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/*
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;
}
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