[speex-dev] narrowband embedded in wideband

Jean-Marc Valin jean-marc.valin at hermes.usherb.ca
Thu Jun 12 20:10:32 PDT 2003


Basically, if you have a wideband stream and you want to decode it in
narrowband, all you have to do is use a narrowband decoder (i.e.
initialize the decoder with speex_nb_mode instead of speex_wb_mode). Of
course, if you want to only transmit the narrowband part, you'd need to
find out where the "boundary" is. There is no function that does that
yet, but I might add it in the future.

Now, there's also the question of whether you want to do that in the
first place. While this is more practical in some ways, it also means
that you can't control the narrowband and wideband bit-rates
independently. For example, if you use the 16.8 kbps wideband more the
corresponding narrowband is 15 kbps, which is probably not what you


Le jeu 12/06/2003 à 20:13, Matthias Granberry a écrit :
> It looks like I'll need to go further into the guts of speex to do
> this.  I do, however, see some lines in nb_celp.c/nb_decode() that
> look interesting.  I guess I'll play with it.  I doubt that it will be
> terribly clean, though.
>  Jean-Marc: Take a look at line 1195 in nb_celp.c (CVS).  It reads
>  "speex_warning ("More than to wideband layers found: corrupted
>  stream?");" when it should be "More than two wideband layers..."
> "Christian.Buchner" <Christian.Buchner1 at epost.de> writes:
> >> Is there any way to access only the narrowband portion of a wideband
> >> stream?
> >
> > Try encoding a stream in UWB or WB mode using speexenc. speexdec has
> > command line options you can use to force it to NB decoding only. So
> > yes, it is possible.  And the implementation in speexdec.c should
> > show you how.
> >
> > Christian
> >
> > --- >8 ----
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Jean-Marc Valin, M.Sc.A.
LABORIUS (http://www.gel.usherb.ca/laborius)
Université de Sherbrooke, Québec, Canada

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