[music-dsp] Envelope Detection and Hilbert Transform

[Citizen Chunk]

hi James. i just did a little reading on the good ole "interweb" and
found this page on the Hilbert Transform:
http://www.numerix-dsp.com/envelope.html

from what I can gather, because of the 90 degree phase shift, the HT
(not hyper threading ;) ) helps to "fill in the gaps" that would be
present in a rectified oscillating signal. this seems a lot like the
RMS value--but RMS is an average level, not the peak level. so the HT
is kind of like an average that just follows the peak value. hope i'm
making sense and properly understanding this thingy.

if you have a sidechain signal that is tracing the rectified peak
signal, it will attack/release as the signal rises/falls, which can
cause envelope ripple. you could get a smoother envelope by using RMS,
but that will slow down reaction time. from what i gather here, if you
use the HT, you get a very smooth peak signal, which can then be
averaged (for something like an RMS) or passed to an attack/release
detector, for typical compressor behavior. so perhaps using the HT can
actually reduce envelope ripple and IM distortion.

or do i have it all wrong? ...

== chunk

On Fri, 24 Sep 2004 11:39:05 -0400, James Chandler Jr
<jchandjr at bellsouth.net> wrote:
> ... 
> I understand how a Hilbert envelope detector would help avoid ripple on 'well
> behaved' signals. But if the object is to minimize envelope ripple regardless of
> wave shape, would a Hilbert envelope detector be smart enough to smooth out
> 'nightmare signals'? Perhaps one would also require post-Hilbert lowpass
> filtering? Dunno.