Envelope follower with different attack and release

  • Author or source: Bram
  • Created: 2003-01-15 00:21:39
notes
xxxx_in_ms is xxxx in milliseconds ;-)
code
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init::

attack_coef = exp(log(0.01)/( attack_in_ms * samplerate * 0.001));
release_coef = exp(log(0.01)/( release_in_ms * samplerate * 0.001));
envelope = 0.0;

loop::

tmp = fabs(in);
if(tmp > envelope)
    envelope = attack_coef * (envelope - tmp) + tmp;
else
    envelope = release_coef * (envelope - tmp) + tmp;

Comments

// the expressions of the form:

xxxx_coef = exp(log(0.01)/( xxxx_in_ms * samplerate * 0.001));

// can be simplified a little bit to:

xxxx_coef = pow(0.01, 1.0/( xxxx_in_ms * samplerate * 0.001));

Here the definition of the attack/release time is the time for the envelope to fall from 100% to 1%.
In the other version, the definition is for the envelope to fall from 100% to 36.7%. So in this one
the envelope is about 4.6 times faster.