Just about everywhere I've looked on the net, people have been talking about how the new iTunes 7.5/QT 7.3 AAC encoder is an noticeable improvement over the iTunes 7.3/QT 7.2 AAC encoder. This has not been my experience at all at the 128 VBR bitrate. A good example (and I have more if one is not sufficient) from a CD that I expect many people have is "What Do You Do for Money Honey" from AC/DC's "Back in Black".
Here is my ABX test between my WavPack image and a 128 VBR encode using iTunes 7.3.1.3 / QT 7.2 for windows:
foo_abx 1.3.1 report
foobar2000 v0.9.5
2008/01/08 17:34:26
File A: F:\AC_DC - Back in Black.wv
File B: E:\Backup\iTunes Music\AC_DC\Back in Black\03 What Do You Do for Money Honey.m4a
17:34:26 : Test started.
17:34:43 : 01/01 50.0%
17:34:57 : 01/02 75.0%
17:35:10 : 01/03 87.5%
17:35:23 : 02/04 68.8%
17:35:37 : 02/05 81.3%
17:35:52 : 03/06 65.6%
17:36:08 : 04/07 50.0%
17:36:23 : 04/08 63.7%
17:36:29 : Test finished.
----------
Total: 4/8 (63.7%)
Here is my ABX test between my WavPack image and a 128 VBR encode using iTunes 7.5.0.2.0 / QT 7.3 for windows:
foo_abx 1.3.1 report
foobar2000 v0.9.5
2008/01/08 17:50:54
File A: F:\AC_DC - Back in Black.wv
File B: C:\Documents and Settings\User\My Documents\My Music\iTunes\iTunes Music\AC_DC\Back in Black\03 What Do You Do for Money Honey.m4a
17:50:54 : Test started.
17:51:08 : 01/01 50.0%
17:51:21 : 02/02 25.0%
17:51:33 : 03/03 12.5%
17:51:46 : 04/04 6.3%
17:51:59 : 05/05 3.1%
17:52:12 : 06/06 1.6%
17:52:28 : 07/07 0.8%
17:52:42 : 08/08 0.4%
17:52:44 : Test finished.
----------
Total: 8/8 (0.4%)
The problems I'm hearing exemplified in the first 10 seconds of the above track are the same cymbal smearing and distortion problems that drove me from iTunes MP3 of old to AAC in the first place (all those years ago).
Is anyone else hearing this? Am I the only one having serious quality problems with the new AAC encoder in iTunes 7.5/QT 7.3?
EDIT: Some quick testing has indicated that iTunes 7.6 / QuickTime 7.4 have done nothing to correct the encoder problems I'm hearing.