stupid envelope follower idea

[Terry Michaels]

Message text written by Martin Czech
>:::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.

Ok, I have to think about that. I guess 6dB/oct filters would do.
In that case a highpass could be derived from the lowpass at the same
edge (you know, in the way frequency splitters were once proposed).
I guess that a sweeping sine then would give a flat envelope, as it should.
<

Hi Martin:

One problem with this approach is the various band filters are bound to
have different group delay times, so waveform peaks passing through the
filters may not line up timewise afterward.  Since harmonics of the input
signal will not coincide after passing through the band filters, they will
not add up algebraically, and you will then detect an envelope that will
have a different shape than the original signal had.  This wouldn't happen
with sine waves, but it likely will with harmonically complex signals.

Terry Michaels