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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "platform/audio/StereoPanner.h"
#include "platform/audio/AudioBus.h"
#include "platform/audio/AudioUtilities.h"
#include "wtf/MathExtras.h"
#include <algorithm>
// Use a 50ms smoothing / de-zippering time-constant.
const float SmoothingTimeConstant = 0.050f;
namespace blink {
// Implement equal-power panning algorithm for mono or stereo input.
// See: http://webaudio.github.io/web-audio-api/#panning-algorithm
std::unique_ptr<StereoPanner> StereoPanner::create(float sampleRate) {
return WTF::wrapUnique(new StereoPanner(sampleRate));
}
StereoPanner::StereoPanner(float sampleRate)
: m_isFirstRender(true), m_pan(0.0) {
// Convert smoothing time (50ms) to a per-sample time value.
m_smoothingConstant = AudioUtilities::discreteTimeConstantForSampleRate(
SmoothingTimeConstant, sampleRate);
}
void StereoPanner::panWithSampleAccurateValues(const AudioBus* inputBus,
AudioBus* outputBus,
const float* panValues,
size_t framesToProcess) {
bool isInputSafe = inputBus && (inputBus->numberOfChannels() == 1 ||
inputBus->numberOfChannels() == 2) &&
framesToProcess <= inputBus->length();
ASSERT(isInputSafe);
if (!isInputSafe)
return;
unsigned numberOfInputChannels = inputBus->numberOfChannels();
bool isOutputSafe = outputBus && outputBus->numberOfChannels() == 2 &&
framesToProcess <= outputBus->length();
ASSERT(isOutputSafe);
if (!isOutputSafe)
return;
const float* sourceL = inputBus->channel(0)->data();
const float* sourceR =
numberOfInputChannels > 1 ? inputBus->channel(1)->data() : sourceL;
float* destinationL =
outputBus->channelByType(AudioBus::ChannelLeft)->mutableData();
float* destinationR =
outputBus->channelByType(AudioBus::ChannelRight)->mutableData();
if (!sourceL || !sourceR || !destinationL || !destinationR)
return;
double gainL, gainR, panRadian;
int n = framesToProcess;
if (numberOfInputChannels == 1) { // For mono source case.
while (n--) {
float inputL = *sourceL++;
m_pan = clampTo(*panValues++, -1.0, 1.0);
// Pan from left to right [-1; 1] will be normalized as [0; 1].
panRadian = (m_pan * 0.5 + 0.5) * piOverTwoDouble;
gainL = std::cos(panRadian);
gainR = std::sin(panRadian);
*destinationL++ = static_cast<float>(inputL * gainL);
*destinationR++ = static_cast<float>(inputL * gainR);
}
} else { // For stereo source case.
while (n--) {
float inputL = *sourceL++;
float inputR = *sourceR++;
m_pan = clampTo(*panValues++, -1.0, 1.0);
// Normalize [-1; 0] to [0; 1]. Do nothing when [0; 1].
panRadian = (m_pan <= 0 ? m_pan + 1 : m_pan) * piOverTwoDouble;
gainL = std::cos(panRadian);
gainR = std::sin(panRadian);
if (m_pan <= 0) {
*destinationL++ = static_cast<float>(inputL + inputR * gainL);
*destinationR++ = static_cast<float>(inputR * gainR);
} else {
*destinationL++ = static_cast<float>(inputL * gainL);
*destinationR++ = static_cast<float>(inputR + inputL * gainR);
}
}
}
}
void StereoPanner::panToTargetValue(const AudioBus* inputBus,
AudioBus* outputBus,
float panValue,
size_t framesToProcess) {
bool isInputSafe = inputBus && (inputBus->numberOfChannels() == 1 ||
inputBus->numberOfChannels() == 2) &&
framesToProcess <= inputBus->length();
ASSERT(isInputSafe);
if (!isInputSafe)
return;
unsigned numberOfInputChannels = inputBus->numberOfChannels();
bool isOutputSafe = outputBus && outputBus->numberOfChannels() == 2 &&
framesToProcess <= outputBus->length();
ASSERT(isOutputSafe);
if (!isOutputSafe)
return;
const float* sourceL = inputBus->channel(0)->data();
const float* sourceR =
numberOfInputChannels > 1 ? inputBus->channel(1)->data() : sourceL;
float* destinationL =
outputBus->channelByType(AudioBus::ChannelLeft)->mutableData();
float* destinationR =
outputBus->channelByType(AudioBus::ChannelRight)->mutableData();
if (!sourceL || !sourceR || !destinationL || !destinationR)
return;
float targetPan = clampTo(panValue, -1.0, 1.0);
// Don't de-zipper on first render call.
if (m_isFirstRender) {
m_isFirstRender = false;
m_pan = targetPan;
}
double gainL, gainR, panRadian;
const double smoothingConstant = m_smoothingConstant;
int n = framesToProcess;
if (numberOfInputChannels == 1) { // For mono source case.
while (n--) {
float inputL = *sourceL++;
m_pan += (targetPan - m_pan) * smoothingConstant;
// Pan from left to right [-1; 1] will be normalized as [0; 1].
panRadian = (m_pan * 0.5 + 0.5) * piOverTwoDouble;
gainL = std::cos(panRadian);
gainR = std::sin(panRadian);
*destinationL++ = static_cast<float>(inputL * gainL);
*destinationR++ = static_cast<float>(inputL * gainR);
}
} else { // For stereo source case.
while (n--) {
float inputL = *sourceL++;
float inputR = *sourceR++;
m_pan += (targetPan - m_pan) * smoothingConstant;
// Normalize [-1; 0] to [0; 1] for the left pan position (<= 0), and
// do nothing when [0; 1].
panRadian = (m_pan <= 0 ? m_pan + 1 : m_pan) * piOverTwoDouble;
gainL = std::cos(panRadian);
gainR = std::sin(panRadian);
// The pan value should be checked every sample when de-zippering.
// See crbug.com/470559.
if (m_pan <= 0) {
// When [-1; 0], keep left channel intact and equal-power pan the
// right channel only.
*destinationL++ = static_cast<float>(inputL + inputR * gainL);
*destinationR++ = static_cast<float>(inputR * gainR);
} else {
// When [0; 1], keep right channel intact and equal-power pan the
// left channel only.
*destinationL++ = static_cast<float>(inputL * gainL);
*destinationR++ = static_cast<float>(inputR + inputL * gainR);
}
}
}
}
} // namespace blink
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