Finalization of the first version of EchoCanceller 3

webrtc/modules/audio_processing/aec3/suppression_gain.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 "webrtc/modules/audio_processing/aec3/suppression_gain.h"
+
+#include <math.h>
+#include <algorithm>
+#include <functional>
+
+namespace webrtc {
+namespace {
+
+const int kNumIterations = 2;
+
+}  // namespace
+
+SuppressionGain::SuppressionGain() {
+  previous_gain_squared_.fill(1.f);
+  previous_masker_.fill(0.f);
+}
+
+void SuppressionGain::GetGain(
+    const std::array<float, kFftLengthBy2Plus1>& nearend_power,
+    const std::array<float, kFftLengthBy2Plus1>& residual_echo_power,
+    const std::array<float, kFftLengthBy2Plus1>& comfort_noise_power,
+    float strong_nearend_margin,
+    std::array<float, kFftLengthBy2Plus1>* gain) {
+  constexpr float kEchoMaskingMargin = 1.f / 10.f;
+  constexpr float kBandMaskingFactor = 1.f / 3.f;
+  constexpr float kTimeMaskingFactor = 1.f / 10.f;
+
+  std::array<float, kFftLengthBy2 - 1> masker;
+  std::array<float, kFftLengthBy2 - 1> same_band_masker;
+  std::array<float, kFftLengthBy2 - 1> one_by_residual_echo_power;
+  std::array<bool, kFftLengthBy2 - 1> strong_nearend;
+  std::array<float, kFftLengthBy2Plus1> neighboring_bands_masker;
+
+  // Precompute 1/residual_echo_power.
+  std::transform(residual_echo_power.begin() + 1, residual_echo_power.end() - 1,
+                 one_by_residual_echo_power.begin(),
+                 [](float a) { return a > 0.f ? 1.f / a : -1.f; });
+
+  // Precompute indicators for bands with strong nearend.
+  std::transform(
+      residual_echo_power.begin() + 1, residual_echo_power.end() - 1,
+      nearend_power.begin() + 1, strong_nearend.begin(),
+      [&](float a, float b) { return a <= strong_nearend_margin * b; });
+
+  //  Precompute masker for the same band.
+  std::transform(comfort_noise_power.begin() + 1, comfort_noise_power.end() - 1,
+                 previous_masker_.begin(), same_band_masker.begin(),
+                 [&](float a, float b) { return a + kTimeMaskingFactor * b; });
+
+  for (int k = 0; k < kNumIterations; ++k) {
+    if (k == 0) {
+      // Add masker from the same band.
+      std::copy(same_band_masker.begin(), same_band_masker.end(),
+                masker.begin());
+    } else {
+      // Add masker for neightboring bands.
+      std::transform(nearend_power.begin(), nearend_power.end(), gain->begin(),
+                     neighboring_bands_masker.begin(),
+                     std::multiplies<float>());
+      std::transform(neighboring_bands_masker.begin(),
+                     neighboring_bands_masker.end(),
+                     comfort_noise_power.begin(),
+                     neighboring_bands_masker.begin(), std::plus<float>());
+      std::transform(
+          neighboring_bands_masker.begin(), neighboring_bands_masker.end() - 2,
+          neighboring_bands_masker.begin() + 2, masker.begin(),
+          [&](float a, float b) { return kBandMaskingFactor * (a + b); });
+
+      // Add masker from the same band.
+      std::transform(same_band_masker.begin(), same_band_masker.end(),
+                     masker.begin(), masker.begin(), std::plus<float>());
+    }
+
+    // Compute new gain as:
+    // G2(t,f) = (comfort_noise_power(t,f) + G2(t-1)*nearend_power(t-1)) *
+    //           kTimeMaskingFactor
+    //           * kEchoMaskingMargin / residual_echo_power(t,f).
+    // or
+    // G2(t,f) = ((comfort_noise_power(t,f) + G2(t-1) *
+    //             nearend_power(t-1)) * kTimeMaskingFactor +
+    //            (comfort_noise_power(t, f-1) + comfort_noise_power(t, f+1) +
+    //             (G2(t,f-1)*nearend_power(t, f-1) +
+    //              G2(t,f+1)*nearend_power(t, f+1)) *
+    //             kTimeMaskingFactor) * kBandMaskingFactor)
+    //           * kEchoMaskingMargin / residual_echo_power(t,f).
+    std::transform(
+        masker.begin(), masker.end(), one_by_residual_echo_power.begin(),
+        gain->begin() + 1, [&](float a, float b) {
+          return b >= 0 ? std::min(kEchoMaskingMargin * a * b, 1.f) : 1.f;
+        });
+
+    // Limit gain for bands with strong nearend.
+    std::transform(gain->begin() + 1, gain->end() - 1, strong_nearend.begin(),
+                   gain->begin() + 1,
+                   [](float a, bool b) { return b ? 1.f : a; });
+
+    // Limit the allowed gain update over time.
+    std::transform(
+        gain->begin() + 1, gain->end() - 1, previous_gain_squared_.begin(),
+        gain->begin() + 1, [](float a, float b) {
+          return b < 0.0001f ? std::min(a, 0.0001f) : std::min(a, b * 2.f);
+        });
+
+    (*gain)[0] = (*gain)[1];
+    (*gain)[kFftLengthBy2] = (*gain)[kFftLengthBy2 - 1];
+  }
+
+  std::copy(gain->begin() + 1, gain->end() - 1, previous_gain_squared_.begin());
+
+  std::transform(gain->begin() + 1, gain->end() - 1, nearend_power.begin() + 1,
+                 previous_masker_.begin(), std::multiplies<float>());
+  std::transform(previous_masker_.begin(), previous_masker_.end(),
+                 comfort_noise_power.begin() + 1, previous_masker_.begin(),
+                 std::plus<float>());
+
+  std::transform(gain->begin(), gain->end(), gain->begin(),
+                 [](float a) { return sqrtf(a); });
+}
+
+}  // namespace webrtc