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Ask the iTunes Guy: Encoding miracles and missing audiobook chapters

Kirk McElhearn | Aug. 25, 2014
It's easy to forget that some of the technology we use is, to paraphrase a great author, nearly indistinguishable from voodoo. One reader wrote in asking for some clarification about lossless compression, and I explain the magic in this week's column. I also look at a question about iOS device backups, and one about missing audiobook chapters in iOS.

It's easy to forget that some of the technology we use is, to paraphrase a great author, nearly indistinguishable from voodoo. One reader wrote in asking for some clarification about lossless compression, and I explain the magic in this week's column. I also look at a question about iOS device backups, and one about missing audiobook chapters in iOS.

It must be magic

Q: I read your column regularly, and really appreciated your recent explanation of AIFF, WAV, and Apple Lossless formats. But I don't get it; how can the file size of Apple Lossless be half that of AIFF without some voodoo going on?

I received this email with the subject: Apple Lossless, Magic?. And I can understand that it can seem like there's some voodoo in this process, but it's actually pretty simple. (At least the concept is simple; the math behind it is a bit above my pay grade.)

Imagine that you have a text file with, say, the complete works of William Shakespeare. This text file contains 908,774 words, and takes up 5.6 MB on disk. If I compress the file using OS X's built-in Zip compression, the same file takes up just over 2 MB, or about 36 percent of the original file size.

Lossless compression for audio works in a similar way. Unlike, say, AAC or MP3 files — where psychoacoustic models are used to determine which parts of the audio can be removed without affecting what you hear — lossless compression formats simply compress all of the data in a file. When played back, these files are decompressed on the fly, so the compressed data becomes audio data again, in a bit-perfect equivalent to the original. Nothing is lost, just as none of Shakespeare's words are lost when I decompress the zipped file.

Bad backup

Q: The lock button on my iPhone broke, so the Apple Store replaced it. I had backed up the iPhone to my MacBook before exchanging it, but when I attempted to restore it to the new phone, iTunes said the backup was corrupt or had software not compatible with the new phone. Is there a way to get that backup onto the new phone?

Alas, no. If a backup is corrupt, then there's not much you can do. And because you can't it's worth thinking about your iPhone backup strategy for the future. If you sync your iPhone often, then each time you do so, iTunes will store a backup. It deletes the previous backups, though, so if the latest one is corrupt, you won't be able to work with it.

However, if you also use Time Machine to back up your Mac, you might be able to restore an older backup. iTunes stores these backups in /Users/yourusername/Library/Application Support/MobileSync/Backup, and each one is in a folder, with a name such as 4e6854637fb74a5a3d47e2bca56eacd7fb46197c3. (This name is your iOS device's UUID, or Universally Unique Identifier.)

 

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