[vorbis-dev] Floor0-decode-curve

[Csaba Szepesvari]

In lsp.c of an older distribution (I did not check if this is still in
lsp.c):

/* side effect: changes *lsp to cosines of lsp */
void mudec_lsp_to_curve(float *curve,int *map,int n,int ln,float *lsp,int m,
                            float amp,float ampoffset){
  int i;
  float wdel=M_PI/ln;
  for(i=0;i<m;i++)lsp[i]=2.f*cos(lsp[i]);

  i=0;
  while(i<n){
    int j,k=map[i];
    float p=.5f;
    float q=.5f;
    float w=2.f*cos(wdel*k);
    for(j=1;j<m;j+=2){
      q *= w-lsp[j-1];
      p *= w-lsp[j];
    }
    if(j==m){
      /* odd order filter; slightly assymetric */
      /* the last coefficient */
      q*=w-lsp[j-1];
      p*=p*(4.f-w*w);
      q*=q;
    }else{
      /* even order filter; still symmetric */
      p*=p*(2.f-w);
      q*=q*(2.f+w);
    }

    q=fromdB(amp/sqrt(p+q)-ampoffset);

    curve[i]*=q;
    while(map[++i]==k)curve[i]*=q;
  }
}

Hope this helped,

Csaba

> -----Original Message-----
> From: owner-vorbis-dev at xiph.org [mailto:owner-vorbis-dev at xiph.org]On
> Behalf Of Christian Wassmer
> Sent: Wednesday, October 15, 2003 12:27 PM
> To: vorbis-dev at xiph.org
> Subject: [vorbis-dev] Floor0-decode-curve
>
>
> Hello  I'm working on a fix-point decoder for AOS/Bluebottle -
> the proprietary  OS of ETH Zurich.  I've some problems with
> Floor0-curve-computation: I don't know what the  little omega
> [cos(w)] stands for, line 3 of the official Vorbis
> documentation. Does anybody knows what this value means?  I've
> tried to get the answer from the jOrbis and Tremor, but both seem
>  to do - among other things - Floor0-Curve-Computation somehow
> different  than the official documentation. Btw, isn't it
> recommed to implement as  the official documentation proposes?
> Thanks Christian Wassmer  --- >8 ---- List archives:
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