AGC2 dummy module: fixed gain param, APM integration, audioproc_f adaptation

webrtc/modules/audio_processing/include/audio_processing.h

 /*
  *  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.
  */
 
@@ skipping 258 matching lines @@
     struct EchoCanceller3 {
       bool enabled = false;
     } echo_canceller3;
 
     // Enables the next generation AGC functionality. This feature replaces the
     // standard methods of gain control in the previous AGC.
     // The functionality is not yet activated in the code and turning this on
     // does not yet have the desired behavior.
     struct GainController2 {
       bool enabled = false;
+      // Fixed digital gain params.
+      float fixed_gain_db = 5.f;

[peah-webrtc, 2017/08/18 04:51:06]

I think the default gain should be 0 (dB).

[aleloi, 2017/08/18 08:28:31]

Idea: make the default gain 0 (dB), but also refuse creating a GainController2
if the gain is 0 by changing the constructor or the Validate method. This is to
make it harder to use the API incorrectly: if you leave GainController2 enabled,
there is no point configuring it in a way that doesn't modify the signal. In the
spirit of making interfaces hard to use incorrectly and simple to use correctly.

The correct way to use AGC2 is to *both* enable it *and* set the constants to
something nonzero. I don't think we want users to enable the AGC without
explicitly choosing a parameter combination.

[peah-webrtc, 2017/08/18 09:12:46]

This is (or at least is intended to be) implemented such that the Validate
method should return false, but that the ApplyConfig should ensure that no
incorrect value is used by modifying incorrect config values.
I like that, as it is safe in the sense that the user ends up in a usable state.

The only way to refuse creating the GainController2 object would be for Create
to return null (or the constructor to crash). I don't think either is nice as
both will happen during runtime and complicates things for the user.

     } gain_controller2;
   };
 
   // TODO(mgraczyk): Remove once all methods that use ChannelLayout are gone.
   enum ChannelLayout {
     kMono,
     // Left, right.
     kStereo,
     // Mono, keyboard, and mic.
     kMonoAndKeyboard,
@@ skipping 809 matching lines @@
   // This does not impact the size of frames passed to |ProcessStream()|.
   virtual int set_frame_size_ms(int size) = 0;
   virtual int frame_size_ms() const = 0;
 
  protected:
   virtual ~VoiceDetection() {}
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_PROCESSING_INCLUDE_AUDIO_PROCESSING_H_