Is an ipod on shuffle truly random?

September 9, 2005 5:49 AM

Is an ipod on shuffle truly random?

or does it weigh songs or artists that you've recently listened to, or ones that are contained in playlists. I have about 6500 songs on my ipod and I've had numerous situations where this seems to have happened.

posted by phirleh to Computers & Internet (19 answers total)

It's truly random, but they know that's a problem -- the new iTunes also you to weight the shuffling, which means iPods will get that before long too.
posted by bonaldi at 5:55 AM on September 9, 2005

Yes.
posted by cillit bang at 5:55 AM on September 9, 2005

One way to get better pseudo-randomness (because truly random shuffling could give you the same songs in the same order every single time you listen) is to create a smart playlist that includes only songs which you haven't played in the past n days. I use 90 days myself.

That way, you're guaranteed to always hear songs you haven't heard in a while.

One caveat: iPod only considers a song played after it has played its last second. So if you hear something in your Pod that you suddenly decide you hate, don't just jump to the next song. Instead, scrub the timeline almost all the way to the end and listen to the last 2-3 seconds of the fadeout of that Toni Basil song.
posted by baltimore at 6:18 AM on September 9, 2005

Truly pseudo-random you mean? There's no way a deterministic device can ever produce true randomness, and whatever pseudo-random number generator is used with the iPod will eventually repeat itself perfectly: at best you can for the PRNG to have a very long period, longer than the actual lifespan of the device.

Now, whether the iPod's PRNG is actually much good is another question, and it's yet another question if something approximating true randomness (e.g., passes the Kolmogorov-Smirnoff test) is what anyone would actually want: given a random sequence, one should expect repeats to occur a lot more often than most people would either desire or expect, with the number of repeats of any song which may be encountered being nearly unbounded. In fact, what I suspect is actually happening with your iPod is that it is using a high-quality PRNG, but the sequence it's producing is clashing with your intuitive expectations of what randomness should look like.
posted by Goedel at 6:30 AM on September 9, 2005

Actually, here is still another possible explanation, though one would hope Apple's programmers wouldn't fall prey to so stupid an error. Stranger things have happened though.
posted by Goedel at 6:36 AM on September 9, 2005

Good stuff about "randomness" in this thread, where I also linked to this discussion on Radosh.net. There are some interesting theories about the shuffle algorithm in the comments section, especially the Beatles experiment.
posted by junkbox at 6:37 AM on September 9, 2005

It is truly random. This is a psychological phenomena, not an iPod quirk or malfunction.
posted by fire&wings at 6:39 AM on September 9, 2005

The "how" of Apple's shuffle has been a hot topic ever since iTunes came out. It always seemed pretty random to me, but there have been enough people who listen to way more music than I do saying that it's "not random enough" to make me think that the algorithm might be wonky.

First Party Shuffle and now the "weighted" shuffle in 5.0 seem to me to be a tacit admission from Apple that this is, indeed, the case. In true Apple fashion, they're spinning this by changing the discussion into "we're giving you more customization."
posted by mkultra at 6:51 AM on September 9, 2005

A random permutation would be a better way to go about things...guarenteed no repeats until you've heard everything. That's how shuffle works in winamp, I think.
posted by mfbridges at 7:01 AM on September 9, 2005

There's a good article on OmniNerd (probably referenced in one of the aforementioned discussion threads, but I didn't look through them all) that states:

Many claim to still see patterns as iTunes rambles through their music collection, but the majority of these patterns are simply multiple songs from the same artist. Think of it this way: If you have 2000 songs and 40 of them are from the same artist, there is always a 2% chance of hearing them next with random play. So right after one of their songs finishes, odds show a 50% chance they will play again within the next 35 songs and a 64% chance they will be played again within the next 50 songs.

It's iTunes instead of an iPod but it gives you a good idea of the math.
posted by bcwinters at 7:43 AM on September 9, 2005

Actually, on a lexicographic point, "shuffle" as used in audio equipment is distinct from "random," and the distinction has been around much longer than iPods. Random means, well, random. The device picks every new track at random, without regard for what it has already played. Set your CD player on random-play you could hear the same track twice in a row, as I occasionally did with my old one. Shuffle play means "play each track exactly once, in a random order."

I have no idea how Apple really does it, but it shouldn't be hard to use time of last sync, duration of last scroll-wheel touch in milliseconds, and other effectively unrepeatable inputs as good random-number seeds.
posted by adamrice at 8:27 AM on September 9, 2005

It's extreemly unlikely that apple's psudo-random number generator is bad enough that it would be noticeable to people during their lifetimes, or thousands more years.

People may be complaning about a lack of variation but that's just a problem with their playlist, not the product. There are PRNGs out there good enough for strong crypto, so there are certanly some that are good enough for a playlist.

Truly pseudo-random you mean? There's no way a deterministic device can ever produce true randomness, and whatever pseudo-random number generator is used with the iPod will eventually repeat itself perfectly

While it's true that no deterministic device will ever be truly random, it is very easy to build a random device. An FM reciver listening to a dead station will work well for this application.
posted by delmoi at 8:48 AM on September 9, 2005

I've had the biggest problem trying to organize my itunes songs on my shuffle to play in order. Everyone says that they can drag and drop before you sync, but I can't figure it out for the world. I can drag items but when I drop they fall right back to their original position.
posted by any major dude at 8:50 AM on September 9, 2005

I can drag items but when I drop they fall right back to their original position.

You're doing this in a playlist, not in the Library, right? Also, make sure you're sorting by the first column, the one with the numbers in it. Just click on the column. Clicking twice toggles the ascending/descending sort.
posted by Mo Nickels at 9:42 AM on September 9, 2005

What bothers me about the shuffle mode is that there is no DO NOT REPEAT option. Before I had an iPod I had an mp3 device on my computer that allowed shuffle/do not repeat, which eliminates the natural assumption that because I've heard the same song twice in two days the shuffle isn't random. It boggles me that this isn't an option.
posted by spicynuts at 10:42 AM on September 9, 2005

<>IWhat bothers me about the shuffle mode is that there is no DO NOT REPEAT option.

IIRC, this is in fact the default behavior -- the iPod will not repeat songs in shuffle mode, as long as you do not turn it off.
posted by kindall at 11:18 AM on September 9, 2005

IIRC, this is in fact the default behavior -- the iPod will not repeat songs in shuffle mode, as long as you do not turn it off.

Perhaps..however I only listen to it on my way to work and on my way home from work. Thus, I want to be able to PERMANENTLY set it to do not repeat so that over the course of several weeks I will not here the same song twice. Seems to me this should be a rather standard and simple to implement feature.
posted by spicynuts at 12:17 PM on September 9, 2005

Aha! I've always tried to drag on the shuffle section. So I need to organize on the playlist then drag to the Shuffle. Thanks Mo!
posted by any major dude at 1:31 PM on September 9, 2005

spicynuts - make a playlist, put everything on it, shuffle the order around yourself.

Then you can play through in order. Just remember where you left off.
posted by jb at 2:49 AM on September 11, 2005