Tuesday, March 20, 2012

And You May Ask Yourself: Mastered for iTunes? Same As It Ever Was.

Apple's Mastered for iTunes process has been publicly criticized for not producing audio files that were subjectively 'closer to the CD' than standard iTunes. Turns out, the test methodology was flawed and the negative conclusion was the only one possible under the test conditions. The conclusion may be true, but is not interesting or informative.

The Mastered for iTunes toolkit (MfI) is free. Anyone can get it. I thought it would be a more interesting exercise to download the tools and process our 24-96 WAV test set and examine whether the result was closer to the source than standard iTunes. My conclusion from the exercise is interesting and informative, but not in the way I expected.

In all cases, MfI produced an AAF file virtually identical to standard iTunes. Darn near entirely identical.

RMS amplitude measured for the difference wave between the MfI AAF file and the WAV master is numerically identical in all cases to the result reported for standard iTunes. And the difference wave between the two AAF files in each case is virtually silent, modulo an occasional burp or murmur. The two files may not be exactly alike, but the difference does not reflect different approaches to processing the audio source.

What do we make of this?

  1. The afconvert program supplied with Mastered for iTunes is the same afconvert program under the hood at iTunes. The Mastered for iTunes tools do not a priori produce better-sounding compressed audio files. According to Apple's white paper, the MfI version is instrumented to optionally produce additional information about the output files, most notable the presence of clipping (sample values outside the [-1, +1] range truncated to fit).
  2. If you are a professional mastering engineer, you already have tools that can detect the presence of clipping in sound. Heck, I am a non-professional doing analog-to-digital audio archiving and restoration at home, and even I have tools that can detect (and allow me to correct for) the presence of clipping.
So mastering engineers have always had the tools and technique to create master recordings optimized for compression, the same way they have created unique masters for other formats, like CD and SACD. By offering transparency into their mastering process and with the carrot of a premium certification in the world's #1 music retail source, Apple is now encouraging the music industry to do it.

Some in the industry have called this a perfectly normal development, a good thing. But as a consumer, I question the value of a label that says that experts certify they have now done what they may have silently been doing all along. Same as it ever was.

Thanks to my Harman colleagues Jonathan Moss and Rahul Misra for their invaluable assistance in data collection.

            Vinyl-to-Digital Restoration #26           

Title: Remain in Light
Artist: Talking Heads
Genre: Alternative
Year: 1980

David Byrne is one of my musical heroes. Put him together with producer Brian Eno, and it's no surprise that Remain in Light is my favorite Talking Heads studio release. I never saw them live, but the once-in-a-lifetime performances of some of this material in Jonathan Demme's Stop Making Sense are mesmerizing.

© 2012 Thomas G. Dennehy. All rights reserved.


  1. If you are buying from iTunes, would a Mastered for iTunes designation influence your purchase decisions?

  2. A very good & respected move from Apple. But i doubt if the majority of the listeners would hear it. Most people don't have very good hearing or are listening to crap headphones. But now we want Logic X haha