3 * Copyright (c) 2006 Justin Ruggles <justin.ruggles@gmail.com>
5 * This file is part of FFmpeg.
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22 #include "libavutil/lls.h"
28 * Levinson-Durbin recursion.
29 * Produces LPC coefficients from autocorrelation data.
31 static void compute_lpc_coefs(const double *autoc, int max_order,
32 double lpc[][MAX_LPC_ORDER], double *ref)
35 double err = autoc[0];
36 double lpc_tmp[MAX_LPC_ORDER];
38 for(i=0; i<max_order; i++) {
39 double r = -autoc[i+1];
42 r -= lpc_tmp[j] * autoc[i-j];
50 for(j=0; j < i>>1; j++) {
51 double tmp = lpc_tmp[j];
52 lpc_tmp[j] += r * lpc_tmp[i-1-j];
53 lpc_tmp[i-1-j] += r * tmp;
57 lpc_tmp[j] += lpc_tmp[j] * r;
60 lpc[i][j] = -lpc_tmp[j];
65 * Quantize LPC coefficients
67 static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
68 int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
75 /* define maximum levels */
76 qmax = (1 << (precision - 1)) - 1;
78 /* find maximum coefficient value */
80 for(i=0; i<order; i++) {
81 cmax= FFMAX(cmax, fabs(lpc_in[i]));
84 /* if maximum value quantizes to zero, return all zeros */
85 if(cmax * (1 << max_shift) < 1.0) {
87 memset(lpc_out, 0, sizeof(int32_t) * order);
91 /* calculate level shift which scales max coeff to available bits */
93 while((cmax * (1 << sh) > qmax) && (sh > 0)) {
97 /* since negative shift values are unsupported in decoder, scale down
98 coefficients instead */
99 if(sh == 0 && cmax > qmax) {
100 double scale = ((double)qmax) / cmax;
101 for(i=0; i<order; i++) {
106 /* output quantized coefficients and level shift */
108 for(i=0; i<order; i++) {
109 error += lpc_in[i] * (1 << sh);
110 lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
116 static int estimate_best_order(double *ref, int min_order, int max_order)
121 for(i=max_order-1; i>=min_order-1; i--) {
131 * Calculate LPC coefficients for multiple orders
133 int ff_lpc_calc_coefs(DSPContext *s,
134 const int32_t *samples, int blocksize, int min_order,
135 int max_order, int precision,
136 int32_t coefs[][MAX_LPC_ORDER], int *shift, int use_lpc,
137 int omethod, int max_shift, int zero_shift)
139 double autoc[MAX_LPC_ORDER+1];
140 double ref[MAX_LPC_ORDER];
141 double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
145 assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER);
148 s->flac_compute_autocorr(samples, blocksize, max_order, autoc);
150 compute_lpc_coefs(autoc, max_order, lpc, ref);
153 double var[MAX_LPC_ORDER+1], weight;
155 for(pass=0; pass<use_lpc-1; pass++){
156 av_init_lls(&m[pass&1], max_order);
159 for(i=max_order; i<blocksize; i++){
160 for(j=0; j<=max_order; j++)
161 var[j]= samples[i-j];
164 double eval, inv, rinv;
165 eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
166 eval= (512>>pass) + fabs(eval - var[0]);
169 for(j=0; j<=max_order; j++)
175 av_update_lls(&m[pass&1], var, 1.0);
177 av_solve_lls(&m[pass&1], 0.001, 0);
180 for(i=0; i<max_order; i++){
181 for(j=0; j<max_order; j++)
182 lpc[i][j]= m[(pass-1)&1].coeff[i][j];
183 ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
185 for(i=max_order-1; i>0; i--)
186 ref[i] = ref[i-1] - ref[i];
188 opt_order = max_order;
190 if(omethod == ORDER_METHOD_EST) {
191 opt_order = estimate_best_order(ref, min_order, max_order);
193 quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
195 for(i=min_order-1; i<max_order; i++) {
196 quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);