stupid envelope follower idea

[Martin Czech]

Yes, as I said, multichannel will loose phase information.
Nevertheless though math does not work, it may work
in real life? Perhaps the hearing system will not bother?

m.c.

:::Date: Wed, 22 Nov 2000 08:40:50 -0500
:::From: Terry Michaels <104065.2340 at compuserve.com>
:::Subject: Re: stupid envelope follower idea
:::To: Martin Czech <czech at Micronas.Com>, synth <synth-diy at node12b53.a2000.nl>
:::Content-Transfer-Encoding: quoted-printable
:::Content-Disposition: inline
:::
:::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