iTunes: Just how random is random?

By David Braue on 08 March 2007

Think that song has appeared in your playlists just a few too many times? David Braue puts the randomness of Apple's song shuffling to the test -- and finds some surprising results.

Quick -- think of a number between one and 20. Now think of another one, and another, and another.

Starting to repeat yourself? No surprise: in practice, many series of random numbers are far less random than you would think.

Computers have the same problem. Although all systems are able to pick random numbers, the method they use is often tied to specific other numbers -- for example, the time -- that means you could get a very similar series of 'random' numbers in different situations.

This tendency manifests itself in many ways. For anyone who uses their iPod heavily, you've probably noticed that your supposedly random 'shuffling' iPod seems to be particularly fond of the Bee Gees, Melissa Etheridge or Pavarotti. Look at a random playlist that iTunes generates for you, and you're likely to notice several songs from one or two artists, while other artists go completely unrepresented.

This phenomenon has been observed widely across the world, with many conspiracy theorists suggesting there was more method than madness to Apple's randomisation routines.

Just what are they implying? Consider, for a minute, that you're a music industry marketer. There could be little more tempting than direct access to the ears -- and, indirectly, the wallets -- of tens of millions of iPod users around the world.

Through payment of a fee, the theory goes, a record label could increase the rotation frequency of their own music by tweaking Apple's randomisation formula. Popular songs and artists from their catalogue would pop up on playlists time and again, potentially explaining why your 50-strong playlist includes half a dozen Jackson 5 tracks but no Jackson Browne.

Less insidiously, iTunes could be tracking the songs you like the most -- it already does this -- then rotating them more often into its playlists.

Concerns over the randomness of Apple's randomness have even reached the ears of Steve Jobs, who has emphatically denied that the iPod's shuffle feature -- and the design of the iPod Shuffle itself -- is anything more than random. Just tell that to the hundreds of forum participants posters who have posted their complaints about the devices' playlist approach.

After an afternoon spent listening to far too much Bon Jovi, we decided to put iTunes to the test.

Building the perfect library
To evaluate iTunes' randomness, we borrowed a Mac Mini from Apple, with its fresh install of Mac OS X ensuring that we were working with an empty iTunes library and an otherwise completely clean slate.

We purchased AU$170 worth of Apple iTunes Music Store prepaid cards, then proceeded to go on a carefully planned shopping spree. As it was necessary to have multiple songs from one artist to observe any untoward clustering, we purchased five songs from each of four artists, with four artists chosen arbitrarily from the online artist lists of each of the major music labels (EMI, Sony, Universal and Warner Music).

This gave us a total of 80 songs. To see whether popular songs were being rotated more frequently, we also purchased 20 more songs from Billboard's current (as of late February) Top 50 chart, which represented a variety of labels. All told, we purchased and downloaded 100 iTunes songs from the iTunes Music Store (download the spreadsheet for the full song list here).

We then used the Smart Playlist feature to force iTunes to make random playlists 25 and 40 songs long, respectively. Ten playlists of each length were created, providing a total of 20 playlists and 650 possible song positions. Each song list was exported to a text file for analysis using Microsoft Excel.

If Apple and the labels were including any information to change songs' priority, it would arguably be stored in the downloaded AAC files. To test this, we also added another 100 MP3 files, previously ripped from a variety of CDs, that definitely contained no extra coding information whatsoever. These artists included Def Leppard, Bon Jovi, Erasure, Maroon 5, Bob Seger and even John Denver & The Muppets for variety.

With 200 songs in the iTunes Library, we then repeated the random playlist test, creating an additional ten playlists with each of 25 and 40 songs.

Topics: apple, itunes, ipod, shuffle, random, music, songs, playlist, song, itune

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Comments (68)

  • Sylvain commented on 30/05/2009 00:35 Report abuse

    Here's an interesting test I found : http://www.plasticvicar.com/iTunes/tracks.html

  • Tweak commented on 22/04/2009 19:53 Report abuse

    4068 songs on my pod and shuffle just played 3 Amy Winehouse songs in a row... Shite!

