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Fix pitch shifter phase wrapping #228

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Merged
sudip-mondal-2002 merged 3 commits into from
May 26, 2026
Merged

Fix pitch shifter phase wrapping #228

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4c3d4da
Fix pitch shifter phase wrapping
donglrd May 25, 2026
f8757f8
Add pitch shifter phase wrap regression test
donglrd May 26, 2026
cfd6d41
Merge branch 'main' into fix-pitch-shifter-phase-wrap
sudip-mondal-2002 May 26, 2026
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18 changes: 10 additions & 8 deletions src/audio/effects/pitch_shifter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,12 @@ static constexpr int P_MIX = 2;
// Grain window size in seconds (~23 ms at 48kHz = 1024 samples)
static constexpr float GRAIN_WINDOW_SEC = 0.023f;

static float wrap_phase(float phase, int buf_size) {
phase = std::fmod(phase, static_cast<float>(buf_size));
if (phase < 0.0f) phase += static_cast<float>(buf_size);
return phase;
}

PitchShifter::PitchShifter() {
params_ = {
{"Shift", 0.0f, -12.0f, 12.0f, 0.0f, "st",
Expand All @@ -35,9 +41,7 @@ void PitchShifter::set_sample_rate(int sample_rate) {
}

float PitchShifter::read_linear(float phase) const {
// Wrap phase into [0, buf_size_)
phase = std::fmod(phase, static_cast<float>(buf_size_));
if (phase < 0.0f) phase += buf_size_;
phase = wrap_phase(phase, buf_size_);

int pos0 = static_cast<int>(phase);
int pos1 = (pos0 + 1) % buf_size_;
Expand Down Expand Up @@ -77,11 +81,9 @@ void PitchShifter::process(float* buffer, int num_samples) {
read_phase_a_ += drift;
read_phase_b_ += drift;

// Wrap phases into [0, buf_size_)
while (read_phase_a_ < 0.0f) read_phase_a_ += buf_size_;
while (read_phase_a_ >= buf_size_) read_phase_a_ -= buf_size_;
while (read_phase_b_ < 0.0f) read_phase_b_ += buf_size_;
while (read_phase_b_ >= buf_size_) read_phase_b_ -= buf_size_;
// Wrap phases into [0, buf_size_) in constant time.
read_phase_a_ = wrap_phase(read_phase_a_, buf_size_);
read_phase_b_ = wrap_phase(read_phase_b_, buf_size_);

// Compute absolute read positions in the buffer
float pos_a = static_cast<float>(write_pos_) - read_phase_a_;
Expand Down
17 changes: 17 additions & 0 deletions tests/test_effects.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1365,6 +1365,23 @@ TEST(pitch_shifter_with_mix_and_shift_differs_from_dry) {
ASSERT_GT(mag_shifted, mag_440 * 0.5f);
}

TEST(pitch_shifter_extreme_shift_wraps_phase_without_instability) {
PitchShifter ps;
ps.set_sample_rate(48000);
ps.params()[0].value = 120.0f;
ps.params()[1].value = 500.0f;
ps.params()[2].value = 1.0f;
ps.reset();

std::vector<float> buf(4096);
fill_sine(buf.data(), static_cast<int>(buf.size()), 440.0f, 48000);

ps.process(buf.data(), static_cast<int>(buf.size()));

ASSERT_TRUE(buffer_is_finite(buf.data(), static_cast<int>(buf.size())));
ASSERT_GT(rms(buf.data(), static_cast<int>(buf.size())), 0.001f);
}

// ============================================================
// MultiBandCompressor tests
// ============================================================
Expand Down
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