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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/time_stretch.h"
#include <algorithm> // min, max
#include <memory>
#include "common_audio/signal_processing/include/signal_processing_library.h"
#include "modules/audio_coding/neteq/background_noise.h"
#include "modules/audio_coding/neteq/cross_correlation.h"
#include "modules/audio_coding/neteq/dsp_helper.h"
#include "rtc_base/numerics/safe_conversions.h"
namespace webrtc {
TimeStretch::ReturnCodes TimeStretch::Process(const int16_t* input,
size_t input_len,
bool fast_mode,
AudioMultiVector* output,
size_t* length_change_samples) {
// Pre-calculate common multiplication with `fs_mult_`.
size_t fs_mult_120 =
static_cast<size_t>(fs_mult_ * 120); // Corresponds to 15 ms.
const int16_t* signal;
std::unique_ptr<int16_t[]> signal_array;
size_t signal_len;
if (num_channels_ == 1) {
signal = input;
signal_len = input_len;
} else {
// We want `signal` to be only the first channel of `input`, which is
// interleaved. Thus, we take the first sample, skip forward `num_channels`
// samples, and continue like that.
signal_len = input_len / num_channels_;
signal_array.reset(new int16_t[signal_len]);
signal = signal_array.get();
size_t j = kRefChannel;
for (size_t i = 0; i < signal_len; ++i) {
signal_array[i] = input[j];
j += num_channels_;
}
}
// Find maximum absolute value of input signal.
max_input_value_ = WebRtcSpl_MaxAbsValueW16(signal, signal_len);
// Downsample to 4 kHz sample rate and calculate auto-correlation.
DspHelper::DownsampleTo4kHz(signal, signal_len, kDownsampledLen,
sample_rate_hz_, true /* compensate delay*/,
downsampled_input_);
AutoCorrelation();
// Find the strongest correlation peak.
static const size_t kNumPeaks = 1;
size_t peak_index;
int16_t peak_value;
DspHelper::PeakDetection(auto_correlation_, kCorrelationLen, kNumPeaks,
fs_mult_, &peak_index, &peak_value);
// Assert that `peak_index` stays within boundaries.
RTC_DCHECK_LE(peak_index, (2 * kCorrelationLen - 1) * fs_mult_);
// Compensate peak_index for displaced starting position. The displacement
// happens in AutoCorrelation(). Here, `kMinLag` is in the down-sampled 4 kHz
// domain, while the `peak_index` is in the original sample rate; hence, the
// multiplication by fs_mult_ * 2.
peak_index += kMinLag * fs_mult_ * 2;
// Assert that `peak_index` stays within boundaries.
RTC_DCHECK_GE(peak_index, static_cast<size_t>(20 * fs_mult_));
RTC_DCHECK_LE(peak_index,
20 * fs_mult_ + (2 * kCorrelationLen - 1) * fs_mult_);
// Calculate scaling to ensure that `peak_index` samples can be square-summed
// without overflowing.
int scaling = 31 - WebRtcSpl_NormW32(max_input_value_ * max_input_value_) -
WebRtcSpl_NormW32(static_cast<int32_t>(peak_index));
scaling = std::max(0, scaling);
// `vec1` starts at 15 ms minus one pitch period.
const int16_t* vec1 = &signal[fs_mult_120 - peak_index];
// `vec2` start at 15 ms.
const int16_t* vec2 = &signal[fs_mult_120];
// Calculate energies for `vec1` and `vec2`, assuming they both contain
// `peak_index` samples.
int32_t vec1_energy =
WebRtcSpl_DotProductWithScale(vec1, vec1, peak_index, scaling);
int32_t vec2_energy =
WebRtcSpl_DotProductWithScale(vec2, vec2, peak_index, scaling);
// Calculate cross-correlation between `vec1` and `vec2`.
int32_t cross_corr =
WebRtcSpl_DotProductWithScale(vec1, vec2, peak_index, scaling);
// Check if the signal seems to be active speech or not (simple VAD).
bool active_speech =
SpeechDetection(vec1_energy, vec2_energy, peak_index, scaling);
int16_t best_correlation;
if (!active_speech) {
SetParametersForPassiveSpeech(signal_len, &best_correlation, &peak_index);
} else {
// Calculate correlation:
// cross_corr / sqrt(vec1_energy * vec2_energy).
