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.