I thought I understood the concept of a compressor, but the more I think of it the less I understand. A compressor looks at the music to see whether it passes a certain limit in amplitude ("volume"). The limit is called the threshold. If the music passes the threshold the compressor pushes the amplitude down by an amount as given by the ratio. Compression can start directly of after a while by increasing the attack time. Compression can remain even though the music has gone below the threshold by incerasing the release time. (Then there's the concept with hard/soft knees and sidechaing, make-up gain and enhancement, but I think I understand all that...) 1. Does the whole amplitude get compressed at the peak or just the part above the threshold (the latter should end up as distortion shouldn't it?) 2. What is the difference between peak compression and RMS compression I've been told that a limiter is essentially a compressor with a ratio of 1:infinity. But in my mind that would produce a clipped peak at the threshold level and it wouldn't sound good at all. 3. How does a limiter really work? 4. When (and why) should I use a limiter? During tracking, mixing, mastering or all of the above?