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78f38416b4
The noise gate and compressor both had the same envelope code, and I'm looking at some more users, so let's just abstract it out and make it more legible in the process. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
71 lines
1.8 KiB
C
71 lines
1.8 KiB
C
// NAME: Compressor [COMPR]
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// PRIORITY: 30
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// POT: "Level" LINEAR(-40.0 0.0) = -20.0 dB
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// POT: "Attack" LINEAR(2.0 100.0) = 15.0 ms
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// POT: "Release" LINEAR(50.0 500.0) = 150.0 ms
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// POT: "Ratio" LINEAR(1.0 20.0) = 4.8 x
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// POT: "Boost" LINEAR(0.0 24.0) = 6.0 dB
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//
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// Compressor Effect
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//
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static struct {
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// Pot values (pre-computed for step calculation convenience)
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float level, ratio, boost;
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// Envelope follower
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struct envelope envelope;
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// Compressor state
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float compression;
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} compressor = {
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.level = 1.0,
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.compression = 1.0
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};
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static inline void compressor_init(unsigned char pot[10])
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{
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float level_db = compressor_pot0(pot[0]);
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compressor.level = db_to_level(level_db);
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float attack_ms = compressor_pot1(pot[1]);
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float release_ms = compressor_pot2(pot[2]);
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envelope_init(&compressor.envelope, attack_ms, release_ms);
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float ratio = compressor_pot3(pot[3]);
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compressor.ratio = 1.0f - (1.0f / ratio);
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float boost_db = compressor_pot4(pot[4]);
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compressor.boost = db_to_level(boost_db);
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}
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// This may be overkill, but we're doing this by the book
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static inline float mypow(float a, float b)
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{
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return pow2(log2f(a) * b);
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}
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static inline float compressor_step(float in)
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{
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// Envelope follower
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float env = envelope_step(&compressor.envelope, in);
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// Compression calculation.
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//
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// When we go over the compression level, we calculate a
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// target compression multiplier:
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//
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// target = (level / env) ^ (1 - 1/ratio)
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//
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float target = 1.0f;
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if (env > compressor.level) {
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target = mypow(compressor.level / env, compressor.ratio);
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compressor_effect.intense = 1;
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}
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// ... and then we smooth the compression factor to prevent clicks
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compressor.compression = linear(0.01f, compressor.compression, target);
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return in * compressor.compression * compressor.boost;
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}
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