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/*
* Copyright (c) 2012 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 "modules/audio_coding/neteq/background_noise.h"
#include <string.h> // memcpy
#include <algorithm> // min, max
#include "common_audio/signal_processing/include/signal_processing_library.h"
#include "modules/audio_coding/neteq/audio_multi_vector.h"
#include "modules/audio_coding/neteq/cross_correlation.h"
namespace webrtc {
namespace {
constexpr size_t kMaxSampleRate = 48000;
} // namespace
// static
constexpr size_t BackgroundNoise::kMaxLpcOrder;
BackgroundNoise::BackgroundNoise(size_t num_channels)
: num_channels_(num_channels),
channel_parameters_(new ChannelParameters[num_channels_]) {
Reset();
}
BackgroundNoise::~BackgroundNoise() {}
void BackgroundNoise::Reset() {
initialized_ = false;
for (size_t channel = 0; channel < num_channels_; ++channel) {
channel_parameters_[channel].Reset();
}
}
bool BackgroundNoise::Update(const AudioMultiVector& sync_buffer) {
bool filter_params_saved = false;
int32_t auto_correlation[kMaxLpcOrder + 1];
int16_t filter_output[kMaxLpcOrder + kResidualLength];
int16_t reflection_coefficients[kMaxLpcOrder];
int16_t lpc_coefficients[kMaxLpcOrder + 1];
for (size_t channel_ix = 0; channel_ix < num_channels_; ++channel_ix) {
ChannelParameters& parameters = channel_parameters_[channel_ix];
int16_t temp_signal_array[kVecLen + kMaxLpcOrder] = {0};
int16_t* temp_signal = &temp_signal_array[kMaxLpcOrder];
RTC_DCHECK_GE(sync_buffer.Size(), kVecLen);
sync_buffer[channel_ix].CopyTo(kVecLen, sync_buffer.Size() - kVecLen,
temp_signal);
int32_t sample_energy =
CalculateAutoCorrelation(temp_signal, kVecLen, auto_correlation);
if (sample_energy < parameters.energy_update_threshold) {
// Generate LPC coefficients.
if (auto_correlation[0] <= 0) {
// Center value in auto-correlation is not positive. Do not update.
return filter_params_saved;
}
// Regardless of whether the filter is actually updated or not,
// update energy threshold levels, since we have in fact observed
// a low energy signal.
if (sample_energy < parameters.energy_update_threshold) {
// Never go under 1.0 in average sample energy.
parameters.energy_update_threshold = std::max(sample_energy, 1);
parameters.low_energy_update_threshold = 0;
}
// Only update BGN if filter is stable, i.e., if return value from
// Levinson-Durbin function is 1.
if (WebRtcSpl_LevinsonDurbin(auto_correlation, lpc_coefficients,
reflection_coefficients,
kMaxLpcOrder) != 1) {
return filter_params_saved;
}
// Generate the CNG gain factor by looking at the energy of the residual.
WebRtcSpl_FilterMAFastQ12(temp_signal + kVecLen - kResidualLength,
filter_output, lpc_coefficients,
kMaxLpcOrder + 1, kResidualLength);
int32_t residual_energy = WebRtcSpl_DotProductWithScale(
filter_output, filter_output, kResidualLength, 0);
// Check spectral flatness.
// Comparing the residual variance with the input signal variance tells
// if the spectrum is flat or not.
// If 5 * residual_energy >= 16 * sample_energy, the spectrum is flat
// enough. Also ensure that the energy is non-zero.
if ((sample_energy > 0) &&
(int64_t{5} * residual_energy >= int64_t{16} * sample_energy)) {
// Spectrum is flat enough; save filter parameters.
// `temp_signal` + `kVecLen` - `kMaxLpcOrder` points at the first of the
// `kMaxLpcOrder` samples in the residual signal, which will form the
// filter state for the next noise generation.
