modules/audio_processing/aec3/coherence_gain.cc - mirrors/cros/chromiumos/third_party/webrtc-apm - Git at Google

 /*
  *  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/coherence_gain.h"

 #include <math.h>

 #include <algorithm>

 #include "rtc_base/checks.h"

 namespace webrtc {

 namespace {

 // Matlab code to produce table:
 // overDriveCurve = [sqrt(linspace(0,1,65))' + 1];
 // fprintf(1, '\t%.4f, %.4f, %.4f, %.4f, %.4f, %.4f,\n', overDriveCurve);
 const float kOverDriveCurve[kFftLengthBy2Plus1] = {
     1.0000f, 1.1250f, 1.1768f, 1.2165f, 1.2500f, 1.2795f, 1.3062f, 1.3307f,
     1.3536f, 1.3750f, 1.3953f, 1.4146f, 1.4330f, 1.4507f, 1.4677f, 1.4841f,
     1.5000f, 1.5154f, 1.5303f, 1.5449f, 1.5590f, 1.5728f, 1.5863f, 1.5995f,
     1.6124f, 1.6250f, 1.6374f, 1.6495f, 1.6614f, 1.6731f, 1.6847f, 1.6960f,
     1.7071f, 1.7181f, 1.7289f, 1.7395f, 1.7500f, 1.7603f, 1.7706f, 1.7806f,
     1.7906f, 1.8004f, 1.8101f, 1.8197f, 1.8292f, 1.8385f, 1.8478f, 1.8570f,
     1.8660f, 1.8750f, 1.8839f, 1.8927f, 1.9014f, 1.9100f, 1.9186f, 1.9270f,
     1.9354f, 1.9437f, 1.9520f, 1.9601f, 1.9682f, 1.9763f, 1.9843f, 1.9922f,
     2.0000f};

 // Matlab code to produce table:
 // weightCurve = [0 ; 0.3 * sqrt(linspace(0,1,64))' + 0.1];
 // fprintf(1, '\t%.4f, %.4f, %.4f, %.4f, %.4f, %.4f,\n', weightCurve);
 const float kWeightCurve[kFftLengthBy2Plus1] = {
     0.0000f, 0.1000f, 0.1378f, 0.1535f, 0.1655f, 0.1756f, 0.1845f, 0.1926f,
     0.2000f, 0.2069f, 0.2134f, 0.2195f, 0.2254f, 0.2309f, 0.2363f, 0.2414f,
     0.2464f, 0.2512f, 0.2558f, 0.2604f, 0.2648f, 0.2690f, 0.2732f, 0.2773f,
     0.2813f, 0.2852f, 0.2890f, 0.2927f, 0.2964f, 0.3000f, 0.3035f, 0.3070f,
     0.3104f, 0.3138f, 0.3171f, 0.3204f, 0.3236f, 0.3268f, 0.3299f, 0.3330f,
     0.3360f, 0.3390f, 0.3420f, 0.3449f, 0.3478f, 0.3507f, 0.3535f, 0.3563f,
     0.3591f, 0.3619f, 0.3646f, 0.3673f, 0.3699f, 0.3726f, 0.3752f, 0.3777f,
     0.3803f, 0.3828f, 0.3854f, 0.3878f, 0.3903f, 0.3928f, 0.3952f, 0.3976f,
     0.4000f};

 int CmpFloat(const void* a, const void* b) {
   const float* da = static_cast<const float*>(a);
   const float* db = static_cast<const float*>(b);
   return (*da > *db) - (*da < *db);
 }

 }  // namespace

 CoherenceGain::CoherenceGain(int sample_rate_hz, size_t num_bands_to_compute)
     : num_bands_to_compute_(num_bands_to_compute),
       sample_rate_scaler_(sample_rate_hz >= 16000 ? 2 : 1) {
   spectra_.Cye.Clear();
   spectra_.Cxy.Clear();
   spectra_.Pe.fill(0.f);
   // Initialize to 1 in order to prevent numerical instability in the first
   // block.
   spectra_.Py.fill(1.f);
   spectra_.Px.fill(1.f);
 }

 CoherenceGain::~CoherenceGain() = default;

 void CoherenceGain::ComputeGain(const FftData& E,
                                 const FftData& X,
                                 const FftData& Y,
                                 rtc::ArrayView<float> gain) {
   std::array<float, kFftLengthBy2Plus1> coherence_ye;
   std::array<float, kFftLengthBy2Plus1> coherence_xy;

