[sdiy] Fast envelope follower circuit needed..

Tom Wiltshire tom at electricdruid.net
Thu Mar 28 14:21:59 CET 2013

Hi JP,

The typical circuit is a precision full-wave rectifier (or sometimes not even a full wave rectifier) followed by a filter. It works pretty well, but is not flawless, especially at low frequencies. The many Auto-wah/envelope filter circuits have examples if you need a schematic.

You're asking for a lot if you want both "fast" and "down to 1Hz". After all, the rise time on a 1Hz sine waveform is 250ms, which in my view is "slow".

Have you considered using a digital solution? Shift the signal to 0-5V range, then feed it to the ADC input of a PIC/AVR (You're a PIC programmer, I know). Digital rectification is easy. Then you could do the smoothing in software. This might allow you to do some clever tricks that you couldn't easily do with analog, like have a filter that responds to the incoming signal frequency. Just a thought.


On 28 Mar 2013, at 12:44, 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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