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 Forum index » Instruments and Equipment » Modular Synthesis
Percussive envelope generator
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françois



Joined: Dec 23, 2006
Posts: 139
Location: Paris (France)
Audio files: 1

PostPosted: Fri Dec 29, 2006 5:15 am    Post subject: Percussive envelope generator Reply with quote  Mark this post and the followings unread

Hello all,

Here is one of my recently designed modules.

I just got tired of those ADSR envelopes, mostly because you can't know exactly what the "attack peak level" is (90% ? 67% ? other ? voltage controlled ?). It turns out that there is a nice smooth function which, when initiated by a trigger (not gate !) pulse, will rise to its full amplitude, and then fall back to zero.

The function is y(t) = t.exp(-t/T) and is plotted below. The differential equation is "easily derived" (did I mention I was much better at math than music ?) as d²y/dt² + 2dy/dt + y = 0 (trust me) and the resulting analog circuit is exactly similar to a state variable filter, except for the resonance factor of 2.

When mixing this with an ASR envelope and playing with the trigger/gate delays you can get some funny envelopes...

- françois


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Sound



Joined: Jun 06, 2006
Posts: 842

Audio files: 1

PostPosted: Wed Jan 03, 2007 12:18 pm    Post subject: Re: Percussive envelope generator Reply with quote  Mark this post and the followings unread

françois wrote:


Here is one of my recently designed modules.






Where is it?

Do you have any photo?

Thanks a lot.
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françois



Joined: Dec 23, 2006
Posts: 139
Location: Paris (France)
Audio files: 1

PostPosted: Fri Jan 05, 2007 4:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello Sound,

Maybe I wasn't clear enough: it is a Spice simulation!

But the circuit is so simple I am confident it will work well on breadboard. Except, probably, for some annoyance due to the OTA's offsets with DC signals. I experimented that already in simulation...

I lack a few $$$ (€€€ in fact) and, more important, I lack room to get a decent lab. I expect to have one shortly but this depends on a friend's good will...

-- françois
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françois



Joined: Dec 23, 2006
Posts: 139
Location: Paris (France)
Audio files: 1

PostPosted: Fri Jan 05, 2007 4:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thinking of it, I did in fact test (simulate) this module. LTSpice can generate .wav files as well as taking them as inputs.

It sounds really dull on a linear VCA. Much better on an exponential one.

BTW, my simulated modules already include several types of VCOs, of VCFs, of EGs... A real simulated modular, but simulated at the transistor level... No surprise I can't get real-time !!!

-- françois
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