[Mp4-tech] Re: 20 bits in AAC

[Ralph Sperschneider]

Regis Rossi A. Faria wrote:
> Dear Schuyler,
> 
> Thanks for the references. ;)
> I wonder if there is an interest or not moving towards 20 bit (or 
> higher) quality for next generation of codecs, for consumer applications.
> 
> Regards,
> Regis

Dear Regis,
I am not sure you fully understood Schuylers comment. For sure you can input 
more than 16 bit per sample to an AAC encoder. For sure you can retrieve more 
than 16 bit per sample out of an AAC decoder.
With regard to the decoder, a certain arithmetic accuracy is required, the 
details can be found in ISO/IEC14496-4. Without restrictions of the arithmetic 
unit used by the decoder (which apply for certain fixed point implementations) 
you can get a rather high accuracy, significantly more than can be presented 
with 16 bit per sample. Therefore, the reference waveforms are provided with 24 
bit per sample.
Anyhow, the decoder can only render what the encoder has considered to be 
psycho-acoustically relevant and could encode based on the bitrate restrictions.
Hope this helps,
Ralph
> 
> Schuyler Quackenbush escreveu:
>> Dear Regis,
>>
>> The AAC specification does not by itself set an output word length, in 
>> that it is not a bit-exact decoding specification. The MPEG-2 and 
>> MPEG-2 Conformance specs for AAC do discuss a procedure to follow to 
>> claim that a decoder has "N-bit compliance" as far as output word length.
>>
>> Best,
>> Schuyler
>>  
>> ----- Original Message ----
>> From: Regis Rossi A. Faria <regis lsi.usp.br>
>> To: Mp4-tech Audio <mp4-tech lists.mpegif.org>
>> Sent: Wednesday, August 22, 2023 11:43:58 PM
>> Subject: [Mp4-tech] 20 bits in AAC
>>
>> Hi all,
>>
>> I have not found in MPEG-4 AAC references to sample bit depth, does 
>> anyone can help provide references and information on restrictions and 
>> bit depth implementation guidelines regarding 20 bits and more?
>>
>> Thanks in advance,
>>
>> Regis R A Faria
>> LSI-TEC/LSI-Univ. Sao Paulo
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>>
>>   
> _______________________________________________
> NOTE: Please use clear subject lines for your posts. Include [audio, 
> [video], [systems], [general] or another apppropriate identifier to 
> indicate the type of question you have.
> 
> Note: Conduct on the mailing list is subject to the Antitrust guidelines 
> found at 
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Dipl.-Ing. Ralph Sperschneider  | Phone: +49 9131 776 344
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