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 WEBRTC_MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_
12 #define WEBRTC_MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_
13 
14 #include <assert.h>
15 #include <string.h>  // memset, size_t
16 
17 #include "webrtc/base/constructormagic.h"
18 #include "webrtc/modules/audio_coding/neteq/audio_multi_vector.h"
19 #include "webrtc/typedefs.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 
TimeStretch(int sample_rate_hz,size_t num_channels,const BackgroundNoise & background_noise)38   TimeStretch(int sample_rate_hz, size_t num_channels,
39               const BackgroundNoise& background_noise)
40       : sample_rate_hz_(sample_rate_hz),
41         fs_mult_(sample_rate_hz / 8000),
42         num_channels_(num_channels),
43         master_channel_(0),  // First channel is master.
44         background_noise_(background_noise),
45         max_input_value_(0) {
46     assert(sample_rate_hz_ == 8000 ||
47            sample_rate_hz_ == 16000 ||
48            sample_rate_hz_ == 32000 ||
49            sample_rate_hz_ == 48000);
50     assert(num_channels_ > 0);
51     assert(master_channel_ < num_channels_);
52     memset(auto_correlation_, 0, sizeof(auto_correlation_));
53   }
54 
~TimeStretch()55   virtual ~TimeStretch() {}
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 
92   const int sample_rate_hz_;
93   const int fs_mult_;  // Sample rate multiplier = sample_rate_hz_ / 8000.
94   const size_t num_channels_;
95   const size_t master_channel_;
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, int32_t vec2_energy,
110                        size_t peak_index, int scaling) const;
111 
112   RTC_DISALLOW_COPY_AND_ASSIGN(TimeStretch);
113 };
114 
115 }  // namespace webrtc
116 #endif  // WEBRTC_MODULES_AUDIO_CODING_NETEQ_TIME_STRETCH_H_
117