text: /*
   *  Copyright (c) 2018 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_AGC2_RNN_VAD_LP_RESIDUAL_H_
  #define MODULES_AUDIO_PROCESSING_AGC2_RNN_VAD_LP_RESIDUAL_H_
  
  #include <stddef.h>
  
  #include "api/array_view.h"
  
  namespace webrtc {
  namespace rnn_vad {
  
  // LPC inverse filter length.
  constexpr size_t kNumLpcCoefficients = 5;
  
  // Given a frame |x|, computes a post-processed version of LPC coefficients
  // tailored for pitch estimation.
  void ComputeAndPostProcessLpcCoefficients(
      rtc::ArrayView<const float> x,
      rtc::ArrayView<float, kNumLpcCoefficients> lpc_coeffs);
  
  // Computes the LP residual for the input frame |x| and the LPC coefficients
  // |lpc_coeffs|. |y| and |x| can point to the same array for in-place
  // computation.
  void ComputeLpResidual(
      rtc::ArrayView<const float, kNumLpcCoefficients> lpc_coeffs,
      rtc::ArrayView<const float> x,
      rtc::ArrayView<float> y);
  
  }  // namespace rnn_vad
  }  // namespace webrtc
  
  #endif  // MODULES_AUDIO_PROCESSING_AGC2_RNN_VAD_LP_RESIDUAL_H_
  