When to use a compressor?What is the cause?

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When to use a compressor?What is the cause?

Post by DarkMedina »

Hello :)

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Re: When to use a compressor?What is the cause?

Post by rghvdberg »

A compressor is used to limit the dynamics (difference between loud and soft parts) on a track.

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Re: When to use a compressor?What is the cause?

Post by Markus »

Hey DarkMedina,

as rghvdberg said - it reduces dynamics. The basic idea is to lower signals above a given threshold by a ratio. After that the makeup raises the signal by a fixed value.


E.g. threshold is set to -12 dB, ratio is 1:2 and makeup is 6dB this would be input -> output:

Code: Select all

-24dB -> -18dB (no change by compression because below threshold, additional makeup)
-12dB ->  -6dB (no change by compression because exactly threshold, additional makeup)
 -6dB ->  -3dB (6dB above threshold, divided by ratio 2 (3dB), additional makeup)
  0dB ->   0dB (12dB above threshold, divided by ratio 2 (6dB), additional makeup)
 12dB ->   6dB (24dB above threshold, divided by ratio 2 (12dB), additional makeup)
These are the basic controls. Additionally there are attack and release. They determine the 'laziness' of the compressor since a direct manipulation would just distort the signal if single peaks would be cut off. They work in a way that the signal has to be n milliseconds above the threshold until the compressor reaches its full gain reduction (attack). On the other hand it has to fall beneath the threshold for n milliseconds until the compressor reduces gain reduction back to 1:1 (release).

A possible knee setting changes the hard cut at the threshold to a soft and round transition. It normally is set in dB which determines the radiant of the knee. This way signals around the threshold will be affected more evenly.


An auto-release switch will change the release time around the given value depending on the input signal. This makes the compression less audible.

A mix knob is used for so called "New York" or parallel compression. It mixes the original signal with the compressed one which results in a "more dynamic" kind of compression (bullshit bingo, try it out yourself).

Why compression?

Normally natural instruments (like the voice) are very dynamic. In modern productions most of the recorded track would get lost in the rest of the music because quieter parts would be acoustically overlapped by other signals. Compression reduces the dynamics of the track and gives a steady presence to the signal.

Please note: Overdoing compression results in dead sound. Additionally wrong attack and release times might lead to "pumping" which means the volume changes to the signal are clearly audible.

Compression is the magic in a mix/master, so this is just a brief overview of the basic concept.

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Re: When to use a compressor?What is the cause?

Post by barbouze »

This link explains pretty well the use of a compressor :D

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Re: When to use a compressor?What is the cause?

Post by JSantos »

Normally, you'll want to use a compressor when there's no other way to steady the dynamics of your instrument.

Compression and clipping can be similar if you set the attack and release fast enough, resulting in an unnatural and somewhat-distorted sound.

Clipping is the distortion you add to guitar/synthesizers. Different tubes give off a "warmer" sound to clipping. And so will compressors set to hard attack and release.

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Re: When to use a compressor?What is the cause?

Post by tnovelli »

There are tons of effects/plugins to smooth out dynamics and increase loudness (as compared to other recordings)...

Distortion & Overdrive
Saturator (Calf Saturator or the builtin tape saturation effect in Mixbus)
Maximizer (Barry's Satan Maximizer.. try it.. pretty crazy :)
Compressor (automatic volume adjustment.. "clean" but not necessarily "good"...)
Limiter (basically prevents hard clipping; sound quality only suffers when the input is too loud)
and some multi-band & side-chain variants
EQ too.. especially bass cut on non-bass tracks, to leave more headroom for bass instruments.

I'm still learning but it seems best to use a little of each effect so none is too noticeable. Slight tape saturation on (almost) every track, compression and/or limiters on tracks that really need it, and more sat/comp/limiter on master out.

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