The Compact Disc: An Introduction

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The Compact Disc. Just, like, radical man. Lasers making the music? What will the technology wizards think of next?

In this video we take a first look at the compact disc and its underlying encoding. Soon we’ll be looking more into CD players and their laser pickup systems, so be sure to subscribe if you haven’t already!

Links!

The How It’s Made episode on CD’s. Really good, but why they skipped the mastering step is beyond me!

The Laserdisc Playlist:

The really great source material on CIRC:

Technology Connections on Twitter:

The Subreddit:

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[kmaxmax]

The pit depth on a CD is about 120 nano-meters, worked as a Process engineer for 15 years in a CD two different CD mastering companies.

[GabrielWB]

Fun fact about the compact disc.

During the design phase of the compact disc at Philips, they had a meeting about the size of the center hole.

Joop Sinjou, head of Philips audio products, grabbed a Dutch 10 cent coin (known as a 'dubbeltje') and placed it on the table and decided that it should be that size.

And to this very day, optical disks like CD-ROMS, DVDS and Blu-rays still have the same 15 mm hole since the release of the original CD in 1982.

[TechnologyConnections]

I only half explained the destructive interference thing. So I'll explain it better in *text form.* Ooh!
Because the pits are 1/4 as deep as the wavelength of light, the light that is reflected back becomes 1/2 its wavelength out of phase with the projected light. This will reduce the intensity of the overall beam due to destructive interference. That's also part of why the change from pit to land is what matters, because depending on how the laser tracks it, pits might very well get reflected more strongly than lands. The pits and lands can be inverted and still encode the same data. There just has to be some concrete change in brightness between the two, which the depth-change accomplishes.

[Henryarsenal]

The CD has been the best media for music imo. Its small enough not to be inconvenient like laserdisc or vinyl, while large enough for proper album art/sleeve to fit with the case. Capacity/quality ratio perfect for a single album of music. Its both hi-tech and old-school simultaneously. When you own an official CD of your fav band/artist, youre connected with them in a way. Theres some old-school shenanigans to be had in the whole process of taking a CD out of the case and popping it into the car audio while exploring the album art and then enjoying the ride to your fav music.

[dentjoener]

Fun fact, this video in 4K is 1.67GB, about 2.5 CD-ROMs worth of content. Which we just went through in about 17 minutes. Not bad :)

[aipx]

Great video. Back in 1992 I applied for a job at a TV repair shop. They told me I'd need to know about CD players and I had only just bought one from Radio Shack. So off to the library at the college I was attending to read. In one afternoon I learned everything you just covered. About the same time I got into ham radio and found that packet radio systems use the same NRZI encoding and reed solomon for FEC (forward error correction). All Very Good Stuff! Thanks for doing this video.

[patemathic]

I remember a CD which was scratched so bad no CD players in our house could play the entire disc. I wowed when the car stereo managed to play the CD just fine.

[Whole_Note]

I just want to say that I'm watching this in 2021 with a brand new BluRay drive in my PC that has now only been used to burn CDs. What a time to be alive.

[pufthemajicdragon]

THIS IS IT! I FOUND IT! The first video with the Jazz at the credits!

[SySoBa]

I love CDs, somehow owning a physical copy of the music I love makes me feel better than just streaming it. But I never really understood how binary code is translated into sound? That’s pure magic right there.

[GiggleSkull]

I love the Dirty Harry reference you squeezed in there, nicely done

[skinnyblinddude]

I fell in love with the compact disc format in the '80s. Well mastered releases can sound amazingly faithful and vastly more so than phonograph records. It does wonders for classical and jazz too!

[Assimilator]

All these years and I’ve NEVER placed a cassette on top of a CD. On my to do list for this weekend.

[Kaziklu]

A total aside but when I was helping a young friend write their first university essays I actually loaded up Wikipedia. They instantly said you can't use that, the Prof was clear on that. Then I showed her my dirty secret. The Reference section. If the information you want is there and it is cited you can use the source and the source will usually have much more information than Wikipedia. She thought that was amazing. I then took her to a reference library and helped her work through that. She had gone to a High School in another country that was primarily artistic so essay's weren't really a thing like they are here.

She was going to an Arts School for university but still had to take humanities. When she handed her first essay in her prof saw the physical books mentioned in the Bibliography and asked her why she didn't just use the internet. I don't have much faith in that school...

The rest of this video is fascinating.

[scottdotjazzman]

Speaking of audio quality, Alec: I have some constructive feedback (pardon the pun), if your workflow supports it:

The placement of your mic works quite well for maintaining consistent volume, but the proximity to your chest means the 200-800Hz range of your voice is about 10 decibels louder than the rest, which makes you sound muffled in comparison to other Youtube creators. May I suggest that you cut that range by 6-7dB before you normalize the audio level on your next video? This will greatly improve intelligibility at lower volumes, at the cost of raising the noise floor slightly.

Always appreciate your videos, by the way. They're always clear, well thought out, and entertaining. Keep doing what you love!

[blaedd]

In this context 2s complement is best thought of as a representation rather than the operation. It just makes basic operations like addition easier at the binary level. You can just add -6 and +8 in 2s complement binary representation and get the right sign in the result (also in 2s complement)

[Felixicity]

This was super fun to watch! My mom, brother, and I have all worked with CD/DVD manufacturing, so it was nice seeing someone else appreciate how they're made and the process to do it.

[Goabnb]

I love my CDs. You're going to be very hard pressed to find a similar or better quality digital copy of music without ripping straight off the CD, at least legally. Not only that, but the liner notes and photos gives you so much material, as opposed to digital files, which could be deleted on a whim.

[ABaumstumpf]

The CD was a marvel at the time - and the audio quality is still the gold standard for listening experience in stereo - simply cause it is 'good enough' for all human ears. But we moved on and now with flash-storage got a medium that is not as long lasting, but far more convenient.

[anonamouse]

Just take those old CD's off the shelf
I'll sit and listen to them by myself
Today's music been compressed to shit
I like my old time Compact Disc