modules/audio_processing/aec3/suppression_gain.cc - src - Git at Google

 /*
  *  Copyright (c) 2017 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/suppression_gain.h"

 #include <math.h>
 #include <stddef.h>
 #include <algorithm>
 #include <numeric>

 #include "modules/audio_processing/aec3/moving_average.h"
 #include "modules/audio_processing/aec3/vector_math.h"
 #include "modules/audio_processing/logging/apm_data_dumper.h"
 #include "rtc_base/atomic_ops.h"
 #include "rtc_base/checks.h"

 namespace webrtc {
 namespace {

 // Adjust the gains according to the presence of known external filters.
 void AdjustForExternalFilters(std::array<float, kFftLengthBy2Plus1>* gain) {
   // Limit the low frequency gains to avoid the impact of the high-pass filter
   // on the lower-frequency gain influencing the overall achieved gain.
   (*gain)[0] = (*gain)[1] = std::min((*gain)[1], (*gain)[2]);

   // Limit the high frequency gains to avoid the impact of the anti-aliasing
   // filter on the upper-frequency gains influencing the overall achieved
   // gain. TODO(peah): Update this when new anti-aliasing filters are
   // implemented.
   constexpr size_t kAntiAliasingImpactLimit = (64 * 2000) / 8000;
   const float min_upper_gain = (*gain)[kAntiAliasingImpactLimit];
   std::for_each(
       gain->begin() + kAntiAliasingImpactLimit, gain->end() - 1,
       [min_upper_gain](float& a) { a = std::min(a, min_upper_gain); });
   (*gain)[kFftLengthBy2] = (*gain)[kFftLengthBy2Minus1];
 }

 // Scales the echo according to assessed audibility at the other end.
 void WeightEchoForAudibility(const EchoCanceller3Config& config,
                              rtc::ArrayView<const float> echo,
                              rtc::ArrayView<float> weighted_echo) {
   RTC_DCHECK_EQ(kFftLengthBy2Plus1, echo.size());
   RTC_DCHECK_EQ(kFftLengthBy2Plus1, weighted_echo.size());

   auto weigh = [](float threshold, float normalizer, size_t begin, size_t end,
                   rtc::ArrayView<const float> echo,
                   rtc::ArrayView<float> weighted_echo) {
     for (size_t k = begin; k < end; ++k) {
       if (echo[k] < threshold) {
         float tmp = (threshold - echo[k]) * normalizer;
         weighted_echo[k] = echo[k] * std::max(0.f, 1.f - tmp * tmp);
       } else {
         weighted_echo[k] = echo[k];
       }
     }
   };

   float threshold = config.echo_audibility.floor_power *
                     config.echo_audibility.audibility_threshold_lf;
   float normalizer = 1.f / (threshold - config.echo_audibility.floor_power);
   weigh(threshold, normalizer, 0, 3, echo, weighted_echo);

   threshold = config.echo_audibility.floor_power *
               config.echo_audibility.audibility_threshold_mf;
   normalizer = 1.f / (threshold - config.echo_audibility.floor_power);
   weigh(threshold, normalizer, 3, 7, echo, weighted_echo);

   threshold = config.echo_audibility.floor_power *
               config.echo_audibility.audibility_threshold_hf;
   normalizer = 1.f / (threshold - config.echo_audibility.floor_power);
   weigh(threshold, normalizer, 7, kFftLengthBy2Plus1, echo, weighted_echo);
 }

 // TODO(peah): Make adaptive to take the actual filter error into account.
 constexpr size_t kUpperAccurateBandPlus1 = 29;

 // Limits the gain in the frequencies for which the adaptive filter has not
 // converged. Currently, these frequencies are not hardcoded to the frequencies
 // which are typically not excited by speech.
 // TODO(peah): Make adaptive to take the actual filter error into account.
 void AdjustNonConvergedFrequencies(
     std::array<float, kFftLengthBy2Plus1>* gain) {
   constexpr float oneByBandsInSum =
       1 / static_cast<float>(kUpperAccurateBandPlus1 - 20);
   const float hf_gain_bound =
       std::accumulate(gain->begin() + 20,
                       gain->begin() + kUpperAccurateBandPlus1, 0.f) *
       oneByBandsInSum;

   std::for_each(gain->begin() + kUpperAccurateBandPlus1, gain->end(),
                 [hf_gain_bound](float& a) { a = std::min(a, hf_gain_bound); });
 }

 }  // namespace

 int SuppressionGain::instance_count_ = 0;

 float SuppressionGain::UpperBandsGain(
     const std::array<float, kFftLengthBy2Plus1>& echo_spectrum,
     const std::array<float, kFftLengthBy2Plus1>& comfort_noise_spectrum,
     const absl::optional<int>& narrow_peak_band,
     bool saturated_echo,
     const std::vector<std::vector<float>>& render,
     const std::array<float, kFftLengthBy2Plus1>& low_band_gain) const {
   RTC_DCHECK_LT(0, render.size());
   if (render.size() == 1) {
     return 1.f;
   }

   if (narrow_peak_band &&
       (*narrow_peak_band > static_cast<int>(kFftLengthBy2Plus1 - 10))) {
     return 0.001f;
   }

   constexpr size_t kLowBandGainLimit = kFftLengthBy2 / 2;
   const float gain_below_8_khz = *std::min_element(
       low_band_gain.begin() + kLowBandGainLimit, low_band_gain.end());

