[Mp4-tech] HE-AAC downsampled synthesis filterbank

[Andy Quan]

Thank you! Is this corrigendum currently under drafting? It is nice if
I can read the details. But do you mean that the documentation you
mentioned is not available from ISO, no matter being free or not?
On 9/25/07, Andreas Schneider <Andreas.Schneider codingtechnologies.com> wrote:
> Hi Andy,
>
> this is no trick. It was a typo in the specification that has been
> corrected by ISO/IEC 14496-3:2005/Cor.4:200X. As the 200X suggests, this
> corrigendum is not yet published.
>
> Kind regards,
>
> Andreas
>
>
> mp4-tech-bounces lists.mpegif.org wrote on 25.09.2023 14:25:14:
>
> > Hi folks,
> >
> > I read the ISO spec 14496-3 Amd 1 on downsampled complex synthesis QMF
> > filter. On page 67, it is said the filterbank coefficients are defined
> > as (1/64)*exp(i*pi*(k+.5)*(2*n-127)/64).
> > However, when I turn to the ISO reference, in ct_polyphase.c, the code
> > defines the coefficients like:cos( PI / 64.0 * (k+0.5) * (2*l-127.5)
> > ).
> >
> > My question is why the spec uses 127 while its reference code
> > implementation uses 127.5. I don't understand this 0.5 trick. Can any
> > one explain this for me? Thanks in advance.
> >
> >
> > --
> > Regards,
> > Andy Quan
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> --
> Andreas Schneider
> Senior Research Engineer
> mailto:snd CodingTechnologies.com
>
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>

-- 
Regards,
Quan Zhengyuan £¨È«ÕýÔª£©