Results of internal 48 kbps test are here (graphs included):

http://www.hydrogenaudio.org/forums/index....showtopic=41191

Test 1: HE-AAC v1 @48 kbps

VBR1 - 3.56
ABR 48 - 3.53
CBR 48 - 3.48
VBR2 - 3.29
MP3 128 - 4.41
MP3 48 - 1.19

Test2: HE-AAC v2 @48 kbps

VBR1 - 3.12
ABR 48 - 3.11
CBR 48 - 3.11
VBR2 - 3.08
MP3 128 - 4.08
MP3 48 - 1.14