   UpdateCoherenceSpectra(E, X, Y);
   ComputeCoherence(coherence_ye, coherence_xy);
   FormSuppressionGain(coherence_ye, coherence_xy, gain);
 }

 // Updates the following smoothed Power Spectral Densities (PSD):
 //  - sd  : near-end
 //  - se  : residual echo
 //  - sx  : far-end
 //  - sde : cross-PSD of near-end and residual echo
 //  - sxd : cross-PSD of near-end and far-end
 //
 void CoherenceGain::UpdateCoherenceSpectra(const FftData& E,
                                            const FftData& X,
                                            const FftData& Y) {
   const float s = sample_rate_scaler_ == 1 ? 0.9f : 0.92f;
   const float one_minus_s = 1.f - s;
   auto& c = spectra_;

   for (size_t i = 0; i < c.Py.size(); i++) {
     c.Py[i] =
         s * c.Py[i] + one_minus_s * (Y.re[i] * Y.re[i] + Y.im[i] * Y.im[i]);
     c.Pe[i] =
         s * c.Pe[i] + one_minus_s * (E.re[i] * E.re[i] + E.im[i] * E.im[i]);
     // We threshold here to protect against the ill-effects of a zero farend.
     // The threshold is not arbitrarily chosen, but balances protection and
     // adverse interaction with the algorithm's tuning.

     // Threshold to protect against the ill-effects of a zero far-end.
     c.Px[i] =
         s * c.Px[i] +
         one_minus_s * std::max(X.re[i] * X.re[i] + X.im[i] * X.im[i], 15.f);

     c.Cye.re[i] =
         s * c.Cye.re[i] + one_minus_s * (Y.re[i] * E.re[i] + Y.im[i] * E.im[i]);
     c.Cye.im[i] =
         s * c.Cye.im[i] + one_minus_s * (Y.re[i] * E.im[i] - Y.im[i] * E.re[i]);

     c.Cxy.re[i] =
         s * c.Cxy.re[i] + one_minus_s * (Y.re[i] * X.re[i] + Y.im[i] * X.im[i]);
     c.Cxy.im[i] =
         s * c.Cxy.im[i] + one_minus_s * (Y.re[i] * X.im[i] - Y.im[i] * X.re[i]);
   }
 }

 void CoherenceGain::FormSuppressionGain(
     rtc::ArrayView<const float> coherence_ye,
     rtc::ArrayView<const float> coherence_xy,
     rtc::ArrayView<float> gain) {
   RTC_DCHECK_EQ(kFftLengthBy2Plus1, coherence_ye.size());
   RTC_DCHECK_EQ(kFftLengthBy2Plus1, coherence_xy.size());
   RTC_DCHECK_EQ(kFftLengthBy2Plus1, gain.size());
   constexpr int kPrefBandSize = 24;
   auto& gs = gain_state_;
   std::array<float, kPrefBandSize> h_nl_pref;
   float h_nl_fb = 0;
   float h_nl_fb_low = 0;
   const int pref_band_size = kPrefBandSize / sample_rate_scaler_;
   const int min_pref_band = 4 / sample_rate_scaler_;

   float h_nl_de_avg = 0.f;
   float h_nl_xd_avg = 0.f;
   for (int i = min_pref_band; i < pref_band_size + min_pref_band; ++i) {
     h_nl_xd_avg += coherence_xy[i];
     h_nl_de_avg += coherence_ye[i];
   }
   h_nl_xd_avg /= pref_band_size;
   h_nl_xd_avg = 1 - h_nl_xd_avg;
   h_nl_de_avg /= pref_band_size;

   if (h_nl_xd_avg < 0.75f && h_nl_xd_avg < gs.h_nl_xd_avg_min) {
     gs.h_nl_xd_avg_min = h_nl_xd_avg;
   }

   if (h_nl_de_avg > 0.98f && h_nl_xd_avg > 0.9f) {
     gs.near_state = true;
   } else if (h_nl_de_avg < 0.95f || h_nl_xd_avg < 0.8f) {
     gs.near_state = false;
   }

   std::array<float, kFftLengthBy2Plus1> h_nl;
   if (gs.h_nl_xd_avg_min == 1) {
     gs.overdrive = 15.f;

