Allow larger arrays up to size 8192 for PeriodicWave

Source/modules/webaudio/PeriodicWave.cpp

Index: Source/modules/webaudio/PeriodicWave.cpp
diff --git a/Source/modules/webaudio/PeriodicWave.cpp b/Source/modules/webaudio/PeriodicWave.cpp
index 5700c3073a9fc1cb375053eddf762367713dc0a6..9fe1903229f831eedbb52ee79014cdc2883558e9 100644
--- a/Source/modules/webaudio/PeriodicWave.cpp
+++ b/Source/modules/webaudio/PeriodicWave.cpp
@@ -37,11 +37,14 @@
 
 namespace blink {
 
-const unsigned PeriodicWaveSize = 4096; // This must be a power of two.
-const unsigned NumberOfRanges = 36; // There should be 3 * log2(PeriodicWaveSize) 1/3 octave ranges.
-const float CentsPerRange = 1200 / 3; // 1/3 Octave.
+// The number of bands per octave.  Each octave will have this many entries in the wave tables.
+const unsigned kNumberOfOctaveBands = 3;
 
-const unsigned PeriodicWave::kMaxPeriodicWaveArraySize = PeriodicWaveSize / 2;
+// The max length of a periodic wave. This must be a power of two greater than or equal to 2048 and
+// must be supported by the FFT routines.
+const unsigned kMaxPeriodicWaveSize = 16384;
+
+const float CentsPerRange = 1200 / kNumberOfOctaveBands;
 
 using namespace VectorMath;
 
@@ -88,13 +91,36 @@ PeriodicWave* PeriodicWave::createTriangle(float sampleRate)
 
 PeriodicWave::PeriodicWave(float sampleRate)
     : m_sampleRate(sampleRate)
-    , m_periodicWaveSize(PeriodicWaveSize)
-    , m_numberOfRanges(NumberOfRanges)
     , m_centsPerRange(CentsPerRange)
 {
     float nyquist = 0.5 * m_sampleRate;
     m_lowestFundamentalFrequency = nyquist / maxNumberOfPartials();
-    m_rateScale = m_periodicWaveSize / m_sampleRate;
+    m_rateScale = periodicWaveSize() / m_sampleRate;
+    // Compute the number of ranges needed to cover the entire frequency range, assuming
+    // kNumberOfOctaveBands per octave.
+    m_numberOfRanges = 0.5 + kNumberOfOctaveBands * log2f(periodicWaveSize());
+}
+
+unsigned PeriodicWave::periodicWaveSize() const
+{
+    // Choose an appropriate wave size for the given sample rate.  This allows us to use shorter
+    // FFTs when possible to limit the complexity.  The breakpoints here are somewhat arbitrary, but
+    // we want sample rates around 44.1 kHz or so to have a size of 4096 to preserve backward
+    // compatibility.
+    if (m_sampleRate <= 24000) {
+        return 2048;
+    }
+
+    if (m_sampleRate <= 88200) {
+        return 4096;
+    }
+
+    return kMaxPeriodicWaveSize;
+}
+
+unsigned PeriodicWave::maxNumberOfPartials() const
+{
+    return periodicWaveSize() / 2;
 }
 
 void PeriodicWave::waveDataForFundamentalFrequency(float fundamentalFrequency, float*& lowerWaveData, float*& higherWaveData, float& tableInterpolationFactor)
@@ -110,13 +136,13 @@ void PeriodicWave::waveDataForFundamentalFrequency(float fundamentalFrequency, f
     float pitchRange = 1 + centsAboveLowestFrequency / m_centsPerRange;
 
     pitchRange = std::max(pitchRange, 0.0f);
-    pitchRange = std::min(pitchRange, static_cast<float>(m_numberOfRanges - 1));
+    pitchRange = std::min(pitchRange, static_cast<float>(numberOfRanges() - 1));
 
     // The words "lower" and "higher" refer to the table data having the lower and higher numbers of partials.
     // It's a little confusing since the range index gets larger the more partials we cull out.
     // So the lower table data will have a larger range index.
     unsigned rangeIndex1 = static_cast<unsigned>(pitchRange);
-    unsigned rangeIndex2 = rangeIndex1 < m_numberOfRanges - 1 ? rangeIndex1 + 1 : rangeIndex1;
+    unsigned rangeIndex2 = rangeIndex1 < numberOfRanges() - 1 ? rangeIndex1 + 1 : rangeIndex1;
 
     lowerWaveData = m_bandLimitedTables[rangeIndex2]->data();
     higherWaveData = m_bandLimitedTables[rangeIndex1]->data();
@@ -125,11 +151,6 @@ void PeriodicWave::waveDataForFundamentalFrequency(float fundamentalFrequency, f
     tableInterpolationFactor = pitchRange - rangeIndex1;
 }
 
