text: /*
   *  Copyright (c) 2011 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.
   */
  
  
  // This file includes specific signal processing tools used in vad_core.c.
  
  #ifndef WEBRTC_COMMON_AUDIO_VAD_VAD_SP_H_
  #define WEBRTC_COMMON_AUDIO_VAD_VAD_SP_H_
  
  #include "vad_core.h"
  
  // Downsamples the signal by a factor 2, eg. 32->16 or 16->8.
  //
  // Inputs:
  //      - signal_in     : Input signal.
  //      - in_length     : Length of input signal in samples.
  //
  // Input & Output:
  //      - filter_state  : Current filter states of the two all-pass filters. The
  //                        |filter_state| is updated after all samples have been
  //                        processed.
  //
  // Output:
  //      - signal_out    : Downsampled signal (of length |in_length| / 2).
  void WebRtcVad_Downsampling(const int16_t* signal_in,
                              int16_t* signal_out,
                              int32_t* filter_state,
                              size_t in_length);
  
  // Updates and returns the smoothed feature minimum. As minimum we use the
  // median of the five smallest feature values in a 100 frames long window.
  // As long as |handle->frame_counter| is zero, that is, we haven't received any
  // "valid" data, FindMinimum() outputs the default value of 1600.
  //
  // Inputs:
  //      - feature_value : New feature value to update with.
  //      - channel       : Channel number.
  //
  // Input & Output:
  //      - handle        : State information of the VAD.
  //
  // Returns:
  //                      : Smoothed minimum value for a moving window.
  int16_t WebRtcVad_FindMinimum(VadInstT* handle,
                                int16_t feature_value,
                                int channel);
  
  #endif  // WEBRTC_COMMON_AUDIO_VAD_VAD_SP_H_
  