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git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@4002 65c4cc65-6c06-0410-ace0-fbb531ad65f3
265 lines
7.2 KiB
C
Executable File
265 lines
7.2 KiB
C
Executable File
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/******************************************************************
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iLBC Speech Coder ANSI-C Source Code
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lsf.c
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Copyright (C) The Internet Society (2004).
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All Rights Reserved.
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******************************************************************/
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#include <string.h>
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#include <math.h>
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#include "iLBC_define.h"
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#include "lsf.h"
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/*----------------------------------------------------------------*
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* conversion from lpc coefficients to lsf coefficients
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*---------------------------------------------------------------*/
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void a2lsf(
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float *freq,/* (o) lsf coefficients */
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float *a /* (i) lpc coefficients */
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){
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float steps[LSF_NUMBER_OF_STEPS] =
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{(float)0.00635, (float)0.003175, (float)0.0015875,
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(float)0.00079375};
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float step;
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int step_idx;
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int lsp_index;
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float p[LPC_HALFORDER];
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float q[LPC_HALFORDER];
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float p_pre[LPC_HALFORDER];
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float q_pre[LPC_HALFORDER];
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float old_p, old_q, *old;
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float *pq_coef;
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float omega, old_omega;
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int i;
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float hlp, hlp1, hlp2, hlp3, hlp4, hlp5;
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for (i=0; i<LPC_HALFORDER; i++) {
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p[i] = (float)-1.0 * (a[i + 1] + a[LPC_FILTERORDER - i]);
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q[i] = a[LPC_FILTERORDER - i] - a[i + 1];
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}
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p_pre[0] = (float)-1.0 - p[0];
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p_pre[1] = - p_pre[0] - p[1];
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p_pre[2] = - p_pre[1] - p[2];
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p_pre[3] = - p_pre[2] - p[3];
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p_pre[4] = - p_pre[3] - p[4];
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p_pre[4] = p_pre[4] / 2;
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q_pre[0] = (float)1.0 - q[0];
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q_pre[1] = q_pre[0] - q[1];
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q_pre[2] = q_pre[1] - q[2];
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q_pre[3] = q_pre[2] - q[3];
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q_pre[4] = q_pre[3] - q[4];
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q_pre[4] = q_pre[4] / 2;
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omega = 0.0;
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old_omega = 0.0;
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old_p = FLOAT_MAX;
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old_q = FLOAT_MAX;
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/* Here we loop through lsp_index to find all the
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LPC_FILTERORDER roots for omega. */
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for (lsp_index = 0; lsp_index<LPC_FILTERORDER; lsp_index++) {
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/* Depending on lsp_index being even or odd, we
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alternatively solve the roots for the two LSP equations. */
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if ((lsp_index & 0x1) == 0) {
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pq_coef = p_pre;
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old = &old_p;
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} else {
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pq_coef = q_pre;
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old = &old_q;
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}
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/* Start with low resolution grid */
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for (step_idx = 0, step = steps[step_idx];
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step_idx < LSF_NUMBER_OF_STEPS;){
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/* cos(10piw) + pq(0)cos(8piw) + pq(1)cos(6piw) +
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pq(2)cos(4piw) + pq(3)cod(2piw) + pq(4) */
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hlp = (float)cos(omega * TWO_PI);
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hlp1 = (float)2.0 * hlp + pq_coef[0];
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hlp2 = (float)2.0 * hlp * hlp1 - (float)1.0 +
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pq_coef[1];
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hlp3 = (float)2.0 * hlp * hlp2 - hlp1 + pq_coef[2];
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hlp4 = (float)2.0 * hlp * hlp3 - hlp2 + pq_coef[3];
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hlp5 = hlp * hlp4 - hlp3 + pq_coef[4];
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if (((hlp5 * (*old)) <= 0.0) || (omega >= 0.5)){
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if (step_idx == (LSF_NUMBER_OF_STEPS - 1)){
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if (fabs(hlp5) >= fabs(*old)) {
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freq[lsp_index] = omega - step;
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} else {
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freq[lsp_index] = omega;
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}
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if ((*old) >= 0.0){
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*old = (float)-1.0 * FLOAT_MAX;
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} else {
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*old = FLOAT_MAX;
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}
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omega = old_omega;
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step_idx = 0;
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step_idx = LSF_NUMBER_OF_STEPS;
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} else {
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if (step_idx == 0) {
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old_omega = omega;
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}
