Up close on various recording media
June 16, 2015 8:48 PM   Subscribe

Ever wonder what a record needle looks like as it travels down a groove? What about the surface of a DVD? Even if you haven't, you should still take a look (SLYT)
posted by Hactar (15 comments total) 34 users marked this as a favorite
Yeah, there's a lot more to this than just "here's a magnification". Very nice.
posted by Bugbread at 9:15 PM on June 16, 2015 [3 favorites]

What happens if you leave the magnets in, when you use the microscope? Is it safe? Can you actually visualize the shape of the magnetic fields from the distortion produced in the image, or do you just get total garbage?
posted by rustcrumb at 9:19 PM on June 16, 2015

I imagine it's much like when you'd hold a magnet up to a CRT.
posted by sbutler at 9:26 PM on June 16, 2015 [1 favorite]

"Ever since setting up this electron microscope in my shop ..." Brilliant.
posted by carter at 9:56 PM on June 16, 2015 [3 favorites]

I managed to find a guide to scanning electron microscopes that has some examples of magnetic distortion: check out figures 35 and 40. I don't know what the shapes of the distorting fields are but it just looks like a little waviness or pincushion distortion.
posted by traveler_ at 10:45 PM on June 16, 2015 [2 favorites]

rustcrumb, it's not unsafe.

To make an analogy to the optical regime, fill a ziplock bag with water, place that on top of a document, and take a picture of it. The bag of water acts as a lens and distorts the subject. You could use this to characterize the optical properties of the bag, if you wanted, but basically it's just a shitty imposition against the precision optics built into your camera. An SEM works the same way, but uses magnets for lenses and an electron beam instead of visible light.
posted by 7segment at 12:08 AM on June 17, 2015 [3 favorites]

For fans of Wendy Carlos, an important note from the comments: "I didn't cut up Switched On Bach. I also bought a Johann Strauss LP and sliced that one into pieces."

(and while Ben covers some of it briefly in the video, this article has a bit more on how he got his hands on a SEM and hooked it up to a Tek oscilloscope.)
posted by effbot at 2:41 AM on June 17, 2015 [2 favorites]

This is really cool. You see how the stylus doesn't just move up and down; it slides sort of diagonally back and forth and up and down because the grove pattern is three dimensional. The movement from bottom left to upper right is one stereo channel and bottom right upper left is the other.

That's one heck of a workshop. A silver sputtering machine AND an electron microscope.
posted by three blind mice at 4:53 AM on June 17, 2015

This is really cool, but because of the mods made to the needle and cartridge and lack of tone arm, I'm not convinced we saw exactly what happens on your home turntable. It's pretty tricky balancing, actually. I suspect the real movement is a little different out of the lab.
posted by clvrmnky at 5:07 AM on June 17, 2015 [1 favorite]

Way back in the day, I did a lot of freelance work for a small ad agency that did a lot of POS (Point Of Sale) pieces for RCA. This was at the time RCA was really pushing that video disc format he showed. It was a horrible thing. We had a unit to play with, and it was always malfunctioning. The whole concept was terribly clunky compared to popping-in a VHS or Beta tape, and the image quality was below that of laser-disc. None of us were sold on the thing, and even some of the RCA reps knew it was a DOA technology.

The worst part was RCA using a tired, old Gene Kelly as their spokesperson. Give Gene props for being an entertainment icon, but, by the 80's, he wasn't a spring chicken and really had no cachet with anyone under the age of 50 or so. He just looked like a thick wax figure in the photos we were given to work with.
posted by Thorzdad at 5:33 AM on June 17, 2015 [2 favorites]

I'm not convinced we saw exactly what happens on your home turntable.

And they explain that in the video. The stylus isn't traveling in the same arc as it would on a turntable so the movement is exaggerated, but it's still a good illustration of what's going on. It makes it really clear how one stylus can pick up two audio channels in the same groove.
posted by three blind mice at 5:55 AM on June 17, 2015

"...and hooked it up to a Tek oscilloscope"

So he samples an entire frame of video output via a top-notch digital scope (donated by the manufacturer), dumps it to a USB drive, then programs a video manipulation application to turn it back to an image.

You or I, we'd use a $30 webcam. And that's why you or I are never given SEMs or top-notch digital scopes.

Lesson learned.

(cool video, btw. Thanks!)
posted by Devonian at 7:52 AM on June 17, 2015

A silver sputtering machine AND an electron microscope.

Two SEMs, even. The old JSM-T200 that was salvaged from a Swedish university, and one he built himself.
posted by effbot at 11:49 AM on June 17, 2015 [2 favorites]

This is outstanding. Cool stuff but also very nicely made expository video.
posted by LobsterMitten at 5:27 PM on June 17, 2015

Just came across this related article which references the OP's linked video to help introduce a classical music collector with a unique talent for recognizing songs by their physical groove patterns on vinyl pressings. I could sort of do this when I used to DJ to help find my favorite track on an EP/LP (bass-heavy parts look darker because the grooves are spread out more), but this guy is on another level.
posted by p3t3 at 9:05 PM on June 17, 2015

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