   // Always attenuate the upper bands when there is saturated echo.
   if (saturated_echo) {
     return std::min(0.001f, gain_below_8_khz);
   }

   // Compute the upper and lower band energies.
   const auto sum_of_squares = [](float a, float b) { return a + b * b; };
   const float low_band_energy =
       std::accumulate(render[0].begin(), render[0].end(), 0.f, sum_of_squares);
   float high_band_energy = 0.f;
   for (size_t k = 1; k < render.size(); ++k) {
     const float energy = std::accumulate(render[k].begin(), render[k].end(),
                                          0.f, sum_of_squares);
     high_band_energy = std::max(high_band_energy, energy);
   }

   // If there is more power in the lower frequencies than the upper frequencies,
   // or if the power in upper frequencies is low, do not bound the gain in the
   // upper bands.
   float anti_howling_gain;
   constexpr float kThreshold = kBlockSize * 10.f * 10.f / 4.f;
   if (high_band_energy < std::max(low_band_energy, kThreshold)) {
     anti_howling_gain = 1.f;
   } else {
     // In all other cases, bound the gain for upper frequencies.
     RTC_DCHECK_LE(low_band_energy, high_band_energy);
     RTC_DCHECK_NE(0.f, high_band_energy);
     anti_howling_gain = 0.01f * sqrtf(low_band_energy / high_band_energy);
   }

   // Bound the upper gain during significant echo activity.
   auto low_frequency_energy = [](rtc::ArrayView<const float> spectrum) {
     RTC_DCHECK_LE(16, spectrum.size());
     return std::accumulate(spectrum.begin() + 1, spectrum.begin() + 16, 0.f);
   };
   const float echo_sum = low_frequency_energy(echo_spectrum);
   const float noise_sum = low_frequency_energy(comfort_noise_spectrum);
   const auto& cfg = config_.suppressor.high_bands_suppression;
   float gain_bound = 1.f;
   if (echo_sum > cfg.enr_threshold * noise_sum &&
       !dominant_nearend_detector_.IsNearendState()) {
     gain_bound = cfg.max_gain_during_echo;
   }

   // Choose the gain as the minimum of the lower and upper gains.
   return std::min(std::min(gain_below_8_khz, anti_howling_gain), gain_bound);
 }

 // Computes the gain to reduce the echo to a non audible level.
 void SuppressionGain::GainToNoAudibleEcho(
     const std::array<float, kFftLengthBy2Plus1>& nearend,
     const std::array<float, kFftLengthBy2Plus1>& echo,
     const std::array<float, kFftLengthBy2Plus1>& masker,
     const std::array<float, kFftLengthBy2Plus1>& min_gain,
     const std::array<float, kFftLengthBy2Plus1>& max_gain,
     std::array<float, kFftLengthBy2Plus1>* gain) const {
   const auto& p = dominant_nearend_detector_.IsNearendState() ? nearend_params_
                                                               : normal_params_;
   for (size_t k = 0; k < gain->size(); ++k) {
     float enr = echo[k] / (nearend[k] + 1.f);  // Echo-to-nearend ratio.
     float emr = echo[k] / (masker[k] + 1.f);   // Echo-to-masker (noise) ratio.
     float g = 1.0f;
     if (enr > p.enr_transparent_[k] && emr > p.emr_transparent_[k]) {
       g = (p.enr_suppress_[k] - enr) /
           (p.enr_suppress_[k] - p.enr_transparent_[k]);
       g = std::max(g, p.emr_transparent_[k] / emr);
     }
     (*gain)[k] = std::max(std::min(g, max_gain[k]), min_gain[k]);
   }
 }

 // Compute the minimum gain as the attenuating gain to put the signal just
 // above the zero sample values.
 void SuppressionGain::GetMinGain(
     rtc::ArrayView<const float> suppressor_input,
     rtc::ArrayView<const float> weighted_residual_echo,
     bool low_noise_render,
     bool saturated_echo,
     rtc::ArrayView<float> min_gain) const {
   if (!saturated_echo) {
     const float min_echo_power =
         low_noise_render ? config_.echo_audibility.low_render_limit
                          : config_.echo_audibility.normal_render_limit;

     for (size_t k = 0; k < suppressor_input.size(); ++k) {
       const float denom =
           std::min(suppressor_input[k], weighted_residual_echo[k]);
       min_gain[k] = denom > 0.f ? min_echo_power / denom : 1.f;
       min_gain[k] = std::min(min_gain[k], 1.f);
     }
     for (size_t k = 0; k < 6; ++k) {
       const auto& dec = dominant_nearend_detector_.IsNearendState()
                             ? nearend_params_.max_dec_factor_lf
                             : normal_params_.max_dec_factor_lf;

       // Make sure the gains of the low frequencies do not decrease too
       // quickly after strong nearend.
       if (last_nearend_[k] > last_echo_[k]) {
         min_gain[k] = std::max(min_gain[k], last_gain_[k] * dec);
         min_gain[k] = std::min(min_gain[k], 1.f);
       }
     }
   } else {
     std::fill(min_gain.begin(), min_gain.end(), 0.f);
   }
 }

