Line data    Source code

       1             : /*
       2             :  *  Copyright (c) 2016 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             : #include "webrtc/modules/audio_processing/level_controller/gain_selector.h"
      12             : 
      13             : #include <math.h>
      14             : #include <algorithm>
      15             : 
      16             : #include "webrtc/base/checks.h"
      17             : #include "webrtc/modules/audio_processing/include/audio_processing.h"
      18             : #include "webrtc/modules/audio_processing/level_controller/level_controller_constants.h"
      19             : 
      20             : namespace webrtc {
      21             : 
      22           0 : GainSelector::GainSelector() {
      23           0 :   Initialize(AudioProcessing::kSampleRate48kHz);
      24           0 : }
      25             : 
      26           0 : void GainSelector::Initialize(int sample_rate_hz) {
      27           0 :   gain_ = 1.f;
      28           0 :   frame_length_ = rtc::CheckedDivExact(sample_rate_hz, 100);
      29           0 :   highly_nonstationary_signal_hold_counter_ = 0;
      30           0 : }
      31             : 
      32             : // Chooses the gain to apply by the level controller such that
      33             : // 1) The level of the stationary noise does not exceed
      34             : //    a predefined threshold.
      35             : // 2) The gain does not exceed the gain that has been found
      36             : //    to saturate the signal.
      37             : // 3) The peak level achieves the target peak level.
      38             : // 4) The gain is not below 1.
      39             : // 4) The gain is 1 if the signal has been classified as stationary
      40             : //    for a long time.
      41             : // 5) The gain is not above the maximum gain.
      42           0 : float GainSelector::GetNewGain(float peak_level,
      43             :                                float noise_energy,
      44             :                                float saturating_gain,
      45             :                                bool gain_jumpstart,
      46             :                                SignalClassifier::SignalType signal_type) {
      47           0 :   RTC_DCHECK_LT(0.f, peak_level);
      48             : 
      49           0 :   if (signal_type == SignalClassifier::SignalType::kHighlyNonStationary ||
      50             :       gain_jumpstart) {
      51           0 :     highly_nonstationary_signal_hold_counter_ = 100;
      52             :   } else {
      53           0 :     highly_nonstationary_signal_hold_counter_ =
      54           0 :         std::max(0, highly_nonstationary_signal_hold_counter_ - 1);
      55             :   }
      56             : 
      57             :   float desired_gain;
      58           0 :   if (highly_nonstationary_signal_hold_counter_ > 0) {
      59             :     // Compute a desired gain that ensures that the peak level is amplified to
      60             :     // the target level.
      61           0 :     desired_gain = kTargetLcPeakLevel / peak_level;
      62             : 
      63             :     // Limit the desired gain so that it does not amplify the noise too much.
      64           0 :     float max_noise_energy = kMaxLcNoisePower * frame_length_;
      65           0 :     if (noise_energy * desired_gain * desired_gain > max_noise_energy) {
      66           0 :       RTC_DCHECK_LE(0.f, noise_energy);
      67           0 :       desired_gain = sqrtf(max_noise_energy / noise_energy);
      68             :     }
      69             :   } else {
      70             :     // If the signal has been stationary for a long while, apply a gain of 1 to
      71             :     // avoid amplifying pure noise.
      72           0 :     desired_gain = 1.0f;
      73             :   }
      74             : 
      75             :   // Smootly update the gain towards the desired gain.
      76           0 :   gain_ += 0.2f * (desired_gain - gain_);
      77             : 
      78             :   // Limit the gain to not exceed the maximum and the saturating gains, and to
      79             :   // ensure that the lowest possible gain is 1.
      80           0 :   gain_ = std::min(gain_, saturating_gain);
      81           0 :   gain_ = std::min(gain_, kMaxLcGain);
      82           0 :   gain_ = std::max(gain_, 1.f);
      83             : 
      84           0 :   return gain_;
      85             : }
      86             : 
      87             : }  // namespace webrtc