asterisk/codecs/ilbc/lsf.c

277 lines
7.5 KiB
C

/******************************************************************
iLBC Speech Coder ANSI-C Source Code
lsf.c
Copyright (C) The Internet Society (2004).
All Rights Reserved.
******************************************************************/
#include <string.h>
#include <math.h>
#include "iLBC_define.h"
/*----------------------------------------------------------------*
* conversion from lpc coefficients to lsf coefficients
*---------------------------------------------------------------*/
void a2lsf(
float *freq,/* (o) lsf coefficients */
float *a /* (i) lpc coefficients */
){
float steps[LSF_NUMBER_OF_STEPS] =
{(float)0.00635, (float)0.003175, (float)0.0015875,
(float)0.00079375};
float step;
int step_idx;
int lsp_index;
float p[LPC_HALFORDER];
float q[LPC_HALFORDER];
float p_pre[LPC_HALFORDER];
float q_pre[LPC_HALFORDER];
float old_p, old_q, *old;
float *pq_coef;
float omega, old_omega;
int i;
float hlp, hlp1, hlp2, hlp3, hlp4, hlp5;
for (i=0; i<LPC_HALFORDER; i++) {
p[i] = (float)-1.0 * (a[i + 1] + a[LPC_FILTERORDER - i]);
q[i] = a[LPC_FILTERORDER - i] - a[i + 1];
}
p_pre[0] = (float)-1.0 - p[0];
p_pre[1] = - p_pre[0] - p[1];
p_pre[2] = - p_pre[1] - p[2];
p_pre[3] = - p_pre[2] - p[3];
p_pre[4] = - p_pre[3] - p[4];
p_pre[4] = p_pre[4] / 2;
q_pre[0] = (float)1.0 - q[0];
q_pre[1] = q_pre[0] - q[1];
q_pre[2] = q_pre[1] - q[2];
q_pre[3] = q_pre[2] - q[3];
q_pre[4] = q_pre[3] - q[4];
q_pre[4] = q_pre[4] / 2;
omega = 0.0;
old_omega = 0.0;
old_p = FLOAT_MAX;
old_q = FLOAT_MAX;
/* Here we loop through lsp_index to find all the
LPC_FILTERORDER roots for omega. */
for (lsp_index = 0; lsp_index<LPC_FILTERORDER; lsp_index++) {
/* Depending on lsp_index being even or odd, we
alternatively solve the roots for the two LSP equations. */
if ((lsp_index & 0x1) == 0) {
pq_coef = p_pre;
old = &old_p;
} else {
pq_coef = q_pre;
old = &old_q;
}
/* Start with low resolution grid */
for (step_idx = 0, step = steps[step_idx];
step_idx < LSF_NUMBER_OF_STEPS;){
/* cos(10piw) + pq(0)cos(8piw) + pq(1)cos(6piw) +
pq(2)cos(4piw) + pq(3)cod(2piw) + pq(4) */
hlp = (float)cos(omega * TWO_PI);
hlp1 = (float)2.0 * hlp + pq_coef[0];
hlp2 = (float)2.0 * hlp * hlp1 - (float)1.0 +
pq_coef[1];
hlp3 = (float)2.0 * hlp * hlp2 - hlp1 + pq_coef[2];
hlp4 = (float)2.0 * hlp * hlp3 - hlp2 + pq_coef[3];
hlp5 = hlp * hlp4 - hlp3 + pq_coef[4];
if (((hlp5 * (*old)) <= 0.0) || (omega >= 0.5)){
if (step_idx == (LSF_NUMBER_OF_STEPS - 1)){
if (fabs(hlp5) >= fabs(*old)) {
freq[lsp_index] = omega - step;
} else {
freq[lsp_index] = omega;
}
if ((*old) >= 0.0){
*old = (float)-1.0 * FLOAT_MAX;
} else {
*old = FLOAT_MAX;
}
omega = old_omega;
step_idx = 0;
step_idx = LSF_NUMBER_OF_STEPS;
} else {
if (step_idx == 0) {
