AAC Encoding problems (#2): Bad mastering to blame?

Yesterday we reported a problem with AAC audio quality where specific songs exhibit muffled sound for a few seconds, then carry on with normal sound. The problem does not occur when using Apple Lossless Encoding, AIFF or WAV.

MacFixIt reader Rick Zeman suggests that bad mastering, rather than a flaw in the AAC codec is causing the issue:

"The problem isn't so much AAC, as it is horrible mastering. The Best of Both Worlds (Ed.- mentioned in the previous report) suffers from being mastered to CD overly loud. (An easy way to tell this visually instead of aurally is to get info on a song in iTunes and look at the volume in the "Summary" tab.) If it's -7.x to -9.x DB, the song is a victim of poor mastering. A lossy codec like AAC (or MP3) at low bitrates just can't handle the overload. BOBW is the 2nd worst CD I have with that malady with Joe Bonamassa's 'So It's Like That' being the worst--that one, unlike Best of Both Worlds, is virtually unlistenable.

"There is a very technical -- but quite enlightening -- explanation of this phenomenon. Unfortunately, this is becoming more and more common, especially as the old-timers are retiring from the studios."

Feedback? Late-breakers@macfixit.com.

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