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time_stretch.h (4184B)

      1 /*
      2 *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
      3 *
      4 *  Use of this source code is governed by a BSD-style license
      5 *  that can be found in the LICENSE file in the root of the source
      6 *  tree. An additional intellectual property rights grant can be found
      7 *  in the file PATENTS.  All contributing project authors may
      8 *  be found in the AUTHORS file in the root of the source tree.
      9 */
     10 
     11 #ifndef MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_
     12 #define MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_
     13 
     14 #include <string.h>  // memset, size_t
     15 
     16 #include <cstdint>
     17 
     18 #include "modules/audio_coding/neteq/audio_multi_vector.h"
     19 #include "rtc_base/checks.h"
     20 
     21 namespace webrtc {
     22 
     23 // Forward declarations.
     24 class BackgroundNoise;
     25 
     26 // This is the base class for Accelerate and PreemptiveExpand. This class
     27 // cannot be instantiated, but must be used through either of the derived
     28 // classes.
     29 class TimeStretch {
     30 public:
     31  enum ReturnCodes {
     32    kSuccess = 0,
     33    kSuccessLowEnergy = 1,
     34    kNoStretch = 2,
     35    kError = -1
     36  };
     37 
     38  TimeStretch(int sample_rate_hz,
     39              size_t num_channels,
     40              const BackgroundNoise& background_noise)
     41      : sample_rate_hz_(sample_rate_hz),
     42        fs_mult_(sample_rate_hz / 8000),
     43        num_channels_(num_channels),
     44        background_noise_(background_noise),
     45        max_input_value_(0) {
     46    RTC_DCHECK(sample_rate_hz_ == 8000 || sample_rate_hz_ == 16000 ||
     47               sample_rate_hz_ == 32000 || sample_rate_hz_ == 48000);
     48    RTC_DCHECK_GT(num_channels_, 0);
     49    memset(auto_correlation_, 0, sizeof(auto_correlation_));
     50  }
     51 
     52  virtual ~TimeStretch() {}
     53 
     54  TimeStretch(const TimeStretch&) = delete;
     55  TimeStretch& operator=(const TimeStretch&) = delete;
     56 
     57  // This method performs the processing common to both Accelerate and
     58  // PreemptiveExpand.
     59  ReturnCodes Process(const int16_t* input,
     60                      size_t input_len,
     61                      bool fast_mode,
     62                      AudioMultiVector* output,
     63                      size_t* length_change_samples);
     64 
     65 protected:
     66  // Sets the parameters `best_correlation` and `peak_index` to suitable
     67  // values when the signal contains no active speech. This method must be
     68  // implemented by the sub-classes.
     69  virtual void SetParametersForPassiveSpeech(size_t input_length,
     70                                             int16_t* best_correlation,
     71                                             size_t* peak_index) const = 0;
     72 
     73  // Checks the criteria for performing the time-stretching operation and,
     74  // if possible, performs the time-stretching. This method must be implemented
     75  // by the sub-classes.
     76  virtual ReturnCodes CheckCriteriaAndStretch(
     77      const int16_t* input,
     78      size_t input_length,
     79      size_t peak_index,
     80      int16_t best_correlation,
     81      bool active_speech,
     82      bool fast_mode,
     83      AudioMultiVector* output) const = 0;
     84 
     85  static const size_t kCorrelationLen = 50;
     86  static const size_t kLogCorrelationLen = 6;  // >= log2(kCorrelationLen).
     87  static const size_t kMinLag = 10;
     88  static const size_t kMaxLag = 60;
     89  static const size_t kDownsampledLen = kCorrelationLen + kMaxLag;
     90  static const int kCorrelationThreshold = 14746;  // 0.9 in Q14.
     91  static constexpr size_t kRefChannel = 0;  // First channel is reference.
     92 
     93  const int sample_rate_hz_;
     94  const int fs_mult_;  // Sample rate multiplier = sample_rate_hz_ / 8000.
     95  const size_t num_channels_;
     96  const BackgroundNoise& background_noise_;
     97  int16_t max_input_value_;
     98  int16_t downsampled_input_[kDownsampledLen];
     99  // Adding 1 to the size of `auto_correlation_` because of how it is used
    100  // by the peak-detection algorithm.
    101  int16_t auto_correlation_[kCorrelationLen + 1];
    102 
    103 private:
    104  // Calculates the auto-correlation of `downsampled_input_` and writes the
    105  // result to `auto_correlation_`.
    106  void AutoCorrelation();
    107 
    108  // Performs a simple voice-activity detection based on the input parameters.
    109  bool SpeechDetection(int32_t vec1_energy,
    110                       int32_t vec2_energy,
    111                       size_t peak_index,
    112                       int scaling) const;
    113 };
    114 
    115 }  // namespace webrtc
    116 #endif  // MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_