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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 <stdint.h>
#include <string.h>
#include "modules/audio_coding/neteq/audio_multi_vector.h"
#include "modules/audio_coding/neteq/audio_vector.h"
namespace webrtc {
// This class contains various signal processing functions, all implemented as
// static methods.
class DspHelper {
// Filter coefficients used when downsampling from the indicated sample rates
// (8, 16, 32, 48 kHz) to 4 kHz. Coefficients are in Q12.
static const int16_t kDownsample8kHzTbl[3];
static const int16_t kDownsample16kHzTbl[5];
static const int16_t kDownsample32kHzTbl[7];
static const int16_t kDownsample48kHzTbl[7];
// Constants used to mute and unmute over 5 samples. The coefficients are
// in Q15.
static const int kMuteFactorStart8kHz = 27307;
static const int kMuteFactorIncrement8kHz = -5461;
static const int kUnmuteFactorStart8kHz = 5461;
static const int kUnmuteFactorIncrement8kHz = 5461;
static const int kMuteFactorStart16kHz = 29789;
static const int kMuteFactorIncrement16kHz = -2979;
static const int kUnmuteFactorStart16kHz = 2979;
static const int kUnmuteFactorIncrement16kHz = 2979;
static const int kMuteFactorStart32kHz = 31208;
static const int kMuteFactorIncrement32kHz = -1560;
static const int kUnmuteFactorStart32kHz = 1560;
static const int kUnmuteFactorIncrement32kHz = 1560;
static const int kMuteFactorStart48kHz = 31711;
static const int kMuteFactorIncrement48kHz = -1057;
static const int kUnmuteFactorStart48kHz = 1057;
static const int kUnmuteFactorIncrement48kHz = 1057;
// Multiplies the signal with a gradually changing factor.
// The first sample is multiplied with `factor` (in Q14). For each sample,
// `factor` is increased (additive) by the `increment` (in Q20), which can
// be negative. Returns the scale factor after the last increment.
static int RampSignal(const int16_t* input,
size_t length,
int factor,
int increment,
int16_t* output);
// Same as above, but with the samples of `signal` being modified in-place.
static int RampSignal(int16_t* signal,
size_t length,
int factor,
int increment);
// Same as above, but processes `length` samples from `signal`, starting at
// `start_index`.
static int RampSignal(AudioVector* signal,
size_t start_index,
size_t length,
int factor,
int increment);
// Same as above, but for an AudioMultiVector.
static int RampSignal(AudioMultiVector* signal,
size_t start_index,
size_t length,
int factor,
int increment);
// Peak detection with parabolic fit. Looks for `num_peaks` maxima in `data`,
// having length `data_length` and sample rate multiplier `fs_mult`. The peak
// locations and values are written to the arrays `peak_index` and
// `peak_value`, respectively. Both arrays must hold at least `num_peaks`
// elements.
static void PeakDetection(int16_t* data,
size_t data_length,
size_t num_peaks,
int fs_mult,
size_t* peak_index,
int16_t* peak_value);
// Estimates the height and location of a maximum. The three values in the
// array `signal_points` are used as basis for a parabolic fit, which is then
// used to find the maximum in an interpolated signal. The `signal_points` are
// assumed to be from a 4 kHz signal, while the maximum, written to
// `peak_index` and `peak_value` is given in the full sample rate, as
// indicated by the sample rate multiplier `fs_mult`.
static void ParabolicFit(int16_t* signal_points,
int fs_mult,
size_t* peak_index,
int16_t* peak_value);
// Calculates the sum-abs-diff for `signal` when compared to a displaced
// version of itself. Returns the displacement lag that results in the minimum
// distortion. The resulting distortion is written to `distortion_value`.
// The values of `min_lag` and `max_lag` are boundaries for the search.
static size_t MinDistortion(const int16_t* signal,
size_t min_lag,
size_t max_lag,
size_t length,
int32_t* distortion_value);
// Mixes `length` samples from `input1` and `input2` together and writes the
// result to `output`. The gain for `input1` starts at `mix_factor` (Q14) and
// is decreased by `factor_decrement` (Q14) for each sample. The gain for
// `input2` is the complement 16384 - mix_factor.
static void CrossFade(const int16_t* input1,
const int16_t* input2,
size_t length,
int16_t* mix_factor,
int16_t factor_decrement,
int16_t* output);
// Scales `input` with an increasing gain. Applies `factor` (Q14) to the first
// sample and increases the gain by `increment` (Q20) for each sample. The
// result is written to `output`. `length` samples are processed.
static void UnmuteSignal(const int16_t* input,
size_t length,
int16_t* factor,
int increment,
int16_t* output);
// Starts at unity gain and gradually fades out `signal`. For each sample,
// the gain is reduced by `mute_slope` (Q14). `length` samples are processed.
static void MuteSignal(int16_t* signal, int mute_slope, size_t length);
// Downsamples `input` from `sample_rate_hz` to 4 kHz sample rate. The input
// has `input_length` samples, and the method will write `output_length`
// samples to `output`. Compensates for the phase delay of the downsampling
// filters if `compensate_delay` is true. Returns -1 if the input is too short
// to produce `output_length` samples, otherwise 0.
static int DownsampleTo4kHz(const int16_t* input,
size_t input_length,
size_t output_length,
int input_rate_hz,
bool compensate_delay,
int16_t* output);
DspHelper(const DspHelper&) = delete;
DspHelper& operator=(const DspHelper&) = delete;
// Table of constants used in method DspHelper::ParabolicFit().
static const int16_t kParabolaCoefficients[17][3];
} // namespace webrtc