 // Compute the maximum gain by limiting the gain increase from the previous
 // gain.
 void SuppressionGain::GetMaxGain(rtc::ArrayView<float> max_gain) const {
   const auto& inc = dominant_nearend_detector_.IsNearendState()
                         ? nearend_params_.max_inc_factor
                         : normal_params_.max_inc_factor;
   const auto& floor = config_.suppressor.floor_first_increase;
   for (size_t k = 0; k < max_gain.size(); ++k) {
     max_gain[k] = std::min(std::max(last_gain_[k] * inc, floor), 1.f);
   }
 }

 // TODO(peah): Add further optimizations, in particular for the divisions.
 void SuppressionGain::LowerBandGain(
     bool low_noise_render,
     const AecState& aec_state,
     const std::array<float, kFftLengthBy2Plus1>& suppressor_input,
     const std::array<float, kFftLengthBy2Plus1>& nearend,
     const std::array<float, kFftLengthBy2Plus1>& residual_echo,
     const std::array<float, kFftLengthBy2Plus1>& comfort_noise,
     std::array<float, kFftLengthBy2Plus1>* gain) {
   const bool saturated_echo = aec_state.SaturatedEcho();

   // Weight echo power in terms of audibility. // Precompute 1/weighted echo
   // (note that when the echo is zero, the precomputed value is never used).
   std::array<float, kFftLengthBy2Plus1> weighted_residual_echo;
   WeightEchoForAudibility(config_, residual_echo, weighted_residual_echo);

   std::array<float, kFftLengthBy2Plus1> min_gain;
   GetMinGain(suppressor_input, weighted_residual_echo, low_noise_render,
              saturated_echo, min_gain);

   std::array<float, kFftLengthBy2Plus1> max_gain;
   GetMaxGain(max_gain);

     GainToNoAudibleEcho(nearend, weighted_residual_echo, comfort_noise,
                         min_gain, max_gain, gain);
     AdjustForExternalFilters(gain);

   // Adjust the gain for frequencies which have not yet converged.
   AdjustNonConvergedFrequencies(gain);

   // Store data required for the gain computation of the next block.
   std::copy(nearend.begin(), nearend.end(), last_nearend_.begin());
   std::copy(weighted_residual_echo.begin(), weighted_residual_echo.end(),
             last_echo_.begin());
   std::copy(gain->begin(), gain->end(), last_gain_.begin());
   aec3::VectorMath(optimization_).Sqrt(*gain);

   // Debug outputs for the purpose of development and analysis.
   data_dumper_->DumpRaw("aec3_suppressor_min_gain", min_gain);
   data_dumper_->DumpRaw("aec3_suppressor_max_gain", max_gain);
   data_dumper_->DumpRaw("aec3_dominant_nearend",
                         dominant_nearend_detector_.IsNearendState());
 }

 SuppressionGain::SuppressionGain(const EchoCanceller3Config& config,
                                  Aec3Optimization optimization,
                                  int sample_rate_hz)
     : data_dumper_(
           new ApmDataDumper(rtc::AtomicOps::Increment(&instance_count_))),
       optimization_(optimization),
       config_(config),
       state_change_duration_blocks_(
           static_cast<int>(config_.filter.config_change_duration_blocks)),
       moving_average_(kFftLengthBy2Plus1,
                       config.suppressor.nearend_average_blocks),
       nearend_params_(config_.suppressor.nearend_tuning),
       normal_params_(config_.suppressor.normal_tuning),
       dominant_nearend_detector_(
           config_.suppressor.dominant_nearend_detection) {
   RTC_DCHECK_LT(0, state_change_duration_blocks_);
   one_by_state_change_duration_blocks_ = 1.f / state_change_duration_blocks_;
   last_gain_.fill(1.f);
   last_nearend_.fill(0.f);
   last_echo_.fill(0.f);
 }

 SuppressionGain::~SuppressionGain() = default;

 void SuppressionGain::GetGain(
     const std::array<float, kFftLengthBy2Plus1>& suppressor_input_spectrum,
     const std::array<float, kFftLengthBy2Plus1>& nearend_spectrum,
     const std::array<float, kFftLengthBy2Plus1>& echo_spectrum,
     const std::array<float, kFftLengthBy2Plus1>& residual_echo_spectrum,
     const std::array<float, kFftLengthBy2Plus1>& comfort_noise_spectrum,
     const FftData& linear_aec_fft,
     const FftData& capture_fft,
     const RenderSignalAnalyzer& render_signal_analyzer,
     const AecState& aec_state,
     const std::vector<std::vector<float>>& render,
     float* high_bands_gain,
     std::array<float, kFftLengthBy2Plus1>* low_band_gain) {
   RTC_DCHECK(high_bands_gain);
   RTC_DCHECK(low_band_gain);
   const auto& cfg = config_.suppressor;

   if (cfg.enforce_transparent) {
     low_band_gain->fill(1.f);
     *high_bands_gain = cfg.enforce_empty_higher_bands ? 0.f : 1.f;
     return;
   }

   std::array<float, kFftLengthBy2Plus1> nearend_average;
   moving_average_.Average(nearend_spectrum, nearend_average);

   // Update the state selection.
   dominant_nearend_detector_.Update(nearend_spectrum, residual_echo_spectrum,
                                     comfort_noise_spectrum, initial_state_);

