[Mp4-tech] Regaring PNS in MPEG4 AAC

[Mody, Mihir]

Hi,
I have couple of queries on PNS module in AAC.
1) 
According to AAC standard, noise energy (nrg) is calculated as follows.
nrg = global_gain - NOISE_OFFSET - 256. 
Does anybody know significance of 256? Does encoder have to to add 256 in
nrg? In that case, can we define NOISE_OFFSET = 90 + 256 = 346?
2) 
According to AAC standard, the quantization of noise_energy during PNS is
done with resolution of  1.5 db. Does it mean following line is valid? 
quantized_noise_energy = (INT) (log2 (noise_energy)) 
Regards,
Mihir
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