[M4IF Technotes] Re: Audio Reference Software

[Ralph Sperschneider]

Luca Piccarreta wrote:
> 
> Hi,
> I was testing the reference software (audio), MPEG4-AAC.
> Main Prediction (the one with Correlation, variance ecc.)
> and noted that there are differences in the output of Release
> and Debug versions.
> These differences are negligible from a human listener point of view
> (2-3 in 16-bit output), but this may be not pleasant when one
> is trying to match his decoder to the ref's one.
> Is there any "audio expert" who wants to discuss about this?
> The incriminated sequence is am02_44.mp4 and the mismatch
> seems to be due to the switch "Improve Float Consistency" in
> the release version (I'm using Visual C++).
> In my opinion, one could object to the way coefficients are stored
> in the reference software (and in the specs). The loss of precision
> is enormous, and I can't think of any reasonable way of doing
> the whole prediction in integer math.
> Thanks in advance to anyone who want to discuss about that.
> Luca Piccarreta.
> 
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Dear Luca,
I assume that you use the "official" reference software available from ISO. This software has been further improved since it was released. I remember that we have also discovered accuracy problems regarding the prediction tool in conjunction with the compiler optimization and that this problem was fixed. Being an MPEG member, you have access to the most recent version of that software. Otherwise, you most likely need to wait until the next edition is issued.
Best regards,
Ralph
-- 
Dipl.-Ing. Ralph Sperschneider  | Phone: +49 9131 776 344
FhG IIS-A                       | Fax:   +49 9131 776 398
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