SaveParameters(channel_ix, lpc_coefficients,
temp_signal + kVecLen - kMaxLpcOrder, sample_energy,
residual_energy);
filter_params_saved = true;
}
} else {
// Will only happen if `sample_energy` is not low enough. Increase the
// threshold for update so that it increases by a factor 4 in 4 seconds.
IncrementEnergyThreshold(channel_ix, sample_energy);
}
}
return filter_params_saved;
}
void BackgroundNoise::GenerateBackgroundNoise(
rtc::ArrayView<const int16_t> random_vector,
size_t channel,
int mute_slope,
bool too_many_expands,
size_t num_noise_samples,
int16_t* buffer) {
constexpr size_t kNoiseLpcOrder = kMaxLpcOrder;
int16_t scaled_random_vector[kMaxSampleRate / 8000 * 125];
RTC_DCHECK_LE(num_noise_samples, (kMaxSampleRate / 8000 * 125));
RTC_DCHECK_GE(random_vector.size(), num_noise_samples);
int16_t* noise_samples = &buffer[kNoiseLpcOrder];
if (initialized()) {
// Use background noise parameters.
memcpy(noise_samples - kNoiseLpcOrder, FilterState(channel),
sizeof(int16_t) * kNoiseLpcOrder);
int dc_offset = 0;
if (ScaleShift(channel) > 1) {
dc_offset = 1 << (ScaleShift(channel) - 1);
}
// Scale random vector to correct energy level.
WebRtcSpl_AffineTransformVector(scaled_random_vector, random_vector.data(),
Scale(channel), dc_offset,
ScaleShift(channel), num_noise_samples);
WebRtcSpl_FilterARFastQ12(scaled_random_vector, noise_samples,
Filter(channel), kNoiseLpcOrder + 1,
num_noise_samples);
SetFilterState(
channel,
{&(noise_samples[num_noise_samples - kNoiseLpcOrder]), kNoiseLpcOrder});
// Unmute the background noise.
int16_t bgn_mute_factor = MuteFactor(channel);
if (bgn_mute_factor < 16384) {
WebRtcSpl_AffineTransformVector(noise_samples, noise_samples,
bgn_mute_factor, 8192, 14,
num_noise_samples);
}
// Update mute_factor in BackgroundNoise class.
SetMuteFactor(channel, bgn_mute_factor);
} else {
// BGN parameters have not been initialized; use zero noise.
memset(noise_samples, 0, sizeof(int16_t) * num_noise_samples);
}
}
int32_t BackgroundNoise::Energy(size_t channel) const {
RTC_DCHECK_LT(channel, num_channels_);
return channel_parameters_[channel].energy;
}
void BackgroundNoise::SetMuteFactor(size_t channel, int16_t value) {
RTC_DCHECK_LT(channel, num_channels_);
channel_parameters_[channel].mute_factor = value;
}
int16_t BackgroundNoise::MuteFactor(size_t channel) const {
RTC_DCHECK_LT(channel, num_channels_);
return channel_parameters_[channel].mute_factor;
}
const int16_t* BackgroundNoise::Filter(size_t channel) const {
RTC_DCHECK_LT(channel, num_channels_);
return channel_parameters_[channel].filter;
}
const int16_t* BackgroundNoise::FilterState(size_t channel) const {
RTC_DCHECK_LT(channel, num_channels_);
return channel_parameters_[channel].filter_state;
}
void BackgroundNoise::SetFilterState(size_t channel,
rtc::ArrayView<const int16_t> input) {
RTC_DCHECK_LT(channel, num_channels_);
size_t length = std::min(input.size(), kMaxLpcOrder);
memcpy(channel_parameters_[channel].filter_state, input.data(),
length * sizeof(int16_t));
}
int16_t BackgroundNoise::Scale(size_t channel) const {
RTC_DCHECK_LT(channel, num_channels_);
return channel_parameters_[channel].scale;
}
int16_t BackgroundNoise::ScaleShift(size_t channel) const {
RTC_DCHECK_LT(channel, num_channels_);
return channel_parameters_[channel].scale_shift;
}
int32_t BackgroundNoise::CalculateAutoCorrelation(
const int16_t* signal,
size_t length,
int32_t* auto_correlation) const {
static const int kCorrelationStep = -1;
const int correlation_scale =
CrossCorrelationWithAutoShift(signal, signal, length, kMaxLpcOrder + 1,
kCorrelationStep, auto_correlation);
// Number of shifts to normalize energy to energy/sample.
