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

[Ralph Sperschneider]

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
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