Pull out the PostFilter to its own NonlinearBeamformer API

webrtc/modules/audio_processing/beamformer/nonlinear_beamformer.h

Index: webrtc/modules/audio_processing/beamformer/nonlinear_beamformer.h
diff --git a/webrtc/modules/audio_processing/beamformer/nonlinear_beamformer.h b/webrtc/modules/audio_processing/beamformer/nonlinear_beamformer.h
index b8953b0a4f8d2d4c1e0083b8de7cba0c37e80dc5..73fc3784662a122336b76bd8ec07742cd3ab44f5 100644
--- a/webrtc/modules/audio_processing/beamformer/nonlinear_beamformer.h
+++ b/webrtc/modules/audio_processing/beamformer/nonlinear_beamformer.h
@@ -26,6 +26,8 @@
 
 namespace webrtc {
 
+class PostFilterTransform;
+
 // Enhances sound sources coming directly in front of a uniform linear array
 // and suppresses sound sources coming from all other directions. Operates on
 // multichannel signals and produces single-channel output.
@@ -35,6 +37,7 @@ namespace webrtc {
 class NonlinearBeamformer
   : public Beamformer<float>,
     public LappedTransform::Callback {
+  friend class PostFilterTransform;
  public:
   static const float kHalfBeamWidthRadians;
 
@@ -53,6 +56,14 @@ class NonlinearBeamformer
   // ChannelBuffer can be passed in as |input| and |output|.
   void ProcessChunk(const ChannelBuffer<float>& input,
                     ChannelBuffer<float>* output) override;
+  // Applies the postfilter mask to one chunk of audio. The audio is expected to

[peah-webrtc, 2016/05/22 21:06:48]

I think that this description is longer than required.

The description of the band splitting should not be needed here. It is rather a
description of ChannelBuffer and if it needs to be clarified further it would be
better to do it in a unittest which illustrates the usage of the method.

I think the requirements on the frame size and the number of channels are better
illustrated by a DCHECK inside the code.

[aluebs-webrtc, 2016/05/26 01:04:45]

I personally think adding more documentation than required is not a problem. It
is also consistent (band splitting and requirements on input) with the
ProcessChunk documentation. There is a DCHECK on place as well.

[peah-webrtc, 2016/05/26 08:48:52]

Great! 

+  // be split into frequency bands inside the ChannelBuffer. The number of
+  // frames must correspond to the constructor parameters and the number of
+  // channels is expected to be 1, since that is the output number of channels
+  // of ProcessChunk(). The same ChannelBuffer can be passed in as |input| and
+  // |output|.
+  void PostFilter(const ChannelBuffer<float>& input,
+                  ChannelBuffer<float>* output) override;
 
   void AimAt(const SphericalPointf& target_direction) override;
 
@@ -116,8 +127,11 @@ class NonlinearBeamformer
   // Compute the means needed for the above frequency correction.
   float MaskRangeMean(size_t start_bin, size_t end_bin);
 
-  // Applies both sets of masks to |input| and store in |output|.
-  void ApplyMasks(const complex_f* const* input, complex_f* const* output);
+  // Applies delay-and-sum mask to |input| and store in |output|.
+  void ApplyDelayAndSum(const complex_f* const* input,
+                        complex_f* const* output);
+  // Applies post-filter mask to |input| and store in |output|.
+  void ApplyPostFilter(const complex_f* input, complex_f* output);
 
   void EstimateTargetPresence();
 
@@ -126,7 +140,8 @@ class NonlinearBeamformer
 
   // Deals with the fft transform and blocking.
   size_t chunk_length_;
-  std::unique_ptr<LappedTransform> lapped_transform_;
+  std::unique_ptr<LappedTransform> process_transform_;
+  std::unique_ptr<LappedTransform> postfilter_transform_;
   float window_[kFftSize];
 
   // Parameters exposed to the user.
@@ -186,6 +201,7 @@ class NonlinearBeamformer
 
   // For processing the high-frequency input signal.
   float high_pass_postfilter_mask_;
+  float old_high_pass_mask_;
 
   // True when the target signal is present.
   bool is_target_present_;