     if (gs.near_state) {
       std::copy(coherence_ye.begin(), coherence_ye.end(), h_nl.begin());
       h_nl_fb = h_nl_de_avg;
       h_nl_fb_low = h_nl_de_avg;
     } else {
       for (size_t i = 0; i < h_nl.size(); ++i) {
         h_nl[i] = 1 - coherence_xy[i];
         h_nl[i] = std::max(h_nl[i], 0.f);
       }
       h_nl_fb = h_nl_xd_avg;
       h_nl_fb_low = h_nl_xd_avg;
     }
   } else {
     if (gs.near_state) {
       std::copy(coherence_ye.begin(), coherence_ye.end(), h_nl.begin());
       h_nl_fb = h_nl_de_avg;
       h_nl_fb_low = h_nl_de_avg;
     } else {
       for (size_t i = 0; i < h_nl.size(); ++i) {
         h_nl[i] = std::min(coherence_ye[i], 1 - coherence_xy[i]);
         h_nl[i] = std::max(h_nl[i], 0.f);
       }

       // Select an order statistic from the preferred bands.
       // TODO(peah): Using quicksort now, but a selection algorithm may be
       // preferred.
       std::copy(h_nl.begin() + min_pref_band,
                 h_nl.begin() + min_pref_band + pref_band_size,
                 h_nl_pref.begin());
       std::qsort(h_nl_pref.data(), pref_band_size, sizeof(float), CmpFloat);

       constexpr float kPrefBandQuant = 0.75f;
       h_nl_fb = h_nl_pref[static_cast<int>(
           floor(kPrefBandQuant * (pref_band_size - 1)))];
       constexpr float kPrefBandQuantLow = 0.5f;
       h_nl_fb_low = h_nl_pref[static_cast<int>(
           floor(kPrefBandQuantLow * (pref_band_size - 1)))];
     }
   }

   // Track the local filter minimum to determine suppression overdrive.
   if (h_nl_fb_low < 0.6f && h_nl_fb_low < gs.h_nl_fb_local_min) {
     gs.h_nl_fb_local_min = h_nl_fb_low;
     gs.h_nl_fb_min = h_nl_fb_low;
     gs.h_nl_new_min = 1;
     gs.h_nl_min_ctr = 0;
   }
   gs.h_nl_fb_local_min =
       std::min(gs.h_nl_fb_local_min + 0.0008f / sample_rate_scaler_, 1.f);
   gs.h_nl_xd_avg_min =
       std::min(gs.h_nl_xd_avg_min + 0.0006f / sample_rate_scaler_, 1.f);

   if (gs.h_nl_new_min == 1) {
     ++gs.h_nl_min_ctr;
   }
   if (gs.h_nl_min_ctr == 2) {
     gs.h_nl_new_min = 0;
     gs.h_nl_min_ctr = 0;
     constexpr float epsilon = 1e-10f;
     gs.overdrive = std::max(
         -18.4f / static_cast<float>(log(gs.h_nl_fb_min + epsilon) + epsilon),
         15.f);
   }

   // Smooth the overdrive.
   if (gs.overdrive < gs.overdrive_scaling) {
     gs.overdrive_scaling = 0.99f * gs.overdrive_scaling + 0.01f * gs.overdrive;
   } else {
     gs.overdrive_scaling = 0.9f * gs.overdrive_scaling + 0.1f * gs.overdrive;
   }

   // Apply the overdrive.
   RTC_DCHECK_LE(num_bands_to_compute_, gain.size());
   for (size_t i = 0; i < num_bands_to_compute_; ++i) {
     if (h_nl[i] > h_nl_fb) {
       h_nl[i] = kWeightCurve[i] * h_nl_fb + (1 - kWeightCurve[i]) * h_nl[i];
     }
     gain[i] = powf(h_nl[i], gs.overdrive_scaling * kOverDriveCurve[i]);
   }
 }

 void CoherenceGain::ComputeCoherence(rtc::ArrayView<float> coherence_ye,
                                      rtc::ArrayView<float> coherence_xy) const {
   const auto& c = spectra_;
   constexpr float epsilon = 1e-10f;
   for (size_t i = 0; i < coherence_ye.size(); ++i) {
     coherence_ye[i] = (c.Cye.re[i] * c.Cye.re[i] + c.Cye.im[i] * c.Cye.im[i]) /
                       (c.Py[i] * c.Pe[i] + epsilon);
     coherence_xy[i] = (c.Cxy.re[i] * c.Cxy.re[i] + c.Cxy.im[i] * c.Cxy.im[i]) /
                       (c.Px[i] * c.Py[i] + epsilon);
   }
 }

