New module for the adaptive level controlling functionality in the audio processing module

webrtc/modules/audio_processing/level_controller/gain_selector.cc

+/*
+ *  Copyright (c) 2016 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/level_controller/gain_selector.h"
+
+#include <math.h>
+#include <algorithm>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/modules/audio_processing/include/audio_processing.h"
+#include "webrtc/modules/audio_processing/level_controller/lc_constants.h"
+
+namespace webrtc {
+
+GainSelector::GainSelector() {
+  Initialize(AudioProcessing::kSampleRate48kHz);
+}
+
+void GainSelector::Initialize(int sample_rate_hz) {
+  gain_ = 1.f;
+  frame_length_ = sample_rate_hz / 100;

[hlundin-webrtc, 2016/06/27 11:21:14]

rtc::CheckedDivExact

[peah-webrtc, 2016/06/27 22:51:47]

Great!

Done.

+}
+
+/* Chooses the gain to apply by the level controller such that

[hlundin-webrtc, 2016/06/27 11:21:14]

Use // style comments.

[peah-webrtc, 2016/06/27 22:51:48]

Done.

+   1) The level of the stationary noise does not exceed
+      a predefined threshold.
+   2) The gain does not exceed the that has been deemed

[hlundin-webrtc, 2016/06/27 11:21:14]

deemed to -> found to

[hlundin-webrtc, 2016/06/27 11:21:14]

"the that" ?

[peah-webrtc, 2016/06/27 22:51:47]

Done.

[peah-webrtc, 2016/06/27 22:51:47]

Done.

+      to saturate the signal.
+   3) Such that the peak level achieves the target peak level.

[hlundin-webrtc, 2016/06/27 11:21:14]

Skip "Such that"; you already have that before the list.

[peah-webrtc, 2016/06/27 22:51:47]

Done.

+   4) The gain is not below 1.
+   5) The gain is not above the maximum gain. */
+float GainSelector::GetNewGain(float peak_level,
+                               float noise_energy,
+                               float saturating_gain) {
+  float desired_gain = gain_;
+
+  RTC_DCHECK_LT(0.f, peak_level);

[hlundin-webrtc, 2016/06/27 11:21:14]

This will fail if peak_level == 0.f. Is this intended?

[peah-webrtc, 2016/06/27 22:51:47]

Yes, the peak level detector should ensure a minimum peak level that is greated
than 0.

By relying on that, it is not needed to check so that the division by peak_level
does not involve a division by 0.

[hlundin-webrtc, 2016/06/28 11:29:00]

Acknowledged.

[peah-webrtc, 2016/06/28 22:19:37]

Acknowledged.

+  desired_gain = kTargetLcPeakLevel / peak_level;
+
+  float max_noise_energy = kMaxLcNoisePower * frame_length_;
+  if (noise_energy * desired_gain * desired_gain > max_noise_energy) {
+    RTC_DCHECK_LE(0.f, noise_energy);
+    desired_gain = sqrtf(max_noise_energy / noise_energy);
+  }
+
+  gain_ += 0.2f * (desired_gain - gain_);
+  gain_ = std::min(gain_, saturating_gain);
+  gain_ = std::min(gain_, kMaxLcGain);
+  gain_ = std::max(gain_, 1.f);
+
+  return gain_;
+}
+
+}  // namespace webrtc