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step_idx++;
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omega -= steps[step_idx];
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/* Go back one grid step */
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step = steps[step_idx];
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}
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} else {
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/* increment omega until they are of different sign,
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and we know there is at least one root between omega
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and old_omega */
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*old = hlp5;
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omega += step;
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}
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}
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}
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for (i = 0; i<LPC_FILTERORDER; i++) {
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freq[i] = freq[i] * TWO_PI;
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}
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}
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/*----------------------------------------------------------------*
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* conversion from lsf coefficients to lpc coefficients
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*---------------------------------------------------------------*/
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void lsf2a(
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float *a_coef, /* (o) lpc coefficients */
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float *freq /* (i) lsf coefficients */
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){
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int i, j;
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float hlp;
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float p[LPC_HALFORDER], q[LPC_HALFORDER];
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float a[LPC_HALFORDER + 1], a1[LPC_HALFORDER],
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a2[LPC_HALFORDER];
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float b[LPC_HALFORDER + 1], b1[LPC_HALFORDER],
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b2[LPC_HALFORDER];
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for (i=0; i<LPC_FILTERORDER; i++) {
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freq[i] = freq[i] * PI2;
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}
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/* Check input for ill-conditioned cases. This part is not
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found in the TIA standard. It involves the following 2 IF
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blocks. If "freq" is judged ill-conditioned, then we first
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modify freq[0] and freq[LPC_HALFORDER-1] (normally
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LPC_HALFORDER = 10 for LPC applications), then we adjust
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the other "freq" values slightly */
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if ((freq[0] <= 0.0) || (freq[LPC_FILTERORDER - 1] >= 0.5)){
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if (freq[0] <= 0.0) {
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freq[0] = (float)0.022;
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}
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if (freq[LPC_FILTERORDER - 1] >= 0.5) {
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freq[LPC_FILTERORDER - 1] = (float)0.499;
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}
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hlp = (freq[LPC_FILTERORDER - 1] - freq[0]) /
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(float) (LPC_FILTERORDER - 1);
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for (i=1; i<LPC_FILTERORDER; i++) {
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freq[i] = freq[i - 1] + hlp;
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}
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}
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memset(a1, 0, LPC_HALFORDER*sizeof(float));
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memset(a2, 0, LPC_HALFORDER*sizeof(float));
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memset(b1, 0, LPC_HALFORDER*sizeof(float));
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memset(b2, 0, LPC_HALFORDER*sizeof(float));
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memset(a, 0, (LPC_HALFORDER+1)*sizeof(float));
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memset(b, 0, (LPC_HALFORDER+1)*sizeof(float));
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/* p[i] and q[i] compute cos(2*pi*omega_{2j}) and
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cos(2*pi*omega_{2j-1} in eqs. 4.2.2.2-1 and 4.2.2.2-2.
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Note that for this code p[i] specifies the coefficients
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used in .Q_A(z) while q[i] specifies the coefficients used
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in .P_A(z) */
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for (i=0; i<LPC_HALFORDER; i++) {
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p[i] = (float)cos(TWO_PI * freq[2 * i]);
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q[i] = (float)cos(TWO_PI * freq[2 * i + 1]);
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}
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a[0] = 0.25;
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b[0] = 0.25;
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for (i= 0; i<LPC_HALFORDER; i++) {
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a[i + 1] = a[i] - 2 * p[i] * a1[i] + a2[i];
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b[i + 1] = b[i] - 2 * q[i] * b1[i] + b2[i];
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a2[i] = a1[i];
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a1[i] = a[i];
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b2[i] = b1[i];
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b1[i] = b[i];
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}
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for (j=0; j<LPC_FILTERORDER; j++) {
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if (j == 0) {
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a[0] = 0.25;
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b[0] = -0.25;
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} else {
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a[0] = b[0] = 0.0;
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}
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for (i=0; i<LPC_HALFORDER; i++) {
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a[i + 1] = a[i] - 2 * p[i] * a1[i] + a2[i];
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b[i + 1] = b[i] - 2 * q[i] * b1[i] + b2[i];
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a2[i] = a1[i];
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a1[i] = a[i];
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b2[i] = b1[i];
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b1[i] = b[i];
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}
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a_coef[j + 1] = 2 * (a[LPC_HALFORDER] + b[LPC_HALFORDER]);
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}
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a_coef[0] = 1.0;
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}
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