root/PeriodicWave.cpp
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DEFINITIONS
This source file includes following definitions.
- create
- createSine
- createSquare
- createSawtooth
- createTriangle
- m_centsPerRange
- waveDataForFundamentalFrequency
- maxNumberOfPartials
- numberOfPartialsForRange
- createBandLimitedTables
- generateBasicWaveform
/*
* Copyright (C) 2012 Google Inc. All rights reserved.
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* modification, are permitted provided that the following conditions
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of Apple Computer, Inc. ("Apple") nor the names of
* its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
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#include "config.h"
#if ENABLE(WEB_AUDIO)
#include "modules/webaudio/PeriodicWave.h"
#include "core/platform/audio/FFTFrame.h"
#include "core/platform/audio/VectorMath.h"
#include "modules/webaudio/OscillatorNode.h"
#include "wtf/OwnPtr.h"
#include <algorithm>
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.
namespace WebCore {
using namespace VectorMath;
PassRefPtr<PeriodicWave> PeriodicWave::create(float sampleRate, Float32Array* real, Float32Array* imag)
{
bool isGood = real && imag && real->length() == imag->length();
ASSERT(isGood);
if (isGood) {
RefPtr<PeriodicWave> periodicWave = adoptRef(new PeriodicWave(sampleRate));
size_t numberOfComponents = real->length();
periodicWave->createBandLimitedTables(real->data(), imag->data(), numberOfComponents);
return periodicWave;
}
return 0;
}
PassRefPtr<PeriodicWave> PeriodicWave::createSine(float sampleRate)
{
RefPtr<PeriodicWave> periodicWave = adoptRef(new PeriodicWave(sampleRate));
periodicWave->generateBasicWaveform(OscillatorNode::SINE);
return periodicWave;
}
PassRefPtr<PeriodicWave> PeriodicWave::createSquare(float sampleRate)
{
RefPtr<PeriodicWave> periodicWave = adoptRef(new PeriodicWave(sampleRate));
periodicWave->generateBasicWaveform(OscillatorNode::SQUARE);
return periodicWave;
}
PassRefPtr<PeriodicWave> PeriodicWave::createSawtooth(float sampleRate)
{
RefPtr<PeriodicWave> periodicWave = adoptRef(new PeriodicWave(sampleRate));
periodicWave->generateBasicWaveform(OscillatorNode::SAWTOOTH);
return periodicWave;
}
PassRefPtr<PeriodicWave> PeriodicWave::createTriangle(float sampleRate)
{
RefPtr<PeriodicWave> periodicWave = adoptRef(new PeriodicWave(sampleRate));
periodicWave->generateBasicWaveform(OscillatorNode::TRIANGLE);
return periodicWave;
}
PeriodicWave::PeriodicWave(float sampleRate)
: m_sampleRate(sampleRate)
, m_periodicWaveSize(PeriodicWaveSize)
, m_numberOfRanges(NumberOfRanges)
, m_centsPerRange(CentsPerRange)
{
ScriptWrappable::init(this);
float nyquist = 0.5 * m_sampleRate;
m_lowestFundamentalFrequency = nyquist / maxNumberOfPartials();
m_rateScale = m_periodicWaveSize / m_sampleRate;
}
void PeriodicWave::waveDataForFundamentalFrequency(float fundamentalFrequency, float* &lowerWaveData, float* &higherWaveData, float& tableInterpolationFactor)
{
// Negative frequencies are allowed, in which case we alias to the positive frequency.
fundamentalFrequency = fabsf(fundamentalFrequency);
// Calculate the pitch range.
float ratio = fundamentalFrequency > 0 ? fundamentalFrequency / m_lowestFundamentalFrequency : 0.5;
float centsAboveLowestFrequency = log2f(ratio) * 1200;
// Add one to round-up to the next range just in time to truncate partials before aliasing occurs.
float pitchRange = 1 + centsAboveLowestFrequency / m_centsPerRange;
pitchRange = std::max(pitchRange, 0.0f);
pitchRange = std::min(pitchRange, static_cast<float>(m_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;
lowerWaveData = m_bandLimitedTables[rangeIndex2]->data();
higherWaveData = m_bandLimitedTables[rangeIndex1]->data();
// Ranges from 0 -> 1 to interpolate between lower -> higher.
