[Mp4-tech] AAC profiles and levels

[Bernhard Grill]

Apala Guha wrote:
> Levels in AAC have been defined in terms of PCU and RCU.
> 
> PCU is defined in terms of MOPS. But what do you consider as an
> operation?
> 
> Also RCU is defined in KWords. What is the length of an word in this
> case?

Dear Apala,
the numbers were estimated based on past experience in implementing AAC (or MP3) 
on DSPs. Therefore, MOPS is roughly equivalent to typical DSP operations (MPY, 
MAC, ADD, SUB) assuming data moves are carried out in parallel, if they occur in 
parallel to arithmetic operations. As far as word length is concerned it is 
assumed that the operations are performed single precision. Typically for an MP3 
or AAC dcecoder a word length of around 20-24 bits is required (depending e.g. 
on the precisision of intermediate results in the ALU) in memory to obtain a PCM 
output precision of 16 bits. If you desire higher output precision (e.g. 24 
bits) the word length will increase.
Best regards,
Bernhard Grill
> 
> Thanking you,
> Apala Guha
> 
> 
> 
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-- 
Dr. Bernhard Grill                                  email: grl iis.fhg.de
Head of Audio Department, FhG-IIS A                 phone: +49 9131 776-351
Am Wolfsmantel 33, D-91058 Erlangen, Germany        FAX:   +49 9131 776-398