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Add cubic interpolation for SF2 playback
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@tmyqlfpir
tmyqlfpir committed Feb 12, 2024
1 parent 7592f12 commit c53a363
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Showing 2 changed files with 75 additions and 13 deletions.
2 changes: 1 addition & 1 deletion source/audiolib/src/driver_sf2.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -163,7 +163,7 @@ int SF2Drv_MIDI_StartPlayback(void)
{
SF2Drv_MIDI_HaltPlayback();

tsf_set_output(sf2_synth, MV_Channels == 1 ? TSF_MONO : TSF_STEREO_INTERLEAVED, MV_MixRate, 0);
tsf_set_output(sf2_synth, MV_Channels == 1 ? TSF_MONO : TSF_STEREO_INTERLEAVED, TSF_INTERP_CUBIC, MV_MixRate, 0);
tsf_channel_set_bank_preset(sf2_synth, 9, 128, 0);
tsf_reset(sf2_synth);

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86 changes: 74 additions & 12 deletions source/audiolib/src/tsf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -124,6 +124,17 @@ enum TSFOutputMode
TSF_MONO
};

// Supported output modes by the render methods
enum TSFInterpolateMode
{
// Holds sample until next sample
TSF_INTERP_NEAREST,
// Linear interpolation
TSF_INTERP_LINEAR,
// Cubic interpolation
TSF_INTERP_CUBIC
};

// Thread safety:
//
// 1. Rendering / voices:
Expand Down Expand Up @@ -151,7 +162,7 @@ enum TSFOutputMode
// outputmode: if mono or stereo and how stereo channel data is ordered
// samplerate: the number of samples per second (output frequency)
// global_gain_db: volume gain in decibels (>0 means higher, <0 means lower)
TSFDEF void tsf_set_output(tsf* f, enum TSFOutputMode outputmode, int samplerate, float global_gain_db CPP_DEFAULT0);
TSFDEF void tsf_set_output(tsf* f, enum TSFOutputMode outputmode, enum TSFInterpolateMode interpolatemode, int samplerate, float global_gain_db CPP_DEFAULT0);

// Set the global gain as a volume factor
// global_gain: the desired volume where 1.0 is 100%
Expand Down Expand Up @@ -338,6 +349,7 @@ struct tsf
unsigned int voicePlayIndex;

enum TSFOutputMode outputmode;
enum TSFInterpolateMode interpolatemode;
float outSampleRate;
float globalGainDB;
int* refCount;
Expand Down Expand Up @@ -1089,6 +1101,30 @@ static void tsf_voice_calcpitchratio(struct tsf_voice* v, float pitchShift, floa
v->pitchOutputFactor = v->region->sample_rate / (tsf_timecents2Secsd(v->region->pitch_keycenter * 100.0) * outSampleRate);
}

static float tsf_voice_interpolate(float* input, unsigned int *pos, float alpha, enum TSFInterpolateMode interpolatemode)
{
// Interpolation methods based off https://paulbourke.net/miscellaneous/interpolation/
switch (interpolatemode)
{
case TSF_INTERP_NEAREST:
return input[pos[0]];
case TSF_INTERP_LINEAR:
return (input[pos[0]] * (1.f - alpha) + input[pos[1]] * alpha);
case TSF_INTERP_CUBIC:
{
const float pointa = input[pos[0]], pointb = input[pos[1]], pointc = input[pos[2]], pointd = input[pos[3]];
float a0, a1, a2, a3, alpha2;

alpha2 = alpha * alpha;
a0 = -0.5f * pointa + 1.5f * pointb - 1.5f * pointc + 0.5f * pointd;
a1 = pointa - 2.5f * pointb + 2.f * pointc - 0.5f * pointd;
a2 = -0.5f * pointa + 0.5f * pointc;
a3 = pointb;
return (a0 * alpha * alpha2 + a1 * alpha2 + a2 * alpha + a3);
}
}
}

static void tsf_voice_render(tsf* f, struct tsf_voice* v, float* outputBuffer, int numSamples)
{
struct tsf_region* region = v->region;
Expand Down Expand Up @@ -1127,8 +1163,9 @@ static void tsf_voice_render(tsf* f, struct tsf_voice* v, float* outputBuffer, i

while (numSamples)
{
float gainMono, gainLeft, gainRight;
float gainMono, gainLeft, gainRight, alpha;
int blockSamples = (numSamples > TSF_RENDER_EFFECTSAMPLEBLOCK ? TSF_RENDER_EFFECTSAMPLEBLOCK : numSamples);
unsigned int pos[4];
numSamples -= blockSamples;

if (dynamicLowpass)
Expand Down Expand Up @@ -1161,10 +1198,18 @@ static void tsf_voice_render(tsf* f, struct tsf_voice* v, float* outputBuffer, i
gainLeft = gainMono * v->panFactorLeft, gainRight = gainMono * v->panFactorRight;
while (blockSamples-- && tmpSourceSamplePosition < tmpSampleEndDbl)
{
unsigned int pos = (unsigned int)tmpSourceSamplePosition, nextPos = (pos >= tmpLoopEnd && isLooping ? tmpLoopStart : pos + 1);
// Get samples.
pos[0] = (unsigned int)tmpSourceSamplePosition;
if (f->interpolatemode != TSF_INTERP_NEAREST)
{
alpha = (float)(tmpSourceSamplePosition - pos[0]);
pos[1] = (pos[0] >= tmpLoopEnd && isLooping ? tmpLoopStart : pos[0] + 1);
if (f->interpolatemode == TSF_INTERP_CUBIC)
pos[2] = (pos[1] >= tmpLoopEnd && isLooping ? tmpLoopStart : pos[1] + 1), pos[3] = (pos[2] >= tmpLoopEnd && isLooping ? tmpLoopStart : pos[2] + 1);
}

