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

webrtc/modules/audio_processing/level_controller/down_sampler.h

Index: webrtc/modules/audio_processing/level_controller/down_sampler.h
diff --git a/webrtc/modules/audio_processing/level_controller/down_sampler.h b/webrtc/modules/audio_processing/level_controller/down_sampler.h
new file mode 100644
index 0000000000000000000000000000000000000000..5c8aaf3dee93c7e8cda4fb0af1203248c0a38538
--- /dev/null
+++ b/webrtc/modules/audio_processing/level_controller/down_sampler.h
@@ -0,0 +1,40 @@
+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_DOWN_SAMPLER_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_DOWN_SAMPLER_H_
+
+#include "webrtc/base/array_view.h"
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/modules/audio_processing/level_controller/biquad_filter.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+
+class DownSampler {
+ public:
+  explicit DownSampler(ApmDataDumper* data_dumper);
+  void Initialize(int sample_rate_hz);
+
+  void DownSample(rtc::ArrayView<const float> in, rtc::ArrayView<float> out);
+
+ private:
+  ApmDataDumper* data_dumper_;
+  int sample_rate_hz_;
+  int down_sampling_factor_;

[aleloi, 2016/06/28 09:35:52]

Could the variables (including data_dumper_) be made const? It should be
possible to both check that 8000 divides sample_rate_hz and make it const at the
same time.

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

The other values cannot be const as they are changed in the Initialize method.
It would be nice to have them const, but with the current design it is not
possible to do that.

data_dumper_ could be made a const pointer, but not pointer to a const object.
I'll change that to be a const pointer.

WDYT? Does that sound ok?

[aleloi, 2016/06/29 14:11:18]

Acknowledged.

+  BiQuadFilter low_pass_filter_;
+
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(DownSampler);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_DOWN_SAMPLER_H_