  • SVS-NS commented on 18/04/2009 23:43 Report abuse

    Hi, I have enjoyed this discussion very much. This has been bugging me since I first started using iTunes. I can't comment on the statistical analysis, but 8 years of continuous use does make one notice certain patterns. It does indeed seem that it is difficult to override the "most played" feature. The playlist can get stuck in patterns that seem hard to break. This can be frustrating. If I happened to listen to a song ten times yesterday, and I switch to "shuffle" today, I might definitely NOT want yesterday's favourite to be weighted heavily in the "random" playlist—but there it is, whether I want it or not. I do realize that in my case, 1000 songs is a small sample, but I must say that there are songs that have NEVER ONCE come up in 8 solid years of shuffle play, and others that come up with far too much frequency . . . which in turn seems to make shuffle pick them again, and so on . . . and this seems to be the source of these questions about "randomness." Also, there are always a few coincidences that seem far to "cute" and "apple-y"—like any time a Leonard Cohen song shuffles up, many, many times it will be followed by Melys' "When You Put Leonard Cohen On." Kind of funny the first time, less funny the fiftieth time. There are a few other combinations that do have the feeling of being "programmed" rather than coincidence. Always intersting to read about the mysterious inner workings of these things that have become such a ubiquitous part of our lives.

  • Mark commented on 12/04/2009 11:11 Report abuse

    I find it very amusing the volume of comments here who think they understand statistics. I'm a professor of statistics at BYU and most of the comments here are idiotic. @A Fangil - the definition of a random variable is "A FUNCTION with assigns a number to an outcome" - to say that random is by definition without a formula or pattern is ridiculous. All "random" events have a pattern and function that defines them. Take a coin flip. It follows a binomial distribution. Take disease survival, it likely follows some sort of Poisson distribution. While it is true that this article doesn't use statistics to justify it's findings, what is ridiculous is to assume that the sample size is too small to make conclusions. And to the person who said that statistics would only tell us the probability of the results being due to chance - well, duh! That's what ALL statistics do. That's the point, if our observed outcome only has a 3% chance of being due to random chance assume our null hypothesis, that could be strong evidence that it WASN'T due to chance. Especially if you repeat the study a second time and get similar results. But still, the sample size is likely fine (did anybody bother to check the expected counts if you're thinking Chi-Square is the way to go?) and NO you don't need to repeat the whole process several times to make your findings legit, you need to make sure you have more than "one subject per treatment" just like they did. There's more than one "top hit" more than one 'randomly' selected artist with 5 songs and there's more than one MP3 song. You don't even need to have each song represented in AAC and MP3 form, ever hear of incomplete block designs for experiments? While the method for selecting artists and songs could have been better, it does seem relatively random.

  • Hillio commented on 13/03/2009 13:16 Report abuse

    I think they removed the randomization "slider" from the latest version of iTunes too...at least I can't find it.

  • mynameisgabe commented on 29/01/2009 08:20 Report abuse

    I listen to iTunes all day on my computer at work, on the iPod on the drive to and from work and on the appleTV at home and I definitely see the same songs on all three devices played more frequently than others. It's really frustrating.

  • madbeppo commented on 17/01/2009 07:11 Report abuse

    I have over 11,000 items on my ipod. By far the greater number are from CDs I have ripped; and by far the greater number are classical. In addition to puzzling near-repeats (same album, same composer) when in shuffle mode, ipod also seems pretty much to ignore albums that were ripped earlier. I could understand if, when shuffling, ipod (or itunes) first made a (random) selection from the whole collection, then shuffled amongst this selection. But why does it seem never to choose albums that were put on earlier? --On my laptop I have an earlier version of my itunes library. Shuffle comes up with a very different selection of music than it does with my complete collection!

  • tfp commented on 05/01/2009 03:50 Report abuse

    It may be merely conjecture but it confirms what I, and others, have noticed while listening to hours of "random" shuffling from iTunes. There is something at play here, and its not just the music.

  • heyjohnny commented on 03/01/2009 21:08 Report abuse

    There's no way it's merely by chance. I have 3 Motorhead albums on my itunes and when I generate a playlist it's always the same 2 or 3 Motorhead songs that are played. There's definitely something off about itunes shuffle algorithm

  • A Fangirl commented on 01/01/2009 18:56 Report abuse

    I agree with everyone who's saying that this article is not proving anything. Random in its literal sense is BY DEFINITION, not having a pattern or formula. While I do agree that it can be annoying hearing the same songs over and over, that's merely by chance. So, all of you people complaining that you want the iPod to look at your playcount for each song, pick new songs, etc is going against the whole point of random. Doing one trial is not enough to shout CONSPIRACY! As someone else said, if you flip a coin 1000 times and all get heads (which is possible. Just because there's a 50-50 chance doesn't mean that there HAS to be half heads and half tails), it doesn't mean it's not fair. Plus, I think there is some psychology to this. If you start thinking that iTunes isn't random, you're going to start looking for patterns. (Which is normal. As humans, we look for patterns in randomness.) And if this is the case, you are focusing on the ones you think you're hearing more than others, when you may be actually hearing a bunch of songs that you haven't heard. Considering the author(s) went into this article already feeling there was a conspiracy or at least that iTunes wasn't that random, of course you'd be looking for examples to prove your point

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