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Calculates the proper key scale rate, though ADSR itself is still lacking that precision.

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This commit is contained in:
Thomas Harte 2020-04-21 22:57:56 -04:00
parent 50d725330c
commit 676dcf7fbb
2 changed files with 8 additions and 4 deletions
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10
Components/OPL2/Implementation/Operator.cpp
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@ -40,7 +40,7 @@ void Operator::set_am_vibrato_hold_sustain_ksr_multiple(uint8_t value) {
apply_amplitude_modulation_ = value & 0x80;
apply_vibrato_ = value & 0x40;
use_sustain_level_ = value & 0x20;
key_scaling_rate_ = value & 0x10;
key_rate_scaling_shift_ = (value & 0x10) ? 0 : 2;
frequency_multiple_ = value & 0xf;
}
@ -99,10 +99,14 @@ void Operator::update(OperatorState &state, bool key_on, int channel_period, int
// "An attack rate value of 52 (AR = 13) has 32 samples in the attack phase, an attack rate value of 48 (AR = 12)
// has 64 samples in the attack phase, but pairs of samples show the same envelope attenuation. I am however struggling to find a plausible algorithm to match the experimental results.
const int key_scaling_rate = ((channel_octave << 1) | (channel_period >> 9)) >> key_rate_scaling_shift_;
assert(key_scaling_rate < 16);
assert((channel_period >> 9) < 2);
const auto current_phase = state.adsr_phase_;
switch(current_phase) {
case OperatorState::ADSRPhase::Attack: {
const int attack_rate = attack_rate_; // TODO: key scaling rate. Which I do not yet understand.
const int attack_rate = attack_rate_ + key_scaling_rate;
// Rules:
//
@ -139,7 +143,7 @@ void Operator::update(OperatorState &state, bool key_on, int channel_period, int
// A rate of 3 means increase 1 per cycle.
// A rate of 4 means increase 1 every other cycle.
// (etc)
const int decrease_rate = (state.adsr_phase_ == OperatorState::ADSRPhase::Decay) ? decay_rate_ : release_rate_; // TODO: again, key scaling rate.
const int decrease_rate = key_scaling_rate + ((state.adsr_phase_ == OperatorState::ADSRPhase::Decay) ? decay_rate_ : release_rate_);
if(decrease_rate) {
// TODO: don't throw away KSR bits.

2
Components/OPL2/Implementation/Operator.hpp
View File

@ -111,7 +111,7 @@ class Operator {
int attenuation_ = 0;
/// Provides a potential faster step through the ADSR envelope. Cf. p12.
bool key_scaling_rate_ = false;
int key_rate_scaling_shift_ = 0;
/// Selects attenuation that is applied as a function of interval. Cf. p14.
int key_level_scaling_ = 0;