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Use transposed direct form 2 for the UHJ all-pass filters

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This has one extra multiply, but avoids two moves and uses almost half as much
memory for the encoder state.
This commit is contained in:
Chris Robinson
2018-04-22 03:34:29 -07:00
parent e10595df31
commit b3ba90f5fa
2 changed files with 17 additions and 17 deletions
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Alc/uhjfilter.c
+14 -14
View File
@@ -18,23 +18,20 @@ static const ALfloat Filter2CoeffSqr[4] = {
static void allpass_process(AllPassState *state, ALfloat *restrict dst, const ALfloat *restrict src, const ALfloat aa, ALsizei todo)
{
ALfloat x0 = state->x[0];
ALfloat x1 = state->x[1];
ALfloat y0 = state->y[0];
ALfloat y1 = state->y[1];
ALfloat z1 = state->z[0];
ALfloat z2 = state->z[1];
ALsizei i;
for(i = 0;i < todo;i++)
{
dst[i] = aa*(src[i] + y1) - x1;
y1 = y0; y0 = dst[i];
x1 = x0; x0 = src[i];
ALfloat input = src[i];
ALfloat output = input*aa + z1;
z1 = z2; z2 = output*aa - input;
dst[i] = output;
}
state->x[0] = x0;
state->x[1] = x1;
state->y[0] = y0;
state->y[1] = y1;
state->z[0] = z1;
state->z[1] = z2;
}
@@ -69,6 +66,7 @@ void EncodeUhj2(Uhj2Encoder *enc, ALfloat *restrict LeftOut, ALfloat *restrict R
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++)
@@ -76,14 +74,15 @@ void EncodeUhj2(Uhj2Encoder *enc, ALfloat *restrict LeftOut, ALfloat *restrict R
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->Filter1_Y[3].y[0];
allpass_process(&enc->Filter1_Y[3], temp[0], temp[1], Filter1CoeffSqr[3], todo);
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++)
@@ -103,10 +102,11 @@ void EncodeUhj2(Uhj2Encoder *enc, ALfloat *restrict LeftOut, ALfloat *restrict R
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);
S[0] = enc->Filter1_WX[3].y[0];
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++)
Alc/uhjfilter.h
+3 -3
View File
@@ -6,8 +6,7 @@
#include "alMain.h"
typedef struct AllPassState {
ALfloat x[2]; /* Last two input samples */
ALfloat y[2]; /* Last two output samples */
ALfloat z[2];
} AllPassState;
/* Encoding 2-channel UHJ from B-Format is done as:
@@ -36,9 +35,10 @@ typedef struct AllPassState {
*/
typedef struct Uhj2Encoder {
AllPassState Filter1_WX[4];
AllPassState Filter1_Y[4];
AllPassState Filter2_WX[4];
AllPassState Filter1_WX[4];
ALfloat LastY, LastWX;
} Uhj2Encoder;
/* Encodes a 2-channel UHJ (stereo-compatible) signal from a B-Format input