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lpc.h
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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>
26 #include "libavutil/avassert.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  */
41 enum FFLPCType {
42  FF_LPC_TYPE_DEFAULT = -1, ///< use the codec default LPC type
43  FF_LPC_TYPE_NONE = 0, ///< do not use LPC prediction or use all zero coefficients
44  FF_LPC_TYPE_FIXED = 1, ///< fixed LPC coefficients
45  FF_LPC_TYPE_LEVINSON = 2, ///< Levinson-Durbin recursion
46  FF_LPC_TYPE_CHOLESKY = 3, ///< Cholesky factorization
47  FF_LPC_TYPE_NB , ///< Not part of ABI
48 };
49 
50 typedef struct LPCContext {
51  int blocksize;
52  int max_order;
54  double *windowed_buffer;
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  */
80  void (*lpc_compute_autocorr)(const double *data, int len, int lag,
81  double *autoc);
82 } LPCContext;
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,
91  int32_t coefs[][MAX_LPC_ORDER], int *shift,
92  enum FFLPCType lpc_type, int lpc_passes,
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  */
101 int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
102  enum FFLPCType lpc_type);
104 
105 /**
106  * Uninitialize LPCContext.
107  */
108 void ff_lpc_end(LPCContext *s);
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  */
120 static inline void compute_ref_coefs(const LPC_TYPE *autoc, int max_order,
121  LPC_TYPE *ref, LPC_TYPE *error)
122 {
123  int i, j;
124  LPC_TYPE err;
125  LPC_TYPE gen0[MAX_LPC_ORDER], gen1[MAX_LPC_ORDER];
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  */
151 static inline int compute_lpc_coefs(const LPC_TYPE *autoc, int max_order,
152  LPC_TYPE *lpc, int lpc_stride, int fail,
153  int normalize)
154 {
155  int i, j;
156  LPC_TYPE err = 0;
157  LPC_TYPE *lpc_last = lpc;
158 
159  av_assert2(normalize || !fail);
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++) {
168  LPC_TYPE r = -autoc[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 
178  lpc[i] = r;
179 
180  for(j=0; j < (i+1)>>1; j++) {
181  LPC_TYPE f = lpc_last[ j];
182  LPC_TYPE b = lpc_last[i-1-j];
183  lpc[ j] = f + r * b;
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 */