   // Compute gain for the lower band.
   bool low_noise_render = low_render_detector_.Detect(render);
   LowerBandGain(low_noise_render, aec_state, suppressor_input_spectrum,
                 nearend_average, residual_echo_spectrum, comfort_noise_spectrum,
                 low_band_gain);

   // Compute the gain for the upper bands.
   const absl::optional<int> narrow_peak_band =
       render_signal_analyzer.NarrowPeakBand();

   *high_bands_gain =
       UpperBandsGain(echo_spectrum, comfort_noise_spectrum, narrow_peak_band,
                      aec_state.SaturatedEcho(), render, *low_band_gain);
   if (cfg.enforce_empty_higher_bands) {
     *high_bands_gain = 0.f;
   }
 }

 void SuppressionGain::SetInitialState(bool state) {
   initial_state_ = state;
   if (state) {
     initial_state_change_counter_ = state_change_duration_blocks_;
   } else {
     initial_state_change_counter_ = 0;
   }
 }

 // Detects when the render signal can be considered to have low power and
 // consist of stationary noise.
 bool SuppressionGain::LowNoiseRenderDetector::Detect(
     const std::vector<std::vector<float>>& render) {
   float x2_sum = 0.f;
   float x2_max = 0.f;
   for (auto x_k : render[0]) {
     const float x2 = x_k * x_k;
     x2_sum += x2;
     x2_max = std::max(x2_max, x2);
   }

   constexpr float kThreshold = 50.f * 50.f * 64.f;
   const bool low_noise_render =
       average_power_ < kThreshold && x2_max < 3 * average_power_;
   average_power_ = average_power_ * 0.9f + x2_sum * 0.1f;
   return low_noise_render;
 }

 SuppressionGain::DominantNearendDetector::DominantNearendDetector(
     const EchoCanceller3Config::Suppressor::DominantNearendDetection config)
     : enr_threshold_(config.enr_threshold),
       enr_exit_threshold_(config.enr_exit_threshold),
       snr_threshold_(config.snr_threshold),
       hold_duration_(config.hold_duration),
       trigger_threshold_(config.trigger_threshold),
       use_during_initial_phase_(config.use_during_initial_phase) {}

 void SuppressionGain::DominantNearendDetector::Update(
     rtc::ArrayView<const float> nearend_spectrum,
     rtc::ArrayView<const float> residual_echo_spectrum,
     rtc::ArrayView<const float> comfort_noise_spectrum,
     bool initial_state) {
   auto low_frequency_energy = [](rtc::ArrayView<const float> spectrum) {
     RTC_DCHECK_LE(16, spectrum.size());
     return std::accumulate(spectrum.begin() + 1, spectrum.begin() + 16, 0.f);
   };
   const float ne_sum = low_frequency_energy(nearend_spectrum);
   const float echo_sum = low_frequency_energy(residual_echo_spectrum);
   const float noise_sum = low_frequency_energy(comfort_noise_spectrum);

   // Detect strong active nearend if the nearend is sufficiently stronger than
   // the echo and the nearend noise.
   if ((!initial_state || use_during_initial_phase_) &&
       echo_sum < enr_threshold_ * ne_sum &&
       ne_sum > snr_threshold_ * noise_sum) {
     if (++trigger_counter_ >= trigger_threshold_) {
       // After a period of strong active nearend activity, flag nearend mode.
       hold_counter_ = hold_duration_;
       trigger_counter_ = trigger_threshold_;
     }
   } else {
     // Forget previously detected strong active nearend activity.
     trigger_counter_ = std::max(0, trigger_counter_ - 1);
   }

   // Exit nearend-state early at strong echo.
   if (echo_sum > enr_exit_threshold_ * ne_sum &&
       echo_sum > snr_threshold_ * noise_sum) {
     hold_counter_ = 0;
   }

   // Remain in any nearend mode for a certain duration.
   hold_counter_ = std::max(0, hold_counter_ - 1);
   nearend_state_ = hold_counter_ > 0;
 }

 SuppressionGain::GainParameters::GainParameters(
     const EchoCanceller3Config::Suppressor::Tuning& tuning)
     : max_inc_factor(tuning.max_inc_factor),
       max_dec_factor_lf(tuning.max_dec_factor_lf) {
   // Compute per-band masking thresholds.
   constexpr size_t kLastLfBand = 5;
   constexpr size_t kFirstHfBand = 8;
   RTC_DCHECK_LT(kLastLfBand, kFirstHfBand);
   auto& lf = tuning.mask_lf;
   auto& hf = tuning.mask_hf;
   RTC_DCHECK_LT(lf.enr_transparent, lf.enr_suppress);
   RTC_DCHECK_LT(hf.enr_transparent, hf.enr_suppress);
   for (size_t k = 0; k < kFftLengthBy2Plus1; k++) {
     float a;
     if (k <= kLastLfBand) {
       a = 0.f;
     } else if (k < kFirstHfBand) {
       a = (k - kLastLfBand) / static_cast<float>(kFirstHfBand - kLastLfBand);
     } else {
       a = 1.f;
     }
     enr_transparent_[k] = (1 - a) * lf.enr_transparent + a * hf.enr_transparent;
     enr_suppress_[k] = (1 - a) * lf.enr_suppress + a * hf.enr_suppress;
     emr_transparent_[k] = (1 - a) * lf.emr_transparent + a * hf.emr_transparent;
   }
 }

