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Attempts to implement the proper attack phase.

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It's sounding pretty good now, but for sustain.
This commit is contained in:
Thomas Harte 2020-05-08 18:59:05 -04:00
parent e51e2425cc
commit dc5654b941
1 changed files with 22 additions and 14 deletions
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36
Components/OPL2/Implementation/EnvelopeGenerator.hpp
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@ -56,7 +56,7 @@ template <int envelope_precision, int period_precision> class EnvelopeGenerator
update_attack(oscillator, attack_rate_ + key_scaling_rate);
// Two possible terminating conditions: (i) the attack rate is 15; (ii) full volume has been reached.
if((attack_rate_ + key_scaling_rate) > 60 || attenuation_ <= 0) {
if(attenuation_ <= 0) {
attenuation_ = 0;
phase_ = Phase::Decay;
}
@ -213,20 +213,28 @@ template <int envelope_precision, int period_precision> class EnvelopeGenerator
};
void update_attack(const LowFrequencyOscillator &oscillator, int rate) {
// Rules:
//
// An attack rate of '13' has 32 samples in the attack phase; a rate of '12' has the same 32 steps, but spread out over 64 samples, etc.
// An attack rate of '14' uses a divide by four instead of two.
// 15 is instantaneous.
if(rate >= 56) {
attenuation_ -= (attenuation_ >> 2) - 1;
} else {
const int sample_length = 1 << (14 - (rate >> 2)); // TODO: don't throw away KSR bits.
if(!(oscillator.counter & (sample_length - 1))) {
attenuation_ -= (attenuation_ >> 3) - 1;
}
// Special case: no attack.
if(rate < 4) {
return;
}
// Special case: instant attack.
if(rate >= 60) {
attenuation_ = 0;
return;
}
// 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.
const int rate_shift = (rate > 55);
const int step = dithering_patterns[rate & 3][(oscillator.counter >> shift_size) & 7];
attenuation_ -= ((attenuation_ >> (3 - rate_shift)) + 1) * step;
}
void update_decay(const LowFrequencyOscillator &oscillator, int rate) {