Digital Delivery: iTunes vs. CD
By Bob Katz

   By Guest Contributor   Categories: Mastering Audio
Mastering music with different digital delivery methods

The combination of the iPod, iPhone, iPad, and the iTunes software has changed both the way record labels release music and the way people buy and listen to it.


When creating masters for both CD and iTunes, be aware of these basic differences:

1) Singles: Every iTunes song becomes available as a single as well as part of an album. This is a bonus, because making iTunes singles is far less expensive than manufacturing CDs: it costs a lot of money to produce, press, release, and market a physical CD with a single song on it. Before iTunes, record labels and producers would think twice about releasing a CD single. Today, making a single is a common practice.

2) Master format: The master for a CD album consists of one audio file, in a proprietary image format, which includes all the gaps between songs, and segues (overlaps) between songs. In contrast, the master for an iTunes album consists of a series of WAV or AIFF files, with the pauses (gaps) between the tunes included at the end of each audio file. 

3) Metadata: The metadata for a CD is built into the CD master’s subcode (the subcode is hidden data that controls the player’s display and operation). Metadata includes: ISRC codes; track marks; pause marks; EAN barcode; CD text (album and track titles, genre, artist); and potentially much more, including graphics, though CDs with graphics are very rare. Mastering engineers produce and error-check the CD masters, and encode this metadata. When there is no time for the producer/A&R to personally approve the final reference, the mastering engineer will typically be asked to proofread any changed metadata and then send the master to the duplication plant. The master format can be a simple physical CD, which the plant replicates, automatically transferring the metadata, or a DDP fileset sent to the plant via ftp, containing all metadata.

By comparison, the individual WAV files delivered to iTunes do not contain metadata. Do not try to encode metadata into these files as it may prove confusing and useless as iTunes will not use it. So the artist or producer must deliver metadata separately; they can no longer depend on the mastering engineer to encode metadata. Metadata for an iTunes album must be entered at the online digital distributors’ websites, or, for larger record labels, into forms that can be submitted direct to iTunes. The person responsible for ensuring that this data is accurate, correctly spelling the titles and artists’ names, and submitting this data, has a tremendous responsibility. If you are an artist or producer submitting information, have as many people as possible check the data before submission, use copy/paste to minimize possible typos, and proofread many times over. Changing information that has already been submitted to iTunes is a time-consuming and frustrating process. Proofread that data! Then proofread it one more time. “Measure twice and cut once.”

Not all distribution services accept all metadata. Some may not accept composer or movement information for classical releases.

4) Pause marks: Pause marks on CDs indicate the gap between tunes. These gaps can also contain audio intentionally excluded in shuffle play. Audio in the gap will not make it to the radio either (unless the radio station plays past the pause mark). It is common to use the CD gap for spoken introductions, count-offs, breaths, applause, laughter, and ambience (in live albums). The CD gap also can be used as a hidden track, heard only by listeners playing the entire album. But there are no pause marks in iTunes, and they may be gone forever. In iTunes, all the “in-between” content appears at the tail of the previous tune, and it will be heard in shuffle play (that can slow down a party). This makes artists hesitant and a bit less adventurous, so you’re less likely to find creative or interesting extras between the tracks of an iTunes album. A related change brought on by iTunes is that the song length includes the gap length, so royalties charged by the licensing agencies (e.g. Harry Fox) increase, since they license songs by their length. This can get costly with live albums. If you’re low on cash, you could create a song or two called “applause.” But then iTunes will charge anyone who downloads it—scratch that idea!

5) Segues and Gapless Playback: Gapless playback on CD is simple and built right into the format. It permits segues (overlaps or crossfades) between tunes. When the CD was King, listeners were not confused cuing to a song and hearing the fade of the previous song mixed over the head of the next. iTunes users can rip singles from their CDs, then put them into their own playlist; but CDs with segues make it hard to extract just one song for multi-album playlists.

iTunes, version 7 and later, and the more recent models of iPods both support gapless playback, as long as crossfade playback is turned off in the preferences. If crossfade playback is turned on, then the checkbox called part of a gapless album must be checked for each individual tune. A bit confusing, but most people do not turn on crossfade playback.

Now that every song can be downloaded as a single, artists have become increasingly reluctant to create an album with segues. They fear that listeners will not understand a song that does not “complete” (i.e., come to a well-defined stop or fade out), or whose beginning contains part of the end of the previous track. When I master an album and suggest a segue to the producer, he often rejects it for these reasons. But crossfades display colors in the artist’s creative palette—the artist’s right to be different! A good solution is to create additional singles that do not contain the segues, also known as the “Radio Version.” Since albums have a fixed price, let’s include the single versions as bonus tracks—though when you hear excerpts from Dark Side of the Moon on the radio, stations will usually play the album version and fade out during the segue. Now that broadcasters can use music from iTunes, will they discover the Radio Version bonus tracks?

Mastering music with different digital delivery methodsExcerpted from iTunes Music: Mastering High Resolution Audio Delivery (Focal Press, 2012), by Bob Katz.

Above image courtesy of RetinaFunk under the Creative Commons license. Click here to see his gallery.

Bob Katz played the B flat clarinet from the age of 10, and his lifelong love of sound and music led him to become a professional recording, mixing and mastering engineer (since 1971). Three of his recordings have garnered the Grammy™ award and many others have been lauded in publications such as Stereo Review, Audio, and Stereophile. He has written over a hundred articles for audio and computer publications, and is an inventor and manufacturer with processors and support gear in use at mastering studios worldwide. His most recent patent-pending inventions, the K-Stereo and K-Surround Processors, fill a missing link in the mastering and post-production pantheon. He has been a workshops, facilities and section chairman of the AES and has given lectures in several countries. Currently, Bob runs Digital Domain Studios just north of Orlando, Florida, and is the author of Mastering Audio and the new iTunes Music: Mastering High Resolution Audio Delivery.



No Comments

Tell us what you think!


The Latest From Routledge