mirror of
https://github.com/cookiengineer/audacity
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52 lines
1.7 KiB
Plaintext
52 lines
1.7 KiB
Plaintext
;; this is the beginnings of a new function that just passes input to output until
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;; a given "release time" at which point the output decays exponentially to zero.
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;; this is hard to do in Nyquist without a new primitive because the amplitude of
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;; the exponential decay depends on the value of the input at some given time.
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;; (Yes, you can evaluate that point, but then you have to compute all the samples,
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;; and they will be held in memory, which might not be a good thing.)
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(EXPREL-ALG
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(NAME "exprel")
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(ARGUMENTS ("sound_type" "signal") ("time_type" "release_time")
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("double" "fall_time"))
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(SUPPORT-FUNCTIONS "#define ST_HOLD 0
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#define ST_FALL 1
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#define ST_FALL_UNTIL 2
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#define ST_OFF 3
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#define ST_OFF_UNTIL 4
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#define ST_RISE 5
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/* Overview:
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This operation passes its input to its output until the release time.
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Then, it takes the last sample output as a starting point for an
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exponential decay, with a duration of falltime.
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*/
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")
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(STATE
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("long" "release_time" "signal->sr * release_time + 0.5")
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("double" "fall_time" "signal->sr * falltime + 0.5")
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("sample_type" "value" "0")
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("bool" "falling" "0"))
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(TERMINATE (MIN signal))
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(LOGICAL-STOP "release_time")
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(LINEAR signal)
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(INNER-LOOP "{
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sample_type result;
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if (falling) {
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value = value * decay;
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result = value;
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} else {
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result = signal;
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if (release_time <= susp->susp.current + cnt + togo - n) {
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value = result;
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falling = 1;
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}
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}
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output = (sample_type) value;
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}")
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)
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need to do logical stop time and termination time
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