I contacted the developer of XLD, "tmkk". He cross-checked it w/ iTunes Plus internal encoding and confirmed this bug and suggested me to contact this forum since here are some of the iTunes' AAC encoder's developers.
I didn't try qaac's "quality" switch, as I don't know what its 0-2 range maps to...
Confirmed under Windows XP via qaac and qtaacenc with foobar2000, QT 7.7.0.Weird "ghost notes" at the beginning, and very distinct distortion on the bass notes after the 2:35 mark.I didn't try qaac's "quality" switch, as I don't know what its 0-2 range maps to, but trying the various quality settings in qtaacenc, the artifacts were consistent with --best, --higher, and --high (the default), but disappeared with --normal.This was true at CBR 256 and 192, as well as --tvbr 90.Good find!
Since 1.00, qaac directly uses CoreAudioToolbox.dll. Therefore, QuickTime installation is no more required. However, Apple Application Support is required.
The glitches were easily hearable when encoding using qaac+CoreAudioToolbox.dll 126.96.36.199 (included in QuickTime 7.7.0 for Windows) and disappeared completely when using CoreAudioToolbox.dll 188.8.131.52 (included in Safari 5.1.4 for Windows). The newest version does not include any changes to the AAC encoder, so it is safe to assume that version 184.108.40.206 (included in QuickTime 7.7.1, iTunes 10.5.3 and Safari 5.1.2) is glitch-free as well. Using newest version of QuickTime/iTunes for Mac should work as well.