stupid envelope follower idea

[Don Tillman]

   Date: Wed, 22 Nov 2000 07:28:46 +0100 (MET)
   From: Martin Czech <czech at Micronas.Com>

   Don:
   :::It's a simple matter to split the input signal into several bands,
   :::perform a separate envelope detection on each, and sum the results.
   :::That way each frequency band can be optimized and you can have both
   :::low ripple and high speed.

   Ok for a sine wave, now, what happens in the case of complicated
   mixtures of partials and noise? I think the total energy would
   divide into the seperate channels, if you pick now the largest
   channel output, you'll loose all other energy. 

Imagine splitting the input signal into three bands with three
envelope detectors:
  20 to 80 Hz, slow envelope detector
  80 to 320 Hz, medium envelope detector
  320 Hz and up, really fast envelope detector

And summing the results.  If the input signal has no content below 320
Hz, you've got a really fast envelope detector.  If you happen to play
one of the two lower strings on the guitar, the really fast envelope
detector catches the harmonics from the initial transient and the
medium speed envelope detector predominates after that.  Only for low
frequency inputs does the slower envelope detector come into play.

   Balanced modulation should give the same envelope, but with less
   low frequency energy, only 50%. Since the lower side band is mirrored,
   even less. 

Ahh, interesting.  But this won't fill in any of the space between
the peaks of the input signal, so I don't see it having much of an
advantage.  

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com