 }  // namespace webrtc
	/*
	* Copyright (c) 2017 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/suppression_gain.h"

	#include <math.h>
	#include <stddef.h>
	#include <algorithm>
	#include <numeric>

	#include "modules/audio_processing/aec3/moving_average.h"
	#include "modules/audio_processing/aec3/vector_math.h"
	#include "modules/audio_processing/logging/apm_data_dumper.h"
	#include "rtc_base/atomic_ops.h"
	#include "rtc_base/checks.h"

	namespace webrtc {
	namespace {

	// Adjust the gains according to the presence of known external filters.
	void AdjustForExternalFilters(std::array<float, kFftLengthBy2Plus1>* gain) {
	// Limit the low frequency gains to avoid the impact of the high-pass filter
	// on the lower-frequency gain influencing the overall achieved gain.
	(gain)[0] = (gain)[1] = std::min((gain)[1], (gain)[2]);

	// Limit the high frequency gains to avoid the impact of the anti-aliasing
	// filter on the upper-frequency gains influencing the overall achieved
	// gain. TODO(peah): Update this when new anti-aliasing filters are
	// implemented.
	constexpr size_t kAntiAliasingImpactLimit = (64 * 2000) / 8000;
	const float min_upper_gain = (*gain)[kAntiAliasingImpactLimit];
	std::for_each(
	gain->begin() + kAntiAliasingImpactLimit, gain->end() - 1,
	[min_upper_gain](float& a) { a = std::min(a, min_upper_gain); });
	(gain)[kFftLengthBy2] = (gain)[kFftLengthBy2Minus1];
	}

	// Scales the echo according to assessed audibility at the other end.
	void WeightEchoForAudibility(const EchoCanceller3Config& config,
	rtc::ArrayView<const float> echo,
	rtc::ArrayView<float> weighted_echo) {
	RTC_DCHECK_EQ(kFftLengthBy2Plus1, echo.size());
	RTC_DCHECK_EQ(kFftLengthBy2Plus1, weighted_echo.size());

	auto weigh = [](float threshold, float normalizer, size_t begin, size_t end,
	rtc::ArrayView<const float> echo,
	rtc::ArrayView<float> weighted_echo) {
	for (size_t k = begin; k < end; ++k) {
	if (echo[k] < threshold) {
	float tmp = (threshold - echo[k]) * normalizer;
	weighted_echo[k] = echo[k] * std::max(0.f, 1.f - tmp * tmp);
	} else {
	weighted_echo[k] = echo[k];
	}
	}
	};

	float threshold = config.echo_audibility.floor_power *
	config.echo_audibility.audibility_threshold_lf;
	float normalizer = 1.f / (threshold - config.echo_audibility.floor_power);
	weigh(threshold, normalizer, 0, 3, echo, weighted_echo);

	threshold = config.echo_audibility.floor_power *
	config.echo_audibility.audibility_threshold_mf;
	normalizer = 1.f / (threshold - config.echo_audibility.floor_power);
	weigh(threshold, normalizer, 3, 7, echo, weighted_echo);

	threshold = config.echo_audibility.floor_power *
	config.echo_audibility.audibility_threshold_hf;
	normalizer = 1.f / (threshold - config.echo_audibility.floor_power);
	weigh(threshold, normalizer, 7, kFftLengthBy2Plus1, echo, weighted_echo);
	}

	// TODO(peah): Make adaptive to take the actual filter error into account.
	constexpr size_t kUpperAccurateBandPlus1 = 29;

	// Limits the gain in the frequencies for which the adaptive filter has not
	// converged. Currently, these frequencies are not hardcoded to the frequencies
	// which are typically not excited by speech.
	// TODO(peah): Make adaptive to take the actual filter error into account.
	void AdjustNonConvergedFrequencies(
	std::array<float, kFftLengthBy2Plus1>* gain) {
	constexpr float oneByBandsInSum =
	1 / static_cast<float>(kUpperAccurateBandPlus1 - 20);
	const float hf_gain_bound =
	std::accumulate(gain->begin() + 20,
	gain->begin() + kUpperAccurateBandPlus1, 0.f) *
	oneByBandsInSum;

	std::for_each(gain->begin() + kUpperAccurateBandPlus1, gain->end(),
	[hf_gain_bound](float& a) { a = std::min(a, hf_gain_bound); });
	}

	} // namespace

	int SuppressionGain::instance_count_ = 0;

	float SuppressionGain::UpperBandsGain(
	const std::array<float, kFftLengthBy2Plus1>& echo_spectrum,
	const std::array<float, kFftLengthBy2Plus1>& comfort_noise_spectrum,
	const absl::optional<int>& narrow_peak_band,
	bool saturated_echo,
	const std::vector<std::vector<float>>& render,
	const std::array<float, kFftLengthBy2Plus1>& low_band_gain) const {
	RTC_DCHECK_LT(0, render.size());
	if (render.size() == 1) {
	return 1.f;
	}

	if (narrow_peak_band &&
	(*narrow_peak_band > static_cast<int>(kFftLengthBy2Plus1 - 10))) {
	return 0.001f;
	}

	constexpr size_t kLowBandGainLimit = kFftLengthBy2 / 2;
	const float gain_below_8_khz = *std::min_element(
	low_band_gain.begin() + kLowBandGainLimit, low_band_gain.end());

