Edit: Ben explains this in the video; there are actually two axes of movement, sort of diagonal to the plane of the disk, each of which encodes one channel of a two-channel stereo recording. I'm sure many LP fans already know this, but it's a revelation to me.
BTW, Ben Krasnow is a heck of a guy. A true polymath and a generous teacher.
These other channels were recorded with FM (frequency modulation) on top of a 30 kHz carrier. The 30 kHz carrier was just high enough to isolate the quad channels from the 0-15 kHz ordinary left/right stereo channels.
And then, the FM portion, centered around 30 kHz, was added to the regular baseband audio signal (0-15 kHz), and all encoded into the diagonal displacements you mention in your comment.
It always baffled me that it also worked on an ordinary stereo - and I sometimes wondered if I had been had.
We now have the tech to encode many channels in one MP4 stream, but don't we don't bother and just stick to 2 for sound. What does that tell us about the future of 3D TV and 360 degree video? Perhaps more of us will stick to the old tin boxes.
Good multi-channel sound immerses you in an experience, and is worth a significantly smaller screen as a trade-off, if you have to make it.
It's obviously too late now, but you can actually get piezoelectric cartridges with no coils or magnets, made for (very) low-end phonographs.
That was my big problem with the video. I'd like to see real-time dynamic behavior of a needle and record. A static image every 10 seconds is not the same thing.
Edit: here's an example of what I mean. It's a slow-motion video of a topfuel dragster. Just positioning that dragster statically down a dragstrip and taking a picture every few feet won't show you the essence of what's happening. Look at the tires. Look at the vibration. Look at the flames.
I dunno. Maybe my unease is not as relevant with something simpler such as a needle and record.
You would need to record several thousand frames per second to produce something other than a blur when looking at a record producing audio in real-time. Human hearing extends up above 20 KHz and vinyl records are designed to handle this. Recording a normal object at tens of thousands of frames per second would require a very expensive camera and intense lighting. Doing this through an optical microscope would be substantially more difficult, and a current world class electron microscope would probably be incapable of such frame rates.
The scale of a vinyl record groove and needle suggests that a good optical microscope would be sufficient. However, this appears to be a case of a fun project chosen to test out a tool, rather than a tool chosen specifically for the project.
https://www.youtube.com/watch?v=xLmpkPjkozs [esp. around 1:00]
"I describe how I made a stop motion animation of a phonograph needle in an LP groove using an electron microscope. I also show electron micrographs of other recording media."
Actually if you would have only an electron microscope, you could play the track without even needing the record player.
It uses microphotography of the disk surface, somewhat similar to that in the OP. They have recordings as early as 1860!
His channel is a lot of fun. https://www.youtube.com/user/bkraz333
I find it interesting that he worked at Valve until recently when he moved to Google X. He doesn't really talk about his jobs in his videos though.
Checked it out and I agree. I have to wonder, though, if his money shrinking experiment is such a good idea. Isn't that sort of treatment of currency prohibited by law?
The aperture size in the SEM is much smaller than that used in a camera or microscope, leading to much higher depth of field for a given geometry and working distance. A camera might be f/16, while this SEM is effectively f/200
The brightness of objects in the image is partially influenced by the material properties and local geometry, so an exposed protrusion or edge will tend to be very bright -- something that doesn't happen with macro photography.
Hey, it's fun to play with scanning electron microscopes.
One of his problems was: if a 33 1/3 rpm record is 12 inches in diameter and plays for 25 minutes, how wide is the groove?
I had a clear visualisation in my head of the problem, including the groove cut into the vinyl. Watching this is like listening to my teacher speaking to me again.
Having said that, I was shocked to see his thermite BBQ video. I don't know whether the people in that video realize how close they came to being maimed.