text: /*
   *  Copyright (c) 2018 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.
   */
  
  #include "modules/audio_processing/aec3/reverb_frequency_response.h"
  
  #include <stddef.h>
  #include <algorithm>
  #include <array>
  #include <numeric>
  
  #include "api/array_view.h"
  #include "modules/audio_processing/aec3/aec3_common.h"
  #include "rtc_base/checks.h"
  #include "system_wrappers/include/field_trial.h"
  
  namespace webrtc {
  
  namespace {
  
  bool EnableSmoothUpdatesTailFreqResp() {
    return !field_trial::IsEnabled(
        "WebRTC-Aec3SmoothUpdatesTailFreqRespKillSwitch");
  }
  
  // Computes the ratio of the energies between the direct path and the tail. The
  // energy is computed in the power spectrum domain discarding the DC
  // contributions.
  float AverageDecayWithinFilter(
      rtc::ArrayView<const float> freq_resp_direct_path,
      rtc::ArrayView<const float> freq_resp_tail) {
    // Skipping the DC for the ratio computation
    constexpr size_t kSkipBins = 1;
    RTC_CHECK_EQ(freq_resp_direct_path.size(), freq_resp_tail.size());
  
    float direct_path_energy =
        std::accumulate(freq_resp_direct_path.begin() + kSkipBins,
                        freq_resp_direct_path.end(), 0.f);
  
    if (direct_path_energy == 0.f) {
      return 0.f;
    }
  
    float tail_energy = std::accumulate(freq_resp_tail.begin() + kSkipBins,
                                        freq_resp_tail.end(), 0.f);
    return tail_energy / direct_path_energy;
  }
  
  }  // namespace
  
  ReverbFrequencyResponse::ReverbFrequencyResponse()
      : enable_smooth_tail_response_updates_(EnableSmoothUpdatesTailFreqResp()) {
    tail_response_.fill(0.f);
  }
  ReverbFrequencyResponse::~ReverbFrequencyResponse() = default;
  
  void ReverbFrequencyResponse::Update(
      const std::vector<std::array<float, kFftLengthBy2Plus1>>&
          frequency_response,
      int filter_delay_blocks,
      const absl::optional<float>& linear_filter_quality,
      bool stationary_block) {
    if (!enable_smooth_tail_response_updates_) {
      Update(frequency_response, filter_delay_blocks, 0.5f);
      return;
    }
  
    if (stationary_block || !linear_filter_quality) {
      return;
    }
  
    Update(frequency_response, filter_delay_blocks, *linear_filter_quality);
  }
  
  void ReverbFrequencyResponse::Update(
      const std::vector<std::array<float, kFftLengthBy2Plus1>>&
          frequency_response,
      int filter_delay_blocks,
      float linear_filter_quality) {
    rtc::ArrayView<const float> freq_resp_tail(
        frequency_response[frequency_response.size() - 1]);
  
    rtc::ArrayView<const float> freq_resp_direct_path(
        frequency_response[filter_delay_blocks]);
  
    float average_decay =
        AverageDecayWithinFilter(freq_resp_direct_path, freq_resp_tail);
  
    const float smoothing = 0.2f * linear_filter_quality;
    average_decay_ += smoothing * (average_decay - average_decay_);
  
    for (size_t k = 0; k < kFftLengthBy2Plus1; ++k) {
      tail_response_[k] = freq_resp_direct_path[k] * average_decay_;
    }
  
    for (size_t k = 1; k < kFftLengthBy2; ++k) {
      const float avg_neighbour =
          0.5f * (tail_response_[k - 1] + tail_response_[k + 1]);
      tail_response_[k] = std::max(tail_response_[k], avg_neighbour);
    }
  }
  
  }  // namespace webrtc
  