	// Always attenuate the upper bands when there is saturated echo.
	if (saturated_echo) {
	return std::min(0.001f, gain_below_8_khz);
	}

	// Compute the upper and lower band energies.
	const auto sum_of_squares = [](float a, float b) { return a + b * b; };
	const float low_band_energy =
	std::accumulate(render[0].begin(), render[0].end(), 0.f, sum_of_squares);
	float high_band_energy = 0.f;
	for (size_t k = 1; k < render.size(); ++k) {
	const float energy = std::accumulate(render[k].begin(), render[k].end(),
	0.f, sum_of_squares);
	high_band_energy = std::max(high_band_energy, energy);
	}

	// If there is more power in the lower frequencies than the upper frequencies,
	// or if the power in upper frequencies is low, do not bound the gain in the
	// upper bands.
	float anti_howling_gain;
	constexpr float kThreshold = kBlockSize * 10.f * 10.f / 4.f;
	if (high_band_energy < std::max(low_band_energy, kThreshold)) {
	anti_howling_gain = 1.f;
	} else {
	// In all other cases, bound the gain for upper frequencies.
	RTC_DCHECK_LE(low_band_energy, high_band_energy);
	RTC_DCHECK_NE(0.f, high_band_energy);
	anti_howling_gain = 0.01f * sqrtf(low_band_energy / high_band_energy);
	}

	// Bound the upper gain during significant echo activity.
	auto low_frequency_energy = [](rtc::ArrayView<const float> spectrum) {
	RTC_DCHECK_LE(16, spectrum.size());
	return std::accumulate(spectrum.begin() + 1, spectrum.begin() + 16, 0.f);
	};
	const float echo_sum = low_frequency_energy(echo_spectrum);
	const float noise_sum = low_frequency_energy(comfort_noise_spectrum);
	const auto& cfg = config_.suppressor.high_bands_suppression;
	float gain_bound = 1.f;
	if (echo_sum > cfg.enr_threshold * noise_sum &&
	!dominant_nearend_detector_.IsNearendState()) {
	gain_bound = cfg.max_gain_during_echo;
	}

	// Choose the gain as the minimum of the lower and upper gains.
	return std::min(std::min(gain_below_8_khz, anti_howling_gain), gain_bound);
	}

	// Computes the gain to reduce the echo to a non audible level.
	void SuppressionGain::GainToNoAudibleEcho(
	const std::array<float, kFftLengthBy2Plus1>& nearend,
	const std::array<float, kFftLengthBy2Plus1>& echo,
	const std::array<float, kFftLengthBy2Plus1>& masker,
	const std::array<float, kFftLengthBy2Plus1>& min_gain,
	const std::array<float, kFftLengthBy2Plus1>& max_gain,
	std::array<float, kFftLengthBy2Plus1>* gain) const {
	const auto& p = dominant_nearend_detector_.IsNearendState() ? nearend_params_
	: normal_params_;
	for (size_t k = 0; k < gain->size(); ++k) {
	float enr = echo[k] / (nearend[k] + 1.f); // Echo-to-nearend ratio.
	float emr = echo[k] / (masker[k] + 1.f); // Echo-to-masker (noise) ratio.
	float g = 1.0f;
	if (enr > p.enr_transparent_[k] && emr > p.emr_transparent_[k]) {
	g = (p.enr_suppress_[k] - enr) /
	(p.enr_suppress_[k] - p.enr_transparent_[k]);
	g = std::max(g, p.emr_transparent_[k] / emr);
	}
	(*gain)[k] = std::max(std::min(g, max_gain[k]), min_gain[k]);
	}
	}

	// Compute the minimum gain as the attenuating gain to put the signal just
	// above the zero sample values.
	void SuppressionGain::GetMinGain(
	rtc::ArrayView<const float> suppressor_input,
	rtc::ArrayView<const float> weighted_residual_echo,
	bool low_noise_render,
	bool saturated_echo,
	rtc::ArrayView<float> min_gain) const {
	if (!saturated_echo) {
	const float min_echo_power =
	low_noise_render ? config_.echo_audibility.low_render_limit
	: config_.echo_audibility.normal_render_limit;

	for (size_t k = 0; k < suppressor_input.size(); ++k) {
	const float denom =
	std::min(suppressor_input[k], weighted_residual_echo[k]);
	min_gain[k] = denom > 0.f ? min_echo_power / denom : 1.f;
	min_gain[k] = std::min(min_gain[k], 1.f);
	}
	for (size_t k = 0; k < 6; ++k) {
	const auto& dec = dominant_nearend_detector_.IsNearendState()
	? nearend_params_.max_dec_factor_lf
	: normal_params_.max_dec_factor_lf;

	// Make sure the gains of the low frequencies do not decrease too
	// quickly after strong nearend.
	if (last_nearend_[k] > last_echo_[k]) {
	min_gain[k] = std::max(min_gain[k], last_gain_[k] * dec);
	min_gain[k] = std::min(min_gain[k], 1.f);
	}
	}
	} else {
	std::fill(min_gain.begin(), min_gain.end(), 0.f);
	}
	}

