Shuffle in iTunes and iPods Is Not as Random as You’d Think

If you’ve used the Shuffle setting on iTunes or an iPod more than a few times, you come to realize that it’s anything but random. Some tracks keep coming up while others are ignored. Why is that?

What happens is that when you choose the Shuffle setting, iTunes or your iPod creates a more-or-less random playlist – and then keeps on using the same playlist going forward.

Part of the problem is with randomness itself, which only means that you cannot predict what will come next or find a repeatable pattern. Randomness is not entropy and doesn’t mean a pattern may not repeat, only that any repetition is part of an even larger randomness. After all, if you make it impossible for a pattern to repeat, you are actually eliminating randomness, just as if you rolled a 6-sided die and rejected any value that had show in the previous five rolls.

Computers are very good at generating pseudo-random numbers, because they only know how to calculate according to established rules. They can simulate randomness by looking at hardware values, such as the system clock, CPU temperature, or how long a system has been running since it was last rebooted. Values such as these can be plugged into a random number generator to produce a series of unpredictable numbers – unpredictable based on the fact that the user doesn’t  know how many microseconds have elapsed since a computer was restarted or CPU temperature to the nearest 1/1000 of a degree.

Computers can further generate randomness by using two or more random number generators together, creating a sequence with even less chance of a pattern.

But if that’s the case, how come Shuffle on your iPod or in iTunes seems to much less than random? It’s not because Apple hasn’t gone out of its way to ensure that a pretty random sequence of tracks is generated, but because once it creates that randomized list, it continues to use it.

What seems like a pattern isn’t due to a failure of randomness or poor shuffling, but to a laziness that sticks with whatever playlist was randomly generated in the first place. You’d expect it to re-randomize every time you access the playlist, but that just isn’t how it works.

As mapgrep notes in Hacker News, “…a shuffled playlist holds its order until it is re-shuffled.”

So How Can I Change It?

Because of the way Shuffle works, the easiest way to randomize the playlist is to uncheck Shuffle and then enable it again. It will now create a new more-or-less random playlist – and continue to use it until you repeat this process.

That’s definitely something a lot of us would love to see Apple address. After all, why shouldn’t it reshuffle every time? But it’s apparently not a priority to Apple.

If it is to you, at least now you know how to re-randomize your shuffle.