[M4IF Technotes] Re: AAC Conformance

[Ralph Sperschneider]

Dear Anil, Alan,
for AAC, there is no such thing than "Fixed-point accuracy". However, there is 
an accuracy measure k for the two conformance tests measurements (RMS and LSB 
test). On default, k=16. If you are designing a decoder which is conform to a 
higher or to a lower level, you might (higher) / must (lower) specify this level 
in your decoder specification.
This variableness has been introduced lately for both, MPEG-2 and MPEG-4 AAC. 
You will find the details in the appropriate conformance corrigenda:
  * ISO/IEC 13818-4:1998/Amd.1:1999/Cor.1
     (N5029, not yet published)
  * ISO/IEC 14496-4:2000/Cor.2
     (N5042, not yet published)
There, you will find the following text:
RMS/LSB Measurement
To fulfill the “RMS/LSB Measurement” test at an accuracy level of “K bit”, an 
ISO/IEC 14496-3 decoder shall provide an output waveform such that the RMS level 
of the difference signal between the output of the decoder under test and the 
supplied reference output is less than 2^-(K-1)/sqrt(12).  In addition, the 
difference signal shall have a maximum absolute value of at most 2^-(K-2) 
relative to full-scale. The “RMS/LSB Measurement” test shall be carried out for 
an accuracy level of K=16 bit unless a different accuracy level is explicitly 
stated.
Best regards,
Ralph
Alan Thomson wrote:
> Not really.
>  
> There are "fixed-point accuracy" criteria (which are much less strict 
> than the full accuracy one) but I believe they only apply to CELP & 
> TwinVQ, not AAC.
>  
> Alan.
> 
>     -----Original Message-----
>     *From:* Anil Kumar [mailto:anil.kumar   ittiam.com]
>     *Sent:* 10 June 2023 13:54
>     *To:* technotes   lists.m4if.org
>     *Subject:* [M4IF Technotes] AAC Conformance
> 
>     Hi all,
>         Is there any such thing as 'Limited Accuracy' conformance for
>     AAC decoder similar to that of MP3 decoder conformance? If so, is it
>     the same as MP3 Limited Accuracy conformance?
>      
>     Thanks in advance,
>     Anil

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Dipl.-Ing. Ralph Sperschneider  | Phone: +49 9131 776 344
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