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/common.h"
23 #include "libavutil/lls.h"
25 #define LPC_USE_DOUBLE
27 #include "libavutil/avassert.h"
31 * Apply Welch window function to audio block
33 static void lpc_apply_welch_window_c(const int32_t *data, int len,
41 c = 2.0 / (len - 1.0);
47 w_data[i] = data[i] * w;
48 w_data[len-1-i] = data[len-1-i] * w;
58 w_data[-i-1] = data[-i-1] * w;
59 w_data[+i ] = data[+i ] * w;
64 * Calculate autocorrelation data from audio samples
65 * A Welch window function is applied before calculation.
67 static void lpc_compute_autocorr_c(const double *data, int len, int lag,
72 for(j=0; j<lag; j+=2){
73 double sum0 = 1.0, sum1 = 1.0;
75 sum0 += data[i] * data[i-j];
76 sum1 += data[i] * data[i-j-1];
84 for(i=j-1; i<len; i+=2){
85 sum += data[i ] * data[i-j ]
86 + data[i+1] * data[i-j+1];
93 * Quantize LPC coefficients
95 static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
96 int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
103 /* define maximum levels */
104 qmax = (1 << (precision - 1)) - 1;
106 /* find maximum coefficient value */
108 for(i=0; i<order; i++) {
109 cmax= FFMAX(cmax, fabs(lpc_in[i]));
112 /* if maximum value quantizes to zero, return all zeros */
113 if(cmax * (1 << max_shift) < 1.0) {
115 memset(lpc_out, 0, sizeof(int32_t) * order);
119 /* calculate level shift which scales max coeff to available bits */
121 while((cmax * (1 << sh) > qmax) && (sh > 0)) {
125 /* since negative shift values are unsupported in decoder, scale down
126 coefficients instead */
127 if(sh == 0 && cmax > qmax) {
128 double scale = ((double)qmax) / cmax;
129 for(i=0; i<order; i++) {
134 /* output quantized coefficients and level shift */
136 for(i=0; i<order; i++) {
137 error -= lpc_in[i] * (1 << sh);
138 lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
144 static int estimate_best_order(double *ref, int min_order, int max_order)
149 for(i=max_order-1; i>=min_order-1; i--) {
158 int ff_lpc_calc_ref_coefs(LPCContext *s,
159 const int32_t *samples, int order, double *ref)
161 double autoc[MAX_LPC_ORDER + 1];
163 s->lpc_apply_welch_window(samples, s->blocksize, s->windowed_samples);
164 s->lpc_compute_autocorr(s->windowed_samples, s->blocksize, order, autoc);
165 compute_ref_coefs(autoc, order, ref, NULL);
170 double ff_lpc_calc_ref_coefs_f(LPCContext *s, const float *samples, int len,
171 int order, double *ref)
174 double signal = 0.0f, avg_err = 0.0f;
175 double autoc[MAX_LPC_ORDER+1] = {0}, error[MAX_LPC_ORDER+1] = {0};
176 const double a = 0.5f, b = 1.0f - a;
178 /* Apply windowing */
179 for (i = 0; i <= len / 2; i++) {
180 double weight = a - b*cos((2*M_PI*i)/(len - 1));
181 s->windowed_samples[i] = weight*samples[i];
182 s->windowed_samples[len-1-i] = weight*samples[len-1-i];
185 s->lpc_compute_autocorr(s->windowed_samples, len, order, autoc);
187 compute_ref_coefs(autoc, order, ref, error);
188 for (i = 0; i < order; i++)
189 avg_err = (avg_err + error[i])/2.0f;
190 return signal/avg_err;
194 * Calculate LPC coefficients for multiple orders
196 * @param lpc_type LPC method for determining coefficients,
197 * see #FFLPCType for details
199 int ff_lpc_calc_coefs(LPCContext *s,
200 const int32_t *samples, int blocksize, int min_order,
201 int max_order, int precision,
202 int32_t coefs[][MAX_LPC_ORDER], int *shift,
203 enum FFLPCType lpc_type, int lpc_passes,
204 int omethod, int max_shift, int zero_shift)
206 double autoc[MAX_LPC_ORDER+1];
207 double ref[MAX_LPC_ORDER] = { 0 };
208 double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
212 av_assert2(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER &&
213 lpc_type > FF_LPC_TYPE_FIXED);
214 av_assert0(lpc_type == FF_LPC_TYPE_CHOLESKY || lpc_type == FF_LPC_TYPE_LEVINSON);
216 /* reinit LPC context if parameters have changed */
217 if (blocksize != s->blocksize || max_order != s->max_order ||
218 lpc_type != s->lpc_type) {
220 ff_lpc_init(s, blocksize, max_order, lpc_type);
226 if (lpc_type == FF_LPC_TYPE_LEVINSON || (lpc_type == FF_LPC_TYPE_CHOLESKY && lpc_passes > 1)) {
227 s->lpc_apply_welch_window(samples, blocksize, s->windowed_samples);
229 s->lpc_compute_autocorr(s->windowed_samples, blocksize, max_order, autoc);
231 compute_lpc_coefs(autoc, max_order, &lpc[0][0], MAX_LPC_ORDER, 0, 1);
233 for(i=0; i<max_order; i++)
234 ref[i] = fabs(lpc[i][i]);
239 if (lpc_type == FF_LPC_TYPE_CHOLESKY) {
240 LLSModel *m = s->lls_models;
241 LOCAL_ALIGNED(32, double, var, [FFALIGN(MAX_LPC_ORDER+1,4)]);
242 double av_uninit(weight);
243 memset(var, 0, FFALIGN(MAX_LPC_ORDER+1,4)*sizeof(*var));
245 for(j=0; j<max_order; j++)
246 m[0].coeff[max_order-1][j] = -lpc[max_order-1][j];
248 for(; pass<lpc_passes; pass++){
249 avpriv_init_lls(&m[pass&1], max_order);
252 for(i=max_order; i<blocksize; i++){
253 for(j=0; j<=max_order; j++)
254 var[j]= samples[i-j];
257 double eval, inv, rinv;
258 eval= m[pass&1].evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
259 eval= (512>>pass) + fabs(eval - var[0]);
262 for(j=0; j<=max_order; j++)
268 m[pass&1].update_lls(&m[pass&1], var);
270 avpriv_solve_lls(&m[pass&1], 0.001, 0);
273 for(i=0; i<max_order; i++){
274 for(j=0; j<max_order; j++)
275 lpc[i][j]=-m[(pass-1)&1].coeff[i][j];
276 ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
278 for(i=max_order-1; i>0; i--)
279 ref[i] = ref[i-1] - ref[i];
282 opt_order = max_order;
284 if(omethod == ORDER_METHOD_EST) {
285 opt_order = estimate_best_order(ref, min_order, max_order);
287 quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
289 for(i=min_order-1; i<max_order; i++) {
290 quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
297 av_cold int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
298 enum FFLPCType lpc_type)
300 s->blocksize = blocksize;
301 s->max_order = max_order;
302 s->lpc_type = lpc_type;
304 s->windowed_buffer = av_mallocz((blocksize + 2 + FFALIGN(max_order, 4)) *
305 sizeof(*s->windowed_samples));
306 if (!s->windowed_buffer)
307 return AVERROR(ENOMEM);
308 s->windowed_samples = s->windowed_buffer + FFALIGN(max_order, 4);
310 s->lpc_apply_welch_window = lpc_apply_welch_window_c;
311 s->lpc_compute_autocorr = lpc_compute_autocorr_c;
319 av_cold void ff_lpc_end(LPCContext *s)
321 av_freep(&s->windowed_buffer);