chromium/third_party/webrtc/common_audio/vad/vad_filterbank.c

/*
 *  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 "common_audio/vad/vad_filterbank.h"

#include "rtc_base/checks.h"
#include "common_audio/signal_processing/include/signal_processing_library.h"

// Constants used in LogOfEnergy().
static const int16_t kLogConst = …;  // 160*log10(2) in Q9.
static const int16_t kLogEnergyIntPart = …;  // 14 in Q10

// Coefficients used by HighPassFilter, Q14.
static const int16_t kHpZeroCoefs[3] = …;
static const int16_t kHpPoleCoefs[3] = …;

// Allpass filter coefficients, upper and lower, in Q15.
// Upper: 0.64, Lower: 0.17
static const int16_t kAllPassCoefsQ15[2] = …;

// Adjustment for division with two in SplitFilter.
static const int16_t kOffsetVector[6] = …;

// High pass filtering, with a cut-off frequency at 80 Hz, if the `data_in` is
// sampled at 500 Hz.
//
// - data_in      [i]   : Input audio data sampled at 500 Hz.
// - data_length  [i]   : Length of input and output data.
// - filter_state [i/o] : State of the filter.
// - data_out     [o]   : Output audio data in the frequency interval
//                        80 - 250 Hz.
static void HighPassFilter(const int16_t* data_in, size_t data_length,
                           int16_t* filter_state, int16_t* data_out) { … }

// All pass filtering of `data_in`, used before splitting the signal into two
// frequency bands (low pass vs high pass).
// Note that `data_in` and `data_out` can NOT correspond to the same address.
//
// - data_in            [i]   : Input audio signal given in Q0.
// - data_length        [i]   : Length of input and output data.
// - filter_coefficient [i]   : Given in Q15.
// - filter_state       [i/o] : State of the filter given in Q(-1).
// - data_out           [o]   : Output audio signal given in Q(-1).
static void AllPassFilter(const int16_t* data_in, size_t data_length,
                          int16_t filter_coefficient, int16_t* filter_state,
                          int16_t* data_out) { … }

// Splits `data_in` into `hp_data_out` and `lp_data_out` corresponding to
// an upper (high pass) part and a lower (low pass) part respectively.
//
// - data_in      [i]   : Input audio data to be split into two frequency bands.
// - data_length  [i]   : Length of `data_in`.
// - upper_state  [i/o] : State of the upper filter, given in Q(-1).
// - lower_state  [i/o] : State of the lower filter, given in Q(-1).
// - hp_data_out  [o]   : Output audio data of the upper half of the spectrum.
//                        The length is `data_length` / 2.
// - lp_data_out  [o]   : Output audio data of the lower half of the spectrum.
//                        The length is `data_length` / 2.
static void SplitFilter(const int16_t* data_in, size_t data_length,
                        int16_t* upper_state, int16_t* lower_state,
                        int16_t* hp_data_out, int16_t* lp_data_out) { … }

// Calculates the energy of `data_in` in dB, and also updates an overall
// `total_energy` if necessary.
//
// - data_in      [i]   : Input audio data for energy calculation.
// - data_length  [i]   : Length of input data.
// - offset       [i]   : Offset value added to `log_energy`.
// - total_energy [i/o] : An external energy updated with the energy of
//                        `data_in`.
//                        NOTE: `total_energy` is only updated if
//                        `total_energy` <= `kMinEnergy`.
// - log_energy   [o]   : 10 * log10("energy of `data_in`") given in Q4.
static void LogOfEnergy(const int16_t* data_in, size_t data_length,
                        int16_t offset, int16_t* total_energy,
                        int16_t* log_energy) { … }

int16_t WebRtcVad_CalculateFeatures(VadInstT* self, const int16_t* data_in,
                                    size_t data_length, int16_t* features) { … }