[Mp4-tech] [AAC] faad critical bug in LP-SBR

[Andy Quan]

With either faad 2.5 or 2.6, I find that when faad runs in low power
SBR mode, it creates incorrect value in certain band of time-frequency
array. This can be observed with Cooledit, with which you will be able
to see spectrum of any time domain signal. Has anyone ever noticed
this?
To explain what I mean, it's better to check the stream
al_sbr_e_32_2.mp4 which is from SBR conformance stream package. Faad
creates an intensive band both in the middle of the spectrum and the
top part, the latter of which is actually a result of replication of
low frequency band. These two highlight bands does not exist in
reference waveforms within conformance package. Neither do they exist
if iso reference software or 3GPP decoder is used.
I find this critical bug in faad 2.5 and assume that it can be fixed
in later version. But so far, 2.6 is nothing different. Any one here
know which part of faad brings this bug? How can I fix it? Thank you!
-- 
Regards,
Andy