I recommend that Apple simply practice better post-premastering. The AAC
conversion program should first look for a sample peak of, say, -3.01 dB
and, if it can't find one, leave the track alone level-wise - just do the
decimation. However, if it finds a sample peak that is higher than -3.01
dB, it should look for the highest peak in the track and reduce the level of
the entire track, with an 80-bit digital audio attenuator (e.g., Metric Halo
Mobile I/O Console), by an amount sufficient that there are no longer any
peaks in the track above -3.01 dB - then do the decimation. Clerks should
already know how to premaster a compact disc. Years are spent honing
techniques of getting levels just under the radar. Nice try at reissues.
Just decimate the original premasters (anew) with adequate headroom and
distribute the output free to authorized customers. The Lavry LE3000S
real-time sample rate converter, for example, reduces the gain of incoming
audio by a small amount so that its DSP result won't clip.


Andrew


On 4/30/12 1:50 PM, "Arthur Gaer" <[log in to unmask]> wrote:

> An interesting, if not highly technical, piece on the effects of "Mastered for
> iTunes" on Ars Technica:
>
> "After our original report on the Mastered for iTunes program, some readers
> were skeptical that anything could be done to make a compressed AAC file sound
> comparable to uncompressed, 16-bit 44.1kHz CD standard audio. Others believed
> users should have access to the original 24-bit 96kHz files created in the
> studio for the best sound. Finally, some readers suggested that few people can
> actually tell the difference between iTunes Plus tracks and CD audio, so why
> bother making any effort to improve iTunes quality?...
>
> "Shepard applauded Apple's technical guidelines, which encourage mastering
> engineers to use less dynamic range compression, to refrain from pushing audio
> levels to the absolute limit, and to submit 24/96 files for direct conversion
> to 16/44.1 compressed iTunes Plus tracks. However, he doubted that submitting
> such high quality files would result in much difference in final sound
> quality. Shepard's conclusions led CE Pro to claim that Mastered for iTunes is
> nothing more than "marketing hype."
>
> "So, we set out to delve deeper into the technical aspects of Mastered for
> iTunes. We also attempted to do some of our own testing to see if there was
> any difference—good or bad—to be had from following the example of Masterdisk.
>
> "We enlisted Chicago Mastering Service engineers Jason Ward and Bob Weston to
> help us out, both of whom were somewhat skeptical that any knob tweaking could
> result in a better iTunes experience. We came away from the process learning
> that it absolutely is possible to improve the quality of compressed iTunes
> Plus tracks with a little bit of work, that Apple's improved compression
> process does result in a better sound, and that 24/96 files aren't a good
> format for consumers."
>
> http://arstechnica.com/apple/news/2012/04/does-mastered-for-itunes-matter-to-m
> usic-ars-puts-it-to-the-test.ars
>
> Over 140 comments made in the last 16 hours since the article was first
> posted--ranging from know-plenty to know-nothings (but think they
> know-it-all).
>
> Arthur Gaer
> [log in to unmask]
>
> Senior Systems Manager
> Harvard University
> Department of Mathematics
> Science Center
> 1 Oxford Street
> Cambridge, MA 02138
> 617-495-1610

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