No one reads the manual for a compressor, and if you did you wouldn't get any warning about the effects of over
compression. I don't mean this in the sense of too much compression, your ears will tell you that, but in the sense
of setting a lower threshold than you need to get the job done. This will always make the sound worse, with the
sole exception of percussive sounds where it might sometimes be a useful effect.
Let's assume a scenario where an instrument plays occasionally with silences in between. This is where over
compression is most likely to happen. When setting the threshold, many users have an idea of how much gain
reduction they want to hear and see on the meter. The amount of gain reduction is controlled by both the
threshold and ratio controls. Suppose these controls are set so that the desired amount of gain reduction, let's
say 12dB for example, is achieved. This should be fine shouldn't it? Look again at the gain reduction meter. While
the instrument is playing, does it ever go all the way down to zero? If it doesn't, if it only goes down to 3dB, then
you haven't applied 12dB of gain reduction, you only have 9dB of compressive gain reduction. The other 3dB could
have been achieved by simply lowering the fader. This, in itself, isn't necessarily a problem. The problem is that,
when the instrument starts to play, the compressor has to go all the way from zero gain reduction to the full
12dB. The necessity of covering that additional 3dB will audibly distort the initial transient. Try it, and you will
hear it for sure.
This leads to rule number one of gain reduction - at some point in the course of the track while the instrument is
playing, the gain reduction meter must indicate zero, otherwise the minimum reading obtained shows wasted gain
reduction and over compression, leading to the distortion of transients that follow silences