Electron Microscopy and Vinyl

[Martin]

This fascinating short video talking about how quadraphonic vinyl works using electron microscopy popped into my algorithm on YouTube this evening.

I did not realize there were two competing quadraphonic systems, CD-4 and SQ. He does a very good job of explaining how they work plus the electron microscope images are stunning. He has another video discussing how stereo vinyl works that I plan to watch next.

Cool stuff!

Martin

 

[Aerobat]

Since electrons pass through vinyl, it has to be plated with metal in order for the electron microscope to see anything. Also, high-frequency sound waves are smaller than the wavelength of light thus can't be seen through a regular microscope.

 

[JeffS7444]

At 6:33, the second video illustrates the dramatic difference between inner and outer grooves.

 

[aaaakkkk]

The first part about vinyl is more informative. With the photos attached to it, you can see there is no radius at the bottom of the groove. Ray loves to tell us so much about this radius.

 

[sqrl]

The first part about vinyl is more informative. With the photos attached to it, you can see there is no radius at the bottom of the groove. Ray loves to tell us so much about this radius.

Maybe he's an early mono collector.

 

[sergeauckland]

There were actually mire than 4 competing systems. SQ and CD-4 were the best known, but also QS was pretty popular as it was royalty-free. A further system, UD-4, never really caught on, and the BBC developped Matrix H for broadcast, but it never went into regular service, and of course Nimbus had their Ambisonics system, which I think may be still going.

Not surprising with all these systems, the public pretty much ignored the whole thing, and it went away after a few years.

S

 

[spyne]

high-frequency sound waves are smaller than the wavelength of light

Either you've written this poorly, or you have a bad understanding of light and sound.
The wavelength of high-frequency sound waves are nowhere near as small as the wavelength of light.
A 20,000Hz sound in air has a wavelength of approx 17mm. Even ultrasonic sounds, let's say the upper end of an ultrasound machine operating at 15MHz, the wavelength is still only about 0.2mm
A "normal" microscope uses visible light (obviously), which has a wavelength range of 0.00038 - 0.00075mm. Four orders of magnitude smaller than the ultrasound machine.

Also, electrons do not pass through vinyl records. PVC is an excellent insulator and acts as a collector of any electrons fired towards it, resulting in smeared/distotred images The scanning electron microscope fires electrons at the subject, which in the case of non-conductive samples, has to be coated, then secondary & backscattered electrons are emitted from the surface of the coated sample which are picked up by detectors, creating a image for us to see.
There are newer SEMs which allow imaging without coating samples, using low-vacuum (instead of high-vacuum) conditions.

 

[somebodyelse]

Either you've written this poorly, or you have a bad understanding of light and sound.
The wavelength of high-frequency sound waves are nowhere near as small as the wavelength of light.
A 20,000Hz sound in air has a wavelength of approx 17mm. Even ultrasonic sounds, let's say the upper end of an ultrasound machine operating at 15MHz, the wavelength is still only about 0.2mm
A "normal" microscope uses visible light (obviously), which has a wavelength range of 0.00038 - 0.00075mm. Four orders of magnitude smaller than the ultrasound machine.

I suspect it was explained poorly, and meant to refer to the wavelength as cut into the vinyl which is much closer to the wavelength of visible light, but still ~0.01mm for 20kHz at the inner groove of an LP (unless I messed up by back of a fag packet calculation...)

 

[aaaakkkk]

I suspect it was explained poorly, and meant to refer to the wavelength as cut into the vinyl which is much closer to the wavelength of visible light, but still ~0.01mm for 20kHz at the inner groove of an LP (unless I messed up by back of a fag packet calculation...)

I believe this refers to optical microscopes, which have a severe resolution constraint; even 0.5 microns is insufficient for comfortable inspection of vinyl record grooves.


Optical microscopes do indeed face a fundamental physical barrier—the Abbe diffraction limit. Conventional light simply cannot resolve details that are smaller than half of its wavelength. For the visible spectrum, this limit is approximately 0.2–0.25 μm.

• Feature size: The width of a vinyl record groove itself is about 40–80 μm, but the depth and micro-profile relief (the wall irregularities that actually generate high-frequency sound) are measured in nanometers.
• Information loss: At a resolution of 0.5 μm, the tiny modulations of the groove responsible for upper audio frequencies will appear as blurred spots.
• Depth of field problem: High-magnification optical microscopes have an extremely shallow depth of field. The groove walls slope downward at an angle, making it physically impossible to focus simultaneously on both the bottom and the edges of the track.