1 files changed, 20 insertions, 16 deletions

diff --git a/alc/effects/pshifter.cpp b/alc/effects/pshifter.cpp
index 257742ed..5087860f 100644
--- a/alc/effects/pshifter.cpp
+++ b/alc/effects/pshifter.cpp
@@ -71,6 +71,7 @@ struct FrequencyBin {
 struct PshifterState final : public EffectState {
     /* Effect parameters */
     size_t mCount;
+    size_t mPos;
     uint mPitchShiftI;
     double mPitchShift;
 
@@ -104,7 +105,8 @@ struct PshifterState final : public EffectState {
 void PshifterState::deviceUpdate(const ALCdevice*, const Buffer&)
 {
     /* (Re-)initializing parameters and clear the buffers. */
-    mCount       = FIFO_LATENCY;
+    mCount       = 0;
+    mPos         = FIFO_LATENCY;
     mPitchShiftI = MixerFracOne;
     mPitchShift  = 1.0;
 
@@ -147,12 +149,12 @@ void PshifterState::process(const size_t samplesToDo, const al::span<const Float
 
     for(size_t base{0u};base < samplesToDo;)
     {
-        const size_t todo{minz(STFT_SIZE-mCount, samplesToDo-base)};
+        const size_t todo{minz(STFT_STEP-mCount, samplesToDo-base)};
 
         /* Retrieve the output samples from the FIFO and fill in the new input
          * samples.
          */
-        auto fifo_iter = mFIFO.begin() + mCount;
+        auto fifo_iter = mFIFO.begin()+mPos + mCount;
         std::transform(fifo_iter, fifo_iter+todo, mBufferOut.begin()+base,
             [](double d) noexcept -> float { return static_cast<float>(d); });
 
@@ -161,14 +163,17 @@ void PshifterState::process(const size_t samplesToDo, const al::span<const Float
         base += todo;
 
         /* Check whether FIFO buffer is filled with new samples. */
-        if(mCount < STFT_SIZE) break;
-        mCount = FIFO_LATENCY;
+        if(mCount < STFT_STEP) break;
+        mCount = 0;
+        mPos = (mPos+STFT_STEP) & (mFIFO.size()-1);
 
         /* Time-domain signal windowing, store in FftBuffer, and apply a
          * forward FFT to get the frequency-domain signal.
          */
-        for(size_t k{0u};k < STFT_SIZE;k++)
-            mFftBuffer[k] = mFIFO[k] * HannWindow[k];
+        for(size_t src{mPos}, k{0u};src < STFT_SIZE;++src,++k)
+            mFftBuffer[k] = mFIFO[src] * HannWindow[k];
+        for(size_t src{0u}, k{STFT_SIZE-mPos};src < mPos;++src,++k)
+            mFftBuffer[k] = mFIFO[src] * HannWindow[k];
         forward_fft(mFftBuffer);
 
         /* Analyze the obtained data. Since the real FFT is symmetric, only
@@ -229,15 +234,14 @@ void PshifterState::process(const size_t samplesToDo, const al::span<const Float
          * for the output with windowing.
          */
         inverse_fft(mFftBuffer);
-        for(size_t k{0u};k < STFT_SIZE;k++)
-            mOutputAccum[k] += HannWindow[k]*mFftBuffer[k].real() * (4.0/OVERSAMP/STFT_SIZE);
-
-        /* Shift FIFO and accumulator. */
-        fifo_iter = std::copy(mFIFO.begin()+STFT_STEP, mFIFO.end(), mFIFO.begin());
-        std::copy_n(mOutputAccum.begin(), STFT_STEP, fifo_iter);
-        auto accum_iter = std::copy(mOutputAccum.begin()+STFT_STEP, mOutputAccum.end(),
-            mOutputAccum.begin());
-        std::fill(accum_iter, mOutputAccum.end(), 0.0);
+        for(size_t dst{mPos}, k{0u};dst < STFT_SIZE;++dst,++k)
+            mOutputAccum[dst] += HannWindow[k]*mFftBuffer[k].real() * (4.0/OVERSAMP/STFT_SIZE);
+        for(size_t dst{0u}, k{STFT_SIZE-mPos};dst < mPos;++dst,++k)
+            mOutputAccum[dst] += HannWindow[k]*mFftBuffer[k].real() * (4.0/OVERSAMP/STFT_SIZE);
+
+        /* Copy out the accumulated result, then clear for the next iteration. */
+        std::copy_n(mOutputAccum.begin() + mPos, STFT_STEP, mFIFO.begin() + mPos);
+        std::fill_n(mOutputAccum.begin() + mPos, STFT_STEP, 0.0);
     }
 
     /* Now, mix the processed sound data to the output. */