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In case anyone was wondering why a "red book" audio compact disc isn't designed to be resiliant in a way that is familiar to a modern technologist (or even comp

In case anyone was wondering why a "red book" audio compact disc isn't designed to be resiliant in a way that is familiar to a modern technologist (or even compared to a CD-ROM disc) the basic reason is that the former is designed to stream with no buffering directly into a DAC chip built with technology from the late 1970s. It had to handle data rates that were incomprehensibly massive for the time, so only the most insanely basic error handling was feasible. Whereas the "yellow book" CD-ROM standard got to take advantage of over four years of technology advancement. Plus it doesn't have a real time requirement, so there's plenty of time to calculate more advanced checksums and error correction codes. In many respects, an audio CD is more like a vinyl record than a data storage format.

pwg 8y ago
> In many respects, an audio CD is more like a vinyl record than a data storage format. The design is nearly identical to what one would get if one simply literally (almost) digitized a vinyl record. A single long spiral of data on a disk. The most significant shift is that vinyl records read from outside in, while audio CD's read from inside out. Even the method of manufacture is essentially a clone (audio CD's are "pressed" just like vinyl records are "pressed", just in different pressing machinery). > built with technology from the late 1970s. It had to handle data rates that were incomprehensibly massive for the time, so only the most insanely basic error handling was feasible. Yes, the limits of late 1970's technology had a huge impact on the overall design, but at the same time the design also took advantage of the fact that audio when being played back in real time is reasonably tolerant of a small level of error resulting from the read-off of the disk. Most listeners would never hear the random errors because they either are below the noise floor of the amplifier tech. at the time, or because the resulting analog wave was close enough to not be noticeably different.
- sjwright 8y ago
  > The most significant shift is that vinyl records read from outside in Equally significant (and equally interesting) is how they spin. Whereas vinyl has constant angular velocity—they spin at the same rate from beginning to end, resulting in lower information density as you get towards the inner grooves—audio CDs have constant linear velocity, meaning that the rotational speed gradually changes as the disc is played so that the information density is equal from beginning to end. For the era, this is very cool tech. (I'm also awestruck about how they managed to get the laser head alignment to work perfectly back then, it's practically magical.)
  - simias 8y ago
    You're right for audio CDs but very fast CD-ROM readers use constant angular velocity (CAV), mainly because they start hitting mechanical constraints (including the integrity of the CD itself).
    - nobleach 8y ago
      Can't remember but, wasn't 52x spin the max (I heard urban legends about the disc spinning apart back in the late 90's)
      - DiabloD3 8y ago
        Depending on how you define 52x, CAV, and the mechanical limits of a CD. Some drives max at an advertised 48x, because early CDs still exploded at 52.
  - theandrewbailey 8y ago
    Techmoan did a video about a record that is recorded "backwards" to take advantage of the increasing fidelity in the outer grooves. https://www.youtube.com/watch?v=5Afikv6k1-c https://www.youtube.com/watch?v=5Afikv6k1-c
    - arthurfm 8y ago
      Techmoan's recent video on extended play (2.5 hour) CDs is also quite interesting. https://youtu.be/5fG1crhGqI0 https://youtu.be/5fG1crhGqI0
  - joss82 8y ago
    > resulting in lower information density as you get towards the inner grooves It's actually the opposite: highest information density (musical notes played per surface unit) is in the innermost grooves. Since linear velocity is lower in the center than the border, the size dedicated to each piece of data is larger in the outermost places, which may increase the quality of songs placed there. I don't really know if the machine making the disc is precise enough and if the human ear is capable of hearing the difference.
- deleted 8y ago
  [deleted]
- simias 8y ago
  >The design is nearly identical to what one would get if one simply literally (almost) digitized a vinyl record. I don't really agree with that, or at least it only makes sense to me if you're willing to go at a level of abstraction so high that makes it relatively meaningless. For one thing CDs store digital data, zeroes and ones, not analog like a vinyl. On top of that the data is written using 8-to-14 modulation (every 8 bits of data is written using a unique 14 bit pattern on disc). This provides very basic error correction and ensures that you never have very long stretches of zeroes. Then on top of that you have a cross-interleaved Reed–Solomon coding. You also have subchannel data that contains things like position in the track and other metadata. You also have a table of content at the beginning of the session to easily seek to individual tracks. Besides the fact that it's disc shaped and read in a spiral I don't find many similarities with vinyls. Sure the format itself is largely driven by the music track format (which is why you still address CD-ROMs with "minutes" and "seconds" even though it's meaningless there) but then so is Spotify.
  - cityroasted 8y ago
    What's interesting is that LaserDisc (the optical ancestors of DVDs that look like giant CDs) are analog. The video and audio streams are encoded with Pulse Width Modulation (PWM)
  - notriddle 8y ago
    > For one thing CDs store digital data, zeroes and ones, not analog like a vinyl. That's not a counterargument. That's literally what "digitized a vinyl record" means.
    - simias 8y ago
      Well that's what the rest of my comment was about, "digitizing a vinyl record" makes it sound like you take a vinyl, pass the analog audio through an ADC and output that directly onto an other disc and you get a CD. In practice it's a lot more complicated than that so I disagree with your original comment: >The design is nearly identical to what one would get if one simply literally (almost) digitized a vinyl record. The rotating disc format is simply due to technical constraints and not caused by vinyl mimicry (unless you also consider that hard disc drives and floppies are nearly identical to vinyls as well). The rest is completely different from a vinyl on almost every level, besides the fact that they both store stereo audio.
simias 8y ago
It's pretty interesting to read the red book and try to figure out why things are done the way they are, it really gives some perspective on the progress we've made in a few decades. An other example of somewhat "obsolete" technology in CDs is that all the track numbers and positions (minute:second:sector) are stored as binary coded decimal which is a bit annoying when you try to manipulate CD data on a modern system. It probably made a lot of sense at the time though, it meant that you could "stream" the BCD data directly to the display without any conversion while binary data would have needed a binary-to-decimal conversion which, I assume, would have been quite costly at the time.
tclancy 8y ago
Wait a minute, you mean the guy in the mall audio store in 1982 or so who claimed you could break the disc and still play it might have been lying to a kid?!

