🛠️🐜 Antkeeper superbuild with dependencies included
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126 lines
4.6 KiB
126 lines
4.6 KiB
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#include "config.h"
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#include "uhjfilter.h"
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#include <algorithm>
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#include "alu.h"
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namespace {
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/* This is the maximum number of samples processed for each inner loop
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* iteration. */
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#define MAX_UPDATE_SAMPLES 128
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constexpr ALfloat Filter1CoeffSqr[4] = {
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0.479400865589f, 0.876218493539f, 0.976597589508f, 0.997499255936f
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};
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constexpr ALfloat Filter2CoeffSqr[4] = {
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0.161758498368f, 0.733028932341f, 0.945349700329f, 0.990599156685f
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};
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void allpass_process(AllPassState *state, ALfloat *dst, const ALfloat *src, const ALfloat aa, ALsizei todo)
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{
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ALfloat z1{state->z[0]};
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ALfloat z2{state->z[1]};
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auto proc_sample = [aa,&z1,&z2](ALfloat input) noexcept -> ALfloat
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{
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ALfloat output = input*aa + z1;
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z1 = z2; z2 = output*aa - input;
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return output;
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};
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std::transform(src, src+todo, dst, proc_sample);
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state->z[0] = z1;
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state->z[1] = z2;
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}
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} // namespace
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/* NOTE: There seems to be a bit of an inconsistency in how this encoding is
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* supposed to work. Some references, such as
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*
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* http://members.tripod.com/martin_leese/Ambisonic/UHJ_file_format.html
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*
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* specify a pre-scaling of sqrt(2) on the W channel input, while other
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* references, such as
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*
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* https://en.wikipedia.org/wiki/Ambisonic_UHJ_format#Encoding.5B1.5D
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* and
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* https://wiki.xiph.org/Ambisonics#UHJ_format
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*
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* do not. The sqrt(2) scaling is in line with B-Format decoder coefficients
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* which include such a scaling for the W channel input, however the original
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* source for this equation is a 1985 paper by Michael Gerzon, which does not
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* apparently include the scaling. Applying the extra scaling creates a louder
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* result with a narrower stereo image compared to not scaling, and I don't
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* know which is the intended result.
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*/
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void Uhj2Encoder::encode(ALfloat *LeftOut, ALfloat *RightOut, ALfloat (*InSamples)[BUFFERSIZE], const ALsizei SamplesToDo)
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{
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alignas(16) ALfloat D[MAX_UPDATE_SAMPLES], S[MAX_UPDATE_SAMPLES];
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alignas(16) ALfloat temp[MAX_UPDATE_SAMPLES];
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ASSUME(SamplesToDo > 0);
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for(ALsizei base{0};base < SamplesToDo;)
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{
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ALsizei todo = mini(SamplesToDo - base, MAX_UPDATE_SAMPLES);
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ASSUME(todo > 0);
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/* D = 0.6554516*Y */
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const ALfloat *RESTRICT input{al::assume_aligned<16>(InSamples[2]+base)};
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for(ALsizei i{0};i < todo;i++)
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temp[i] = 0.6554516f*input[i];
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allpass_process(&mFilter1_Y[0], temp, temp, Filter1CoeffSqr[0], todo);
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allpass_process(&mFilter1_Y[1], temp, temp, Filter1CoeffSqr[1], todo);
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allpass_process(&mFilter1_Y[2], temp, temp, Filter1CoeffSqr[2], todo);
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allpass_process(&mFilter1_Y[3], temp, temp, Filter1CoeffSqr[3], todo);
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/* NOTE: Filter1 requires a 1 sample delay for the final output, so
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* take the last processed sample from the previous run as the first
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* output sample.
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*/
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D[0] = mLastY;
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for(ALsizei i{1};i < todo;i++)
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D[i] = temp[i-1];
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mLastY = temp[todo-1];
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/* D += j(-0.3420201*W + 0.5098604*X) */
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const ALfloat *RESTRICT input0{al::assume_aligned<16>(InSamples[0]+base)};
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const ALfloat *RESTRICT input1{al::assume_aligned<16>(InSamples[1]+base)};
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for(ALsizei i{0};i < todo;i++)
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temp[i] = -0.3420201f*input0[i] + 0.5098604f*input1[i];
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allpass_process(&mFilter2_WX[0], temp, temp, Filter2CoeffSqr[0], todo);
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allpass_process(&mFilter2_WX[1], temp, temp, Filter2CoeffSqr[1], todo);
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allpass_process(&mFilter2_WX[2], temp, temp, Filter2CoeffSqr[2], todo);
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allpass_process(&mFilter2_WX[3], temp, temp, Filter2CoeffSqr[3], todo);
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for(ALsizei i{0};i < todo;i++)
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D[i] += temp[i];
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/* S = 0.9396926*W + 0.1855740*X */
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for(ALsizei i{0};i < todo;i++)
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temp[i] = 0.9396926f*input0[i] + 0.1855740f*input1[i];
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allpass_process(&mFilter1_WX[0], temp, temp, Filter1CoeffSqr[0], todo);
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allpass_process(&mFilter1_WX[1], temp, temp, Filter1CoeffSqr[1], todo);
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allpass_process(&mFilter1_WX[2], temp, temp, Filter1CoeffSqr[2], todo);
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allpass_process(&mFilter1_WX[3], temp, temp, Filter1CoeffSqr[3], todo);
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S[0] = mLastWX;
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for(ALsizei i{1};i < todo;i++)
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S[i] = temp[i-1];
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mLastWX = temp[todo-1];
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/* Left = (S + D)/2.0 */
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ALfloat *RESTRICT left = al::assume_aligned<16>(LeftOut+base);
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for(ALsizei i{0};i < todo;i++)
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left[i] += (S[i] + D[i]) * 0.5f;
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/* Right = (S - D)/2.0 */
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ALfloat *RESTRICT right = al::assume_aligned<16>(RightOut+base);
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for(ALsizei i{0};i < todo;i++)
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right[i] += (S[i] - D[i]) * 0.5f;
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base += todo;
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}
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}
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