[sdiy] Fast envelope follower circuit needed..

cheater cheater cheater00 at gmail.com
Thu Mar 28 19:00:15 CET 2013


On Thu, Mar 28, 2013 at 6:45 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
> If he's trying to get the envelope, he'd want to see a 100 second sine wave, wouldn't he, since that's what the volume curve looks like?

That's the question: what is his definition of volume curve. Or let's
even start with: definition of volume.

There are many different ways to approach this subject.

> Either rectified or not, depending on whether it was a 2 or 4-quadrant amplitude modulator you used.  Or am I missing something? - I can't imagine where you got square waves from.

I read "to a rectified 0-5v wave" and interpreted that as it possibly
being a logic signal so I asked to clarify and possibly strike off
that idea.

> That example wouldn't even be that difficult since you've got sufficient space (x100) between the modulation signal or envelope and the carrier, so you could filter at a very low frequency (say 0.02Hz) and recover the modulation signal.

Yes. In fact, I am thinking that the best thing to simply have a
normal LPF-based envelope follower with adjustable cutoff.

You could have CV input for the cutoff which would react to the
frequency of the input. A simple way to use this would be to use a
frequency counter. A more involved way would be to have a vocoding
pitch detector. That's a vocoding bank, where each band outputs the
current level, and the levels get compared and based on that, the
final detected frequency is computed. This can be done completely in
analog, without any sampling or counting or PLL. I have never seen a
realization of this idea in hardware, though.

Cheers,
D.

> On 28 Mar 2013, at 17:19, cheater cheater <cheater00 at gmail.com> wrote:
>
>> So what should happen when a 1Hz sinewave, amplitude-modulated by a
>> 0.01 Hz sinewave, is fed into your box? Do you expect to get a 1Hz
>> square wave? 2Hz square wave? 0.01 Hz square wave?
>>
>> On Thu, Mar 28, 2013 at 1:44 PM, Jean-Pierre Desrochers
>> <jpdesroc at oricom.ca> wrote:
>>> Hi List,
>>> I'm sure this has been already discussed in the past
>>> but I'm looking for a fast envelope follower circuit
>>> schematic to rectify an incoming +/-2.5v AC waveform
>>> to a rectified 0-5v wave.. The wave frequency could
>>> go as low as 1 hz and sometimes will not be symetrical.
>>> Any circuits welcomed !
>>> JP
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