iTunes + 24-bit + mono = ?

Reader David Eglington is confounded by a GarageBand podcast that appears to convert too quickly in iTunes. He writes:

I recorded a podcast with GarageBand ’08 and exported it to iTunes in full quality. In iTunes I’ve been trying to convert it to a mono, 64kbps MP3 file and when I do, iTunes appears to convert the file in under a second. But then I can’t find this converted file. What’s going on?

Launch GarageBand and then its preferences. Click the Advanced tab and look at the Audio Resolution pop-up menu. If it reads Best, there’s your problem.

By choosing Best you’ve elected to export your uncompressed, full-quality tracks as 24-bit AIFF files. You’ll find that when you bring such files into iTunes and attempt to convert them to mono—regardless of whether you choose MP3, AAC, AIFF, or WAV (Apple Lossless doesn’t give you the mono option when you choose Custom from its Setting pop-up menu)—iTunes quickly produces that “okey-dokey” sound yet doesn’t deliver the goods.

You have a couple of ways around it. The most obvious is to change the quality of the export. You may have changed the Audio Resolution setting to Best for a music project (or simply because Best sounded like, well, the best option). Regardless of how this happened, I can’t think of a reason on earth why a podcast needs to be exported as a 24-bit audio file.

Or, if you desire to ultimately have that mono MP3 file, export it as such from GarageBand. Choose Share -> Send Podcast to iTunes and in the resulting sheet choose Mono Podcast from the Audio Settings pop-up menu. (Similar to iTunes’ Setting pop-up menu, this one contains a Custom option so you can tweak your settings if the pre-configured ones don’t meet your needs.)

Or, if you’d rather not return to iTunes, you can select your 24-bit file in iTunes, convert it to a 16-bit AIFF file, and then convert it to an MP3 file. You convert it by moving to iTunes’ Advanced preference, clicking the Importing tab, and choosing AIFF from the Import Using pop-up menu and Automatic from the Setting pop-up menu. Once it’s 16-bit, iTunes will have no objection to converting it to a mono file.

  
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