How Many Matches Does iTunes Match Match, When iTunes Match Does Match Matches?

Apple introduced iTunes Match earlier this week, and I haven’t written anything about it, given that my colleagues at Macworld have done such a good job. I’m also busy working on an update to my Take Control of iTunes 10: The FAQ, which I hope to have finished very soon. (I also have some criticism of iTunes Match, which I wrote about for Macworld: iTunes Match shouldn’t shun those with big libraries.)

In the meantime, what has perplexed me in my experiments with iTunes Match is the number of tracks that aren’t matched. In some cases, a single song may not be matched, even though the rest of an album is matched – Lex Friedman, writing at Macworld, pointed out that in many cases, one song on The Beatles’ Abbey Road (She Came In Through the Bathroom Window) wasn’t matched, even though all the others were. (It turns out that in Lex’s survey of people who tried to match that album, I was the only person who did see that song matched.)

But it’s very odd that some things match and others don’t. I don’t think it has to do with Apple’s recognition algorithm, and suspect that it’s more of a bug. I’ve seen a number of cases where one or more tracks won’t match, even among items that I had purchased from the iTunes Store.

This morning I did an experiment for the people at Hyperion Records (who are one of my sponsors). They asked me to check two albums: one that is sold on the iTunes Store, and has sold quite well, and another, a compilation, that is not on the iTunes Store, but whose individual tracks are all available from the iTunes Store on different discs. The results were surprising: in both cases, some, but not all tracks were matched. In the first example, two of 14 tracks were not matched and had to be uploaded; in the second example, only 8 of 20 tracks were matched. The screen shot below shows the results (click to see a larger screen shot).

I’m perplexed by this, and I wonder how exactly Apple matches tracks. The album above that is sold on the iTunes Store uses exactly the same tags as in the files I tried to match, so if Apple were only matching by tags (which they are not), it would be a perfect match. I know they use some sort of acoustic fingerprinting, and I wonder what causes certain tracks to not be matched.

I have no answers here, simply evidence of the oddity of iTunes Match. If you have other interesting examples to share, feel free to mention them in the comments.

Addendum: it’s worth noting that if you have iTunes match files with poor or non-existent tags, you won’t get tagged versions of those tracks when you redownload them. iTunes stores your tags, and doesn’t supply tags based on their matches.