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.

A Xerox of a Poloroid of a Photo of a Painting

What format and bit rate should you choose for ephemeralizing your LPs?

While it may be popular, lossy compressed audio has its detractors. In an interview, Grammy-winning producer T. Bone Burnett likened its fidelity to the sonic equivalent of "a xerox of a poloroid of a photo of a painting."

[Image: low-res Beatles Sgt. Pepper album cover.]


Nonetheless, the 256 KBit/sec MP3 has become the de facto standard for purchasing and streaming music in the cloud.

Like WMA and AAC, MP3 is a lossy compressed format. (The three formats are interchangeable for the purpose of this discussion.) You can't uncompress an MP3 and get back the original audio. Some information is thrown away in the compression process to gain additional compaction over lossless compressed formats.

Lossless uncompressed formats incorporating linear pulse-code modulation (LPCM) capture a direct digital representation of an analog wave. "CD-quality" uses 16-bit samples taken at 44.1 KHz. The equivalent bit rate of 1411.2 KBit/sec transmits more than 5x the information in MP3 audio, with no loss due to compression. (See figure at right.)

Even a CD-quality copy introduces downsampling from the original. Most digital studio recordings are made with 24-bit samples taken at 96 KHz. The equivalent bit rate of 4608 KBit/sec transmits 18x the information in MP3 audio and more than 3x the information in CD audio.

It is possible to make 24-bit/96KHz recordings at home, 18x richer than a "good" MP3. Gigahertz computer clocks facilitate high sampling rates. Near-zero cost of storage makes compression unnecessary.  But is it worth generating and storing all those bits? Can anyone really hear the difference?

My Harman colleague Dr. Sean Olive, Director of Acoustic Research, is actively seeking a scientific answer to that latter question. My answer is simple: I don't care.

When it comes to information, more is always better. The digital transfer pipeline is software-driven. You may or may not be able to "hear" the difference, but your software tools can "see" the difference and work better when they have more to chew on. I'll use use the next couple posts to try to convince you to seek and preserve as many bits as possible when recording and processing, even if you ultimately choose a compressed format in which to store and enjoy your end products.


              Analog-to-Digital Restoration #8             

Title: Diamonds and Pearls
Artist: Prince & the New Power Generation
Genre: Soul and R&B
Year: 1991



Everything we've said regarding digital transfer of LPs applies identically to other analog source material. If you still have the equipment to play something, you can usher it into the digital future. I recently bought a like-new Denon DRS-810 at an estate sale for $25—a real find—to add to my recording station. My wife's equally like-new cassette copy of this Prince title is now ephemeralized.


© 2012 Thomas G. Dennehy. All rights reserved.