old_omega = omega;
}
step_idx++;
omega -= steps[step_idx];
/* Go back one grid step */
step = steps[step_idx];
}
} else {
/* increment omega until they are of different sign,
and we know there is at least one root between omega
and old_omega */
*old = hlp5;
omega += step;
}
}
}
for (i = 0; i<LPC_FILTERORDER; i++) {
freq[i] = freq[i] * TWO_PI;
}
}
/*----------------------------------------------------------------*
* conversion from lsf coefficients to lpc coefficients
*---------------------------------------------------------------*/
void lsf2a(
float *a_coef, /* (o) lpc coefficients */
float *freq /* (i) lsf coefficients */
){
int i, j;
float hlp;
float p[LPC_HALFORDER], q[LPC_HALFORDER];
float a[LPC_HALFORDER + 1], a1[LPC_HALFORDER],
a2[LPC_HALFORDER];
float b[LPC_HALFORDER + 1], b1[LPC_HALFORDER],
b2[LPC_HALFORDER];
for (i=0; i<LPC_FILTERORDER; i++) {
freq[i] = freq[i] * PI2;
}
/* Check input for ill-conditioned cases. This part is not
found in the TIA standard. It involves the following 2 IF
blocks. If "freq" is judged ill-conditioned, then we first
modify freq[0] and freq[LPC_HALFORDER-1] (normally
LPC_HALFORDER = 10 for LPC applications), then we adjust
the other "freq" values slightly */
if ((freq[0] <= 0.0) || (freq[LPC_FILTERORDER - 1] >= 0.5)){
if (freq[0] <= 0.0) {
freq[0] = (float)0.022;
}
if (freq[LPC_FILTERORDER - 1] >= 0.5) {
freq[LPC_FILTERORDER - 1] = (float)0.499;
}
hlp = (freq[LPC_FILTERORDER - 1] - freq[0]) /
(float) (LPC_FILTERORDER - 1);
for (i=1; i<LPC_FILTERORDER; i++) {
freq[i] = freq[i - 1] + hlp;
}
}
memset(a1, 0, LPC_HALFORDER*sizeof(float));
memset(a2, 0, LPC_HALFORDER*sizeof(float));
memset(b1, 0, LPC_HALFORDER*sizeof(float));
memset(b2, 0, LPC_HALFORDER*sizeof(float));
memset(a, 0, (LPC_HALFORDER+1)*sizeof(float));
memset(b, 0, (LPC_HALFORDER+1)*sizeof(float));
/* p[i] and q[i] compute cos(2*pi*omega_{2j}) and
cos(2*pi*omega_{2j-1} in eqs. 4.2.2.2-1 and 4.2.2.2-2.
Note that for this code p[i] specifies the coefficients
used in .Q_A(z) while q[i] specifies the coefficients used
in .P_A(z) */
for (i=0; i<LPC_HALFORDER; i++) {
p[i] = (float)cos(TWO_PI * freq[2 * i]);
q[i] = (float)cos(TWO_PI * freq[2 * i + 1]);
}
a[0] = 0.25;
b[0] = 0.25;
for (i= 0; i<LPC_HALFORDER; i++) {
a[i + 1] = a[i] - 2 * p[i] * a1[i] + a2[i];
b[i + 1] = b[i] - 2 * q[i] * b1[i] + b2[i];
a2[i] = a1[i];
a1[i] = a[i];
b2[i] = b1[i];
b1[i] = b[i];
}
for (j=0; j<LPC_FILTERORDER; j++) {
if (j == 0) {
a[0] = 0.25;
b[0] = -0.25;
} else {
a[0] = b[0] = 0.0;
}
for (i=0; i<LPC_HALFORDER; i++) {
a[i + 1] = a[i] - 2 * p[i] * a1[i] + a2[i];
b[i + 1] = b[i] - 2 * q[i] * b1[i] + b2[i];
a2[i] = a1[i];
a1[i] = a[i];
b2[i] = b1[i];
b1[i] = b[i];
}
a_coef[j + 1] = 2 * (a[LPC_HALFORDER] + b[LPC_HALFORDER]);
}
a_coef[0] = 1.0;
}