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

[Roman Sowa]

You just cant's make something a 4th order filter by modifying one 
capacitor. Besides, this will only alter DC bias, passing all AC intact, 
so any filtering should be placed after this circuit (I've attached the 
circuit you posted for reference).

So when input signal goes down, C1 is charged via diode to prevent Vo 
going below Vref. When input finally starts to go up again, the diode 
cuts off opamp from the cap, and charged voltage on C1 is added to 
rising input. But when suddenly input amplitude drops, this circuit will 
not respond immediately. AC will still pass, but the charge collected 
oat C1 during most negative peak is still there so it will have the same 
DC offset like the moment befere when amplitude was bigger. C1 must be 
discharged with external resistor connected to Vo, and this makes it 
release rate typical for 1st order RC circuit. So you're basicaly at 
square 1 again.

Roman

W dniu 2021-12-17 o 16:33, Jean-Pierre Desrochers pisze:
>>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> *De la part de* Tom 
> Wiltshire
> *Envoyé :* 17 décembre 2021 08:37
> *À :* Martin Klang <mars at pingdynasty.com>
> *Cc :* 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.
> 
> 
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