stupid envelope follower idea

[Hairy Harry]

Hi everybody...

I use a "stupid envelope follower" of my own... its really intended
for percussive attacts (like guitar) but hell if you have a wimpy
attack then speed REALLY isn't an issue anyway....

I use a peak detector, with a slow detector operating a "squelch"
circuit. So the peak detector (fast / low ripple) follows the
envelope, and the second circuit makes the peak detector follow
fast downward changes in amplitude (such as string mute).

The evil ones (rol at nd...) have a very cool circuit idea for
low ripple / fast response. The gist of it is a phase shift
stage with rectifier output, feeding a single small cap... so
the ripple peaks fill in the gaps from the alternate phases.

This was on a pitch to CV converter... I forget the model number.

H^)  harry

>From: "danial stocks" <diode at hotmail.com>
>To: synth-diy at node12b53.a2000.nl
>Subject: Re: stupid envelope follower idea
>Date: Wed, 22 Nov 2000 15:22:17
>
>This all sounds like far too much extra circuits for perhaps only a really
>small gain in performance...  maybe not even a gain in performance..
>personally, I'd stick to a 1/2 wave precis rect, separate res for atk &
>decay... then you could tweak these parameters separately, or even have 
>pots
>for user control... this sys does have a rather hi o/p impedance, so needs 
>a
>op amp buffer.. but still, 2 op amps simplicity and it works.. after all, 
>in
>the design of the effect, you dont really need ultra precision math
>necessarily, you just need to make it pleasing to the ear and have good
>tweakability...[in the music shop.. oh yes, the envelop filter delux.. it
>has fourier transform envelope calculations for high precision dynamics
>tracking... stoned guitarist scratches head.. but will it sound good if I
>play hendrix ?]
>Cheers,
>Dan
>
>>
>>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?
>>
>
>>:::
>>:::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
>>
>
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