modules/audio_processing/aec3/residual_echo_estimator.cc

/*
 *  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/residual_echo_estimator.h"

#include <numeric>
#include <vector>

#include "rtc_base/checks.h"
#include "system_wrappers/include/field_trial.h"

namespace webrtc {
namespace {

bool EnableSoftTransparentMode() {
  return !field_trial::IsEnabled("WebRTC-Aec3SoftTransparentModeKillSwitch");
}

}  // namespace

ResidualEchoEstimator::ResidualEchoEstimator(const EchoCanceller3Config& config)
    : config_(config),
      S2_old_(config_.filter.main.length_blocks),
      soft_transparent_mode_(EnableSoftTransparentMode()) {
  Reset();
}

ResidualEchoEstimator::~ResidualEchoEstimator() = default;

void ResidualEchoEstimator::Estimate(
    const AecState& aec_state,
    const RenderBuffer& render_buffer,
    const std::array<float, kFftLengthBy2Plus1>& S2_linear,
    const std::array<float, kFftLengthBy2Plus1>& Y2,
    std::array<float, kFftLengthBy2Plus1>* R2) {
  RTC_DCHECK(R2);

  // Estimate the power of the stationary noise in the render signal.
  RenderNoisePower(render_buffer, &X2_noise_floor_, &X2_noise_floor_counter_);

  // Estimate the residual echo power.
  if (aec_state.UsableLinearEstimate()) {
    RTC_DCHECK(!aec_state.SaturatedEcho());
    LinearEstimate(S2_linear, aec_state.Erle(), R2);
    AddEchoReverb(S2_linear, aec_state.FilterDelayBlocks(),
                  aec_state.ReverbDecay(), R2);
  } else {
    // Estimate the echo generating signal power.
    std::array<float, kFftLengthBy2Plus1> X2;

    // Computes the spectral power over the blocks surrounding the delay.
    size_t window_start = std::max(
        0, aec_state.FilterDelayBlocks() -
               static_cast<int>(config_.echo_model.render_pre_window_size));
    size_t window_end =
        aec_state.FilterDelayBlocks() +
        static_cast<int>(config_.echo_model.render_post_window_size);
    EchoGeneratingPower(render_buffer, window_start, window_end,
                        !aec_state.UseStationaryProperties(), &X2);

    // Subtract the stationary noise power to avoid stationary noise causing
    // excessive echo suppression.
    std::transform(X2.begin(), X2.end(), X2_noise_floor_.begin(), X2.begin(),
                   [&](float a, float b) {
                     return std::max(
                         0.f, a - config_.echo_model.stationary_gate_slope * b);
                   });

    float echo_path_gain = aec_state.TransparentMode() && soft_transparent_mode_
                               ? 0.01f
                               : aec_state.EchoPathGain();
    NonLinearEstimate(echo_path_gain, X2, Y2, R2);

    // If the echo is saturated, estimate the echo power as the maximum echo
    // power with a leakage factor.
    if (aec_state.SaturatedEcho()) {
      R2->fill((*std::max_element(R2->begin(), R2->end())) * 100.f);
    }

    AddEchoReverb(*R2, config_.filter.main.length_blocks,
                  aec_state.ReverbDecay(), R2);
  }

  if (aec_state.UseStationaryProperties()) {
    // Scale the echo according to echo audibility.
    std::array<float, kFftLengthBy2Plus1> residual_scaling;
    aec_state.GetResidualEchoScaling(residual_scaling);
    for (size_t k = 0; k < R2->size(); ++k) {
      (*R2)[k] *= residual_scaling[k];
      if (residual_scaling[k] == 0.f) {
        R2_hold_counter_[k] = 0;
      }
    }
  }
  if (!soft_transparent_mode_) {
    // If the echo is deemed inaudible, set the residual echo to zero.
    if (aec_state.TransparentMode()) {
      R2->fill(0.f);
      R2_old_.fill(0.f);
      R2_hold_counter_.fill(0.f);
    }
  }

  std::copy(R2->begin(), R2->end(), R2_old_.begin());
}

void ResidualEchoEstimator::Reset() {
  X2_noise_floor_counter_.fill(config_.echo_model.noise_floor_hold);
  X2_noise_floor_.fill(config_.echo_model.min_noise_floor_power);
  R2_reverb_.fill(0.f);
  R2_old_.fill(0.f);
  R2_hold_counter_.fill(0.f);
  for (auto& S2_k : S2_old_) {
    S2_k.fill(0.f);
  }
}

void ResidualEchoEstimator::LinearEstimate(
    const std::array<float, kFftLengthBy2Plus1>& S2_linear,
    const std::array<float, kFftLengthBy2Plus1>& erle,
    std::array<float, kFftLengthBy2Plus1>* R2) {
  std::fill(R2_hold_counter_.begin(), R2_hold_counter_.end(), 10.f);
  std::transform(erle.begin(), erle.end(), S2_linear.begin(), R2->begin(),
                 [](float a, float b) {
                   RTC_DCHECK_LT(0.f, a);
                   return b / a;
                 });
}

void ResidualEchoEstimator::NonLinearEstimate(
    float echo_path_gain,
    const std::array<float, kFftLengthBy2Plus1>& X2,
    const std::array<float, kFftLengthBy2Plus1>& Y2,
    std::array<float, kFftLengthBy2Plus1>* R2) {

