Speex dev - Feb 2010 - Fwd: Re: Fixed Point on wideband-mode: Single Frame loss on 2000 Hz sine causes "freak off"

Hi Jean-Marc,
I'm currently trying to analyze the LPC synthesis filter. For this, can you
please tell me the exact format of the LPC coeffs (in variable interp_qlpc),
please?

cheers,
Frank

-----Urspr?ngliche Nachricht-----
Von: "Frank Lorenz" <Frank_wtal at web.de>
Gesendet: 02.02.10 11:00:16
An: jean-marc.valin at usherbrooke.ca
CC: speex-dev at xiph.org
Betreff: Re: [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> 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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Basically, if you have coefficients [a, b, c, d], then it means that your filter
is: 1 + a*z^-1 + b*z^-2 + c*z^-3 + d*z^-4
In fixed-point mode, the scaling factor is 8192 (i.e. Q13).

   Jean-Marc

Quoting Frank Lorenz <Frank_wtal at web.de>:
> Hi Jean-Marc,
> I'm currently trying to analyze the LPC synthesis filter. For this, can
you
> please tell me the exact format of the LPC coeffs (in variable
interp_qlpc),
> please?
>
> cheers,
> Frank
>
> -----Urspr?ngliche Nachricht-----
> Von: "Frank Lorenz" <Frank_wtal at web.de>
> Gesendet: 02.02.10 11:00:16
> An: jean-marc.valin at usherbrooke.ca
> CC: speex-dev at xiph.org
> Betreff: Re: [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> 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
>
>
> ______________________________________________________
> GRATIS f?r alle WEB.DE-Nutzer: Die maxdome Movie-FLAT!
> Jetzt freischalten unter http://movieflat.web.de
>
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