TER wrote on Wed, 12 April 2006 16:34 |
compressors increase gain on the release... think double negative. compressors decrease gain reduction as the compressor releases.
z-mix... can you explain this:
"If the threshold is set to -10dB and the ratio is 2:1 then a signal entering the compressor at 0dB will exit at -5dB and a signal entering the compressor at -20dB will leave at -15dB."
where does the 5dB gain increase come from on the -20dB signal? this equation would say that a signal entering your compressor at -50dB will leave it at -30.
if you've applied 5dB of makeup gain, your 0dB signal would exit at 0dB, not -5.
to the best of my knowledge a compressor is a gain REDUCTION device, no?
-t
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Not correct on the second paragraph, threshold does not change ratio. Knee does somewhat. If you input the comp at -20dB with a 2:1 ratio, your gain reduction would be -10dB. If your ratio is 5:1 and threshold is -10dB your signal is reduced in gain by -2dB. Ratio is fixed and threshold only determines the level where the compressor comes on and starts reducing gain.
Knee determines how gradual or sharp the leveling slope is when the compressor reaches threshold level. A soft knee cuts the compressor on gradually and a hard knee cuts the compressor on faster. In this way full ratio is not reached immediately with a soft knee, but eventually will reach full ratio, whereas a very hard knee will reach the ratio immediately.
On the last point, a compressor is a gain reduction device, yes. By lowering gain above the threshold, more headroom can be applied, output level can be increased, RMS goes up, so when you make up gain, perceived loudness goes up and louder than the input signal. It is technically a gain reduction device that is used to increase gain on output. By keeping transients down, constant gain can be turned up louder, thus more impact and what a compressor is commonly used for. Bringing lower sounds up while keeping the sharper louder transients down. A brickwall limiter is typically a compressor set to infinity ratio and knee very hard.
Compressors don't exactly increase gain on release, they simply pass the same input signal when the signal falls below the threshold level, so a better way to look at it, is that the signal is restored to unity when the compression is released, not increasing gain when released. IOW, when the signal is below the threshold level, the input and output are at unity gain, no effective ratio, no effective knee, nothing but the input signal untouched by the compressor and only increased in gain from the signal when it was compressed, not from input, so no real increase in the signal when the compression is released.