[sdiy] Fast envelope generation

Neil Johnson neil.johnson97 at ntlworld.com
Tue Dec 18 15:57:27 CET 2012

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:


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

Modules and more: http://www.cesyg.com
Homepage: http://www.njohnson.co.uk

More information about the Synth-diy mailing list