LC,HE,HEv2 on mobile devices

[galinette69]

Is there a table of the supported AAC audio formats of portable devices (ipod, PSP, etc...)?

I have read in that article:
http://starkersrants.blogspot.com/2007/11/aac-hev2.html

That it's possible to support HE and HEv2 but with very bad quality (only the LC part is decoded, not the additionnal info). Is that true? Is there portable devices that support these formats but just do the crappy decoding?

Thanks,

Etienne

[shon3i]

That it's possible to support HE and HEv2 but with very bad quality (only the LC part is decoded, not the additionnal info). Is that true? Yes, it is true.

Every LC-AAC decoder can decode all AAC formats but not with full quality, so some AAC format need special decoders.


because HE-AAC is maded from two parts, classical LC-AAC and SBR, which means, during encoding with HE-AAC, LC-AAC encoder encode spectrum up to 11khz, and for everything upper (high frequency) is encoded as SBR. SBR (Spectral Band Replication) is only info about high frequency, which is reconstructed during encoding.

So that mean if you play HE-AAC on LC-AAC decoder, SBR part will not be reconstructed, that mean you will get quaility like listening 22khz instead full 44khz file.