Compression Ratios and what they mean

Ðësantis

New member
I've been mixing by ear for awhile now and kind of play around with knobs to get the sound I want but I'd like to know exactly what the compression ratios are for and what applications/instruments each #:1 would be used for in most cases. In mixing and mastering applications? I usually get a decent sound out of compressing but the ratios are a mystery to me. Please dumb this down big time I am an idiot.. I'm sure other newbies would like this answered as well.
 
im also interested in this..also i have question after yours...can i make a kick without changing the treshold in compressor? im mean im always do it (with +10db on treshold) but i saw one output formula so it confused me for a moment hah
 
Last edited:
What compression ratio is ( from wikipedia )

The amount of gain reduction is determined by ratio: a ratio of 4:1 means that if input level is 4 dB over the threshold, the output signal level will be 1 dB over the threshold. The gain (level) has been reduced by 3 dB:
Threshold = −10 dB
Input = −6 dB (4 dB above the threshold)
Output = −9 dB (1 dB above the threshold)

Here is a link of videos which helped me a lot to understand how the compressor
works (There are some general rules in those vids but i wouldnt stick to them , there are just to get you started )

Compression now is used almost everywhere ( even a little bit ) ( on vocals , guitars , drums etc ) but i would suggest to learn how to use it , then you will know in which applications is needed . ( I study via internet music and still dont get the results i want , so dont get disappointed , just keep trying )

Yeah , both mixing and mastering use compression as a tool

Good luck , hope it helped .






 
Last edited:
Pretty much, ratio is how hard you're "compressing" (or squashing down) the sound wave.

Probably the most used settings for ratio are around 3:1 - 4:1.

Wherever you set your threshold, the compressor will squash everything above that point according to how hard you drive the ratio.

So if you have the threshold set super low on the sound wave, but only a 1:1 ratio, nothing is actually being compressed since the ratios are the same. Increase that to 10:1 and you'll hear a suuuper compressed sound.

Be sure to experiment w/ the atk and rel times as well (and knee settings) as those impact the sound a lot too. Or if you're looking for the simplest compressor ever, download the free compressor here. It's quality and only 2 knobs (1 of those being post gain)

Tin Brooke Tales (TbT) TLs-3127, a freeware VST effect plug-in for Windows PC

Hope that helps!
 
better yet read a manual for any compressor on the sw or hw market (easy enough to obtain)

however the nuts and bolts are easy enough to identify
  • threshold: the signal level at which the compressor starts to work
  • attack time: how long after the signal crosses the threshold the compressor starts to work
  • release time: how long after the signal falls below the threshold the compressor stops working
  • ratio: two numbers X:Y (X in the ratio to Y - mathematically this means a fraction is applied, see below)
    • left hand number is how many dB of signal goes into the compressor
    • right hand number is how many dB of signal comes out as a result of the compressor working

when we put a signal into a compressor it can be above, at or below the threshold. If above the threshold then it begins to act by subtracting the threshold from the signal then reducing the gain of the signal by the ratio

signal in -> threshold -> above: compress difference signal by ratio; at or below: let signal pass through unchanged -> output (compressed signal)

best way to understand is

if the signal is above the threshold then output = threshold+(difference * Y/X),
otherwise output = input;

where difference is the amount of signal above the threshold i.e. signal level-threshold level
(e.g a threshold of -20dB results in a difference of 1dB if the signal level is -19dB i.e. -19dB--20dB = -19dB+20dB = 1dB)

e.g.

in each of the 3 following examples the compressor has threshold of -20dBfs
example 1
ratio is set at 2:1 which means for each rise of 2dB above the threshold we only get a rise of 1dB out

inputdifferencecompressedoutput
-30dBfs-10dBfs--30.00dBfs
-20dBfs0dBfs--20.00dBfs
-19dBfs1dBfs0.50dBfs-19.50dBfs
-18dBfs2dBfs1.00dBfs-19.00dBfs
-17dBfs3dBfs1.50dBfs-18.50dBfs
-16dBfs4dBfs2.00dBfs-18.00dBfs
-15dBfs5dBfs2.50dBfs-17.50dBfs
-14dBfs6dBfs3.00dBfs-17.00dBfs
-13dBfs7dBfs3.50dBfs-16.50dBfs
-12dBfs8dBfs4.00dBfs-16.00dBfs
-11dBfs9dBfs4.50dBfs-15.50dBfs

example 2
ratio is set at 4:1 which means for each rise of 4dB above the threshold we only get a rise of 1dB out

inputdifferencecompressedoutput
-30dBfs-10dBfs--30.00dBfs
-20dBfs0dBfs--20.00dBfs
-19dBfs1dBfs0.25dBfs-19.75dBfs
-18dBfs2dBfs0.50dBfs-19.50dBfs
-17dBfs3dBfs0.75dBfs-19.25dBfs
-16dBfs4dBfs1.00dBfs-19.00dBfs
-15dBfs5dBfs1.25dBfs-18.75dBfs
-14dBfs6dBfs1.50dBfs-18.50dBfs
-13dBfs7dBfs1.75dBfs-18.25dBfs
-12dBfs8dBfs2.00dBfs-18.00dBfs
-11dBfs9dBfs2.25dBfs-17.75dBfs

example 3
ratio is set at 10:1 which means for each rise of 10dB above the threshold we only get a rise of 1dB out

inputdifferencecompressedoutput
-30dBfs-10dBfs--30.00dBfs
-20dBfs0dBfs--20.00dBfs
-19dBfs1dBfs0.10dBfs-19.90dBfs
-18dBfs2dBfs0.20dBfs-19.80dBfs
-17dBfs3dBfs0.30dBfs-19.70dBfs
-16dBfs4dBfs0.40dBfs-19.60dBfs
-15dBfs5dBfs0.50dBfs-19.50dBfs
-14dBfs6dBfs0.60dBfs-19.40dBfs
-13dBfs7dBfs0.70dBfs-19.30dBfs
-12dBfs8dBfs0.80dBfs-19.20dBfs
-11dBfs9dBfs0.90dBfs-19.10dBfs
 
Last edited:
Back
Top