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