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Comment by xigency | Hacker News Reader

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...

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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]

https://www.youtube.com/watch?v=laIvjmdM0Ww

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.

http://www.cleanlp.com/CleanLPMicroscopePhotos.tpl

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

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