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Old 27th February 2008
Lives for gear

The usual reason for choosing the RMS method of detection is "leveling". Please understand that often when using compression , you let peaks get through!
Inside the compressor when the detection circuit looks at the envelope ( there is always a lag between when the over threshold situation is detected and when the turn it down thing happens ! It may be in thousands of a secound , but it happens , that's why digital limiting has look-ahead so as to not let things slip through ; but thats a different subject).

So since you asked about RMS detection, keep in mind that the detector now has to calculate what the average loudness (RMS ) is before it decides about wheter that value is over threshold. So it's a little slower at this . You set your threshold around the place where the RMS is "modulating" ( These are all averaged values so it does'nt have anything to do with those spikes you see in a waveform) ; thus "leveling".

There are RMS mode compressors that have lookahead, but this will only help to not let burst (not instantaineous peaks!) of loudness ( a :mini-chunk ) get through. This is also realted to attack settings , where as you , once again , are not trying to stomp down peaks , so the attack settings can be set slower , but lookahead in this context ( rms leveling) lets you set attack slower ( for a natural sound ) but still catch "peaks" (mini burst of average loudness , not peaks. ( this stuff happens in milliseconds so remember were just trying to "visuallize whats happening).

Some people like to put 2 compressors in a row , with the first one in a more instantaineous , peak catching set-up and then the "leveling" rms compressor, or , vice versa!!

While your studying, look into "Crest Factor" and remember , that this is one of those subjects that you almost always have to keep after as there are so many different ways to approach and put "Dynamics processing" into practice!

Read the "compression uncompressed tuitorial hereIndependent Recording Network

it's good

Good Luck!!