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

[Chris McDowell]

>  the "charging capacitor" style of envelope we're familiar
> with building in hardware is somewhat more difficult to produce.

Interesting! My journey has always been pretty narrowly focused on what I like, so I'm always surprised to see anyone not defaulting to an RC style envelope. For example, I was excited to play with the synthio library that comes with Circuit Python (I teach at a highschool and it would have been very accessible) but was sad to find it only has linear envelopes, no anti-aliasing on waveforms, and no modulation of filter cutoff... I'm too much of a snob to subject them to such a thing. 

I had someone push back saying my treasured DX7 has linear envelopes, but it most certainly does not. I've never compared them to RC curves vs exponential vs some hilarious quarter sine wave LUT (they would), but they are certainly curvy! 

Thanks again,
Chris McDowell 

> On Nov 5, 2025, at 5:33 PM, mskala at northcoastsynthesis.com wrote:
> 
> On Wed, 5 Nov 2025, Chris McDowell wrote:
> 
>> out. They don't even claim to be simulating a capacitor, it really is an
>> "exponential envelope".
>> 
>> I promise I have thought and thought (and thought again, for decades)
>> about the shape I want the envelopes to take :) I did NOT think
>> critically about what that fella's code is actually doing, but it's
>> clear now.
> 
> To be clear I wasn't suggesting you didn't know, only that you'd want
> to use that choice in picking which algorithm to go with.
> 
> One thing that made me wary of this as a possible issue was that just the
> same thing comes up with "exponential" envelopes in Csound - the common
> "expseg" opcode produces something that looks like exp() of a linear
> envelope, and the "charging capacitor" style of envelope we're familiar
> with building in hardware is somewhat more difficult to produce.
> 
> -- 
> Matthew Skala
> North Coast Synthesis Ltd.