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Fun fact about laser discs. They are analogue not digital. CD’s store digital information with the presence or absence of pits. Fairly ancient but still fundamentally feels like a very old version of a thumb drive.

Laser discs are not digital. They encode the analogue video signal’s value as the length of the pit. It is digitized in the time domain - sampled at some frequency, but the “vertical” signal value is stored entirely analogue. In terms of encoding it’s more similar to a VHS tape than a CD. Kinda crazy.



yeah i remember learning this as a kid and being surprised. i originally thought laserdiscs were modern high tech, but then they turned out to actually be from the late 70s/early 80s with the primitive analog video encoding where red book audio cds of the mid to late 80s were actually digital.


BUT... Pioneer put AC-3 (Dolby Digital) surround on LaserDiscs before DVDs came out. So LaserDiscs were the first video medium to offer digital sound at home.

And at that point, most players sold were combo players that could also play CDs.

And there was one more disc format: CD Video. It was a CD-sized digital single that also had a LaserDisc section for the (analog) music video. I have a couple; one is Bon Jovi.


Was CD video compressed? I thought it existed at the same time as DVD but cheaper.


That's Video CD. It existed before DVD but survived alongside it (mainly in Asia) as a cheaper alternative.


no, apparently there was both. i was familiar with video cd which was mpeg-1 on a cd-rom (with some weird partitioning scheme). cd video is apparently a very obscure hybrid format with an analog video section and a digital audio section. https://en.wikipedia.org/wiki/CD_Video


No; it was analog LaserDisc video. I think "Video CD" was a flavor of CD-I, which was very popular in China and was used way, way beyond the introduction of DVD. Well into the 2000s, I think.


I just learned this in my 40s and am surprised. Very cool.


> Laser discs are not digital... It is digitized in the time domain

Laser disks are 100% digital (as you said, they store digits in the time domain).

They don't encode their data using binary like a CD does.

"Binary" and "digital" are two separate and unrelated concepts.


Um... I think they store "PCM encoded-ish" but the length of the pits are not discrete on / off like on a CD but various arbitrary lengths, so analog.

The sound was also analog to begin with, then the same encoding as CDs, then after that AC-3 and DTS.


"Digital" means you represent information using digits. Discrete numbers. "on/off" is binary. "Analog" means not using digits but instead an alternative (analogous) representation of the original data, usually continuous.

The grooves in a vinyl LP directly represent (are analogous to) the variations in sound pressure interpreted by our ears as sound. The grooves are continuously varying in direct proportion to the continuously varying sound waves. That's analog.

Converting analog video signals into a sequence of integral digits (even if it's pulsed-code modulation) is an analog-to-digital conversion, and storing those digits on a medium makes that a digital medium. It may just not be a binary digital medium.


So how does writes work? Does an analog signal translate into pit-lengths with absolute precision?


Everything is analog when it gets to real world




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