Refactoring of the noise suppressor and adding true multichannel support

This CL adds proper multichannel support to the noise suppressor.
To accomplish that in a safe way, a full refactoring of the noise
suppressor code has been done.

Due to floating point precision, the changes made are not entirely
bitexact. They are, however, very close to being bitexact.

As a safety measure, the former noise suppressor code is preserved
and a kill-switch is added to allow revering to the legacy noise
suppressor in case issues arise.

Bug: webrtc:10895, b/143344262
Change-Id: I0b071011b23265ac12e6d4b3956499d122286657
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/158407
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29646}

modules/audio_processing/ns/noise_suppressor.h

@@ -0,0 +1,83 @@
+/*
+ *  Copyright (c) 2012 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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_NS_NOISE_SUPPRESSOR_H_
+#define MODULES_AUDIO_PROCESSING_NS_NOISE_SUPPRESSOR_H_
+
+#include <memory>
+#include <vector>
+
+#include "api/array_view.h"
+#include "modules/audio_processing/audio_buffer.h"
+#include "modules/audio_processing/ns/noise_estimator.h"
+#include "modules/audio_processing/ns/ns_common.h"
+#include "modules/audio_processing/ns/ns_config.h"
+#include "modules/audio_processing/ns/ns_fft.h"
+#include "modules/audio_processing/ns/speech_probability_estimator.h"
+#include "modules/audio_processing/ns/wiener_filter.h"
+
+namespace webrtc {
+
+// Class for suppressing noise in a signal.
+class NoiseSuppressor {
+ public:
+  NoiseSuppressor(const NsConfig& config,
+                  size_t sample_rate_hz,
+                  size_t num_channels);
+  NoiseSuppressor(const NoiseSuppressor&) = delete;
+  NoiseSuppressor& operator=(const NoiseSuppressor&) = delete;
+
+  // Analyses the signal (typically applied before the AEC to avoid analyzing
+  // any comfort noise signal).
+  void Analyze(const AudioBuffer& audio);
+
+  // Applies noise suppression.
+  void Process(AudioBuffer* audio);
+
+ private:
+  const size_t num_bands_;
+  const size_t num_channels_;
+  const SuppressionParams suppression_params_;
+  int32_t num_analyzed_frames_ = -1;
+  NrFft fft_;
+
+  struct ChannelState {
+    ChannelState(const SuppressionParams& suppression_params, size_t num_bands);
+
+    SpeechProbabilityEstimator speech_probability_estimator;
+    WienerFilter wiener_filter;
+    NoiseEstimator noise_estimator;
+    std::array<float, kFftSizeBy2Plus1> prev_analysis_signal_spectrum;
+    std::array<float, kFftSize - kNsFrameSize> analyze_analysis_memory;
+    std::array<float, kOverlapSize> process_analysis_memory;
+    std::array<float, kOverlapSize> process_synthesis_memory;
+    std::vector<std::array<float, kOverlapSize>> process_delay_memory;
+  };
+
+  struct FilterBankState {
+    std::array<float, kFftSize> real;
+    std::array<float, kFftSize> imag;
+    std::array<float, kFftSize> extended_frame;
+  };
+
+  std::vector<FilterBankState> filter_bank_states_heap_;
+  std::vector<float> upper_band_gains_heap_;
+  std::vector<float> energies_before_filtering_heap_;
+  std::vector<float> gain_adjustments_heap_;
+  std::vector<std::unique_ptr<ChannelState>> channels_;
+
+  // Aggregates the Wiener filters into a single filter to use.
+  void AggregateWienerFilters(
+      rtc::ArrayView<float, kFftSizeBy2Plus1> filter) const;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_NS_NOISE_SUPPRESSOR_H_