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/*
* Copyright (C) 2010, Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
* ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#if ENABLE(WEB_AUDIO)
#include "AudioUtilities.h"
#include <random>
#include <wtf/CryptographicallyRandomNumber.h>
#include <wtf/HashMap.h>
#include <wtf/MathExtras.h>
#include <wtf/WeakRandom.h>
namespace WebCore {
namespace AudioUtilities {
double discreteTimeConstantForSampleRate(double timeConstant, double sampleRate)
{
return 1 - exp(-1 / (sampleRate * timeConstant));
}
size_t timeToSampleFrame(double time, double sampleRate, SampleFrameRounding rounding)
{
// To compute the desired frame number, we pretend we're actually running the
// context at a much higher sample rate (by a factor of |oversampleFactor|).
// Round this to get the nearest frame number at the higher rate. Then
// convert back to the original rate to get a new frame number that may not be
// an integer. Then use the specified |rounding_mode| to round this to the
// integer frame number that we need.
//
// Doing this partially solves the issue where Fs * (k / Fs) != k when doing
// floating point arithmtic for integer k and Fs is the sample rate. By
// oversampling and rounding, we'll get k back most of the time.
//
// The oversampling factor MUST be a power of two so as not to introduce
// additional round-off in computing the oversample frame number.
constexpr double oversampleFactor = 1024;
double frame = std::round(time * sampleRate * oversampleFactor) / oversampleFactor;
switch (rounding) {
case SampleFrameRounding::Nearest:
frame = std::round(frame);
break;
case SampleFrameRounding::Down:
frame = std::floor(frame);
break;
case SampleFrameRounding::Up:
frame = std::ceil(frame);
break;
}
// Just return the largest possible size_t value if necessary.
if (frame >= static_cast<double>(std::numeric_limits<size_t>::max()))
return std::numeric_limits<size_t>::max();
return static_cast<size_t>(frame);
}
void applyNoise(float* values, size_t numberOfElementsToProcess, float standardDeviation)
{
std::random_device device;
std::mt19937 generator(device());
std::normal_distribution<float> distribution(1, standardDeviation);
HashMap<float, float> noiseMultipliers;
auto computeNoiseMultiplier = [&](float rawValue) {
if (!noiseMultipliers.isValidKey(rawValue))
return distribution(generator);
auto result = noiseMultipliers.ensure(rawValue, [&] {
return distribution(generator);
}).iterator->value;
static constexpr auto maxNoiseMultiplierMapSize = 250000;
if (noiseMultipliers.size() >= maxNoiseMultiplierMapSize)
noiseMultipliers.remove(noiseMultipliers.random());
return result;
};
for (size_t i = 0; i < numberOfElementsToProcess; ++i)
values[i] *= computeNoiseMultiplier(values[i]);
}
} // AudioUtilites
} // WebCore
#endif // ENABLE(WEB_AUDIO)
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