modules/audio_processing/splitting_filter.h

/*
 *  Copyright (c) 2014 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.
 */

#ifndef MODULES_AUDIO_PROCESSING_SPLITTING_FILTER_H_
#define MODULES_AUDIO_PROCESSING_SPLITTING_FILTER_H_

#include <cstring>
#include <memory>
#include <vector>

#include "common_audio/channel_buffer.h"
#include "modules/audio_processing/three_band_filter_bank.h"

namespace webrtc {

struct TwoBandsStates {
  TwoBandsStates() {
    memset(analysis_state1, 0, sizeof(analysis_state1));
    memset(analysis_state2, 0, sizeof(analysis_state2));
    memset(synthesis_state1, 0, sizeof(synthesis_state1));
    memset(synthesis_state2, 0, sizeof(synthesis_state2));
  }

  static const int kStateSize = 6;
  int analysis_state1[kStateSize];
  int analysis_state2[kStateSize];
  int synthesis_state1[kStateSize];
  int synthesis_state2[kStateSize];
};

// Splitting filter which is able to split into and merge from 2 or 3 frequency
// bands. The number of channels needs to be provided at construction time.
//
// For each block, Analysis() is called to split into bands and then Synthesis()
// to merge these bands again. The input and output signals are contained in
// ChannelBuffers and for the different bands an array of ChannelBuffers is
// used.
class SplittingFilter {
 public:
  SplittingFilter(size_t num_channels, size_t num_bands, size_t num_frames);
  ~SplittingFilter();

  void Analysis(const ChannelBuffer<float>* data, ChannelBuffer<float>* bands);
  void Synthesis(const ChannelBuffer<float>* bands, ChannelBuffer<float>* data);

 private:
  // Two-band analysis and synthesis work for 640 samples or less.
  void TwoBandsAnalysis(const ChannelBuffer<float>* data,
                        ChannelBuffer<float>* bands);
  void TwoBandsSynthesis(const ChannelBuffer<float>* bands,
                         ChannelBuffer<float>* data);
  void ThreeBandsAnalysis(const ChannelBuffer<float>* data,
                          ChannelBuffer<float>* bands);
  void ThreeBandsSynthesis(const ChannelBuffer<float>* bands,
                           ChannelBuffer<float>* data);
  void InitBuffers();

  const size_t num_bands_;
  std::vector<TwoBandsStates> two_bands_states_;
  std::vector<ThreeBandFilterBank> three_band_filter_banks_;
};

}  // namespace webrtc

#endif  // MODULES_AUDIO_PROCESSING_SPLITTING_FILTER_H_