On Wed, 28 Nov 2007 02:10:42 +0100 Roman Haefeli reduzierer@yahoo.de wrote:
hm.. don't quite know, how to answer this, i'd say yes and no. basically 'waveshaping' means adding non-linear distortions to a signal, a process, which enriches the frequency spectrum of the signal (-> spectrum is altered). the goal of all dynamic processing fx as gates, compressors, limters, expanders is to only affect the dynamics of the signal, but not the spectrum. but yeah, they are somehow related: if you use very insane settings for a compressor, let's say 0ms for attack and decay, then you have actually a waveshaper.
You can hear this when applying a traditional compressor to low frequency sounds like electric bass and 808 kick drum where the wavelength of the signal is comparable with the compressor changes. Each cycle gets treated as if it were a separate event. Where compressor and waveshaper diverge is at Gabor period, 20ms (50Hz), it's no coincidence that where perception of frequency vanishes at the lower bound perception of amplitude picks up.
let's say you use very small values but not 0, then it is actually not exactly a waveshaper anymore, althouth the spectrum might still be altered. a waveshaper uses table look-up, so each input value has its corresponding output value, but a compressor with very short attack and decay is more kind of an 'adaptive waveshaper' (i am not that much an expert, so this term might not make any sense). however, what happens is more complex, because the current output value is not only dependent on the actual input value, but also on previous input values (and also if we are actually in 'attack' state or 'release' state).
I suppose, technically, you could say it has become a filter since the current instantaneous output depends on the average of previous input values.
There are really two kinds of compressor. Feed forward compression places the averaging function parallel with the signal path and modifies the output gain. Look-ahead compression delays the signal path and calculates the gain reduction in anticipation. Each has its merits. The "attack" control on a traditional compressor actually does the opposite of what some people expect, it holds off the gain reduction to allow the initial transient through. That's desirable in mixing where you want to change the perception of loudness without needing a limiter since the apparent loudenss is a function of both amplitude and time - so you reduce the "body" of the sound while allowing the subtleties of the attack to come through and leave it clearly defined in the mix - good examples of use are for guitar, bass and drums. A feed forward method is superior here because we don't mess with the timing, which is what we want for percussive sounds. The other kind of use is averaging the overall level, as in vocal passages, in which case a look ahead compressor is better. Legato sounds like vocals and strings are less sensitive to being shifted a few milliseconds back but the levelling process benefits greatly from having a small amount of the signal to anticipate.
a.