1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
|
/*
vox - a musical real-time vocoder. version 1.0
Copyright (C) 2000 Simon MORLAT (simon.morlat@free.fr)
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#include "tables.h"
#include "lpc.h"
#define THRES 0.06
#define Dmin 10.81e-3
/* Levinson Durbin algorithm for computing LPC coefficients using
autocorrelation fonction */
void lev_durb(double *corr,double *lpc_coef)
{
double k[11],tab[11];
double err,acc;
int i,j;
double *a=tab;
double *prev_a=lpc_coef;
double *exch;
/*init vectors*/
for (i=0; i<11; i++)
{
prev_a[i]=0;
a[i]=0;
};
err=corr[0];
for(i=1; i<11; i++)
{
prev_a[0]=1;
acc=0;
for(j=0; j<i; j++)
{
acc=acc+prev_a[j]*corr[i-j];
};
a[i]=k[i]=-acc/err;
for(j=1; j<i; j++)
{
a[j]=prev_a[j]+k[i]*prev_a[i-j];
};
err=(1-k[i]*k[i])*err;
exch=prev_a;
prev_a=a;
a=exch;
};
}
void comp_lpc(double *buf_x,double *corr,double *lpc_coef,int n)
{
double buffer[n*3];
double acc,max=0;
int i,j;
/* computes LPC analysis for one subframe */
/* hamming windowing*/
acc=0;
for(i=0; i<2*n; i++)
{
acc+=buf_x[i]*buf_x[i];
};
if (acc>THRES)
{
for(i=0; i<3*n; i++)
{
buffer[i]=buf_x[i-n]*HammingWindowTable[i];
};
/* autocorrelation computation*/
for(i=0; i<11; i++)
{
acc=0;
for(j=i; j<n*3; j++)
{
acc=acc+buffer[j]*buffer[j-i];
};
/* correction with binomial coeffs */
corr[i]=acc;//*BinomialWindowTable[i];
};
corr[0]=corr[0]*(1.0+1.0/1024.0);
lev_durb(corr,lpc_coef);
}
else
{
for(i=0; i<11; i++)
{
lpc_coef[i]=0;
};
}
}
/* LPC to LSP coefficients conversion */
/* evaluate function C(x) (whose roots are LSP coeffs)*/
double evalc(double cw,double *fonc)
{
double b[7];
double x,res;
int k;
x=cw;
b[5]=1;
b[6]=0;
for(k=4; k>0; k--)
{
b[k]=2*x*b[k+1]-b[k+2]+fonc[5-k];
};
res=x*b[1]-b[2]+fonc[5]/2;
return(res);
}
/* converts LPC vector into LSP frequency vector */
/* all LSP frenquencies are in [0;PI] but are normalized to be in [0;1] */
void lpc2lsp(double lpc_coef[],double *f1,double *f2,double lsp_coef[])
{
int i,k=1;
double *fonc,*prev_f,*f_exch;
double prev_sign1,sign,prev_sign2;
double *s, *prev_s,*s_exch;
double lpc_exp[11];
/* first computes an additional bandwidth expansion on LPC coeffs*/
for(i=1; i<11; i++)
{
lpc_exp[i]=lpc_coef[i]*BandExpTable[i];
};
/* computes the F1 and F2 coeffs*/
f1[0]=f2[0]=1;
for(i=0; i<5; i++)
{
f1[i+1]=lpc_exp[i+1]+lpc_exp[10-i]-f1[i];
f2[i+1]=lpc_exp[i+1]-lpc_exp[10-i]+f2[i];
};
/*find the roots of C(x) alternatively for F1 and F2*/
fonc=f1;
prev_f=f2;
prev_sign1=evalc(1.0,f1);
prev_sign2=evalc(1.0,f2);
s=&prev_sign1;
prev_s=&prev_sign2;
for(i=1; i<256; i++)
{
sign=evalc(CosineTable[i],fonc);
if ((sign)*(*s)<0)
{
/* interpolate to find root*/
lsp_coef[k]=((double)i-(*s)/(sign-(*s)))/256.0;
k++;
/* chek if all roots are found */
if (k==11) i=257;
(*s)=sign;
/* pointers exchange */
s_exch=s;
s=prev_s;
prev_s=s_exch;
f_exch=fonc;
fonc=prev_f;
prev_f=f_exch;
}
else (*s)=sign;
}
/* if here all roots are not found , use lspDC vector */
if (k!=11)
{
for(i=1; i<11; i++)
{
lsp_coef[i]=LspDcTable[i];
};
};
}
/* converts lsp frequencies to lpc coeffs */
void lsp2lpc(double *lsp_coef,double *lpc_coef)
{
int i,j=0,index,ok=1;
double lspcos[11],delta,tmp,p_avg;
double F1[12],F2[12]; /* begin at indice two*/
F1[0]=0;
F1[1]=1;
F2[0]=0;
F2[1]=1;
/* stability check */
while(ok && (j<11))
{
ok=0;
for(i=1; i<10; i++)
{
if( (lsp_coef[i+1]-lsp_coef[i]) < Dmin)
{
ok=1;
p_avg=(lsp_coef[i]+lsp_coef[i+1])/2.0;
lsp_coef[i]=p_avg-Dmin/2.0;
lsp_coef[i+1]=p_avg+Dmin/2.0;
};
};
j++;
}
/* first converts lsp frequencies to lsp coefficients */
for (i=1; i<11; i++)
{
/* interpolation */
tmp=lsp_coef[i]*255.0;
index=(int)tmp;
delta=CosineTable[index+1]-CosineTable[index];
lspcos[i]=CosineTable[index]+delta*(tmp-index);
};
for(i=2; i<7; i++)
{
F1[i]=-2*lspcos[2*i-3]*F1[i-1]+2*F1[i-2];
F2[i]=-2*lspcos[2*i-2]*F2[i-1]+2*F2[i-2];
for(j=i-1; j>1; j--)
{
F1[j]=F1[j]-2*lspcos[2*i-3]*F1[j-1]+F1[j-2];
F2[j]=F2[j]-2*lspcos[2*i-2]*F2[j-1]+F2[j-2];
};
};
for(i=6; i>1; i--)
{
F1[i]=F1[i]+F1[i-1];
F2[i]=F2[i]-F2[i-1];
};
for(i=2; i<7; i++)
{
lpc_coef[i-1]=(F1[i]+F2[i])*0.5;
lpc_coef[i+4]=(F1[8-i]-F2[8-i])*0.5;
};
lpc_coef[0]=1;
}
|
