Greetings,
I have been working on envelopes lately, and I have come up with
something that I'd like to share. I started out with the basic ADSR in
Miller's examples; I wanted variable envelope curves, but I didn't want
the overhead of on-the-fly sqrt's or complex expr's. Therefore,
[multiCurveAdsr] uses table-lookup for enveloping, with just one
multiplication for level-scaling. The lookup table only needs to be
computed when the "curve factor" is changed.
Three basic curve types are possible. C (curve factor) = 1 gives the
basic linear envelope. C > 1 gives a continuous range of fatter,
"ead"-like envelopes. C < 1 is a special case; for any value of C less
than 1, you get one "quadric"-like, hollow curve. (I really like the
way this one sounds, by the way).
The math in the [pd makeTable] subpatch is not elegant -- I took an
empirical approach, tweaking things until I got the shapes I wanted --
but it works well enough. One little hitch I ran into was that sustain
level varied with different curve factors, so I made a corrective
subpatch that keeps sustain values consistent across the different
curves. This subpatch only comes into play when the sustain value or
curve factor changes.
The right output emits 1 on attack, and 0 after release is complete. I
use this to switch~ the voice being enveloped, for further CPU-cycle
economy.
The help patch shows the effect of the different curve factors
graphically. I don't think there are any dependencies outside of
"Miller Vanilla" PD.
I use [multiCurveAdsr] for my own synthesis abstractions, and find that
it sounds pretty good, plus it's thrifty on CPU-usage, even with many
voices. I hope somebody else finds it useful. Any suggestions for
improvement will be greatly appreciated.
Phil Stone
Davis, CA
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#X text 75 304 ATTACK;
#X obj 240 525 outlet~;
#X text 54 74 if zero;
#X text 55 91 release;
#X text 44 109 bang if attack;
#X text 320 2 When you send this patch a nonzero trigger it schedules
a line~ to do an attack and decay \, and if zero \, it starts the release
ramp.;
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#X text 17 1 Multi-curve ADSR;
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level (proportion of overall level 0 - 100) \, release time;
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#X text 388 83 > 1 - exponential (fat) curves \, varying with C;
#X msg 502 159 1;
#X text 118 58 This adsr uses table-lookup for envelope curves \,;
#X text 119 73 so it should be pretty cpu-efficient.;
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#X text 2 212 cancel decay \,;
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#X text 91 -208 Hit bang or MIDI key to see current envelope;
#X text 293 -79 Curve Factors;
#X text 229 -62 < 1 - "quadric-like" (hollow) curve \, C=-0.214;
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#X text 229 -32 > 1 - exponential (fat) curves \, varying with C;
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