 }  // namespace webrtc
	/*
	* 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/coherence_gain.h"

	#include <math.h>

	#include <algorithm>

	#include "rtc_base/checks.h"

	namespace webrtc {

	namespace {

	// Matlab code to produce table:
	// overDriveCurve = [sqrt(linspace(0,1,65))' + 1];
	// fprintf(1, '\t%.4f, %.4f, %.4f, %.4f, %.4f, %.4f,\n', overDriveCurve);
	const float kOverDriveCurve[kFftLengthBy2Plus1] = {
	1.0000f, 1.1250f, 1.1768f, 1.2165f, 1.2500f, 1.2795f, 1.3062f, 1.3307f,
	1.3536f, 1.3750f, 1.3953f, 1.4146f, 1.4330f, 1.4507f, 1.4677f, 1.4841f,
	1.5000f, 1.5154f, 1.5303f, 1.5449f, 1.5590f, 1.5728f, 1.5863f, 1.5995f,
	1.6124f, 1.6250f, 1.6374f, 1.6495f, 1.6614f, 1.6731f, 1.6847f, 1.6960f,
	1.7071f, 1.7181f, 1.7289f, 1.7395f, 1.7500f, 1.7603f, 1.7706f, 1.7806f,
	1.7906f, 1.8004f, 1.8101f, 1.8197f, 1.8292f, 1.8385f, 1.8478f, 1.8570f,
	1.8660f, 1.8750f, 1.8839f, 1.8927f, 1.9014f, 1.9100f, 1.9186f, 1.9270f,
	1.9354f, 1.9437f, 1.9520f, 1.9601f, 1.9682f, 1.9763f, 1.9843f, 1.9922f,
	2.0000f};

	// Matlab code to produce table:
	// weightCurve = [0 ; 0.3 * sqrt(linspace(0,1,64))' + 0.1];
	// fprintf(1, '\t%.4f, %.4f, %.4f, %.4f, %.4f, %.4f,\n', weightCurve);
	const float kWeightCurve[kFftLengthBy2Plus1] = {
	0.0000f, 0.1000f, 0.1378f, 0.1535f, 0.1655f, 0.1756f, 0.1845f, 0.1926f,
	0.2000f, 0.2069f, 0.2134f, 0.2195f, 0.2254f, 0.2309f, 0.2363f, 0.2414f,
	0.2464f, 0.2512f, 0.2558f, 0.2604f, 0.2648f, 0.2690f, 0.2732f, 0.2773f,
	0.2813f, 0.2852f, 0.2890f, 0.2927f, 0.2964f, 0.3000f, 0.3035f, 0.3070f,
	0.3104f, 0.3138f, 0.3171f, 0.3204f, 0.3236f, 0.3268f, 0.3299f, 0.3330f,
	0.3360f, 0.3390f, 0.3420f, 0.3449f, 0.3478f, 0.3507f, 0.3535f, 0.3563f,
	0.3591f, 0.3619f, 0.3646f, 0.3673f, 0.3699f, 0.3726f, 0.3752f, 0.3777f,
	0.3803f, 0.3828f, 0.3854f, 0.3878f, 0.3903f, 0.3928f, 0.3952f, 0.3976f,
	0.4000f};

	int CmpFloat(const void* a, const void* b) {
	const float* da = static_cast<const float*>(a);
	const float* db = static_cast<const float*>(b);
	return (da > db) - (da < db);
	}

	} // namespace

	CoherenceGain::CoherenceGain(int sample_rate_hz, size_t num_bands_to_compute)
	: num_bands_to_compute_(num_bands_to_compute),
	sample_rate_scaler_(sample_rate_hz >= 16000 ? 2 : 1) {
	spectra_.Cye.Clear();
	spectra_.Cxy.Clear();
	spectra_.Pe.fill(0.f);
	// Initialize to 1 in order to prevent numerical instability in the first
	// block.
	spectra_.Py.fill(1.f);
	spectra_.Px.fill(1.f);
	}

	CoherenceGain::~CoherenceGain() = default;

	void CoherenceGain::ComputeGain(const FftData& E,
	const FftData& X,
	const FftData& Y,
	rtc::ArrayView<float> gain) {
	std::array<float, kFftLengthBy2Plus1> coherence_ye;
	std::array<float, kFftLengthBy2Plus1> coherence_xy;

