near_field_processor.h

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/*

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_NEAR_FIELD_PROCESSOR_H_

#define RESONANCE_AUDIO_DSP_NEAR_FIELD_PROCESSOR_H_

#include "base/audio_buffer.h"

#include "dsp/biquad_filter.h"

#include "dsp/delay_filter.h"

namespace vraudio {

// Class which applies an approximate near field effect to a source mono input.

// The effect consists of a +6dB bass boost (shelf-filter) as well as phase

// correction (HRTF group delay compensation) when the signal is to be combined

// with the binaural output.

//

// For more information: [internal ref]

class NearFieldProcessor {

 public:

  // Constructor of the |NearFieldProcessor|, uses the following parameters:

//

  // @param sample_rate Sampling rate in [Hz].

  // @param frames_per_buffer Number of frames per buffer in the input/output

  //     signal.

  NearFieldProcessor(int sample_rate, size_t frames_per_buffer);

  // Returns currently used delay compensation in samples.

  size_t GetDelayCompensation() const { return delay_compensation_; }

  // Applies approximate near field effect to the source mono input signal.

//

  // @param input Mono input channel.

  // @param output Pointer to mono output channel.

  // @param enable_hrtf Whether to enable delay compensation for HRTF filtering.

  void Process(const AudioBuffer::Channel& input, AudioBuffer::Channel* output,

               bool enable_hrtf);

 private:

  // Number of frames per buffer.

  const size_t frames_per_buffer_;

  // Delay compensation computed as average group delay of the HRTF filter

  // minus average group delay of the shelf-filter. Should be disabled when

  // using with stereo-panned sound sources.

  const size_t delay_compensation_;

  // Biquad filters that apply frequency splitting of the input mono signal.

  BiquadFilter lo_pass_filter_;

  BiquadFilter hi_pass_filter_;

  // Buffer for the low-passed signal. We do not modify the high-passed signal

  // so we can write it directly to the output channel.

  AudioBuffer low_passed_buffer_;

  // Delay filter used to delay the incoming input mono buffer.

  DelayFilter delay_filter_;

};

}  // namespace vraudio

#endif  // RESONANCE_AUDIO_DSP_NEAR_FIELD_PROCESSOR_H_