// Simple linear interpolation.
float alpha = (float)(tmpSourceSamplePosition - pos), val = (input[pos] * (1.0f - alpha) + input[nextPos] * alpha);
// Interpolation.
float val = tsf_voice_interpolate(input, pos, alpha, f->interpolatemode);

// Low-pass filter.
if (tmpLowpass.active) val = tsf_voice_lowpass_process(&tmpLowpass, val);
Expand All @@ -1182,10 +1227,18 @@ static void tsf_voice_render(tsf* f, struct tsf_voice* v, float* outputBuffer, i
gainLeft = gainMono * v->panFactorLeft, gainRight = gainMono * v->panFactorRight;
while (blockSamples-- && tmpSourceSamplePosition < tmpSampleEndDbl)
{
unsigned int pos = (unsigned int)tmpSourceSamplePosition, nextPos = (pos >= tmpLoopEnd && isLooping ? tmpLoopStart : pos + 1);
// Get samples.
pos[0] = (unsigned int)tmpSourceSamplePosition;
if (f->interpolatemode != TSF_INTERP_NEAREST)
{
alpha = (float)(tmpSourceSamplePosition - pos[0]);
pos[1] = (pos[0] >= tmpLoopEnd && isLooping ? tmpLoopStart : pos[0] + 1);
if (f->interpolatemode == TSF_INTERP_CUBIC)
pos[2] = (pos[1] >= tmpLoopEnd && isLooping ? tmpLoopStart : pos[1] + 1), pos[3] = (pos[2] >= tmpLoopEnd && isLooping ? tmpLoopStart : pos[2] + 1);
}

// Simple linear interpolation.
float alpha = (float)(tmpSourceSamplePosition - pos), val = (input[pos] * (1.0f - alpha) + input[nextPos] * alpha);
// Interpolation.
float val = tsf_voice_interpolate(input, pos, alpha, f->interpolatemode);

// Low-pass filter.
if (tmpLowpass.active) val = tsf_voice_lowpass_process(&tmpLowpass, val);
Expand All @@ -1202,10 +1255,18 @@ static void tsf_voice_render(tsf* f, struct tsf_voice* v, float* outputBuffer, i
case TSF_MONO:
while (blockSamples-- && tmpSourceSamplePosition < tmpSampleEndDbl)
{
unsigned int pos = (unsigned int)tmpSourceSamplePosition, nextPos = (pos >= tmpLoopEnd && isLooping ? tmpLoopStart : pos + 1);
// Get samples.
pos[0] = (unsigned int)tmpSourceSamplePosition;
if (f->interpolatemode != TSF_INTERP_NEAREST)
{
alpha = (float)(tmpSourceSamplePosition - pos[0]);
pos[1] = (pos[0] >= tmpLoopEnd && isLooping ? tmpLoopStart : pos[0] + 1);
if (f->interpolatemode == TSF_INTERP_CUBIC)
pos[2] = (pos[1] >= tmpLoopEnd && isLooping ? tmpLoopStart : pos[1] + 1), pos[3] = (pos[2] >= tmpLoopEnd && isLooping ? tmpLoopStart : pos[2] + 1);
}

// Simple linear interpolation.
float alpha = (float)(tmpSourceSamplePosition - pos), val = (input[pos] * (1.0f - alpha) + input[nextPos] * alpha);
// Interpolation.
float val = tsf_voice_interpolate(input, pos, alpha, f->interpolatemode);

// Low-pass filter.
if (tmpLowpass.active) val = tsf_voice_lowpass_process(&tmpLowpass, val);
Expand Down Expand Up @@ -1389,9 +1450,10 @@ TSFDEF const char* tsf_bank_get_presetname(const tsf* f, int bank, int preset_nu
return tsf_get_presetname(f, tsf_get_presetindex(f, bank, preset_number));
}

TSFDEF void tsf_set_output(tsf* f, enum TSFOutputMode outputmode, int samplerate, float global_gain_db)
TSFDEF void tsf_set_output(tsf* f, enum TSFOutputMode outputmode, enum TSFInterpolateMode interpolatemode, int samplerate, float global_gain_db)
{
f->outputmode = outputmode;
f->interpolatemode = interpolatemode;
f->outSampleRate = (float)(samplerate >= 1 ? samplerate : 44100.0f);
f->globalGainDB = global_gain_db;
}
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