To prevent all this compressor confusion and serve the many questions thast reached us in the last weeks here a few short remarks about audio compressor plugins.
A compressor is a automatic volume control invented in the days when the radio was the streaming provider of former times. it reduces the dynamic of audio material to prevent overdrive and make quiet signals louder.
The technical background is defined by this:
Threshold
The threshold is the level at which the compressor starts to work. Lets take a threshold of -10 dB and a input signal of -6 dB. so the signal is 4 dB over the threshold. and here comes the ratio.
Ratio
In our case we have 4 dB over the threshold. With a given ratio of 1:2 for example we have to reduce the 4 dB down to 2 dB, would we take a ratio of 1:4 there would remain 1 dB an so on. Just the difference between signal and threshold devided by the ratio. So we have a threshold of -10 dB, a remaining level of 2 dB (1:2) which means to regulate the signal 2 dB down.
Attack
How fast the compressor does this is defined by the attack time. Our compressors offer two ways to handle this: The difference mode regulates this in the given attack time, the constant mode sets down a signal with dB per second.
Release
In our case the compressor reduces a signal. What if the next signal is under the threshold ? Well the compressor turns the signal louder opposite in the given mode. How fast to do that is defined with the release time.
Makeup Gain
In our case we have a signal which is mostly around -10 dB or less, so we add gain to lift this up to a level of -1 dB or whatever we want.
Mix
Our compressors as well as most other provide to mix the original input signal with the compressed to balance a harmonic sounding result.
Reference
To do all this the compressor needs a reference signal to calculate how much we are about the threshold in a musical event. It could be the peak of all channels or the average or sum. Some of our compressors provide a low cut filter so bass and kick are not compressed so much as the other signals.
I think it's obviously why a compressor with a ratio of 1:1 does nothing. I know there are some plugins on the market which show a gain reduction even when you adjust a ratio of 1:1. Others compress a signal of - 15 dB although the threshold is about -5 dB. I utterly would not recommend to use those software riddles, you never can be sure to get what you want.
But all this are theoretical basics, everything depends on what kind of musical events we have, which result we need and so on. Some compressors do calculate with VU instead of dB and much more variations. At last - just trust your ears.
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