Re: envelope extraction

["Richard F. Lyon" <DickLyon@xxxxxxx>]

Ben, if what you're looking for is envelope extraction, then there's 
no reason to prefer half-wave to full-wave rectification; use a time 
constant consistent with the needs of your application; in speech 
recognition, 50 Hz is consistent with smoothing away pitch effects, 
pretty much.

The half-wave rectifier makes sense if you wan to model and use the 
sort of fine temporal structure that the cochlea sends up the 
auditory nerve to the brain.  It's capable of representing details up 
to a couple of kHz at least, and half-wave is needed to keep a 
consistent represenation of different types of pitch, and to agree 
with known physiology.  A filter corner around 1.5 kHz is typical, I 
think.  I haven't looked at refs on this for a long time, but I 
always had the impression that the psychophysics implied a wider band 
than the physiologists were able to observe.  I don't know if it's 
settled.

Dick