it can definitely be that aac is more complex than mp3
the aac guys again claim that vorbis is even more complex than aac etc...
hm i am surely not the right one to ask, what format needs what processor power on what devices aso
hm about he-aac i also guess that compared to aac its harder to decode, but he-aac is also used by the digital radio mondial system, which maybe also had "small devices" as recievers in mind...
well whatever, as long as it decodes on my poor p3 866mhz