[Mp4-tech] [M4IF Technotes] Could 16-bit AAC decoder's PCM output pass RMS test of AAC LC conformance test

[Lijie Tang]

Hi, audio experts
I'm implementing the AAC LC conformance test on my 16-bit AAC LC
decoder. My decoder failed in case "al00_08.mp4" and "al00_08.mp4". I'm
surprised to find that even FAAD float point LC decoder and ISO mpeg2
reference float point decoder failed in these two cases (both decoders
output 16-bit wav). Then I try to convert the reference 24-bit wav
"al00_08.wav" to 16-bit wav with rounding then test the RMS level of
this 16-bit wav, it still failed. I'm not quite sure if the failure was
caused by incorrect RMS calculation or the 16 bit AAC LC decoder could
never pass the RMS test. 
My question is: 
Does anyone know if a 16-bit AAC LC decoder has the possibility to pass
RMS test defined in ISO 14496-4? Is there any 16-bit third party LC
decoder that has passed the conformance test?
Or maybe my RMS calculation is incorrect. Is there any reliable RMS
testing tools?
Here is detailed info of my RMS test implementation:
RMS threshold for 16 bit is: 8.809666e-006
RMS level of FAAD 16-bit float point decoder is: 8.821491e-006
RMS level of ISO mpeg2 reference 16-bit float point decoder is:
8.821491e-006
RMS level of 16-bit wav derived from reference 24-bit wav is:
8.821491e-006
Aac stream and reference 24-bit wav are all from ISO Conformance test
CD.
Thanks.
Lijie
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