int energy_sample_shift = kLogVecLen - correlation_scale;
return auto_correlation[0] >> energy_sample_shift;
}
void BackgroundNoise::IncrementEnergyThreshold(size_t channel,
int32_t sample_energy) {
// TODO(hlundin): Simplify the below threshold update. What this code
// does is simply "threshold += (increment * threshold) >> 16", but due
// to the limited-width operations, it is not exactly the same. The
// difference should be inaudible, but bit-exactness would not be
// maintained.
RTC_DCHECK_LT(channel, num_channels_);
ChannelParameters& parameters = channel_parameters_[channel];
int32_t temp_energy =
(kThresholdIncrement * parameters.low_energy_update_threshold) >> 16;
temp_energy +=
kThresholdIncrement * (parameters.energy_update_threshold & 0xFF);
temp_energy +=
(kThresholdIncrement * ((parameters.energy_update_threshold >> 8) & 0xFF))
<< 8;
parameters.low_energy_update_threshold += temp_energy;
parameters.energy_update_threshold +=
kThresholdIncrement * (parameters.energy_update_threshold >> 16);
parameters.energy_update_threshold +=
parameters.low_energy_update_threshold >> 16;
parameters.low_energy_update_threshold =
parameters.low_energy_update_threshold & 0x0FFFF;
// Update maximum energy.
// Decrease by a factor 1/1024 each time.
parameters.max_energy = parameters.max_energy - (parameters.max_energy >> 10);
if (sample_energy > parameters.max_energy) {
parameters.max_energy = sample_energy;
}
// Set `energy_update_threshold` to no less than 60 dB lower than
// `max_energy_`. Adding 524288 assures proper rounding.
int32_t energy_update_threshold = (parameters.max_energy + 524288) >> 20;
if (energy_update_threshold > parameters.energy_update_threshold) {
parameters.energy_update_threshold = energy_update_threshold;
}
}
void BackgroundNoise::SaveParameters(size_t channel,
const int16_t* lpc_coefficients,
const int16_t* filter_state,
int32_t sample_energy,
int32_t residual_energy) {
RTC_DCHECK_LT(channel, num_channels_);
ChannelParameters& parameters = channel_parameters_[channel];
memcpy(parameters.filter, lpc_coefficients,
(kMaxLpcOrder + 1) * sizeof(int16_t));
memcpy(parameters.filter_state, filter_state, kMaxLpcOrder * sizeof(int16_t));
// Save energy level and update energy threshold levels.
// Never get under 1.0 in average sample energy.
parameters.energy = std::max(sample_energy, 1);
parameters.energy_update_threshold = parameters.energy;
parameters.low_energy_update_threshold = 0;
// Normalize residual_energy to 29 or 30 bits before sqrt.
int16_t norm_shift = WebRtcSpl_NormW32(residual_energy) - 1;
if (norm_shift & 0x1) {
norm_shift -= 1; // Even number of shifts required.
}
residual_energy = WEBRTC_SPL_SHIFT_W32(residual_energy, norm_shift);
// Calculate scale and shift factor.
parameters.scale = static_cast<int16_t>(WebRtcSpl_SqrtFloor(residual_energy));
// Add 13 to the `scale_shift_`, since the random numbers table is in
// Q13.
// TODO(hlundin): Move the "13" to where the `scale_shift_` is used?
parameters.scale_shift =
static_cast<int16_t>(13 + ((kLogResidualLength + norm_shift) / 2));
initialized_ = true;
}
} // namespace webrtc