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/*
* Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "common_audio/audio_converter.h"
#include <algorithm>
#include <cmath>
#include <memory>
#include <vector>
#include "common_audio/channel_buffer.h"
#include "common_audio/resampler/push_sinc_resampler.h"
#include "rtc_base/arraysize.h"
#include "test/gtest.h"
namespace webrtc {
typedef std::unique_ptr<ChannelBuffer<float>> ScopedBuffer;
// Sets the signal value to increase by `data` with every sample.
ScopedBuffer CreateBuffer(const std::vector<float>& data, size_t frames) {
const size_t num_channels = data.size();
ScopedBuffer sb(new ChannelBuffer<float>(frames, num_channels));
for (size_t i = 0; i < num_channels; ++i)
for (size_t j = 0; j < frames; ++j)
sb->channels()[i][j] = data[i] * j;
return sb;
}
void VerifyParams(const ChannelBuffer<float>& ref,
const ChannelBuffer<float>& test) {
EXPECT_EQ(ref.num_channels(), test.num_channels());
EXPECT_EQ(ref.num_frames(), test.num_frames());
}
// Computes the best SNR based on the error between `ref_frame` and
// `test_frame`. It searches around `expected_delay` in samples between the
// signals to compensate for the resampling delay.
float ComputeSNR(const ChannelBuffer<float>& ref,
const ChannelBuffer<float>& test,
size_t expected_delay) {
VerifyParams(ref, test);
float best_snr = 0;
size_t best_delay = 0;
// Search within one sample of the expected delay.
for (size_t delay = std::max(expected_delay, static_cast<size_t>(1)) - 1;
delay <= std::min(expected_delay + 1, ref.num_frames()); ++delay) {
float mse = 0;
float variance = 0;
float mean = 0;
for (size_t i = 0; i < ref.num_channels(); ++i) {
for (size_t j = 0; j < ref.num_frames() - delay; ++j) {
float error = ref.channels()[i][j] - test.channels()[i][j + delay];
mse += error * error;
variance += ref.channels()[i][j] * ref.channels()[i][j];
mean += ref.channels()[i][j];
}
}
const size_t length = ref.num_channels() * (ref.num_frames() - delay);
mse /= length;
variance /= length;
mean /= length;
variance -= mean * mean;
float snr = 100; // We assign 100 dB to the zero-error case.
if (mse > 0)
snr = 10 * std::log10(variance / mse);
if (snr > best_snr) {
best_snr = snr;
best_delay = delay;
}
}
printf("SNR=%.1f dB at delay=%zu\n", best_snr, best_delay);
return best_snr;
}
// Sets the source to a linearly increasing signal for which we can easily
// generate a reference. Runs the AudioConverter and ensures the output has
// sufficiently high SNR relative to the reference.
void RunAudioConverterTest(size_t src_channels,
int src_sample_rate_hz,
size_t dst_channels,
int dst_sample_rate_hz) {
const float kSrcLeft = 0.0002f;
const float kSrcRight = 0.0001f;
const float resampling_factor =
(1.f * src_sample_rate_hz) / dst_sample_rate_hz;
const float dst_left = resampling_factor * kSrcLeft;
const float dst_right = resampling_factor * kSrcRight;
const float dst_mono = (dst_left + dst_right) / 2;
const size_t src_frames = static_cast<size_t>(src_sample_rate_hz / 100);
const size_t dst_frames = static_cast<size_t>(dst_sample_rate_hz / 100);
std::vector<float> src_data(1, kSrcLeft);
if (src_channels == 2)
src_data.push_back(kSrcRight);
ScopedBuffer src_buffer = CreateBuffer(src_data, src_frames);
std::vector<float> dst_data(1, 0);
std::vector<float> ref_data;
if (dst_channels == 1) {
if (src_channels == 1)
ref_data.push_back(dst_left);
else
ref_data.push_back(dst_mono);
} else {
dst_data.push_back(0);
ref_data.push_back(dst_left);
if (src_channels == 1)
ref_data.push_back(dst_left);
else
ref_data.push_back(dst_right);
}
ScopedBuffer dst_buffer = CreateBuffer(dst_data, dst_frames);
ScopedBuffer ref_buffer = CreateBuffer(ref_data, dst_frames);
// The sinc resampler has a known delay, which we compute here.
const size_t delay_frames =
src_sample_rate_hz == dst_sample_rate_hz
? 0
: static_cast<size_t>(
PushSincResampler::AlgorithmicDelaySeconds(src_sample_rate_hz) *
dst_sample_rate_hz);
// SNR reported on the same line later.
printf("(%zu, %d Hz) -> (%zu, %d Hz) ", src_channels, src_sample_rate_hz,
dst_channels, dst_sample_rate_hz);
std::unique_ptr<AudioConverter> converter = AudioConverter::Create(
src_channels, src_frames, dst_channels, dst_frames);
converter->Convert(src_buffer->channels(), src_buffer->size(),
dst_buffer->channels(), dst_buffer->size());
EXPECT_LT(43.f,
ComputeSNR(*ref_buffer.get(), *dst_buffer.get(), delay_frames));
}
TEST(AudioConverterTest, ConversionsPassSNRThreshold) {
const int kSampleRates[] = {8000, 11025, 16000, 22050, 32000, 44100, 48000};
const int kChannels[] = {1, 2};
for (int src_rate : kSampleRates) {
for (int dst_rate : kSampleRates) {
for (size_t src_channels : kChannels) {
for (size_t dst_channels : kChannels) {
RunAudioConverterTest(src_channels, src_rate, dst_channels, dst_rate);
}
}
}
}
}
} // namespace webrtc
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