[vorbis-dev] Possible bug in psy.c

[Martin Reinecke]

Hi all,

I'm quite new to Vorbis, so please excuse me if I'm writing complete
nonsense (and, if possible, tell me where I'm wrong).

While searching for optimization possibilities in lib/psy.c, I found the following
piece of code in _vp_compute_mask():

  if(p->vi->smoothp){
    /* compute power^.5 of three neighboring bins to smooth for peaks
       that get split twixt bins/peaks that nail the bin.  This evens
       out treatment as we're not doing additive masking any longer. */
    double acc=work[0]*work[0]+work[1]*work[1];
    double prev=work[0];

    work[0]=sqrt(acc);
    for(i=1;i<n-1;i++){
      double this=work[i];
      acc+=work[i+1]*work[i+1];
      work[i]=sqrt(acc);
      acc-=prev*prev;
      prev=this;
    }
    work[n-1]=sqrt(acc);
  }

If this is intended to be a simple smoothing operation, I would expect that
work[0] and work[n-1] must be divided by sqrt(2) and all other entries in work
must be divided by sqrt(3) in order to renormalize work[].

Is there something I overlooked?

Cheers,
  Martin

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