Reader Terry Southern (no, not
Terry Southern), is confounded by an interaction between iMovie and GarageBand. He writes:
While working on an iMovie project I extracted the audio from a movie clip and copied it to GarageBand so I could use some of GarageBand’s effects on it. The audio plays normally in iMovie but it’s slower and deeper in GarageBand. I’ve tried changing the tempo in GarageBand but that doesn’t speed up the audio track. What’s going on?
That audio clip you extracted is formatted as a 48kHz AIFF file, which plays back normally in iMovie. When you import it into GarageBand, its sample rate is converted to 44.1kHz. When you change an audio file’s sample rate, its length and pitch can also be changed unless the converter compensates for it. GarageBand doesn’t and that’s why your file’s sound is deeper.
Thankfully, iTunes does compensate for sample rate conversion—playing a converted file at its proper length and pitch. So the secret is to first import the audio clip into iTunes, convert it using the Advanced > Convert Selection To command, and then bring the converted file into GarageBand where it will play back normally.
By default iTunes will convert the selection to AAC, but you can change the file format to something else—AIFF, WAV, MP3, or Apple Lossless—in iTunes’ preferences (iTunes > Preferences > Advanced > Importing).
Note that if you want to keep the file as an AIFF but convert it to 44.1kHz, you’ll need to manually choose its sample rate as iTunes will keep the sample rate at 48kHz unless you tell it otherwise. To do so, while in the Importing area of the Advanced preference, choose AIFF Encoder from the Import Using pop-up menu, Custom from the Setting pop-up menu, and 44.100kHz from the Sample Rate pop-up menu that appears in the AIFF Encoder window.