When I choose a processor to be applied to my audio signal, I always ask myself this question: Do I want this machine to do its duty in an “invisible” way (that is, in the final result not to notice the application of the machine), or do I want this machine to “put a nice recognizable signature” to the final sound?

But are the compressors all the same?

For the more experienced sound engineers, this answer is obviously useless, but I’m mostly directly this question towards those people who are beginning to appear in the world of sound, and the answer is obviously not. They differ in their type of construction (Vari-Mu, VCA, FET, OPTO , etc.), whether they possess the classic controls such as Threshold, Compression Ratio, Attack Speed, Release Speed ​​or if they possess further controls, such as Knee, Dry / Wet for parallel compression, or if they have a separate entrance for the side-chain that I will explain later.

In short, there are compressors famous for their transparency and others that are loved for their “aggressiveness” and ability to manipulate dynamics in a heavy, but beautiful way, as the signal passes through them.

In the world of compression…

For example of the dynamics processors, looking for the effect of the second option from above, that is a “characterized” sound, you can unintentionally generate some “faults”; “pumping” and “breathing” are an example of such a characterized sound.

The problem of “Pumping”

Just as the name describes, this “defect” manifests precisely with an evident sensation when crushing the signal and a subsequent progressive ascent during the weaker portion of the signal.

The problem of “Breathing”

Also in this case, as the name describes, this “phenomenon” manifests when a possible background noise or rustling in the signal, rises and drops in level clearly between a portion and the other of the main sound, creating a sensation of “breath”.

In both cases then, as mentioned, we are clearly in the search for a “characteristic” sound from our dynamics processor.

But are these phenomena really caused by compression “faults?”

In reality, in the world of audio production, in the hands of an expert sound engineer, these phenomena are precisely sought to creatively reach the desired sound.

Speaking for example of “Pumping“, an effect often achieved is a particular effect added to the long sustained notes of piano, where on the initial transient you can feel a strong crushing of the signal and then gradually feel an increase in the level of the weaker part of the sustain of the tail and all its beautiful harmonics. This is usually achieved by applying a large compression ratio to the signal with a fast attack time and a release time adjusted based on the distance between a played note and the next or adjusted according to the desired rise time, within the limits of the possibilities offered by the chosen compressor model.

Piano Original
Piano Pumping Effect

Speaking instead of the “Breathing” effect, it is not nice to hear the noise or hum of an audio signal go up and down, except for the hypothesis that this is specially created for creative and artistic purposes, but this technique can often be found in dance or pop productions using the side-chain function of some compression models, where for example a keyboard pad, otherwise stopped, starts to “breathe” between a note of kick drum and other, or between a bass note and more or more between both …

Synth Pads Original
Synth Pads Breathing Effect
All Together Pump and Breathe

The Side-Chain entrance

Through the side-Chain input it is possible to send the compressor a secondary pilot signal that will control the action of the compressor (as said for example a sound of bass and/or kick drum) on the main signal where the compressor is applied (as said for example a keyboard pad sound). In order to have a good result, also in this case it is important to adjust the compressor release time well, based on the distance between a note of bass or kick drum and the other. As for the attack time, I would stay on quick settings, while for the compression ratio here the choice becomes wider and each technician will surely find the setting of his own liking.


Finally, I remember as always that it is not always necessary to use compression processors if the starting sound satisfies us, but it is always necessary to keep in mind the two approaches (transparent or characteristic) to follow and I recommend … always keep an eye on the Gain Reduction Meter!

By Andrea “Potter” CristoforiSound Engineer and Mixing Engineer (Oil On Canvas – The Watcher Of The Trees – Joba – Eroma – Valentina Costa)