You know mixtapes, right? Back in the day, people used to use cassettes to record songs directly off the airwaves, or off other cassettes, to make custom playlists that were limited to the size of one cassette. Those apparently stored 60/90/120 minutes per cassette depending on how fancy you went, and there was an intermission halfway through where you had to stop playback, flip the cassette over and resume. That’s technically a limitation, though in my experience 60–120 minutes is a really good size for a playlist anyway so I’m sure it worked out pretty well for our ancestors there.

Unrelated, but have you ever burned a blank CD? You know how it says “700 MB/80 min”? 700 MB is the amount of pirated video game you can fit on it, but what about the time duration? That’s right, the Audio CD format can store 80 minutes of uncompressed audio in it¹. Why 80 minutes, you might ask? Well, it used to be 74 minutes and a bit, because Sony vice-president Norio Ohga really wanted Beethoven’s Ninth Symphony to fit in its entirety on one disc. Later, as CD manufacturers got into high gear and got their tolerances in order, they realized that they could place the concentric tracks that store data on a CD slightly closer together, giving them room to fit an extra track or two and get the length up to 80 minutes—a really good size for a playlist, as established above.

Anyway, I acquired a car a few months ago. I frequently listen to music in it as I’m driving around places, and for that I often use YouTube Music’s “your supermix” feature, which is basically The Algorithm™ deciding what you listen to next. Now, I welcome our new AI overlords as much as the next guy², but they haven’t quite figured out music yet, so it would be nice to have some manually-curated content. Plus, since my car is a vintage³ model, it comes with a CD drive, so I figured I could just create some playlists manually and burn them to disc for in-car entertainment. Wouldn’t be too big of a lift, since looking at most of my playlists, most of them were around the 60–90 minute mark anyway.

Oh, also, I started dating somebody, also a while back now. Nothing serious yet, but we enjoy each other’s company. It’s great fun. A while ago, I asked them what their music taste was like, because that seems like the kinda thing to ask someone you’re dating. They asked me for the same, and we both shared playlists with each other filled with our preferred kinds of music. Then—and this was unplanned, but maybe it’s just the obvious thing to do—we both also exchanged which of each other’s songs we enjoyed the most. One set intersection later, I had a set of songs that we both enjoyed, sampling about equally from both of our playlists. And the total duration of this set of songs was… about 85 minutes! A really good size for a playlist, especially after I removed Live & Learn.

A really annoying thing about sets is that they’re not ordered. Sometimes it really feels like they should be, like the one time where I merged a PR at work, hashing the JSON representation of a set to quickly figure out if it changed before I made an expensive network request with it. Ordering that set into a list was easy—sort by the unique key—but sorting a set of songs into a playlist is much harder. A quick hack I figured out was to match the vibe of the last few seconds. So if a song ends on an upbeat electric guitar note, follow it up with one that starts with an upbeat electric guitar note. After that, select a first song, and from there you can construct a list with the match-vibe rule. It’s only a partial ordering, but it’s sufficient for my use case, which is just to sort about 80 minutes of songs that, by virtue of being the intersection of music taste of two people, are all pretty similar anyway.

Before we go further, I have to tell you about my favorite fucked-up little son, francium. He’s a Sony Vaio VPCZ1 laptop that I bought from a computer store that was about to shut down, for “the price of the charger”, $20 or something. Someday I’ll go into more depth about him—he honestly deserves his own article—but the upshot is that he’s the only computer I own with a BluRay drive. He’s also just a very convenient computer, since he has all the old ports (SD, MemoryStick, BluRay/DVD/CD) as well as all the new ones (USB). Because of this, it was pretty easy to install a CD burner on him, copy over 80 minutes of songs, and burn, baby, burn.

Now, francium isn’t my only questionable electronics purchase—I have many, but the second-most-useful one after him is probably bromine, my printer. I also bought her for about 20 bucks, and she came with a full laser toner and a full tray of paper. To date I have never bought more of either, which should give you an idea of how much I use her. But when I need her, she comes in so handy. For example, I’d just burned myself two copies of an audio CD—one for me, one for my partner—but I didn’t have a jewel case⁴ to put the disc in. But thanks to bromine, I could just print off a template for a CD sleeve, cut and fold it to spec, write the track list on it, and boom, a perfectly sized sleeve to fit a CD containing a perfectly sized playlist.

I would also like to make questionable car purchases someday, but for now I vicariously live through local car shows, where people bring out their cool project cars to show. I recently went to one that was pretty close to where the person I’m dating lives, so I decided to invite them to it. We had a great time! We saw a restored 1960s hearse, a panel-by-panel custom-built car with the license plate ITSLEGAL, and an AMC Gremlin that starred on Canada’s Worst Driver. My favorite car was my partner’s Mini Cooper though—such a delightful little car, charmingly designed interior and cute-as-hell exterior. As I got in it to go get lunch with them, I remembered that I had a thing for them—a disc containing about a mixtape’s worth of songs, which I think is a pretty good size for a playlist.