[sdiy] Fast envelope generation

[Neil Johnson]

On 18 December 2012 13:44, Scott Gravenhorst <music.maker at gte.net> wrote:
>
> When I've needed an exponential response for an envelope, I've used a single pole
> lowpass IIR filt.  So far, I've used this only for the release phase of an ADSR, but it
> works very nicely (in an FPGA) and I've not had a problem with it's computational expense.
>
> BUT - perhaps I don't understand what you are doing?  Or am I confusing logarithmic and
> exponential?

A low-pass IIR filter is the obvious way of doing it as it models the
RC circuit of a real ADSR.  And it is computationally simple:

http://ece124web.groups.et.byu.net/labs/HowTos/Simple%20Software%20Lowpass%20Filter.pdf

But, you might be right Scott, perhaps there's something we're missing...?

Then again, if I was going to do a straight-line segment I'd use
Bresenham's algorithm rather than mess around with linear
interpolation.

Cheers,
Neil
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