[sdiy] Enveloppe follower

[Florian Anwander]

Hi Jean

Am 04.12.19 um 17:31 schrieb Jean Bender:
> discovered that most of them was pretty good for following musical
> instruments signals, but not so much for more electronic audio
> signal..
> I mean, i play a lot of ambient and noise stuff, including sounds
> without so much attack, even if they have some relief.
>
> And that's my point :  i'd like to build myself an enveloppe follower
> able to be really subtle, and able to be effective even on droning
> sounds...
> So where should i take a look ? What i have to be careful of ?

Brian wrote all the theory already.

Your main problem is: drones typically don't have a significant change 
in amplitude. On the other side: drones often change the colour of 
sound, the spectrum.

So I think you don't need a simple envelope-Follower, but you might need 
something more complex. I could imagine something like the analysis 
section of a vocoder, with an circuit after it, that outputs a voltage 
that corresponds to the frequency range or frequency weight.


I did not think it completely over, but a first attempt might look like 
this:

A state-variable-filter splits the signal in two signals: high and low. 
Both signals then are fed through an  envelope follower each. Now the 
output voltages of the two env-followers are subtracted. The result 
would be something like:

  * full frequency-spectrum = 0V
  * only high frequencies = +maxV
  * only low frequencies = -maxV

I am not sure, whether the result is really interesting or usable, but 
it might be worth a try.


Florian

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