// Start with calculating scale values.
int energy1_scale = std::max(0, 16 - WebRtcSpl_NormW32(vec1_energy));
int energy2_scale = std::max(0, 16 - WebRtcSpl_NormW32(vec2_energy));
// Make sure total scaling is even (to simplify scale factor after sqrt).
if ((energy1_scale + energy2_scale) & 1) {
// The sum is odd.
energy1_scale += 1;
}
// Scale energies to int16_t.
int16_t vec1_energy_int16 =
static_cast<int16_t>(vec1_energy >> energy1_scale);
int16_t vec2_energy_int16 =
static_cast<int16_t>(vec2_energy >> energy2_scale);
// Calculate square-root of energy product.
int16_t sqrt_energy_prod =
WebRtcSpl_SqrtFloor(vec1_energy_int16 * vec2_energy_int16);
// Calculate cross_corr / sqrt(en1*en2) in Q14.
int temp_scale = 14 - (energy1_scale + energy2_scale) / 2;
cross_corr = WEBRTC_SPL_SHIFT_W32(cross_corr, temp_scale);
cross_corr = std::max(0, cross_corr); // Don't use if negative.
best_correlation = WebRtcSpl_DivW32W16(cross_corr, sqrt_energy_prod);
// Make sure `best_correlation` is no larger than 1 in Q14.
best_correlation = std::min(static_cast<int16_t>(16384), best_correlation);
}
// Check accelerate criteria and stretch the signal.
ReturnCodes return_value =
CheckCriteriaAndStretch(input, input_len, peak_index, best_correlation,
active_speech, fast_mode, output);
switch (return_value) {
case kSuccess:
*length_change_samples = peak_index;
break;
case kSuccessLowEnergy:
*length_change_samples = peak_index;
break;
case kNoStretch:
case kError:
*length_change_samples = 0;
break;
}
return return_value;
}
void TimeStretch::AutoCorrelation() {
// Calculate correlation from lag kMinLag to lag kMaxLag in 4 kHz domain.
int32_t auto_corr[kCorrelationLen];
CrossCorrelationWithAutoShift(
&downsampled_input_[kMaxLag], &downsampled_input_[kMaxLag - kMinLag],
kCorrelationLen, kMaxLag - kMinLag, -1, auto_corr);
// Normalize correlation to 14 bits and write to `auto_correlation_`.
int32_t max_corr = WebRtcSpl_MaxAbsValueW32(auto_corr, kCorrelationLen);
int scaling = std::max(0, 17 - WebRtcSpl_NormW32(max_corr));
WebRtcSpl_VectorBitShiftW32ToW16(auto_correlation_, kCorrelationLen,
auto_corr, scaling);
}
bool TimeStretch::SpeechDetection(int32_t vec1_energy,
int32_t vec2_energy,
size_t peak_index,
int scaling) const {
// Check if the signal seems to be active speech or not (simple VAD).
// If (vec1_energy + vec2_energy) / (2 * peak_index) <=
// 8 * background_noise_energy, then we say that the signal contains no
// active speech.
// Rewrite the inequality as:
// (vec1_energy + vec2_energy) / 16 <= peak_index * background_noise_energy.
// The two sides of the inequality will be denoted `left_side` and
// `right_side`.
int32_t left_side = rtc::saturated_cast<int32_t>(
(static_cast<int64_t>(vec1_energy) + vec2_energy) / 16);
int32_t right_side;
if (background_noise_.initialized()) {
right_side = background_noise_.Energy(kRefChannel);
} else {
// If noise parameters have not been estimated, use a fixed threshold.
right_side = 75000;
}
int right_scale = 16 - WebRtcSpl_NormW32(right_side);
right_scale = std::max(0, right_scale);
left_side = left_side >> right_scale;
right_side =
rtc::dchecked_cast<int32_t>(peak_index) * (right_side >> right_scale);
// Scale `left_side` properly before comparing with `right_side`.
// (`scaling` is the scale factor before energy calculation, thus the scale
// factor for the energy is 2 * scaling.)
if (WebRtcSpl_NormW32(left_side) < 2 * scaling) {
// Cannot scale only `left_side`, must scale `right_side` too.
int temp_scale = WebRtcSpl_NormW32(left_side);
left_side = left_side << temp_scale;
right_side = right_side >> (2 * scaling - temp_scale);
} else {
left_side = left_side << 2 * scaling;
}
return left_side > right_side;
}
} // namespace webrtc