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GB Audio: Improve channel 4 accuracy

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This commit is contained in:
Vicki Pfau 2018-09-21 21:41:57 -07:00
parent b6f3a2929d
commit 555122e0a1
2 changed files with 32 additions and 13 deletions
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3
include/mgba/internal/gb/audio.h
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@ -137,6 +137,9 @@ struct GBAudioNoiseChannel {
int length;
uint32_t lfsr;
int nSamples;
int samples;
int8_t sample;
};

42
src/gb/audio.c
View File

@ -37,6 +37,8 @@ static bool _updateSweep(struct GBAudioSquareChannel* sweep, bool initial);
static void _updateSquareSample(struct GBAudioSquareChannel* ch);
static int32_t _updateSquareChannel(struct GBAudioSquareChannel* ch);
static int8_t _coalesceNoiseChannel(struct GBAudioNoiseChannel* ch);
static void _updateFrame(struct mTiming* timing, void* user, uint32_t cyclesLate);
static void _updateChannel1(struct mTiming* timing, void* user, uint32_t cyclesLate);
static void _updateChannel2(struct mTiming* timing, void* user, uint32_t cyclesLate);
@ -118,6 +120,7 @@ void GBAudioReset(struct GBAudio* audio) {
audio->ch1 = (struct GBAudioSquareChannel) { .envelope = { .dead = 2 } };
audio->ch2 = (struct GBAudioSquareChannel) { .envelope = { .dead = 2 } };
audio->ch3 = (struct GBAudioWaveChannel) { .bank = 0 };
audio->ch4 = (struct GBAudioNoiseChannel) { .nSamples = 0 };
// TODO: DMG randomness
audio->ch3.wavedata8[0] = 0x00;
audio->ch3.wavedata8[1] = 0xFF;
@ -564,11 +567,13 @@ void GBAudioUpdateFrame(struct GBAudio* audio, struct mTiming* timing) {
--audio->ch4.envelope.nextStep;
if (audio->ch4.envelope.nextStep == 0) {
int8_t sample = audio->ch4.sample > 0;
audio->ch4.samples -= audio->ch4.sample;
_updateEnvelope(&audio->ch4.envelope);
if (audio->ch4.envelope.dead == 2) {
mTimingDeschedule(timing, &audio->ch4Event);
}
audio->ch4.sample = sample * audio->ch4.envelope.currentVolume;
audio->ch4.samples += audio->ch4.sample;
}
}
break;
@ -611,12 +616,13 @@ void GBAudioSamplePSG(struct GBAudio* audio, int16_t* left, int16_t* right) {
}
if (audio->playingCh4 && !audio->forceDisableCh[3]) {
int8_t sample = _coalesceNoiseChannel(&audio->ch4);
if (audio->ch4Left) {
sampleLeft += audio->ch4.sample;
sampleLeft += sample;
}
if (audio->ch4Right) {
sampleRight += audio->ch4.sample;
sampleRight += sample;
}
}
@ -745,6 +751,17 @@ static int32_t _updateSquareChannel(struct GBAudioSquareChannel* ch) {
}
}
static int8_t _coalesceNoiseChannel(struct GBAudioNoiseChannel* ch) {
if (!ch->nSamples) {
return ch->sample;
}
// TODO keep track of timing
int8_t sample = ch->samples / ch->nSamples;
ch->nSamples = 0;
ch->samples = 0;
return sample;
}
static void _updateEnvelope(struct GBAudioEnvelope* envelope) {
if (envelope->direction) {
++envelope->currentVolume;
@ -895,18 +912,17 @@ static void _updateChannel4(struct mTiming* timing, void* user, uint32_t cyclesL
struct GBAudio* audio = user;
struct GBAudioNoiseChannel* ch = &audio->ch4;
int32_t baseCycles = ch->ratio ? 2 * ch->ratio : 1;
baseCycles <<= ch->frequency;
baseCycles *= 8 * audio->timingFactor;
int32_t cycles = 0;
int32_t cycles = ch->ratio ? 2 * ch->ratio : 1;
cycles <<= ch->frequency;
cycles *= 8 * audio->timingFactor;
int lsb = ch->lfsr & 1;
ch->sample = lsb * ch->envelope.currentVolume;
++ch->nSamples;
ch->samples += ch->sample;
ch->lfsr >>= 1;
ch->lfsr ^= (lsb * 0x60) << (ch->power ? 0 : 8);
do {
int lsb = ch->lfsr & 1;
ch->sample = lsb * ch->envelope.currentVolume;
ch->lfsr >>= 1;
ch->lfsr ^= (lsb * 0x60) << (ch->power ? 0 : 8);
cycles += baseCycles;
} while (cycles + baseCycles < audio->sampleInterval);
mTimingSchedule(timing, &audio->ch4Event, cycles - cyclesLate);
}