Add an option to change the UHJ decoder method
For 2-channel UHJ, two decoding equations are provided in the original paper. The alternative one is most often referenced for 2-channel UHJ decoding, but the original/general one can also be used by assuming T is fully attenuated (which the format allows for, as T can be variably attenuated by a factor between 0 and 1 to deal with an imperfect transmission medium). Neither method can be perfect for 2-channel UHJ, it's irrevocably lossy to the original source, but my subjective testing indicates the general equation produces less audibly errant results.
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Chris Robinson
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@ -130,8 +130,8 @@ struct UhjDecoder {
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alignas(16) std::array<float,BufferLineSize + sFilterSize*2> mTemp{};
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void decode(const float *RESTRICT InSamples, const al::span<FloatBufferLine> OutSamples,
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const size_t SamplesToDo);
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void decode(const float *RESTRICT InSamples, const size_t InChannels,
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const al::span<FloatBufferLine> OutSamples, const size_t SamplesToDo);
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void decode2(const float *RESTRICT InSamples, const al::span<FloatBufferLine,3> OutSamples,
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const size_t SamplesToDo);
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@ -307,7 +307,7 @@ void allpass_process(al::span<float> dst, const float *RESTRICT src)
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}
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/* Decoding 3- and 4-channel UHJ is done as:
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/* Decoding UHJ is done as:
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*
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* S = Left + Right
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* D = Left - Right
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@ -317,7 +317,10 @@ void allpass_process(al::span<float> dst, const float *RESTRICT src)
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* Y = 0.795954*D - 0.676406*T + j(0.186626*S)
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* Z = 1.023332*Q
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*
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* where j is a +90 degree phase shift. 3-channel UHJ excludes Q/Z.
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* where j is a +90 degree phase shift. 3-channel UHJ excludes Q, while 2-
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* channel excludes Q and T. The B-Format signal reconstructed from 2-channel
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* UHJ should not be run through a normal B-Format decoder, as it needs
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* different shelf filters.
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*
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* NOTE: Some sources specify
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*
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@ -377,13 +380,11 @@ void allpass_process(al::span<float> dst, const float *RESTRICT src)
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*
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* Not halving produces a result matching the original input.
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*/
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void UhjDecoder::decode(const float *RESTRICT InSamples,
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void UhjDecoder::decode(const float *RESTRICT InSamples, const size_t InChannels,
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const al::span<FloatBufferLine> OutSamples, const size_t SamplesToDo)
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{
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ASSUME(SamplesToDo > 0);
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const size_t Channels{OutSamples.size()};
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float *woutput{OutSamples[0].data()};
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float *xoutput{OutSamples[1].data()};
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float *youtput{OutSamples[2].data()};
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@ -394,27 +395,29 @@ void UhjDecoder::decode(const float *RESTRICT InSamples,
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/* S = Left + Right */
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for(size_t i{0};i < SamplesToDo;++i)
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mS[sFilterSize+i] = InSamples[i*Channels + 0] + InSamples[i*Channels + 1];
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mS[sFilterSize+i] = InSamples[i*InChannels + 0] + InSamples[i*InChannels + 1];
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/* D = Left - Right */
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for(size_t i{0};i < SamplesToDo;++i)
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mD[sFilterSize+i] = InSamples[i*Channels + 0] - InSamples[i*Channels + 1];
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mD[sFilterSize+i] = InSamples[i*InChannels + 0] - InSamples[i*InChannels + 1];
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/* T */
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for(size_t i{0};i < SamplesToDo;++i)
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mT[sFilterSize+i] = InSamples[i*Channels + 2];
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if(Channels > 3)
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if(InChannels > 2)
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{
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/* T */
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for(size_t i{0};i < SamplesToDo;++i)
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mT[sFilterSize+i] = InSamples[i*InChannels + 2];
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}
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if(InChannels > 3)
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{
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/* Q */
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for(size_t i{0};i < SamplesToDo;++i)
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mQ[sFilterSize+i] = InSamples[i*Channels + 3];
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mQ[sFilterSize+i] = InSamples[i*InChannels + 3];
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}
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/* Precompute j(0.828347*D + 0.767835*T) and store in xoutput. */
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auto tmpiter = std::copy(mDTHistory.cbegin(), mDTHistory.cend(), mTemp.begin());
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std::transform(mD.cbegin(), mD.cbegin()+SamplesToDo+sFilterSize, mT.cbegin(), tmpiter,
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[](const float D, const float T) noexcept { return 0.828347f*D + 0.767835f*T; });
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[](const float d, const float t) noexcept { return 0.828347f*d + 0.767835f*t; });
