a physical ceiling: The Threshold would define the height of the ceiling, and the Ratio would define the density of the ceiling.
In short, think of the ratio as the material the ceiling is made of. Is it concrete? Then you would have a brick wall limiter on your hands. Or is it a thin layer of cotton or soft card board that most peaks would be allowed to penetrate – or somewhere in between that would take out many peaks but not squash everything.
Here is a quick example of how a compressor can smoothen out dynamics. The sound clips are taken from the BBE OptiComp review and first you can hear the dry sound where the slapped notes are clearly louder than the rest. In the next two examples compression is applied by 25% and 50% respectively.
As mentioned, one of the consequences of wanting to master the dynamics is that your overall level decreases. That is why you have the GAIN parameter, which is often referred to as ‘Make Up Gain’ on rack units and on pedals it could be Output, Volume or Level.
Another thing that is often compromised during (relatively heavy) compression is your tonal character, which is why some compressor pedals – such as the Wampler EGO, the Diamond BCP1 or the Ovnifx Smoothie – also feature a Tone or EQ knob to compensate for lost highs and/or lows.
Some of the more recent compressor pedals offer a visual representation of how much your signal is being attenuated.
It could be by a row of LEDs as on the MXR M87 Bass Compressor, or it could be just one LED that will light up brighter and brighter as more compression is applied.
While visual representation can be nice to have, it’s essential to first of all judge compression using your ears. Which is exactly why visual representation of the compression, in my opinion, is a ‘nice to have’ and not ‘need to have’ feature.
Finally, I want to touch base on one very essential parameter. Until quite recently (considering the long history of recording music), compression was considered an insert type effect, meaning that it was typically ‘inserted’ on a track and would process the full signal on that track.
On the other hand, send/return type effects would be set up on an AUX channel and sent to from various channels. Then you would blend in the ‘wet’ AUX track with the others. A typical example would be reverb.
However, at some point someone decided to experiment with splitting the signal and apply heavy compression on one track while leaving the other dry. Rumors has it that it was done on drum overhead mics as an experiment – and parallel compression was born.
Now, many compressor pedals feature a blend or mix knob that allows you to blend in some of your clean, dry tone with the compressed signal. This is extremely usable and versatile for bass. I love being able to maintain some of my basic and fundamental tone.
In fact, this approach is not just for compression. For effects like overdrive and envelope filters it’s great to be able to blend in some of your natural tone. In a perfect world, all pedals had a Blend knob. But hey, you can always get a Boss LS-2 that will cater for all your blending needs!
Unfortunately, if we look at parameter names on compressor pedals, confusion may occur. Some pedals use some of the basic parameter names as described above. Others only use a few, combine some of them and/or rename all or some of them… Confused yet?
I would love to add a ‘compressor pedal parameter dictionary’… And maybe I will some day! But for now, I just want to share that – to me at least – it really helps to always keep that virtual ceiling approach in mind when noodling with the knobs on a compressor pedal. And from then on it’s simply a matter of using your ears
There are a lot of more in-depth guides to understanding compression – especially for studio applications, but in particular Ovnilab has a great FAQ on compression in a pedal context. Check out these great resources on compression.