-unsigned PeriodicWave::maxNumberOfPartials() const
-{
-    return m_periodicWaveSize / 2;
-}
-
 unsigned PeriodicWave::numberOfPartialsForRange(unsigned rangeIndex) const
 {
     // Number of cents below nyquist where we cull partials.
@@ -151,53 +172,44 @@ void PeriodicWave::createBandLimitedTables(const float* realData, const float* i
 {
     float normalizationScale = 1;
 
-    unsigned fftSize = m_periodicWaveSize;
+    unsigned fftSize = periodicWaveSize();
     unsigned halfSize = fftSize / 2;
     unsigned i;
 
     numberOfComponents = std::min(numberOfComponents, halfSize);
 
-    m_bandLimitedTables.reserveCapacity(m_numberOfRanges);
+    m_bandLimitedTables.reserveCapacity(numberOfRanges());
 
-    for (unsigned rangeIndex = 0; rangeIndex < m_numberOfRanges; ++rangeIndex) {
+    for (unsigned rangeIndex = 0; rangeIndex < numberOfRanges(); ++rangeIndex) {
         // This FFTFrame is used to cull partials (represented by frequency bins).
         FFTFrame frame(fftSize);
         float* realP = frame.realData();
         float* imagP = frame.imagData();
 
-        // Copy from loaded frequency data and scale.
-        float scale = fftSize;
-        vsmul(realData, 1, &scale, realP, 1, numberOfComponents);
-        vsmul(imagData, 1, &scale, imagP, 1, numberOfComponents);
-
-        // If fewer components were provided than 1/2 FFT size, then clear the remaining bins.
-        for (i = numberOfComponents; i < halfSize; ++i) {
-            realP[i] = 0;
-            imagP[i] = 0;
-        }
-
-        // Generate complex conjugate because of the way the inverse FFT is defined.
+        // Copy from loaded frequency data and generate the complex conjugate because of the way the
+        // inverse FFT is defined versus the values in the arrays.  Note also that although the IFFT
+        // does a scaling by 1/N, we take care of this when the normalization scaling is done.
         float minusOne = -1;
-        vsmul(imagP, 1, &minusOne, imagP, 1, halfSize);
+        memcpy(realP, realData, numberOfComponents * sizeof(*realP));
+        vsmul(imagData, 1, &minusOne, imagP, 1, numberOfComponents);
 
-        // Find the starting bin where we should start culling.
-        // We need to clear out the highest frequencies to band-limit the waveform.
+        // Find the starting bin where we should start culling.  We need to clear out the highest
+        // frequencies to band-limit the waveform.
         unsigned numberOfPartials = numberOfPartialsForRange(rangeIndex);
 
-        // Cull the aliasing partials for this pitch range.
-        for (i = numberOfPartials + 1; i < halfSize; ++i) {
+        // If fewer components were provided than 1/2 FFT size, then clear the remaining bins.
+        // We also need to cull the aliasing partials for this pitch range.
+        for (i = std::min(numberOfComponents, numberOfPartials + 1); i < halfSize; ++i) {
             realP[i] = 0;
             imagP[i] = 0;
         }
-        // Clear packed-nyquist if necessary.
-        if (numberOfPartials < halfSize)
-            imagP[0] = 0;
 
-        // Clear any DC-offset.
+        // Clear packed-nyquist and any DC-offset.
         realP[0] = 0;
+        imagP[0] = 0;
 
         // Create the band-limited table.
-        OwnPtr<AudioFloatArray> table = adoptPtr(new AudioFloatArray(m_periodicWaveSize));
+        OwnPtr<AudioFloatArray> table = adoptPtr(new AudioFloatArray(periodicWaveSize()));
         m_bandLimitedTables.append(table.release());
 
         // Apply an inverse FFT to generate the time-domain table data.
@@ -207,14 +219,14 @@ void PeriodicWave::createBandLimitedTables(const float* realData, const float* i
         // For the first range (which has the highest power), calculate its peak value then compute normalization scale.
         if (!rangeIndex) {
             float maxValue;
-            vmaxmgv(data, 1, &maxValue, m_periodicWaveSize);
+            vmaxmgv(data, 1, &maxValue, fftSize);
 
             if (maxValue)
                 normalizationScale = 1.0f / maxValue;
         }
 
         // Apply normalization scale.
-        vsmul(data, 1, &normalizationScale, data, 1, m_periodicWaveSize);
+        vsmul(data, 1, &normalizationScale, data, 1, fftSize);
     }
 }