AW: Re: Envelope Follower
HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Thu Feb 29 20:55:00 CET 1996
> Oh yeah I fergot to mention the multiplier type of envelope follower -
> basically this is made by running the audio signal into both inputs of
> a ring modulator, and smoothing it with an integrator like Don says.
> This acts as a full-wave rectifier with a logarithmic transfer
> function. Probably you could get the same results with an amplitude
> recovery rectifier followed by a log generator (right?).
The problem would be the offset voltage of the multiplier which would
limit the dynamic range.
> I remember seeing an untested design proposal way back in an old
> Electronotes - it consisted of two multipliers, with the audio signal
> running into a wideband 90-degree phase difference network, with the
> SIN output going to both inputs of one multiplier, and the COS output
> going into both inputs of the other multiplier, and the outputs of
> each multiplier averaged together. The proposal was that the valleys
> on the SIN multiplier's output would be filled in by the peaks of the
> COS multiplier's output, and vice versa. This way there would be no
> smoothing filter required, or so it seems. Would this work?
Should work !! (in case that the offset problem is solved)
For every spectral component (A*sin(wt))**2 + (A*cos(wt))**2 should be
A**2, indepenent of wt, just the envelope information as desired.
Tietze/Schenk (the "Electronic Bible" in Germany) show such a
circuit for a precise ripple-free amplitude regulation of a Quadrature
Sine-/Cosine-wave generator. *There* it works on a single frequency
but this shouldn't make any difference.
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