[Speex-dev] Fwd: Re: Fixed Point on wideband-mode: Single Frame loss on 2000 Hz sine causes "freak off"

Jean-Marc Valin Jean-Marc.Valin at USherbrooke.ca
Tue Feb 2 08:57:30 PST 2010

Just had a look and the fixed-point residual *does* look odd. That's worth
investigating (though I don't think it's related to LPC stability).


Quoting Frank Lorenz <Frank_wtal at web.de>:

> Jean-Marc Valin <Jean-Marc.Valin at USherbrooke.ca> hat am 1. Februar 2010 um
> 17:29 geschrieben:
> > Can you look at the residual signal? i.e. what it looks like after the
> pitch is
> > removed. Any significant difference there? Also, the pitch gain can be
> > informative.
> >
> I catched the "orignal" residual (st->exc from line 400 inside nb_celp.c)
> plus the "synthesized" one (exc on line 880 inside nb_celp.c) both for fixed
> and floating point.
> There is a significant difference in the residual signal -- the fixed point
> signal shows some kind of "glitches" (see attachments) while the floating
> point version looks more or less smooth. But it is interesting that the huge
> overdrive you can observe in the re-synthesized output signal isn't present
> in the synthesized residual. This leads to an instable LPC synthesis filter,
> or am I wrong?
> cheers,
> Frank
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