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Microscopic footage of a needle moving across the grooves of a record (dangerousminds.net)
353 points by batbomb on June 16, 2015 | hide | past | favorite | 60 comments

Wow! I never knew the needle move side-to-side! I always assumed phonograph needles moved up and down.

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.

Poking around on wikipedia (https://en.wikipedia.org/wiki/Compatible_Discrete_4), I learned that true four-channel quadraphonic sound, for LPs, was obtained by further recording two more signal streams in the same groove.

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.

Brilliant - so that's how the my copy of Mike Oldfield "Boxed" (https://en.wikipedia.org/wiki/Boxed_%28Mike_Oldfield_album%2...) was supposed to work. As I didn't have the cash to buy a quad player I never got to hear it in "Glorious quadrophonic sound", I had to use an "old tin box".

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.


Netflix sent me 6 channels for Daredevil, and the sound production was amazing. If you've only heard it via stereo, you missed out on all sorts of excitement.

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.

That's the perfect movie for demonstrating the potential of multi-channel audio. The only problem is that you're also relying on the viewer to have proper speaker placement, sound levels and speaker calibration. Autocalibration (YPAO) is simple and easy but hardly anyone knows to use it when installing their $300 home-theater-in-a-box.

Master and Commander is another film with great surround sound. A number of years ago now, Dolby Labs used the sound from that movie as a showpiece in their SOMA theatre.

Brave? It was the first Atmos movie, so I've just assumed that the downmix to 7.1 and 5.1 is equally as good.

There are some really interesting mastering techniques that are needed because of this, too - for instance, bass content (< 200ish Hz) on vinyl usually gets summed to mono to prevent a loud bass note on one of the stereo channels from making the needle jump out of the groove. With the loud bass content in mono, the needle jumps vertically and stays in the correct groove.

I've always liked this layman's animated FAQ:


Lateral recording was a patent workaround. Thomas Edison had patented vertical recording and was not interested in licensing it to anyone else, so Berliner used the noisier, but available, lateral technique.

Fuck patents.

Yeah, I love his channel. Many hours of fun, interesting information and techniques.

I am stoked to see my work on the front page of HN! Let me know if you have any questions. I've lurked on this forum for a long time, but rarely post.

Would you consider selling posters of that needle shot as a way to support you? I'd love to get a poster of that to hang and I'd love to be able to fund you doing more cool stuff (your channel is great).

Thanks! I really appreciate it. My source image is 1000x1500, which redbubble.com says is not large enough for a poster. I admit, even at 150dpi, it wouldn't be much of a poster. As I upgrade my SEM image acquisition hardware, I'll be able to make higher res images. If you'd like the raw PNG, check out my blog: http://benkrasnow.blogspot.com/

Thanks so much. It's a really cool image and thank you for making it available.

That's a great idea. He certainly would get my money.

Cool as hell, as usual! You consistently seem to find just the right mixture of inspiration and perspiration. I love how you just turned the knob and hit a button every few minutes, while I'd have spent six weeks trying to automate the stop-motion process.

It's obviously too late now, but you can actually get piezoelectric cartridges with no coils or magnets, made for (very) low-end phonographs.

In the slow-motion video, there's a dark area to the top right that disappears partway through. What's happening to cause this effect?

I suspect the dark area was a piece of lightweight dirt (a tiny lint ball, or sawdust) that began accumulating charge as it was imaged by the electron beam. After 20 minutes or so (20 frames in realtime), the dirt developed enough repulsion force to be launched off the surface of the record. It's sort of like a charged comb or other object repelling styrofoam particles.

The only thing is, the needle isn't moving here. This is an animation of what a needle would look like moving across a record, but taken in stop-motion style. I wonder if the use of an electron microscope is really needed? The grooves in a record are hardly small enough to escape visible light...

the needle isn't moving here

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[1] 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.

[1] https://youtu.be/Lt6iltuxD48?t=120

As the fellow states in his video, he was limited by the capabilities of the microscope. The quality of images he took required 10 seconds per frame. The microscope was capable of producing something much blurrier at 60 fps.

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.

Maybe you could use a strobe effect: Have an audio sample that loops every 1/100th of a second, and then put a "fan" spinning at the same rate in front of the electron source, which blocks the electrons except for 1/60th or less of the 1/100th of a second. As you vary the phase of the fan, you capture the needle at different positions in the loop.

