Does anybody have any more info on the new QT release from Apple? In another thread it seems like the lossless compression is roughly the same and some people report not having decoding issues that existed with their AAC files. From MacMinute:

According to several people, they nailed the 16khz bug that was introduced in QT 6.5.1. It also seems to be a tad faster, I now get about 24X when encoding @ 192kbps from CD's, which I think is pretty darn good!

Good luck finding any official detailed fix-list though, Apple is notoriously secretive about that.

Did this issue (with high-frequency "ringing") ALSO occur for QT 6.5, or was it only in the 6.5.1 that Apple released in April?

Early this year, in February and March, I did lots of archiving (of old tapes) with 6.5 for Mac (not 6.5.1), and I'm hoping these AAC-files don't have the troubles reported for 6.5.1. Do they? Does 6.5-for-Mac have qood quality? (I'll upgrade to 6.5.2 now, since reports on it are good, but I'm wondering about the files I've already made.)

IIRC, the issue was present since 6.5, but I might be wrong.

It was not present in QT 6.5 (that one used the exact same encoder as QT 6.4 btw.)

Busemann says, "It [the "ringing" bug at > 16 kHz] was not present in QT 6.5 (that one used the exact same encoder as QT 6.4 btw.)"

Thanks for the information.
:<)
This is what I was hoping to hear, since I don't want artifacts in my ecoded archives.

But I'm curious about something. Earlier, you said "Good luck finding any official detailed fix-list though, Apple is notoriously secretive about that." So I'm wondering, how do you know that 6.5 is the same as 6.4, but 6.5.1 is changed? From listening-experiments, or from information in official statements released by Apple? Or both?

experiments: Evidently there are clearly audible artifacts in 6.5.1 -- in another thread, you claim that you can easily ABX it versus earlier versions. And others in the HA forum say this, too.

official statements: What you say is also consistent with what is claimed (by Apple, I assume) in the information at versiontracker.com, which describes the changes in each version:
* in 6.5, there is no mention of improvements in the AAC codec (therefore 6.5 = 6.4?)
* but in 6.5.1 they claim "Significant improvements to AAC encoding, resulting in high-quality sound over a full range of audio frequencies." -- so maybe they did TOO MUCH "over the full range" and introduced artifacts in the higher end of the range, to produce the ringing issue;
* and in 6.5.2, they claim "enhancements in the Apple… AAC codecs" which agrees with the feedback about 6.5.2, which (based on listening) seems to be improved over 6.5.1, by eliminating the ringing.

Or is there a technical way to compare two encoded files to see if they're identical or different? (and you find that 6.4 and 6.5 are identical, but 6.5.1 is different than 6.4-and-6.5) Or is there "inside information" from Apple?

Exactly. There are programs that do bit for bit comparisons between two files. Those produced with 6.4 and 6.5 are identical.

When this is done for 16-bit audio files (WAV or AIFF) encoded with QT-6.5.2 using the "better" and "best" settings, are these files identical? I've heard that "best" gives improved AAC quality (compared with "better") only when encoding 24-bit audio, but for 16-bit audio the AAC-files are identical with both settings. Is this true?

Or has Apple stated that settings of "better" and "best" produce the same quality for 16-bit audio?

I haven't seen any bit-for-bit comparisons, but one of the Quicktime engineers said "Best" is only optimized for 24bit material and should be equal to "Better" on 16bit files.