chromium/third_party/webrtc/common_audio/signal_processing/splitting_filter.c

/*
 *  Copyright (c) 2011 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.
 */

/*
 * This file contains the splitting filter functions.
 *
 */

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

// Maximum number of samples in a low/high-band frame.
enum
{ … };

// QMF filter coefficients in Q16.
static const uint16_t WebRtcSpl_kAllPassFilter1[3] = …;
static const uint16_t WebRtcSpl_kAllPassFilter2[3] = …;

///////////////////////////////////////////////////////////////////////////////////////////////
// WebRtcSpl_AllPassQMF(...)
//
// Allpass filter used by the analysis and synthesis parts of the QMF filter.
//
// Input:
//    - in_data             : Input data sequence (Q10)
//    - data_length         : Length of data sequence (>2)
//    - filter_coefficients : Filter coefficients (length 3, Q16)
//
// Input & Output:
//    - filter_state        : Filter state (length 6, Q10).
//
// Output:
//    - out_data            : Output data sequence (Q10), length equal to
//                            `data_length`
//

static void WebRtcSpl_AllPassQMF(int32_t* in_data,
                                 size_t data_length,
                                 int32_t* out_data,
                                 const uint16_t* filter_coefficients,
                                 int32_t* filter_state)
{ … }

void WebRtcSpl_AnalysisQMF(const int16_t* in_data, size_t in_data_length,
                           int16_t* low_band, int16_t* high_band,
                           int32_t* filter_state1, int32_t* filter_state2)
{ … }

void WebRtcSpl_SynthesisQMF(const int16_t* low_band, const int16_t* high_band,
                            size_t band_length, int16_t* out_data,
                            int32_t* filter_state1, int32_t* filter_state2)
{ … }