Finalization of the first version of EchoCanceller 3

webrtc/modules/audio_processing/aec3/comfort_noise_generator.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/comfort_noise_generator.h"
+
+#include <math.h>
+#include <algorithm>
+#include <array>
+#include <functional>
+#include <numeric>
+
+#include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
+
+namespace webrtc {
+
+ComfortNoiseGenerator::ComfortNoiseGenerator()
+    : seed_(42), N2_initial_(new std::array<float, kFftLengthBy2Plus1>()) {
+  N2_initial_->fill(0.f);
+  Y2_smoothed_.fill(0.f);
+  N2_.fill(1.0e6f);
+}
+
+ComfortNoiseGenerator::~ComfortNoiseGenerator() = default;
+
+void ComfortNoiseGenerator::Compute(
+    const std::array<float, kFftLengthBy2Plus1>& capture_spectrum,
+    FftData* lower_band_noise,
+    FftData* upper_band_noise) {
+  RTC_DCHECK(lower_band_noise);
+  RTC_DCHECK(upper_band_noise);
+  const std::array<float, kFftLengthBy2Plus1>& Y2 = capture_spectrum;

[ivoc, 2017/02/10 13:52:33]

I would prefer const auto&

[peah-webrtc, 2017/02/20 07:37:15]

Nice!
Done.

+  FftData* N_low = lower_band_noise;
+  FftData* N_high = upper_band_noise;
+
+  // Smooth Y2.
+  std::transform(Y2_smoothed_.begin(), Y2_smoothed_.end(), Y2.begin(),
+                 Y2_smoothed_.begin(),
+                 [](float a, float b) { return a + 0.1f * (b - a); });

[ivoc, 2017/02/10 13:52:33]

Out of curiousity, what kind of filter is this?

[peah-webrtc, 2017/02/20 07:37:15]

This is a low-pass filter: Y2_smoothed(t)=0.9f*Y2_smoothed(t) + 0.1*Y2;

[ivoc, 2017/02/21 17:26:00]

ah, I should have seen that :)

[peah-webrtc, 2017/02/22 23:51:35]

No worries! Good question!

+
+  if (N2_counter_ > 50) {
+    // Update N2 from Y2_smoothed.
+    std::transform(N2_.begin(), N2_.end(), Y2_smoothed_.begin(), N2_.begin(),
+                   [](float a, float b) {
+                     return b < a ? (0.9f * b + 0.1f * a) * 1.0002f
+                                  : a * 1.0002f;
+                   });
+  }
+
+  if (N2_initial_) {
+    if (++N2_counter_ == 1000) {
+      N2_initial_.reset();
+    } else {
+      // Compute initial N2 from N2.

[ivoc, 2017/02/10 13:52:33]

This is a bit confusing. I would rephrase as "Compute N2_initial from N2."

[peah-webrtc, 2017/02/20 07:37:15]

Done.

+      std::transform(
+          N2_.begin(), N2_.end(), N2_initial_->begin(), N2_initial_->begin(),
+          [](float a, float b) { return a > b ? b + 0.001f * (a - b) : a; });
+    }
+  }
+
+  // Choose N2 estimate to use.
+  const std::array<float, kFftLengthBy2Plus1>& N2 =
+      N2_initial_ ? *N2_initial_ : N2_;
+
+  // Compute square root spectrum.
+  std::array<float, kFftLengthBy2Plus1> N;
+  std::transform(N2.begin(), N2.end(), N.begin(),
+                 [](float a) { return sqrtf(a); });
+
+  // Compute the noise level for the upper bands.
+  const float high_band_noise_level =
+      std::accumulate(N.begin() + kFftLengthBy2Plus1 / 2, N.end(), 0.f,
+                      [](float a, float b) { return a + b; }) /

[ivoc, 2017/02/10 13:52:33]

The last argument (the lambda) is not needed, accumulate sums things by default.

[peah-webrtc, 2017/02/20 07:37:15]

Done.

+      (kFftLengthBy2Plus1 / 2 + 1);
+
+  // Generate complex noise.
+  std::array<int16_t, kFftLengthBy2 - 1> random_values_int;
+  WebRtcSpl_RandUArray(random_values_int.data(), random_values_int.size(),
+                       &seed_);
+
+  std::array<float, kFftLengthBy2 - 1> sin;
+  std::array<float, kFftLengthBy2 - 1> cos;
+  const float kScale = 6.28318530717959f * 1.f / 32768.0f;

[ivoc, 2017/02/10 13:52:33]

The "* 1.f" can be removed, right? Also, this can be constexpr.

[peah-webrtc, 2017/02/20 07:37:15]

Done.

+  std::transform(random_values_int.begin(), random_values_int.end(),
+                 sin.begin(), [&](int16_t a) { return -sinf(kScale * a); });
+  std::transform(random_values_int.begin(), random_values_int.end(),
+                 cos.begin(), [&](int16_t a) { return cosf(kScale * a); });
+
+  // Form low-frequency noise via spectral shaping.
+  N_low->re[0] = N_low->re[kFftLengthBy2] = N_high->re[0] =
+      N_high->re[kFftLengthBy2] = 0.f;
+  std::transform(cos.begin(), cos.end(), N.begin() + 1, N_low->re.begin() + 1,
+                 std::multiplies<float>());
+  std::transform(sin.begin(), sin.end(), N.begin() + 1, N_low->im.begin() + 1,
+                 std::multiplies<float>());
+
+  // Form the high-frequency noise via simple levelling.
+  std::transform(cos.begin(), cos.end(), N_high->re.begin() + 1,
+                 [&](float a) { return high_band_noise_level * a; });
+  std::transform(sin.begin(), sin.end(), N_high->im.begin() + 1,
+                 [&](float a) { return high_band_noise_level * a; });
+
+  // TODO(peah): Remove when landing.

[ivoc, 2017/02/10 13:52:33]

Is that now?

[peah-webrtc, 2017/02/20 07:37:15]

Should be :-) Thanks!
Done-

+  std::array<float, kFftLength> noiseP;
+  std::array<float, kFftLength> noise_high_bandP;
+  N_low->CopyToPackedArray(&noiseP);
+  N_high->CopyToPackedArray(&noise_high_bandP);
+}
+
+}  // namespace webrtc