1 /*
2 * LPC utility code
3 * Copyright (c) 2006 Justin Ruggles <justin.ruggles@gmail.com>
4 *
5 * This file is part of FFmpeg.
6 *
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.
11 *
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.
16 *
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
20 */
21
22 #ifndef AVCODEC_LPC_H
23 #define AVCODEC_LPC_H
24
25 #include <stdint.h>
27
28 #define ORDER_METHOD_EST 0
29 #define ORDER_METHOD_2LEVEL 1
30 #define ORDER_METHOD_4LEVEL 2
31 #define ORDER_METHOD_8LEVEL 3
32 #define ORDER_METHOD_SEARCH 4
33 #define ORDER_METHOD_LOG 5
34
35 #define MIN_LPC_ORDER 1
36 #define MAX_LPC_ORDER 32
37
38 /**
39 * LPC analysis type
40 */
48 };
49
56
57 /**
58 * Apply a Welch window to an array of input samples.
59 * The output samples have the same scale as the input, but are in double
60 * sample format.
61 * @param data input samples
62 * @param len number of input samples
63 * @param w_data output samples
64 */
66 double *w_data);
67 /**
68 * Perform autocorrelation on input samples with delay of 0 to lag.
69 * @param data input samples.
70 * constraints: no alignment needed, but must have at
71 * least lag*sizeof(double) valid bytes preceding it, and
72 * size must be at least (len+1)*sizeof(double) if data is
73 * 16-byte aligned or (len+2)*sizeof(double) if data is
74 * unaligned.
75 * @param len number of input samples to process
76 * @param lag maximum delay to calculate
77 * @param autoc output autocorrelation coefficients.
78 * constraints: array size must be at least lag+1.
79 */
81 double *autoc);
83
84
85 /**
86 * Calculate LPC coefficients for multiple orders
87 */
89 const int32_t *samples,
int blocksize,
int min_order,
90 int max_order, int precision,
93 int omethod, int max_shift, int zero_shift);
94
96 const int32_t *samples,
int order,
double *ref);
97
98 /**
99 * Initialize LPCContext.
100 */
104
105 /**
106 * Uninitialize LPCContext.
107 */
109
110 #ifdef LPC_USE_DOUBLE
111 #define LPC_TYPE double
112 #else
113 #define LPC_TYPE float
114 #endif
115
116 /**
117 * Schur recursion.
118 * Produces reflection coefficients from autocorrelation data.
119 */
122 {
123 int i, j;
126
127 for (i = 0; i < max_order; i++)
128 gen0[i] = gen1[i] = autoc[i + 1];
129
130 err = autoc[0];
131 ref[0] = -gen1[0] / err;
132 err += gen1[0] * ref[0];
133 if (error)
134 error[0] = err;
135 for (i = 1; i < max_order; i++) {
136 for (j = 0; j < max_order - i; j++) {
137 gen1[j] = gen1[j + 1] + ref[i - 1] * gen0[j];
138 gen0[j] = gen1[j + 1] * ref[i - 1] + gen0[j];
139 }
140 ref[i] = -gen1[0] / err;
141 err += gen1[0] * ref[i];
142 if (error)
143 error[i] = err;
144 }
145 }
146
147 /**
148 * Levinson-Durbin recursion.
149 * Produce LPC coefficients from autocorrelation data.
150 */
152 LPC_TYPE *lpc,
int lpc_stride,
int fail,
153 int normalize)
154 {
155 int i, j;
158
160
161 if (normalize)
162 err = *autoc++;
163
164 if (fail && (autoc[max_order - 1] == 0 || err <= 0))
165 return -1;
166
167 for(i=0; i<max_order; i++) {
169
170 if (normalize) {
171 for(j=0; j<i; j++)
172 r -= lpc_last[j] * autoc[i-j-1];
173
174 r /= err;
175 err *= 1.0 - (r *
r);
176 }
177
179
180 for(j=0; j < (i+1)>>1; j++) {
184 lpc[i-1-j] = b + r * f;
185 }
186
187 if (fail && err < 0)
188 return -1;
189
190 lpc_last = lpc;
191 lpc += lpc_stride;
192 }
193
194 return 0;
195 }
196
197 #endif /* AVCODEC_LPC_H */