/****************************************************************** | |
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; | |
} | |