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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_AMBISONICS_AMBISONIC_BINAURAL_DECODER_H_
#define RESONANCE_AUDIO_AMBISONICS_AMBISONIC_BINAURAL_DECODER_H_
#include <vector>
#include "base/audio_buffer.h"
#include "dsp/fft_manager.h"
#include "dsp/partitioned_fft_filter.h"
namespace vraudio {
// Decodes an Ambisonic sound field, of an arbitrary order, to binaural stereo,
// by performing convolution in the spherical harmonics domain. The order (hence
// the number of channels) of the input must match the order (hence the number
// of channels) of the spherical harmonic-encoded Head Related Impulse Responses
// (HRIRs). Assumes that HRIRs are symmetric with respect to the sagittal plane.
class AmbisonicBinauralDecoder {
public:
// Constructs an |AmbisonicBinauralDecoder| from an |AudioBuffer| containing
// spherical harmonic representation of HRIRs. The order of spherical
// harmonic-encoded HRIRs (hence the number of channels) must match the order
// of the Ambisonic sound field input.
//
// @param sh_hrirs |AudioBuffer| containing time-domain spherical harmonic
// encoded symmetric HRIRs.
// @param frames_per_buffer Number of frames in each input/output buffer.
// @param fft_manager Pointer to a manager to perform FFT transformations.
AmbisonicBinauralDecoder(const AudioBuffer& sh_hrirs,
size_t frames_per_buffer, FftManager* fft_manager);
// Processes an Ambisonic sound field input and outputs a binaurally decoded
// stereo buffer.
//
// @param input Input buffer to be processed.
// @param output Pointer to a stereo output buffer.
void Process(const AudioBuffer& input, AudioBuffer* output);
private:
// Manager for all FFT related functionality (not owned).
FftManager* const fft_manager_;
// Spherical Harmonic HRIR filter kernels.
std::vector<std::unique_ptr<PartitionedFftFilter>> sh_hrir_filters_;
// Frequency domain representation of the input signal.
PartitionedFftFilter::FreqDomainBuffer freq_input_;
// Temporary audio buffer to store the convolution output for asymmetric or
// symmetric spherical harmonic HRIR.
AudioBuffer filtered_input_;
};
} // namespace vraudio
#endif // RESONANCE_AUDIO_AMBISONICS_AMBISONIC_BINAURAL_DECODER_H_
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