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#include "config.h"
#include "alu.h"
#include "uhjfilter.h"
/* This is the maximum number of samples processed for each inner loop
* iteration. */
#define MAX_UPDATE_SAMPLES 128
static const ALfloat Filter1CoeffSqr[4] = {
0.479400865589f, 0.876218493539f, 0.976597589508f, 0.997499255936f
};
static const ALfloat Filter2CoeffSqr[4] = {
0.161758498368f, 0.733028932341f, 0.945349700329f, 0.990599156685f
};
static void allpass_process(AllPassState *state, ALfloat *RESTRICT dst, const ALfloat *RESTRICT src, const ALfloat aa, ALsizei todo)
{
ALfloat z1 = state->z[0];
ALfloat z2 = state->z[1];
ALsizei i;
for(i = 0;i < todo;i++)
{
ALfloat input = src[i];
ALfloat output = input*aa + z1;
z1 = z2; z2 = output*aa - input;
dst[i] = output;
}
state->z[0] = z1;
state->z[1] = z2;
}
/* 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 EncodeUhj2(Uhj2Encoder *enc, ALfloat *RESTRICT LeftOut, ALfloat *RESTRICT RightOut, ALfloat (*RESTRICT InSamples)[BUFFERSIZE], ALsizei SamplesToDo)
{
ALfloat D[MAX_UPDATE_SAMPLES], S[MAX_UPDATE_SAMPLES];
ALfloat temp[2][MAX_UPDATE_SAMPLES];
ALsizei base, i;
ASSUME(SamplesToDo > 0);
for(base = 0;base < SamplesToDo;)
{
ALsizei todo = mini(SamplesToDo - base, MAX_UPDATE_SAMPLES);
ASSUME(todo > 0);
/* D = 0.6554516*Y */
for(i = 0;i < todo;i++)
temp[0][i] = 0.6554516f*InSamples[2][base+i];
allpass_process(&enc->Filter1_Y[0], temp[1], temp[0], Filter1CoeffSqr[0], todo);
allpass_process(&enc->Filter1_Y[1], temp[0], temp[1], Filter1CoeffSqr[1], todo);
allpass_process(&enc->Filter1_Y[2], temp[1], temp[0], Filter1CoeffSqr[2], todo);
allpass_process(&enc->Filter1_Y[3], temp[0], temp[1], 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] = enc->LastY;
for(i = 1;i < todo;i++)
D[i] = temp[0][i-1];
enc->LastY = temp[0][i-1];
/* D += j(-0.3420201*W + 0.5098604*X) */
for(i = 0;i < todo;i++)
temp[0][i] = -0.3420201f*InSamples[0][base+i] +
0.5098604f*InSamples[1][base+i];
allpass_process(&enc->Filter2_WX[0], temp[1], temp[0], Filter2CoeffSqr[0], todo);
allpass_process(&enc->Filter2_WX[1], temp[0], temp[1], Filter2CoeffSqr[1], todo);
allpass_process(&enc->Filter2_WX[2], temp[1], temp[0], Filter2CoeffSqr[2], todo);
allpass_process(&enc->Filter2_WX[3], temp[0], temp[1], Filter2CoeffSqr[3], todo);
for(i = 0;i < todo;i++)
D[i] += temp[0][i];
/* S = 0.9396926*W + 0.1855740*X */
for(i = 0;i < todo;i++)
temp[0][i] = 0.9396926f*InSamples[0][base+i] +
0.1855740f*InSamples[1][base+i];
allpass_process(&enc->Filter1_WX[0], temp[1], temp[0], Filter1CoeffSqr[0], todo);
allpass_process(&enc->Filter1_WX[1], temp[0], temp[1], Filter1CoeffSqr[1], todo);
allpass_process(&enc->Filter1_WX[2], temp[1], temp[0], Filter1CoeffSqr[2], todo);
allpass_process(&enc->Filter1_WX[3], temp[0], temp[1], Filter1CoeffSqr[3], todo);
S[0] = enc->LastWX;
for(i = 1;i < todo;i++)
S[i] = temp[0][i-1];
enc->LastWX = temp[0][i-1];
/* Left = (S + D)/2.0 */
for(i = 0;i < todo;i++)
*(LeftOut++) += (S[i] + D[i]) * 0.5f;
/* Right = (S - D)/2.0 */
for(i = 0;i < todo;i++)
*(RightOut++) += (S[i] - D[i]) * 0.5f;
base += todo;
}
}
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