[sdiy] software / firmware envelopes in C (or anything else)

[Chris McDowell]

> Probably because you are neurotypical person. I feel sick if the envelope doesn't decay within 16-bit 1LSB of the destination I want it to go.

lol! 

With floats, I set the attack target to 2.0 and the threshold at 1.0, then clamp because it will overshoot that mid point at short attack times. 

When velocity is involved, I set the attack target to 2 * velocity, and the sustain level to sustain * velocity, instead of multiplying the envelope output by velocity.  this has some side effects but feels a lot more natural to me



Cheers,
Chris 

> On Nov 6, 2025, at 5:34 AM, Roman Sowa via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> 
> 
> W dniu 2025-11-06 o 11:45, Gordonjcp pisze:
>>> Anyway, I do it exactly like in your equation. Target is changing between 0,
>>> full scale and sustain level, depending on ADSR phase.
>> Ah - you have to watch that!
> 
> no, I don't, because it works :)
> 
>> You've got to flip to the decay phase at somewhat less than full scale because the "RC network" charges asymptotically to the rail.
> 
> and I do, I didn't say at which point though. Target is at full scale, attack trigger point is at half scale. TBH this is still not all I do there, but for the sake of discussion this is enough.
> 
> 
>>> All done in fixed point math, but 24 bits is a must, as 16-bit truncation
>>> errors spoil the ends of decaying phases.
>> Can't say I've noticed this.
> 
> Probably because you are neurotypical person. I feel sick if the envelope doesn't decay within 16-bit 1LSB of the destination I want it to go.
> 
> 
>> The Juno 106 has roughly half its voice ROM full of such tables, just to make the controls work nicely ;-)
> 
> and to avoid complex, repeating calculations, given that every instruction of processor time is precious.
> 
> 
> 
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