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

[Tom Wiltshire]

Here's a link to that page of the discussion:

https://modwiggler.com/forum/viewtopic.php?f=17&t=109067&start=175 <https://modwiggler.com/forum/viewtopic.php?f=17&t=109067&start=175>

TBH, Harald, I think the comparison is a bit unfair. You're comparing a 24dB active SK filter to a passive RC. Clearly one is going to have better filtering response to the other. 

Whether the FWR gives better performance than the peak-hold method is an interesting question, but that's not really dealt with. Also the test signal is very artificial. The slower decay on the Bissell envelope (not that slow - 150msecs?) actually matches typical guitar envelopes rather well, so perhaps that's why many people rate it highly, at least in the pedal world.

I do think your experiment makes a good point though - if you want a smoother output, you need better filtering. Many designs get by with a simple passive RC and leave it at that. With such a simple filter there *will* always be a trade-off between speed and ripple.


> On 15 Dec 2021, at 09:44, Harald <sdiy at haraldswerk.de> wrote:
> 
> Well,
> 
> scroll a little back in this thread to page 7/8 and have a look at my comparison. Harry Bissell' envelope follower is in no way better than the classical approach. It is slower, has more ripple and is about 500mV off.
> Harald
> 
> Am 15.12.21 um 10:08 schrieb Tom Wiltshire:
>> 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 <https://modwiggler.com/forum/viewtopic.php?t=109067> <https://modwiggler.com/forum/viewtopic.php?t=109067 <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 <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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