Ken Thompson’s Jukebox for the Ages

For the closing keynote of the Southern California Linux Expo, 80-year-old Unix pioneer Ken Thompson delivered the tale of his 75-year project that combined his technologist’s spirit and his sense of humor — as well as his love of music.

Thompson first jerry-rigged his own cutting-edge digital jukebox at Bell Labs in 1985, and then over the years pursued the project through more and more inventive permutations. For his closing keynote, Thompson took a look back at the long arc of his evolving interests, sharing all the odd and inspirational twists along the way.

Music, Music, Music

When Thompson turned 14, he used his savings to buy one of the first commercially available tape recorders ever produced. “It cost me $127… And I loved it. I took it everywhere.” With its tape-splicing equipment and spare reels, it weighed over 30 pounds. Young Thompson used it to provide the voice of a robot he’d built — and to record the music of a three-person band he’d joined.

And then his talk flashed forward to 1982 — and to where this fascination ultimately led. A few years after Thompson co-created the Unix operating system, Thompson was still working on research at Bell Labs — which conveniently also had its own acoustic department.

There James “JJ” Johnston had developed his own cutting-edge sound-encoding format called “perceptual audio coding”, which was actually modeled after the functioning of the human ear. Thompson found an old design for a specialized microprocessor built to decode Johnston’s audio format and had it redesigned by another Bell Lab audio wizard named Schuyler Quackenbush, eventually creating his own printed circuit board.

Thompson showed a slide with one of many incarnations of the device: a plug-in card connected to the rest of the system by a cable in a kind of home-brewed SCSI connection (using the power of the system’s original CD drive) — that could now play the audio files.

One incarnation was a remarkably early digital tape recorder. But still another incarnation had a floppy disk reader — back then a 3.5-inch floppy disk could store 1.44 megabytes, roughly enough space to hold the audio for a single song. “You’d plug it in, it would play the song, and then spit it out.” Just like putting vinyl records onto a DIY phonograph.

Soon Thompson’s interest had led him even closer to the cutting edge of recorded music. He had Bell Labs buy an early CD burner. “It cost $20,000” told the audience — reminding them that was worth more back in those pre-dotcom days. Thompson also bought two fast CD rippers, attached them to a multiprocessor, “and asked everybody in all of Bell Labs to come in and stick their CD collection into the hole.”

Was this a pioneering effort in music piracy? “Everybody started getting worried about copyright,” Thompson tells the audience. But he’d actually talked to the legal department at Bell Labs, and they’d waved it through — possibly making an exception because it was for purposes of research. “I was very surprised — but I wasn’t going to question them.”

Thompson notes copyright law includes an exception for research, and “This is a research institution doing research on audio — so I can steal CDs, right?” The audience applauded.

The Music Man

Billboard magazine had its listing of the top 100 most popular songs every week — and Thompson wanted to see if he could recreate every single song that appeared in the top 100 during 1957. He procured copies of Billboard magazine for every week of 1957, then created a master list of every single song and title. In some cases, he had to digitize the audio from old “singles” — the smaller vinyl records that spun at 45 revolutions per minute.

And eventually, Thompson had roughly 80% of the songs for his master list.

But the tinkering wasn’t done, and Thompson remembers the inspiration for his next idea — at a street fair in Toms River, New Jersey. There he’d spotted what he describes as the table-top jukebox interface you’d find on tables in 1950s diners. Using a Raspberry Pi, Thompson created a kind of Franken-machine, connecting the authentic jukebox interface to his homebrewed collection of pirated music. “And I had 200 songs, which of course were all 1957 songs. And it was cool.”

Thompson continued working on his project over the years. In the year 2000, he converted all the music files to mp3 format. And in 2010 he made a fateful decision. He’d collected the top songs from 1955 to 1959. But now he wanted to expand his collection so it ran from the years 1900 to 1999.

This is trickier than it sounds. Popular music recording was very primitive before 1925 — and of course, there was no Billboard 100 for the earliest decades. Thompson began doing what he could do assess popularity — collecting 78 rpm vinyl records, statistics on the sales of records, sheet music, even the rolls for player pianos.

Thompson will tell you proudly that he finally found 99% of the songs he’d been looking for. But during a later question-and-answer session, he admits his quest also left him with five double-cabinets, each with seven or eight drawers filled to the brim with stacks of CDs (removed from their jewel cases, for extra space). “Probably 10,000 CDs,” he says. In 2023 his next project will be feeding them all into CD readers so he can digitize them — and then take the original storage media to a music shop.

But Thompson’s project took a final strange twist. In 2015 — at a pinball arcade in Dixon, California — Thompson spotted a “magnificent” 1952 Wurlitzer jukebox for sale. Thompson found schematics on the internet, and decided to replace its original control panel with iPad displays. His original idea was to have its 24 buttons trigger the launch of the record-playing mechanism — but while actually playing the audio from a corresponding mp3 music file.

Instead of being limited to the 24 buttons, Thompson dropped in his own collection of 60,000 songs — including both R&B and country and western hits from the years 1942 through 1999. Not just any 60,000 songs, but the 60,000 he’d identified as each year’s top hits — and then hunted down, one by one, “with the help of the internet.”

Finally, in 2018 he added a voice interface, which makes the displayed list of available songs update to include your requested song — next to a button that will play it.

In 2020, he discovered a Tennessee company that restores player pianos, and Thompson eventually bought an ornate 1908 model. “It’s backlit — these are windows, like church windows… It’s very nice.”

Ironically, it was controlled by an iPhone app — which Thompson didn’t like. So of course he replaced with one he’d created himself. A Raspberry Pi converts the notes of a MIDI sound file into “key up” and “key down” messages — and then sends them to the player piano. And then Thompson tried to find MIDI versions of songs from his jukebox (orchestrated for just a single piano).

And then he connected the player piano to the jukebox — so if you selected a song that was piano-only, it suddenly started playing not on the jukebox, but on his player piano

At the end of the presentation, Thompson was given a SCaLE jersey with his name on the back — with the presenter joking that Thompson will probably find a way to connect it up to his player piano.

Thompson had already wowed the crowd by playing a video showing his contraption in action — and the audience applauded, as Thompson delivered a final summation.

“That’s my talk on my 75-year project.”