Inverted parabolic envelope

  • Author or source: James McCartney
  • Type: envellope generation
  • Created: 2002-01-17 00:57:43
code
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dur = duration in samples
midlevel = amplitude at midpoint
beglevel = beginning and ending level (typically zero)

amp = midlevel - beglevel;

rdur = 1.0 / dur;
rdur2 = rdur * rdur;

level = beglevel;
slope = 4.0 * amp * (rdur - rdur2);
curve = -8.0 * amp * rdur2;

...

for (i=0; i<dur; ++i) {
        level += slope;
        slope += curve;
}

Comments

This parabola approximation seems more like a linear than a parab/expo envelope... or i'm mistaking something but i tryed everything and is only linear.

slope is linear, but 'slope' is a function of 'curve'. If you imagine you threw a ball upwards, think of 'curve' as the gravity, 'slope' as the vertical velocity, and 'level' as the vertical displacement.
  • Date: 2005-01-17 07:39:28
  • By: asynth(at)io(dot)com
This is not an approximation of a parabola, it IS a parabola.
This entry has become corrupted since it was first posted. Should be:

for (i=0; i<dur; ++i) {
    out = level;
    level += slope;
    slope += curve;
}