Monday Mystery: A Hard Day's Night
Musicians, musicologists, and fans have been debating for over fifty years now what, exactly, goes into the opening clang in the Beatles' famous tune, "A Hard Day's Night". The movie mix above is slightly different from the single and the album -- the album/single releases were in mono; the movie was in STEREO! Zowie! -- but there's only one set of source tapes, so the chord is the same.
You could ask the Beatles what it was, and people have. Amusingly, none of them could really remember. Some of them have guessed at what it was from time to time, but their guesses were never consistent. George Harrison seems to have had the best idea, but even he had no idea what Macca was doing over at his mic. None of them read or wrote formal music notation, either; when they needed to give complicated instruction to session musicians, they went through someone else. Often it was their producer, George Martin, a legend in the industry.
(He has now passed that title on to his son, Giles, who still works on various Beatles projects whenever they pop up. The surround mix from LOVE, mentioned in the link above, is to a Cirque du Soleil show that ran, and is possibly still running, in Las Vegas. Quite a lovely show; I've seen it. If you know a lot about their work and history, it might make you cry a couple of times.)
Randy Bachman -- as in Bachman-Turner Overdrive -- has a pretty good guess, and gives it in his Guitarology show. It doesn't quite fit with the other seven million guesses I've seen, but it sounds remarkably good. Other randoms on the internet have had a go as well, and a few are down in the links below.
A mathematician at Dalhousie University took another, much more complicated stab at it, and concluded it was two guitars, a bass, and George Martin on the piano. There's a friendly explanation of the paper at NPR's archives.
For those among us who may be bored, I also include the Usenet Guide to Beatles Recording Variations, a webpage which has not changed in the slightest since I obsessively read the entire thing over a decade ago. And a playlist which purports to have the entirety of the movie A Hard Day's Night, although I have not checked -- I have the collector's DVD set, which beats the tar out of YouTube for picture quality.