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

[Mike Bryant]

Well I might be misunderstanding what the OP is trying to do as the conversation did seem to go off in several directions, but I’ve seen comments that the group delay introduced by higher order filters or the output lag if using a lower order filter is a problem.

If you use wavelet decomposition you’re going to generate a moving output array of scale factors which represent the instantaneous amplitude of the wavelets the input has been decomposed into.  These won’t appear at the same time – the lower frequencies lag the upper ones.  These can either be used separately to reconstruct something based on the incoming signal, which is how some voice synthesisers or some autotunes (but not the original) work, or the scale factors could be combined to produce a series of envelopes which is what I do in my additive synth.

But I don’t see why you couldn’t produce just a single envelope amplitude if that is what the OP wanted.  But maybe it isn’t what he wanted in which case you’re right, this isn’t the correct approach.

From: Guy McCusker [mailto:guy.mccusker at gmail.com]
Sent: 18 December 2021 12:03
To: Mike Bryant
Cc: Mr&MrsAccount; Jean-Pierre Desrochers; Tom Wiltshire; synth-diy at synth-diy.org
Subject: Re: [sdiy] Best & fastest envelope follower schematic.. anybody ?

Can you give us a clue on how a wavelet transform would be useful in an envelope follower? I don't know much about the area but at first glance it does not seem like the right tool for the job.

On Fri, Dec 17, 2021 at 11:25 PM Mike Bryant <mbryant at futurehorizons.com<mailto:mbryant at futurehorizons.com>> wrote:
If anybody is thinking of doing this digitally, you might want to read up on the Continuous Wavelet Transform.   Then once you realise your DSP isn’t up to it, have a look at the Discrete Sub Band Transform, aka Wavelet Packet Decomposition.  This gives as accurate results as the Discrete Wavelet Transform with less group delay problems, and given enough processing power is able to decompose even the human voice in real time.


From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org<mailto:synth-diy-bounces at synth-diy.org>] On Behalf Of Mr&MrsAccount
Sent: 17 December 2021 21:41
To: Jean-Pierre Desrochers; 'Tom Wiltshire'
Cc: synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>
Subject: Re: [sdiy] Best & fastest envelope follower schematic.. anybody ?

Remember that high order filters don't come without their own baggage...

They suffer from greater group delay (which could be a problem) and poor transient response (also a problem).

Especially in a use where the input could start at zero or suddenly return to zero, the overshoots can be a killer.

I've been making filters to isolate the fundamental of Guitars for many (now many mnay) years.   The settling times are longer than the delay of the guitar signal itself, therefore the delays...

________________________________
From: Jean-Pierre <jpdesroc at oricom.ca<mailto:jpdesroc at oricom.ca>>
To: 'Tom <tom at electricdruid.net<mailto:tom at electricdruid.net>>
Cc: synth-diy <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>>
Date: Friday, 17 December 2021 10:39 AM EST
Subject: Re: [sdiy] Best & fastest envelope follower schematic.. anybody ?
> This would be the digital equivalent to the single pole RC. It should be possible to get better ripple suppression by using higher order filters. Harald showed that he got a better response using a fourth-order filter.

So.. how can I modify the C1 section to get for example a fourth-order filter ?
To do it the way the signal flows across C1 is a bit confusing..
The signal comes from the left side but the clamping comes from D1 at right side.
I know how to implement high order filters in circuits but only
if I know the signal flow direction..


De : Synth-diy <synth-diy-bounces at synth-diy.org<mailto:synth-diy-bounces at synth-diy.org>> De la part de Tom Wiltshire
Envoyé : 17 décembre 2021 08:37
À : Martin Klang <mars at pingdynasty.com<mailto:mars at pingdynasty.com>>
Cc : synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>
Objet : Re: [sdiy] Best & fastest envelope follower schematic.. anybody ?

This would be the digital equivalent to the single pole RC. It should be possible to get better ripple suppression by using higher order filters. Harald showed that he got a better response using a fourth-order filter.


On 16 Dec 2021, at 16:26, Martin Klang <mars at pingdynasty.com<mailto:mars at pingdynasty.com>> wrote:

I think an envelope follower with no lag is called a rectifier.
Jokes aside, there are a number of options available but ultimately it comes down to filtering.
For digital envelope followers, I like to use a simple exponential average (aka leaky integrator, a first-order IIR filter) on the fully rectified signal and tune the time constant to the expected input signal. Generally you want it to be fast, but not so fast as to track the waveform oscillations, even at say 20 Hz. This makes a computationally very efficient follower with predictable results.

best,

Martin

On 16/12/2021 01:36, Jean-Pierre Desrochers wrote:
Here is my goal..
I need a circuit that will take an AC signal and will shift level it from
a DC offset extracted from its min & max Peaks..
Ex: Suppose you have steady +/- 5v peak sine wave coming in this circuit,
The output would be the same waveform but shifted up to +5vdc.
So 0 to +10vdc.
That final waveform would be much usable for a 0-5vdc control voltage input
than the original AC waveform.
Now the challenge is to do the same with a level changing AC signal.
In the case of a steady waveform this ‘level shifter’ could be an opamp that would add half of the peak to peak voltage as an offset DC voltage,
But here I’m looking for something that will be more versatile
to handle varying level waveform.

_______________________________________________
Synth-diy mailing list
Synth-diy at synth-diy.org<mailto:Synth-diy at synth-diy.org>
http://synth-diy.org/mailman/listinfo/synth-diy
Selling or trading? Use marketplace at synth-diy.org<mailto:marketplace at synth-diy.org>

_______________________________________________
Synth-diy mailing list
Synth-diy at synth-diy.org<mailto:Synth-diy at synth-diy.org>
http://synth-diy.org/mailman/listinfo/synth-diy
Selling or trading? Use marketplace at synth-diy.org<mailto:marketplace at synth-diy.org>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20211218/54289210/attachment.htm>