	UpdateCoherenceSpectra(E, X, Y);
	ComputeCoherence(coherence_ye, coherence_xy);
	FormSuppressionGain(coherence_ye, coherence_xy, gain);
	}

	// Updates the following smoothed Power Spectral Densities (PSD):
	// - sd : near-end
	// - se : residual echo
	// - sx : far-end
	// - sde : cross-PSD of near-end and residual echo
	// - sxd : cross-PSD of near-end and far-end
	//
	void CoherenceGain::UpdateCoherenceSpectra(const FftData& E,
	const FftData& X,
	const FftData& Y) {
	const float s = sample_rate_scaler_ == 1 ? 0.9f : 0.92f;
	const float one_minus_s = 1.f - s;
	auto& c = spectra_;

	for (size_t i = 0; i < c.Py.size(); i++) {
	c.Py[i] =
	s * c.Py[i] + one_minus_s * (Y.re[i] * Y.re[i] + Y.im[i] * Y.im[i]);
	c.Pe[i] =
	s * c.Pe[i] + one_minus_s * (E.re[i] * E.re[i] + E.im[i] * E.im[i]);
	// We threshold here to protect against the ill-effects of a zero farend.
	// The threshold is not arbitrarily chosen, but balances protection and
	// adverse interaction with the algorithm's tuning.

	// Threshold to protect against the ill-effects of a zero far-end.
	c.Px[i] =
	s * c.Px[i] +
	one_minus_s * std::max(X.re[i] * X.re[i] + X.im[i] * X.im[i], 15.f);

	c.Cye.re[i] =
	s * c.Cye.re[i] + one_minus_s * (Y.re[i] * E.re[i] + Y.im[i] * E.im[i]);
	c.Cye.im[i] =
	s * c.Cye.im[i] + one_minus_s * (Y.re[i] * E.im[i] - Y.im[i] * E.re[i]);

	c.Cxy.re[i] =
	s * c.Cxy.re[i] + one_minus_s * (Y.re[i] * X.re[i] + Y.im[i] * X.im[i]);
	c.Cxy.im[i] =
	s * c.Cxy.im[i] + one_minus_s * (Y.re[i] * X.im[i] - Y.im[i] * X.re[i]);
	}
	}

	void CoherenceGain::FormSuppressionGain(
	rtc::ArrayView<const float> coherence_ye,
	rtc::ArrayView<const float> coherence_xy,
	rtc::ArrayView<float> gain) {
	RTC_DCHECK_EQ(kFftLengthBy2Plus1, coherence_ye.size());
	RTC_DCHECK_EQ(kFftLengthBy2Plus1, coherence_xy.size());
	RTC_DCHECK_EQ(kFftLengthBy2Plus1, gain.size());
	constexpr int kPrefBandSize = 24;
	auto& gs = gain_state_;
	std::array<float, kPrefBandSize> h_nl_pref;
	float h_nl_fb = 0;
	float h_nl_fb_low = 0;
	const int pref_band_size = kPrefBandSize / sample_rate_scaler_;
	const int min_pref_band = 4 / sample_rate_scaler_;

	float h_nl_de_avg = 0.f;
	float h_nl_xd_avg = 0.f;
	for (int i = min_pref_band; i < pref_band_size + min_pref_band; ++i) {
	h_nl_xd_avg += coherence_xy[i];
	h_nl_de_avg += coherence_ye[i];
	}
	h_nl_xd_avg /= pref_band_size;
	h_nl_xd_avg = 1 - h_nl_xd_avg;
	h_nl_de_avg /= pref_band_size;

	if (h_nl_xd_avg < 0.75f && h_nl_xd_avg < gs.h_nl_xd_avg_min) {
	gs.h_nl_xd_avg_min = h_nl_xd_avg;
	}

	if (h_nl_de_avg > 0.98f && h_nl_xd_avg > 0.9f) {
	gs.near_state = true;
	} else if (h_nl_de_avg < 0.95f \|\| h_nl_xd_avg < 0.8f) {
	gs.near_state = false;
	}

	std::array<float, kFftLengthBy2Plus1> h_nl;
	if (gs.h_nl_xd_avg_min == 1) {
	gs.overdrive = 15.f;