  // Compute preliminary residual echo.
  std::transform(X2.begin(), X2.end(), R2->begin(), [echo_path_gain](float a) {
    return a * echo_path_gain * echo_path_gain;
  });

  for (size_t k = 0; k < R2->size(); ++k) {
    // Update hold counter.
    R2_hold_counter_[k] = R2_old_[k] < (*R2)[k] ? 0 : R2_hold_counter_[k] + 1;

    // Compute the residual echo by holding a maximum echo powers and an echo
    // fading corresponding to a room with an RT60 value of about 50 ms.
    (*R2)[k] =
        R2_hold_counter_[k] < config_.echo_model.nonlinear_hold
            ? std::max((*R2)[k], R2_old_[k])
            : std::min(
                  (*R2)[k] + R2_old_[k] * config_.echo_model.nonlinear_release,
                  Y2[k]);
  }
}

void ResidualEchoEstimator::AddEchoReverb(
    const std::array<float, kFftLengthBy2Plus1>& S2,
    size_t delay,
    float reverb_decay_factor,
    std::array<float, kFftLengthBy2Plus1>* R2) {
  // Compute the decay factor for how much the echo has decayed before leaving
  // the region covered by the linear model.
  auto integer_power = [](float base, int exp) {
    float result = 1.f;
    for (int k = 0; k < exp; ++k) {
      result *= base;
    }
    return result;
  };
  RTC_DCHECK_LE(delay, S2_old_.size());
  const float reverb_decay_for_delay =
      integer_power(reverb_decay_factor, S2_old_.size() - delay);

  // Update the estimate of the reverberant residual echo power.
  S2_old_index_ = S2_old_index_ > 0 ? S2_old_index_ - 1 : S2_old_.size() - 1;
  const auto& S2_end = S2_old_[S2_old_index_];
  std::transform(
      S2_end.begin(), S2_end.end(), R2_reverb_.begin(), R2_reverb_.begin(),
      [reverb_decay_for_delay, reverb_decay_factor](float a, float b) {
        return (b + a * reverb_decay_for_delay) * reverb_decay_factor;
      });

  // Update the buffer of old echo powers.
  std::copy(S2.begin(), S2.end(), S2_old_[S2_old_index_].begin());

  // Add the power of the echo reverb to the residual echo power.
  std::transform(R2->begin(), R2->end(), R2_reverb_.begin(), R2->begin(),
                 std::plus<float>());
}

void ResidualEchoEstimator::EchoGeneratingPower(
    const RenderBuffer& render_buffer,
    size_t min_delay,
    size_t max_delay,
    bool apply_noise_gating,
    std::array<float, kFftLengthBy2Plus1>* X2) const {
  X2->fill(0.f);
  for (size_t k = min_delay; k <= max_delay; ++k) {
    std::transform(X2->begin(), X2->end(), render_buffer.Spectrum(k).begin(),
                   X2->begin(),
                   [](float a, float b) { return std::max(a, b); });
  }

  if (apply_noise_gating) {
    // Apply soft noise gate.
    std::for_each(X2->begin(), X2->end(), [&](float& a) {
      if (config_.echo_model.noise_gate_power > a) {
        a = std::max(0.f, a - config_.echo_model.noise_gate_slope *
                                  (config_.echo_model.noise_gate_power - a));
      }
    });
  }
}

void ResidualEchoEstimator::RenderNoisePower(
    const RenderBuffer& render_buffer,
    std::array<float, kFftLengthBy2Plus1>* X2_noise_floor,
    std::array<int, kFftLengthBy2Plus1>* X2_noise_floor_counter) const {
  RTC_DCHECK(X2_noise_floor);
  RTC_DCHECK(X2_noise_floor_counter);

  const auto render_power = render_buffer.Spectrum(0);
  RTC_DCHECK_EQ(X2_noise_floor->size(), render_power.size());
  RTC_DCHECK_EQ(X2_noise_floor_counter->size(), render_power.size());

  // Estimate the stationary noise power in a minimum statistics manner.
  for (size_t k = 0; k < render_power.size(); ++k) {
    // Decrease rapidly.
    if (render_power[k] < (*X2_noise_floor)[k]) {
      (*X2_noise_floor)[k] = render_power[k];
      (*X2_noise_floor_counter)[k] = 0;
    } else {
      // Increase in a delayed, leaky manner.
      if ((*X2_noise_floor_counter)[k] >=
          static_cast<int>(config_.echo_model.noise_floor_hold)) {
        (*X2_noise_floor)[k] =
            std::max((*X2_noise_floor)[k] * 1.1f,
                     config_.echo_model.min_noise_floor_power);
      } else {
        ++(*X2_noise_floor_counter)[k];
      }
    }
  }
}

}  // namespace webrtc