	// Compute the maximum gain by limiting the gain increase from the previous
	// gain.
	void SuppressionGain::GetMaxGain(rtc::ArrayView<float> max_gain) const {
	const auto& inc = dominant_nearend_detector_.IsNearendState()
	? nearend_params_.max_inc_factor
	: normal_params_.max_inc_factor;
	const auto& floor = config_.suppressor.floor_first_increase;
	for (size_t k = 0; k < max_gain.size(); ++k) {
	max_gain[k] = std::min(std::max(last_gain_[k] * inc, floor), 1.f);
	}
	}

	// TODO(peah): Add further optimizations, in particular for the divisions.
	void SuppressionGain::LowerBandGain(
	bool low_noise_render,
	const AecState& aec_state,
	const std::array<float, kFftLengthBy2Plus1>& suppressor_input,
	const std::array<float, kFftLengthBy2Plus1>& nearend,
	const std::array<float, kFftLengthBy2Plus1>& residual_echo,
	const std::array<float, kFftLengthBy2Plus1>& comfort_noise,
	std::array<float, kFftLengthBy2Plus1>* gain) {
	const bool saturated_echo = aec_state.SaturatedEcho();

	// Weight echo power in terms of audibility. // Precompute 1/weighted echo
	// (note that when the echo is zero, the precomputed value is never used).
	std::array<float, kFftLengthBy2Plus1> weighted_residual_echo;
	WeightEchoForAudibility(config_, residual_echo, weighted_residual_echo);

	std::array<float, kFftLengthBy2Plus1> min_gain;
	GetMinGain(suppressor_input, weighted_residual_echo, low_noise_render,
	saturated_echo, min_gain);

	std::array<float, kFftLengthBy2Plus1> max_gain;
	GetMaxGain(max_gain);

	GainToNoAudibleEcho(nearend, weighted_residual_echo, comfort_noise,
	min_gain, max_gain, gain);
	AdjustForExternalFilters(gain);

	// Adjust the gain for frequencies which have not yet converged.
	AdjustNonConvergedFrequencies(gain);

	// Store data required for the gain computation of the next block.
	std::copy(nearend.begin(), nearend.end(), last_nearend_.begin());
	std::copy(weighted_residual_echo.begin(), weighted_residual_echo.end(),
	last_echo_.begin());
	std::copy(gain->begin(), gain->end(), last_gain_.begin());
	aec3::VectorMath(optimization_).Sqrt(*gain);

	// Debug outputs for the purpose of development and analysis.
	data_dumper_->DumpRaw("aec3_suppressor_min_gain", min_gain);
	data_dumper_->DumpRaw("aec3_suppressor_max_gain", max_gain);
	data_dumper_->DumpRaw("aec3_dominant_nearend",
	dominant_nearend_detector_.IsNearendState());
	}

	SuppressionGain::SuppressionGain(const EchoCanceller3Config& config,
	Aec3Optimization optimization,
	int sample_rate_hz)
	: data_dumper_(
	new ApmDataDumper(rtc::AtomicOps::Increment(&instance_count_))),
	optimization_(optimization),
	config_(config),
	state_change_duration_blocks_(
	static_cast<int>(config_.filter.config_change_duration_blocks)),
	moving_average_(kFftLengthBy2Plus1,
	config.suppressor.nearend_average_blocks),
	nearend_params_(config_.suppressor.nearend_tuning),
	normal_params_(config_.suppressor.normal_tuning),
	dominant_nearend_detector_(
	config_.suppressor.dominant_nearend_detection) {
	RTC_DCHECK_LT(0, state_change_duration_blocks_);
	one_by_state_change_duration_blocks_ = 1.f / state_change_duration_blocks_;
	last_gain_.fill(1.f);
	last_nearend_.fill(0.f);
	last_echo_.fill(0.f);
	}

	SuppressionGain::~SuppressionGain() = default;

	void SuppressionGain::GetGain(
	const std::array<float, kFftLengthBy2Plus1>& suppressor_input_spectrum,
	const std::array<float, kFftLengthBy2Plus1>& nearend_spectrum,
	const std::array<float, kFftLengthBy2Plus1>& echo_spectrum,
	const std::array<float, kFftLengthBy2Plus1>& residual_echo_spectrum,
	const std::array<float, kFftLengthBy2Plus1>& comfort_noise_spectrum,
	const FftData& linear_aec_fft,
	const FftData& capture_fft,
	const RenderSignalAnalyzer& render_signal_analyzer,
	const AecState& aec_state,
	const std::vector<std::vector<float>>& render,
	float* high_bands_gain,
	std::array<float, kFftLengthBy2Plus1>* low_band_gain) {
	RTC_DCHECK(high_bands_gain);
	RTC_DCHECK(low_band_gain);
	const auto& cfg = config_.suppressor;

	if (cfg.enforce_transparent) {
	low_band_gain->fill(1.f);
	*high_bands_gain = cfg.enforce_empty_higher_bands ? 0.f : 1.f;
	return;
	}

	std::array<float, kFftLengthBy2Plus1> nearend_average;
	moving_average_.Average(nearend_spectrum, nearend_average);

	// Update the state selection.
	dominant_nearend_detector_.Update(nearend_spectrum, residual_echo_spectrum,
	comfort_noise_spectrum, initial_state_);