	if (gs.near_state) {
	std::copy(coherence_ye.begin(), coherence_ye.end(), h_nl.begin());
	h_nl_fb = h_nl_de_avg;
	h_nl_fb_low = h_nl_de_avg;
	} else {
	for (size_t i = 0; i < h_nl.size(); ++i) {
	h_nl[i] = 1 - coherence_xy[i];
	h_nl[i] = std::max(h_nl[i], 0.f);
	}
	h_nl_fb = h_nl_xd_avg;
	h_nl_fb_low = h_nl_xd_avg;
	}
	} else {
	if (gs.near_state) {
	std::copy(coherence_ye.begin(), coherence_ye.end(), h_nl.begin());
	h_nl_fb = h_nl_de_avg;
	h_nl_fb_low = h_nl_de_avg;
	} else {
	for (size_t i = 0; i < h_nl.size(); ++i) {
	h_nl[i] = std::min(coherence_ye[i], 1 - coherence_xy[i]);
	h_nl[i] = std::max(h_nl[i], 0.f);
	}

	// Select an order statistic from the preferred bands.
	// TODO(peah): Using quicksort now, but a selection algorithm may be
	// preferred.
	std::copy(h_nl.begin() + min_pref_band,
	h_nl.begin() + min_pref_band + pref_band_size,
	h_nl_pref.begin());
	std::qsort(h_nl_pref.data(), pref_band_size, sizeof(float), CmpFloat);

	constexpr float kPrefBandQuant = 0.75f;
	h_nl_fb = h_nl_pref[static_cast<int>(
	floor(kPrefBandQuant * (pref_band_size - 1)))];
	constexpr float kPrefBandQuantLow = 0.5f;
	h_nl_fb_low = h_nl_pref[static_cast<int>(
	floor(kPrefBandQuantLow * (pref_band_size - 1)))];
	}
	}

	// Track the local filter minimum to determine suppression overdrive.
	if (h_nl_fb_low < 0.6f && h_nl_fb_low < gs.h_nl_fb_local_min) {
	gs.h_nl_fb_local_min = h_nl_fb_low;
	gs.h_nl_fb_min = h_nl_fb_low;
	gs.h_nl_new_min = 1;
	gs.h_nl_min_ctr = 0;
	}
	gs.h_nl_fb_local_min =
	std::min(gs.h_nl_fb_local_min + 0.0008f / sample_rate_scaler_, 1.f);
	gs.h_nl_xd_avg_min =
	std::min(gs.h_nl_xd_avg_min + 0.0006f / sample_rate_scaler_, 1.f);

	if (gs.h_nl_new_min == 1) {
	++gs.h_nl_min_ctr;
	}
	if (gs.h_nl_min_ctr == 2) {
	gs.h_nl_new_min = 0;
	gs.h_nl_min_ctr = 0;
	constexpr float epsilon = 1e-10f;
	gs.overdrive = std::max(
	-18.4f / static_cast<float>(log(gs.h_nl_fb_min + epsilon) + epsilon),
	15.f);
	}

	// Smooth the overdrive.
	if (gs.overdrive < gs.overdrive_scaling) {
	gs.overdrive_scaling = 0.99f * gs.overdrive_scaling + 0.01f * gs.overdrive;
	} else {
	gs.overdrive_scaling = 0.9f * gs.overdrive_scaling + 0.1f * gs.overdrive;
	}

	// Apply the overdrive.
	RTC_DCHECK_LE(num_bands_to_compute_, gain.size());
	for (size_t i = 0; i < num_bands_to_compute_; ++i) {
	if (h_nl[i] > h_nl_fb) {
	h_nl[i] = kWeightCurve[i] * h_nl_fb + (1 - kWeightCurve[i]) * h_nl[i];
	}
	gain[i] = powf(h_nl[i], gs.overdrive_scaling * kOverDriveCurve[i]);
	}
	}

	void CoherenceGain::ComputeCoherence(rtc::ArrayView<float> coherence_ye,
	rtc::ArrayView<float> coherence_xy) const {
	const auto& c = spectra_;
	constexpr float epsilon = 1e-10f;
	for (size_t i = 0; i < coherence_ye.size(); ++i) {
	coherence_ye[i] = (c.Cye.re[i] * c.Cye.re[i] + c.Cye.im[i] * c.Cye.im[i]) /
	(c.Py[i] * c.Pe[i] + epsilon);
	coherence_xy[i] = (c.Cxy.re[i] * c.Cxy.re[i] + c.Cxy.im[i] * c.Cxy.im[i]) /
	(c.Px[i] * c.Py[i] + epsilon);
	}
	}

	} // namespace webrtc