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std::copy_n(mTemp.cbegin()+SamplesToDo, mDTHistory.size(), mDTHistory.begin());
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allpass_process({xoutput, SamplesToDo}, mTemp.data());
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@ -438,7 +441,7 @@ void UhjDecoder::decode(const float *RESTRICT InSamples,
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youtput[i] = 0.795954f*mD[i] - 0.676406f*mT[i] + 0.186626f*youtput[i];
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}
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if(Channels > 3)
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if(OutSamples.size() > 3)
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{
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float *zoutput{OutSamples[3].data()};
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/* Z = 1.023332*Q */
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@ -452,12 +455,12 @@ void UhjDecoder::decode(const float *RESTRICT InSamples,
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std::copy(mQ.begin()+SamplesToDo, mQ.begin()+SamplesToDo+sFilterSize, mQ.begin());
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}
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/* There is a difference with decoding 2-channel UHJ compared to 3-channel, due
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* to 2-channel having lost some of the original signal. The B-Format signal
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* reconstructed from 2-channel UHJ should not be run through a normal B-Format
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* decoder, as it needs different shelf filters.
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/* This is an alternative equation for decoding 2-channel UHJ. Not sure what
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* the intended benefit is over the above equation as this slightly reduces the
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* amount of the original left response and has more of the phase-shifted
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* forward response on the left response.
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*
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* 2-channel UHJ decoding is done as:
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* This decoding is done as:
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*
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* S = Left + Right
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* D = Left - Right
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@ -523,13 +526,32 @@ int main(int argc, char **argv)
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{
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if(argc < 2 || std::strcmp(argv[1], "-h") == 0 || std::strcmp(argv[1], "--help") == 0)
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{
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printf("Usage: %s <filename.wav...>\n", argv[0]);
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printf("Usage: %s <[options] filename.wav...>\n\n"
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" Options:\n"
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" --general Use the general equations for 2-channel UHJ (default).\n"
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" --alternative Use the alternative equations for 2-channel UHJ.\n"
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"\n"
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"Note: When decoding 2-channel UHJ to an .amb file, the result should not use\n"
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"the normal B-Format shelf filters! Only 3- and 4-channel UHJ can accurately\n"
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"reconstruct the original B-Format signal.",
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argv[0]);
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return 1;
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}
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size_t num_files{0}, num_decoded{0};
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bool use_general{true};
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for(int fidx{1};fidx < argc;++fidx)
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{
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if(std::strcmp(argv[fidx], "--general") == 0)
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{
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use_general = true;
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continue;
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}
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if(std::strcmp(argv[fidx], "--alternative") == 0)
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{
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use_general = false;
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continue;
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}
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++num_files;
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SF_INFO ininfo{};
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SndFilePtr infile{sf_open(argv[fidx], SFM_READ, &ininfo)};
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@ -553,7 +575,8 @@ int main(int argc, char **argv)
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fprintf(stderr, "%s is not a 2-, 3-, or 4-channel file\n", argv[fidx]);
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continue;
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}
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printf("Converting %s from %d-channel UHJ...\n", argv[fidx], ininfo.channels);
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printf("Converting %s from %d-channel UHJ%s...\n", argv[fidx], ininfo.channels,
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(ininfo.channels == 2) ? use_general ? " (general)" : " (alternative)" : "");
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std::string outname{argv[fidx]};
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auto lastslash = outname.find_last_of('/');
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@ -634,10 +657,10 @@ int main(int argc, char **argv)
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}
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auto got = static_cast<size_t>(sgot);
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if(ininfo.channels == 2)
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if(ininfo.channels > 2 || use_general)
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decoder->decode(inmem.get(), static_cast<uint>(ininfo.channels), decmem, got);
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else
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decoder->decode2(inmem.get(), decmem, got);
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else if(ininfo.channels == 3 || ininfo.channels == 4)
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decoder->decode(inmem.get(), decmem, got);
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for(size_t i{0};i < got;++i)
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{
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for(size_t j{0};j < outchans;++j)
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