[sdiy] Best & fastest envelope follower schematic.. anybody ?

Tom Wiltshire tom at electricdruid.net
Thu Dec 16 01:22:07 CET 2021


I think this ignores the considerable influence of both compression and the "autowah" or envelope-followed filter on popular music over the last three or four decades. Neither of which function without envelope followers. While (live) they might have necessary limitations due to physics and not being able to see the future, the fact remains that they are useful and musical, despite the imperfections.

I think it's instructive to study some of the "classic" effects circuits. I was *amazed* at how technically *bad* some of them are. But no-one cares. They're still classics, and now people are spending time and money developing digital emulations that capture every single failing of the original circuit, because it turns out that technical perfection just doesn't sound as good, or at least it doesn't sound like the thing that everyone wants it to sound like.

It's not all about minimising lag time. Realistic envelopes of actual instruments have significant decay. Envelope followers that mimic that can work well. Us synth people expect every parameter to be highly variable, but guitars and electric pianos don't have a "Decay" control so their players expectations are quite different.


> On 15 Dec 2021, at 15:31, Benjamin Tremblay <btremblay at me.com> wrote:
> 
> I lost all interest in envelope followers when I tried out some designs and observed the lag. 
> These are mostly “envelope smoothers” and most are barely any better than an old incandescent vactrol attenuator circuit used in FM broadcast.
> They mostly just drive non-musical effects under the category “something weird happens when I play my guitar”.  Pre-filtering the audio probably helps but there’s no guidance on best all-round EQ.
> Only The Residents got much mileage out of envelope followers over the years.
> 
>> On Dec 15, 2021, at 10:05 AM, Jean-Pierre Desrochers <jpdesroc at oricom.ca> wrote:
>> 
>> Hi Tom,
>> 
>>> Harry Bissell's envelope follower is well thought of for its combination of speed and accuracy.
>>> https://modwiggler.com/forum/viewtopic.php?t=109067
>> 
>> This is a very clever project and neat design.
>> But still too much ‘lag’ on the falling edges incoming signal.
>> So far.. a PIC would do best with least components..
>> Hmmmm...
>> As usual.. Thank you for you good suggestion anyway !
>> JP
>> 
>> 
>> De : Tom Wiltshire <tom at electricdruid.net> 
>> Envoyé : 15 décembre 2021 04:08
>> À : Jean-Pierre Desrochers <jpdesroc at oricom.ca>
>> Cc : Synth-diy at synth-diy.org
>> Objet : Re: [sdiy] Best & fastest envelope follower schematic.. anybody ?
>> 
>> Hi JP,
>> 
>> Harry Bissell's envelope follower is well thought of for its combination of speed and accuracy.
>> 
>> https://modwiggler.com/forum/viewtopic.php?t=109067
>> 
>> It's a good circuit, but pretty complicated, especially for an effect pedal design. So like you, I thought "PIC!", and had a go at implementing it in firmware.
>> 
>> The round-robin three peaks detectors are easy enough. Doing the output filtering is more demanding on a chip with no multiply, but I managed it by being choosy about the filter coefficients and keeping things binary friendly. The end result was pretty good and used a little PIC to the maximum extent.
>> 
>> HTH,
>> Tom
>> 
>> ==================
>>      Electric Druid
>> Synth & Stompbox DIY
>> ==================
>> 
>> 
>> 
>> 
>> On 15 Dec 2021, at 01:34, Jean-Pierre Desrochers <mailto:jpdesroc at oricom.ca> wrote:
>> 
>> Hi all,
>> I’m looking for a fast and accurate voltage follower circuit.
>> There are plenty of them on the web to build but they all
>> suffer of inaccuracy and lag on the final DC output (final stage of low pass to smooth off the incoming peaks).
>> The incoming voltage will be a varying 0 to +/-5v peak.
>> I thought about implementing a solution using a small PIC with ADC/DAC
>> but even if these micros are very cheap this solution would be overkill.. would it be ?
>> So far the available circuits have too much lag on their DC output.
>> (The envelope takes too much time to get back to zero after a fast incoming peak)
>> Any known & reliable circuits ?
>> JP
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