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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.
*/
#include "ambisonics/ambisonic_binaural_decoder.h"
#include "ambisonics/utils.h"
#include "base/constants_and_types.h"
namespace vraudio {
AmbisonicBinauralDecoder::AmbisonicBinauralDecoder(const AudioBuffer& sh_hrirs,
size_t frames_per_buffer,
FftManager* fft_manager)
: fft_manager_(fft_manager),
freq_input_(kNumMonoChannels, NextPowTwo(frames_per_buffer) * 2),
filtered_input_(kNumMonoChannels, frames_per_buffer) {
CHECK(fft_manager_);
CHECK_NE(frames_per_buffer, 0U);
const size_t num_channels = sh_hrirs.num_channels();
const size_t filter_size = sh_hrirs.num_frames();
CHECK_NE(num_channels, 0U);
CHECK_NE(filter_size, 0U);
sh_hrir_filters_.reserve(num_channels);
for (size_t i = 0; i < num_channels; ++i) {
sh_hrir_filters_.emplace_back(
new PartitionedFftFilter(filter_size, frames_per_buffer, fft_manager_));
sh_hrir_filters_[i]->SetTimeDomainKernel(sh_hrirs[i]);
}
}
void AmbisonicBinauralDecoder::Process(const AudioBuffer& input,
AudioBuffer* output) {
DCHECK(output);
DCHECK_EQ(kNumStereoChannels, output->num_channels());
DCHECK_EQ(input.num_frames(), output->num_frames());
DCHECK_EQ(input.num_channels(), sh_hrir_filters_.size());
output->Clear();
AudioBuffer::Channel* freq_input_channel = &freq_input_[0];
AudioBuffer::Channel* filtered_input_channel = &filtered_input_[0];
AudioBuffer::Channel* output_channel_0 = &(*output)[0];
AudioBuffer::Channel* output_channel_1 = &(*output)[1];
for (size_t channel = 0; channel < input.num_channels(); ++channel) {
const int degree = GetPeriphonicAmbisonicDegreeForChannel(channel);
fft_manager_->FreqFromTimeDomain(input[channel], freq_input_channel);
sh_hrir_filters_[channel]->Filter(*freq_input_channel);
sh_hrir_filters_[channel]->GetFilteredSignal(filtered_input_channel);
if (degree < 0) {
// Degree is negative: spherical harmonic is asymetric.
// So add contributions to the left channel and subtract from the right
// channel.
*output_channel_0 += *filtered_input_channel;
*output_channel_1 -= *filtered_input_channel;
} else {
// Degree is zero or positive: spherical harmonic is symetric.
// So add contributions to both left and right channels.
*output_channel_0 += *filtered_input_channel;
*output_channel_1 += *filtered_input_channel;
}
}
}
} // namespace vraudio
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