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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 "third_party/blink/renderer/platform/audio/audio_utilities.h"
#include "third_party/blink/renderer/platform/wtf/assertions.h"
#include "third_party/blink/renderer/platform/wtf/math_extras.h"
namespace blink {
namespace audio_utilities {
float DecibelsToLinear(float decibels) {
return powf(10, 0.05f * decibels);
}
float LinearToDecibels(float linear) {
DCHECK_GE(linear, 0);
return 20 * log10f(linear);
}
double DiscreteTimeConstantForSampleRate(double time_constant,
double sample_rate) {
// From the WebAudio spec, the formula for setTargetAtTime is
//
// v(t) = V1 + (V0 - V1)*exp(-t/tau)
//
// where tau is the time constant, V1 is the target value and V0 is
// the starting value.
//
// Rewrite this as
//
// v(t) = V0 + (V1 - V0)*(1-exp(-t/tau))
//
// The implementation of setTargetAtTime uses this form. So at the
// sample points, we have
//
// v(n/Fs) = V0 + (V1 - V0)*(1-exp(-n/(Fs*tau)))
//
// where Fs is the sample rate of the sampled systme. Thus, the
// discrete time constant is
//
// 1 - exp(-1/(Fs*tau)
return 1 - exp(-1 / (sample_rate * time_constant));
}
size_t TimeToSampleFrame(double time,
double sample_rate,
enum SampleFrameRounding rounding_mode) {
DCHECK_GE(time, 0);
// To compute the desired frame number, we pretend we're actually running the
// context at a much higher sample rate (by a factor of |oversample_factor|).
// 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.
const double oversample_factor = 1024;
double frame =
round(time * sample_rate * oversample_factor) / oversample_factor;
switch (rounding_mode) {
case kRoundToNearest:
frame = round(frame);
break;
case kRoundDown:
frame = floor(frame);
break;
case kRoundUp:
frame = ceil(frame);
break;
default:
NOTREACHED();
}
// Just return the largest possible size_t value if necessary.
if (frame >= std::numeric_limits<size_t>::max()) {
return std::numeric_limits<size_t>::max();
}
return static_cast<size_t>(frame);
}
bool IsValidAudioBufferSampleRate(float sample_rate) {
return sample_rate >= MinAudioBufferSampleRate() &&
sample_rate <= MaxAudioBufferSampleRate();
}
float MinAudioBufferSampleRate() {
// crbug.com/344375
return 3000;
}
float MaxAudioBufferSampleRate() {
// <video> tags support sample rates up 384 kHz so audio context
// should too.
return 384000;
}
bool IsPowerOfTwo(size_t x) {
// From Hacker's Delight. x & (x - 1) turns off (zeroes) the
// rightmost 1-bit in the word x. If x is a power of two, then the
// result is, of course, 0.
return x > 0 && ((x & (x - 1)) == 0);
}
} // namespace audio_utilities
} // namespace blink