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.
float centsToCull = rangeIndex * m_centsPerRange;
// A value from 0 -> 1 representing what fraction of the partials to keep.
float cullingScale = pow(2, -centsToCull / 1200);
// The very top range will have all the partials culled.
unsigned numberOfPartials = cullingScale * maxNumberOfPartials();
return numberOfPartials;
}
// Convert into time-domain wave buffers.
// One table is created for each range for non-aliasing playback at different playback rates.
// Thus, higher ranges have more high-frequency partials culled out.
void PeriodicWave::createBandLimitedTables(const float* realData, const float* imagData, unsigned numberOfComponents)
{
float normalizationScale = 1;
unsigned fftSize = m_periodicWaveSize;
unsigned halfSize = fftSize / 2;
unsigned i;
numberOfComponents = std::min(numberOfComponents, halfSize);
m_bandLimitedTables.reserveCapacity(m_numberOfRanges);
for (unsigned rangeIndex = 0; rangeIndex < m_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.
float minusOne = -1;
vsmul(imagP, 1, &minusOne, imagP, 1, halfSize);
// 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) {
realP[i] = 0;
imagP[i] = 0;
}
// Clear packed-nyquist if necessary.
if (numberOfPartials < halfSize)
imagP[0] = 0;
// Clear any DC-offset.
realP[0] = 0;
// Create the band-limited table.
OwnPtr<AudioFloatArray> table = adoptPtr(new AudioFloatArray(m_periodicWaveSize));
m_bandLimitedTables.append(table.release());
// Apply an inverse FFT to generate the time-domain table data.
float* data = m_bandLimitedTables[rangeIndex]->data();
frame.doInverseFFT(data);
// 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);
if (maxValue)
normalizationScale = 1.0f / maxValue;
}
// Apply normalization scale.
vsmul(data, 1, &normalizationScale, data, 1, m_periodicWaveSize);
}
}
void PeriodicWave::generateBasicWaveform(int shape)
{
unsigned fftSize = periodicWaveSize();
unsigned halfSize = fftSize / 2;
AudioFloatArray real(halfSize);
AudioFloatArray imag(halfSize);
float* realP = real.data();
float* imagP = imag.data();
// Clear DC and Nyquist.
realP[0] = 0;
imagP[0] = 0;
for (unsigned n = 1; n < halfSize; ++n) {
float omega = 2 * piFloat * n;
float invOmega = 1 / omega;
// Fourier coefficients according to standard definition.
float a; // Coefficient for cos().
float b; // Coefficient for sin().
// Calculate Fourier coefficients depending on the shape.
// Note that the overall scaling (magnitude) of the waveforms is normalized in createBandLimitedTables().
switch (shape) {
case OscillatorNode::SINE:
// Standard sine wave function.
a = 0;
b = (n == 1) ? 1 : 0;
break;
case OscillatorNode::SQUARE:
// Square-shaped waveform with the first half its maximum value and the second half its minimum value.
a = 0;
b = invOmega * ((n & 1) ? 2 : 0);
break;
case OscillatorNode::SAWTOOTH:
// Sawtooth-shaped waveform with the first half ramping from zero to maximum and the second half from minimum to zero.
a = 0;
b = -invOmega * cos(0.5 * omega);
break;
case OscillatorNode::TRIANGLE:
// Triangle-shaped waveform going from its maximum value to its minimum value then back to the maximum value.
a = (4 - 4 * cos(0.5 * omega)) / (n * n * piFloat * piFloat);
b = 0;
break;
default:
ASSERT_NOT_REACHED();
a = 0;
b = 0;
break;
}
realP[n] = a;
imagP[n] = b;
}
createBandLimitedTables(realP, imagP, halfSize);
}
} // namespace WebCore
#endif // ENABLE(WEB_AUDIO)