[sdiy] Enveloppe follower

Dave Magnuson abide at dmdrafting.com
Thu Dec 5 17:43:57 CET 2019



From: Synth-diy <synth-diy-bounces at synth-diy.org> On Behalf Of Florian Anwander
Sent: Thursday, December 5, 2019 11:13 AM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] Enveloppe follower


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
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
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.




I think Florian has a great point regarding spectrum versus loudness.    

 I wonder (brainstorming) if something akin to a “color organ” would be interesting here, too?     Divide the input into 3-4 frequency bands and provide an envelope follower on each.   

Then you could mix / match use each output in a different manner?


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