[Mp4-tech] Re: AAC - dynamic range control

[Sarvesh Kumar]

Hi,
Just ignore the next channel or frame for DRC calculation. Use previous
history parameter i.e. stored earlier and continue processing for next
channel or frame. if we are ignoring the frame or channel that has
dependencies on previous channel or frame then drc value may be wrong. So,
we check the dependencies (parameter) present, previous and next frame.
Thanks&Regards,
Sarvesh Kumar
On 2/20/08, Ralph Sperschneider <ralph.sperschneider iis.fraunhofer.de>
wrote:
>
> Pinaki S. Chanda wrote:
> >
> >
> > Dear group,
> >
> > This is regarding the excl_chn_mask[] bits in the dynamic-range_info()
> > of the AAC bit stream. Assume the excl_chn_mask[] bit is set for a
> > channel in the AAC bit stream.
> >
> > Does that mean?
> >
> > 1. we are not interested to change the DRC values (no. of bands, gain
> > etc) for this channel using the recently transmitted DRC parameters
> > but the DRC processing (spectral line multiplication) must go on this
> > channel with the previously transmitted values.
> >
> > or
> >
> > 2. we would like to stop DRC processing for this channel from now on
> > till we get the DRC parameters for this channel in a later frame.
> >
> > or
> >
> > 3. we would like to stop DRC processing (spectral line multiplication)
> > on this frame for this channel but continue DRC processing from  next
> > frame using the previous value.
> >
> > Which one is correct ?
> >
> > Thanks and regards,
> > Pinaki
> >
> >
>
> Dear Pinaki,
>
> the standard reads:
> "If there is no DRC information in a given frame for a given channel,
> use the information that was used in the previous frame."
>
> It also reads:
> "... if a channel is excluded via the appropriate exclude_mask[] bit,
> then effectively no information is transmitted for that channel ..."
>
> Due to this, your answer (1) is the correct one.
>
> Hope this helps,
> Ralph
>
> --
> Dipl.-Ing. Ralph Sperschneider  | Phone: +49 9131 776 344
> Fraunhofer IIS                  | Fax:   +49 9131 776 398
> Am Wolfsmantel 33               | mailto:
> ralph.sperschneider iis.fraunhofer.de
> D 91058 Erlangen                | http://www.iis.fraunhofer.de/amm/
>
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