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Attempts to implement decay and release the right way around and with full precision.

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Higher numbers = decay/release more quickly, not more slowly.
This commit is contained in:
Thomas Harte 2020-05-08 18:40:49 -04:00
parent 95c6b9b55d
commit e51e2425cc
1 changed files with 25 additions and 29 deletions
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50
Components/OPL2/Implementation/EnvelopeGenerator.hpp
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@ -29,6 +29,8 @@ namespace OPL {
This code considers application of tremolo to be a function of the envelope generator; This code considers application of tremolo to be a function of the envelope generator;
this is largely for logical conformity with the phase generator that necessarily has to this is largely for logical conformity with the phase generator that necessarily has to
apply vibrato. apply vibrato.
TODO: use envelope_precision.
*/ */
template <int envelope_precision, int period_precision> class EnvelopeGenerator { template <int envelope_precision, int period_precision> class EnvelopeGenerator {
public: public:
@ -43,7 +45,7 @@ template <int envelope_precision, int period_precision> class EnvelopeGenerator
const int key_scaling_rate = key_scale_rate_ >> key_scale_rate_shift_; const int key_scaling_rate = key_scale_rate_ >> key_scale_rate_shift_;
switch(phase_) { switch(phase_) {
case Phase::Damp: case Phase::Damp:
update_decay(oscillator, 12); update_decay(oscillator, 12 << 2);
if(attenuation_ == 511) { if(attenuation_ == 511) {
(*will_attack_)(); (*will_attack_)();
phase_ = Phase::Attack; phase_ = Phase::Attack;
@ -203,6 +205,13 @@ template <int envelope_precision, int period_precision> class EnvelopeGenerator
int sustain_level_ = 0; int sustain_level_ = 0;
bool use_sustain_level_ = false; bool use_sustain_level_ = false;
static constexpr int dithering_patterns[4][8] = {
{0, 1, 0, 1, 0, 1, 0, 1},
{0, 1, 0, 1, 1, 1, 0, 1},
{0, 1, 1, 1, 0, 1, 1, 1},
{0, 1, 1, 1, 1, 1, 1, 1},
};
void update_attack(const LowFrequencyOscillator &oscillator, int rate) { void update_attack(const LowFrequencyOscillator &oscillator, int rate) {
// Rules: // Rules:
// //
@ -221,36 +230,23 @@ template <int envelope_precision, int period_precision> class EnvelopeGenerator
} }
void update_decay(const LowFrequencyOscillator &oscillator, int rate) { void update_decay(const LowFrequencyOscillator &oscillator, int rate) {
// Rules: // Special case: no decay.
// if(rate < 4) {
// (relative to a 511 scale) return;
//
// A rate of 0 is no decay at all.
// A rate of 1 means increase 4 per cycle.
// A rate of 2 means increase 2 per cycle.
// A rate of 3 means increase 1 per cycle.
// A rate of 4 means increase 1 every other cycle.
// A rate of 5 means increase once every fourth cycle.
// etc.
// eighth, sixteenth, 32nd, 64th, 128th, 256th, 512th, 1024th, 2048th, 4096th, 8192th
if(rate) {
// TODO: don't throw away low two bits of the rate.
switch(rate >> 2) {
case 1: attenuation_ += 32; break;
case 2: attenuation_ += 16; break;
default: {
const int sample_length = 1 << ((rate >> 2) - 4);
if(!(oscillator.counter & (sample_length - 1))) {
attenuation_ += 8;
}
} break;
} }
// Clamp to the proper range. // Work out the number of cycles between each adjustment tick, and stop now
// if not at the next adjustment boundary.
const int shift_size = 13 - (std::min(rate, 52) >> 2);
if(oscillator.counter & ((1 << shift_size) - 1)) {
return;
}
// Apply dithered adjustment and clamp.
const int rate_shift = 1 + (rate > 59) + (rate > 55);
attenuation_ += dithering_patterns[rate & 3][(oscillator.counter >> shift_size) & 7] * (4 << rate_shift);
attenuation_ = std::min(attenuation_, 511); attenuation_ = std::min(attenuation_, 511);
} }
}
}; };
} }