Q: I’m a 5th grader doing a science fair project: Is the iPod’s shuffle mode truly random? Can you tell me if the iPod’s shuffle feature uses random or pseudo-random number selection? Do you believe your iPod gets to “know” what people like or dislike?
A: The iPod’s shuffle mode works as follows: when you start playing music in this mode, the iPod shuffles all your tracks (much like a deck of cards) and creates an internal list for your library (or for a selected playlist, genre, artist, etc.). It then plays the songs in this order until it reaches the end of the list.
The next time you turn on shuffle mode, the iPod does the same thing. If you listen to 20 songs one day, then listen to another 20 songs the next day, it is possible that one or more of the first 20 songs will come up in the second set of 20. Random playback means that each time you start playing the iPod in shuffle mode the songs are mixed up; therefore, each song has an equal probability of coming first in the list, second, third, and so on.
There is a difference between this shuffle mode and true random playback, however. The shuffle mode creates a list of songs and plays them in that order; random playback would give each song an equal probability of coming up next, which would lead to some songs coming up several times in continuous play.
As long as you keep your iPod playing in shuffle mode (without syncing it, playing other albums or playlists, or doing something that stops the shuffle play), you’ll hear every song on your iPod once, and only once, until it gets to the end of the list.
And, no, your iPod probably doesn’t get to know what you like, unless you use the rating feature or an iTunes Smart Playlist based on your most frequently played songs.