[PD] analog-style adsr

[Ben Saylor]

Hi,

I took a shot at making an analog-style adsr envelope generator.  Rather
than using straight line segments, it uses ones that are curved such
that the rate of change in 'voltage' decreases as it approaches the
target voltage.  Also, the attack begins at the current output value
rather than zero for nice legato sequences.  I've attached it along with
a test patch in case anyone might find it useful.

Ben
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#X text 410 19 analog-style envelope generator;
#X msg 360 334 <attack> <decay> <sustain> <release>;
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#X text 372 493 Ben Saylor <bsaylor at macalester.edu>;
#X text 359 353 (times are in ms \, sustain level is 0..1);
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