	// Compute gain for the lower band.
	bool low_noise_render = low_render_detector_.Detect(render);
	LowerBandGain(low_noise_render, aec_state, suppressor_input_spectrum,
	nearend_average, residual_echo_spectrum, comfort_noise_spectrum,
	low_band_gain);

	// Compute the gain for the upper bands.
	const absl::optional<int> narrow_peak_band =
	render_signal_analyzer.NarrowPeakBand();

	*high_bands_gain =
	UpperBandsGain(echo_spectrum, comfort_noise_spectrum, narrow_peak_band,
	aec_state.SaturatedEcho(), render, *low_band_gain);
	if (cfg.enforce_empty_higher_bands) {
	*high_bands_gain = 0.f;
	}
	}

	void SuppressionGain::SetInitialState(bool state) {
	initial_state_ = state;
	if (state) {
	initial_state_change_counter_ = state_change_duration_blocks_;
	} else {
	initial_state_change_counter_ = 0;
	}
	}

	// Detects when the render signal can be considered to have low power and
	// consist of stationary noise.
	bool SuppressionGain::LowNoiseRenderDetector::Detect(
	const std::vector<std::vector<float>>& render) {
	float x2_sum = 0.f;
	float x2_max = 0.f;
	for (auto x_k : render[0]) {
	const float x2 = x_k * x_k;
	x2_sum += x2;
	x2_max = std::max(x2_max, x2);
	}

	constexpr float kThreshold = 50.f * 50.f * 64.f;
	const bool low_noise_render =
	average_power_ < kThreshold && x2_max < 3 * average_power_;
	average_power_ = average_power_ * 0.9f + x2_sum * 0.1f;
	return low_noise_render;
	}

	SuppressionGain::DominantNearendDetector::DominantNearendDetector(
	const EchoCanceller3Config::Suppressor::DominantNearendDetection config)
	: enr_threshold_(config.enr_threshold),
	enr_exit_threshold_(config.enr_exit_threshold),
	snr_threshold_(config.snr_threshold),
	hold_duration_(config.hold_duration),
	trigger_threshold_(config.trigger_threshold),
	use_during_initial_phase_(config.use_during_initial_phase) {}

	void SuppressionGain::DominantNearendDetector::Update(
	rtc::ArrayView<const float> nearend_spectrum,
	rtc::ArrayView<const float> residual_echo_spectrum,
	rtc::ArrayView<const float> comfort_noise_spectrum,
	bool initial_state) {
	auto low_frequency_energy = [](rtc::ArrayView<const float> spectrum) {
	RTC_DCHECK_LE(16, spectrum.size());
	return std::accumulate(spectrum.begin() + 1, spectrum.begin() + 16, 0.f);
	};
	const float ne_sum = low_frequency_energy(nearend_spectrum);
	const float echo_sum = low_frequency_energy(residual_echo_spectrum);
	const float noise_sum = low_frequency_energy(comfort_noise_spectrum);

	// Detect strong active nearend if the nearend is sufficiently stronger than
	// the echo and the nearend noise.
	if ((!initial_state \|\| use_during_initial_phase_) &&
	echo_sum < enr_threshold_ * ne_sum &&
	ne_sum > snr_threshold_ * noise_sum) {
	if (++trigger_counter_ >= trigger_threshold_) {
	// After a period of strong active nearend activity, flag nearend mode.
	hold_counter_ = hold_duration_;
	trigger_counter_ = trigger_threshold_;
	}
	} else {
	// Forget previously detected strong active nearend activity.
	trigger_counter_ = std::max(0, trigger_counter_ - 1);
	}

	// Exit nearend-state early at strong echo.
	if (echo_sum > enr_exit_threshold_ * ne_sum &&
	echo_sum > snr_threshold_ * noise_sum) {
	hold_counter_ = 0;
	}

	// Remain in any nearend mode for a certain duration.
	hold_counter_ = std::max(0, hold_counter_ - 1);
	nearend_state_ = hold_counter_ > 0;
	}

	SuppressionGain::GainParameters::GainParameters(
	const EchoCanceller3Config::Suppressor::Tuning& tuning)
	: max_inc_factor(tuning.max_inc_factor),
	max_dec_factor_lf(tuning.max_dec_factor_lf) {
	// Compute per-band masking thresholds.
	constexpr size_t kLastLfBand = 5;
	constexpr size_t kFirstHfBand = 8;
	RTC_DCHECK_LT(kLastLfBand, kFirstHfBand);
	auto& lf = tuning.mask_lf;
	auto& hf = tuning.mask_hf;
	RTC_DCHECK_LT(lf.enr_transparent, lf.enr_suppress);
	RTC_DCHECK_LT(hf.enr_transparent, hf.enr_suppress);
	for (size_t k = 0; k < kFftLengthBy2Plus1; k++) {
	float a;
	if (k <= kLastLfBand) {
	a = 0.f;
	} else if (k < kFirstHfBand) {
	a = (k - kLastLfBand) / static_cast<float>(kFirstHfBand - kLastLfBand);
	} else {
	a = 1.f;
	}
	enr_transparent_[k] = (1 - a) * lf.enr_transparent + a * hf.enr_transparent;
	enr_suppress_[k] = (1 - a) * lf.enr_suppress + a * hf.enr_suppress;
	emr_transparent_[k] = (1 - a) * lf.emr_transparent + a * hf.emr_transparent;
	}
	}

	} // namespace webrtc