mono_pole_filter.h

/*
Copyright 2018 Google Inc. All Rights Reserved.
 
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 
    http://www.apache.org/licenses/LICENSE-2.0
 
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS-IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
 
#ifndef RESONANCE_AUDIO_DSP_MONO_POLE_FILTER_H_
#define RESONANCE_AUDIO_DSP_MONO_POLE_FILTER_H_
 
#include "base/audio_buffer.h"
 
namespace vraudio {
 
// Class representing a mono pole filter. This class also performs filtering.
class MonoPoleFilter {
 public:
  // Constructs a |MonoPoleFilter| given a single coefficient.
  //
  // @param coefficient A single coefficient between 0.0f and 1.0f.
  explicit MonoPoleFilter(float coefficient);
 
  // Filter method for use with AudioBuffer::Channel.
  //
  // @param input |AudioBuffer::Channel| of input to be processed.
  // @param output Pointer to output |AudioBuffer::Channel|.
  // @return Returns false if the filter has an allpass configuration. This
  //     helps to avoid copies whenever the output is expected to be identical
  //     to the input.
  bool Filter(const AudioBuffer::Channel& input, AudioBuffer::Channel* output);
 
  // Sets the filter's coefficent.
  //
  // @param coefficient A mono pole filter coefficient.
  void SetCoefficient(float coefficient);
 
 private:
  // The previous frame computed by the filter.
  float previous_output_;
 
  // Represents and maintains the state of the filter in terms of its
  // transfer function coefficient.
  float coefficient_;
};
 
}  // namespace vraudio
 
#endif  // RESONANCE_AUDIO_DSP_MONO_POLE_FILTER_H_