MOTM

Paul Haneberg wrote:
> It seems to me I read something once about using multiple FWRs as
> frequency doublers in envelope followers.  This is supposed to improve
> the response time.  I may have read this somewhere in ElectroNotes, I'm
> not sure.  I'm out of town at the present time and unable to verify the
> source.  It might be interesting to have outputs from multiple FWRs on a
> module such as this.

Yes, this is my understanding.  And yes, Electronotes #60, #86, #88 & #89 -
good memory!  There is a trade off when determining the time constant of the
filter between being able to detect snappy envelopes and reducing the amount
of voltage ripple on the detected envelope for lower frequencies.  Obviously
fast envelopes at low frequencies is the biggest problem.

So by adding say two additional FWR sections, this would quadruple the
frequency of the signal (in theory) thereby allowing the low-pass filter
cutoff frequency to be increased, which in turn improves the speed (response
time) of the envelope detection.  From what I understand however, FWR does
not work properly for sine waves (or other predominantly even-harmonic
waveforms), as the subsequent waveforms are not symmetrical about the x axis
and do not frequency double.  An AC-coupled peak-correction circuit can be
used in conjunction with each FWR section, to add in the appropriate amt of
offset voltage to the FWR section to make up for the non-symmetry in the
waveform.  (I think I've got that right :)

Anyway, I have yet another crazy feature that may be nice.  I think I
remember reading about it somewhere, the MAM filter or something?  Have
three envelope follower sections, each tracking a separate frequency range,
say low, mid and high.  Then the envelope output of each of those could be
sent to the three inputs on the OMS-410 filter companion module.  Woah -
sounds like fun!

One more thought (like beads of water on the forehead, eh? :) .. until a
MOTM equivalent is available, if one has a Wavefolder and a MOTM-820, a
simple envelope follower could be patched up.

Cheers,
George