Fellow blogger, Clay Burrell, made the excellent suggestion via comment to ScreenCast directions for how to do the ABACABA Music Form in Garage Band. Here is the video. I used Screencast-o-matic. I had never used it before and it was so easy that this video was done in one try. Nothing to download, it is totally done with the browser. My voice is actually lower than the video, but it shows the screen all the same.
Watch the full-size version here.