The compact disc has been a staple of music storage for decades. But there’s a lot more to the CD format than most people are aware of.
Computer Data
Most people are probably familiar with this, but perhaps the youngsters (says me, the 21-year-old) don’t know this. CDs can hold computer files, up to 700MB of them (this used to be a lot).
High Quality Audio
CDs may have come out in the 80s, but the audio quality is still surprisingly good. CDs have up to 80 minutes of uncompressed 16-bit, 44.1 kHz audio. That’s the type of quality that studios record in, although some studios today go a little higher with 24-bit/48 kHz (only people with amazing speakers and well-trained ears can actually tell the difference between these). CDs actually have a higher quality than Spotify, and a quality equal to Apple Music in many cases.
CD Graphics
It’s not used a lot now, but CDs can actually have simple graphics included. The CD+G format has been used to add karaoke lyrics to CDs. A normal player will play it like a normal CD, but a karaoke machine will show lyrics alongside the music.
CD-MIDI
MIDI is an American-Japanese technical standard that describes a communication protocol, digital interface, and electrical connectors that connect a wide variety of electronic musical… MIDI is way too much to unpack here. Basically a CD-MIDI holds a sort of digital sheet music that instructs synthesizers. MIDI files used to be very popular online, since instead of sending a whole audio file over dial-up, you’d just send a file with the notes, and your computer would play them with an array of virtual instruments. For an example, here’s 150,000 midi files from some old webpages. CD-MIDI is super rare, as are CD-MIDI players, so good luck finding any of them!
Video CD (VCD)
Not only can you do karaoke lyrics, you can put entire videos onto CDs! The VCD is like a DVD, but absolute potato quality. And since the video took so much space they had to make the audio terrible too. Here’s an example of what a VCD would have looked like. It was actually pretty popular in a lot of Asian countries, but it was quickly replaced by DVDs. There was also the Super Video CD (SVCD) which was slightly better.
Hidden Tracks
This is a fun one. Audio CDs have a stream of audio and a table of contents (TOC) that says where each track begins and ends. Tracks are also split into multiple indices which are mostly not used. CD players start a CD by going to track 1, index 1. However, before the first track there is an “index 0.” The original standard was to put 2 seconds of silence. This is because early CD players had trouble lining up the laser at the right spot, so this gave a little wiggle-room. This area is called the pregap.
However, you can actually make the pregap as long as you want, and you can put any audio in there, not just silence. Many CDs have hidden audio tracks here. You can access the hidden track by rewinding into it. Unfortunately this doesn’t work on a lot of CD players, so if you actually want people to hear a track don’t put it here. It’s a great Easter egg though.
Mixed-Mode CDs
This is a really fun one. It’s possible to make a CD that has both regular CD audio as well as computer files. These CDs will play normally in a CD player, but when opened on a computer you can access additional files. Original mixed-mode CDs had an issue where some CD players would try to play the data track as sound, which of course does NOT sound good. As an example, here’s what the video from earlier would sound like if a CD player mistook it for an audio track.
Not good. Fortunately modern CDs can be formatted as a multi-session “Enhanced CD.” This fixes the issues with CD players. It’s not very common, but some CDs have this. For instance, the enhanced version of Billy Joel’s “An Innocent Man” has music videos included as a bonus feature.
Conclusion
CDs, while often used only for music, actually have a lot of potential uses. Although some are basically not compatible with anything.
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