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Diffstat (limited to 'lpc.c')
| -rw-r--r-- | lpc.c | 252 |
1 files changed, 252 insertions, 0 deletions
@@ -0,0 +1,252 @@ +/* +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; +} + |