That would have been possible if he were able to observe the vinyl in action and had a circular track of audio on the record, instead of working with a square slice.

Not exactly what you're after, but a taste:

https://www.youtube.com/watch?v=xLmpkPjkozs [esp. around 1:00]


Yes, the first video you shared shows the timescale and the second shows the size.

I wonder how/if the inertia of the needle affects the sound. It seems to me that at 20 kHz, the needle would bounce around in the track. I should do the math...

Yes, "high-frequency mistracking" is a thing in hi-fi record player design, resulting from high "effective tip mass".

Actually, standard grooves are only ~40uM (0.0015in) wide. That's small enough that's it going to be really hard to photograph clearly - and that's the width from peak-to-peak, the modulations are smaller.

Here is a source of LP images that are the same scale as the YouTube video, using a normal microscope.


Those are shot directly perpendicular from a hair's width away. Perspective shots are a lot harder.

I highly recommend everyone check out other videos on Ben Krasnow's youtube channel [0]. I've been following him for about a year now, really awesome stuff!

[0] https://www.youtube.com/user/bkraz333

This is just blogspam. Link to directly to the video instead. There are a lot of videos worth watching on Ben's channel.

Having a written summary/introduction is quite nice IMHO.

Like, say, the video description?

"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."

The YouTube channel [1] where this video comes from is a treasure trove for the intellectually curious, and it's one of my favourite things on the internet. The guy behind it, Ben Krasnow, is an engineer at Google. From explaining and demonstrating (reverse) spherification to encoding information in fucking fire and picking it up with his oscilloscope, this channel will interest and delight most folks who enjoy HN for hours.

[1] https://www.youtube.com/channel/UCivA7_KLKWo43tFcCkFvydw

> You would think that if you have an electron microscope and a record player, you’re most of the way there to being able to record close-up footage of a needle traversing the grooves of a long-player record.

Actually if you would have only an electron microscope, you could play the track without even needing the record player.

This has sort of been done with a flatbed scanner: http://www.cs.huji.ac.il/~springer/DigitalNeedle/index.html

It's also available commercially in the form of laser turntables: https://en.wikipedia.org/wiki/Laser_turntable and http://www.laserturntable.com

And don't miss the part about the IRENE system, at the bottom of your wikipedia page:


It uses microphotography of the disk surface, somewhat similar to that in the OP. They have recordings as early as 1860!

This guy is a real jedi. Did he build his own Ag evaporator?

Yes. That's not even though most impressive thing. He built his own scanning electron microscope (though that's not the one he used to produce these images).

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.

>His channel is a lot of fun.

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?

It's along the lines of the machines at tourist attractions that stretch out and stamp a penny.

I've inspected such a machine thoroughly on one occasion and was able to determine that the machine switched the penny for a dummy before performing the flatten and stamp operation.

Perhaps that particular machine did (I suspect you're mistaken though), but that is not the norm. Mutilating coins is not illegal in the United States.

My favorite is 'I've got this oscilloscope and wanted to test it, so why not do this in style and connect it to my DeLorean.'

Apparently so. He says his sputtering chamber is out of order at the moment, though, so he used vapor deposition.

Am I the only one who could listen to him narrate just about anything for hours at length?

Been watching his videos for years now. He's great.

Why was an electron microscope necessary? Surely at this scale a conventional light microscope would have done the job, wouldn't have needed all these workarounds, and could have recorded live footage of a needle actually playing a record?

It's true that a SEM wasn't strictly necessary, but there are a few interesting features that make SEM images visually different, and perhaps more appealing, than light microscope images. The electron signal emitted by the surface of the objects in the chamber doesn't behave like light bouncing off an object's surface. Normally shadows are cast by photons traveling in straight lines, and our minds have become accustomed to this behavior. The electrons in the SEM can travel in curved paths, so the illumination in the SEM image can effectively go around corners, leading to surreal shadows and highlights.

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.

A bit OT, but this reminds me of an inspirational mathematics teacher I had, who loved to present the subject as a series of applied problem-solving exercises, rather than the usual learn-by-rote.

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.

Funny, I was just watching this last night. I'm in awe of the Applied Science guy, and am really grateful for the information he's shared.

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.


The "root post" is just the youtube video itself.

The guy's diction is flawless.

noticed this as well.

First time I get to see one of this legendary video vinyl ... Thanks.

Next up - laser hitting a compact disc.

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