pwg 8y ago

> In many respects, an audio CD is more like a vinyl record than a data storage format. The design is nearly identical to what one would get if one simply literally (almost) digitized a vinyl record. A single long spiral of data on a disk. The most significant shift is that vinyl records read from outside in, while audio CD's read from inside out. Even the method of manufacture is essentially a clone (audio CD's are "pressed" just like vinyl records are "pressed", just in different pressing machinery). > built with technology from the late 1970s. It had to handle data rates that were incomprehensibly massive for the time, so only the most insanely basic error handling was feasible. Yes, the limits of late 1970's technology had a huge impact on the overall design, but at the same time the design also took advantage of the fact that audio when being played back in real time is reasonably tolerant of a small level of error resulting from the read-off of the disk. Most listeners would never hear the random errors because they either are below the noise floor of the amplifier tech. at the time, or because the resulting analog wave was close enough to not be noticeably different.

sjwright 8y ago
> The most significant shift is that vinyl records read from outside in Equally significant (and equally interesting) is how they spin. Whereas vinyl has constant angular velocity—they spin at the same rate from beginning to end, resulting in lower information density as you get towards the inner grooves—audio CDs have constant linear velocity, meaning that the rotational speed gradually changes as the disc is played so that the information density is equal from beginning to end. For the era, this is very cool tech. (I'm also awestruck about how they managed to get the laser head alignment to work perfectly back then, it's practically magical.)
- simias 8y ago
  You're right for audio CDs but very fast CD-ROM readers use constant angular velocity (CAV), mainly because they start hitting mechanical constraints (including the integrity of the CD itself).
  - nobleach 8y ago
    Can't remember but, wasn't 52x spin the max (I heard urban legends about the disc spinning apart back in the late 90's)
    - DiabloD3 8y ago
      Depending on how you define 52x, CAV, and the mechanical limits of a CD. Some drives max at an advertised 48x, because early CDs still exploded at 52.
- theandrewbailey 8y ago
  Techmoan did a video about a record that is recorded "backwards" to take advantage of the increasing fidelity in the outer grooves. https://www.youtube.com/watch?v=5Afikv6k1-c https://www.youtube.com/watch?v=5Afikv6k1-c
  - arthurfm 8y ago
    Techmoan's recent video on extended play (2.5 hour) CDs is also quite interesting. https://youtu.be/5fG1crhGqI0 https://youtu.be/5fG1crhGqI0
- joss82 8y ago
  > resulting in lower information density as you get towards the inner grooves It's actually the opposite: highest information density (musical notes played per surface unit) is in the innermost grooves. Since linear velocity is lower in the center than the border, the size dedicated to each piece of data is larger in the outermost places, which may increase the quality of songs placed there. I don't really know if the machine making the disc is precise enough and if the human ear is capable of hearing the difference.
deleted 8y ago
[deleted]
simias 8y ago
>The design is nearly identical to what one would get if one simply literally (almost) digitized a vinyl record. I don't really agree with that, or at least it only makes sense to me if you're willing to go at a level of abstraction so high that makes it relatively meaningless. For one thing CDs store digital data, zeroes and ones, not analog like a vinyl. On top of that the data is written using 8-to-14 modulation (every 8 bits of data is written using a unique 14 bit pattern on disc). This provides very basic error correction and ensures that you never have very long stretches of zeroes. Then on top of that you have a cross-interleaved Reed–Solomon coding. You also have subchannel data that contains things like position in the track and other metadata. You also have a table of content at the beginning of the session to easily seek to individual tracks. Besides the fact that it's disc shaped and read in a spiral I don't find many similarities with vinyls. Sure the format itself is largely driven by the music track format (which is why you still address CD-ROMs with "minutes" and "seconds" even though it's meaningless there) but then so is Spotify.
- cityroasted 8y ago
  What's interesting is that LaserDisc (the optical ancestors of DVDs that look like giant CDs) are analog. The video and audio streams are encoded with Pulse Width Modulation (PWM)
- notriddle 8y ago
  > For one thing CDs store digital data, zeroes and ones, not analog like a vinyl. That's not a counterargument. That's literally what "digitized a vinyl record" means.
  - simias 8y ago
    Well that's what the rest of my comment was about, "digitizing a vinyl record" makes it sound like you take a vinyl, pass the analog audio through an ADC and output that directly onto an other disc and you get a CD. In practice it's a lot more complicated than that so I disagree with your original comment: >The design is nearly identical to what one would get if one simply literally (almost) digitized a vinyl record. The rotating disc format is simply due to technical constraints and not caused by vinyl mimicry (unless you also consider that hard disc drives and floppies are nearly identical to vinyls as well). The rest is completely different from a vinyl on almost every level, besides the fact that they both store stereo audio.

simias 8y ago

It's pretty interesting to read the red book and try to figure out why things are done the way they are, it really gives some perspective on the progress we've made in a few decades. An other example of somewhat "obsolete" technology in CDs is that all the track numbers and positions (minute:second:sector) are stored as binary coded decimal which is a bit annoying when you try to manipulate CD data on a modern system. It probably made a lot of sense at the time though, it meant that you could "stream" the BCD data directly to the display without any conversion while binary data would have needed a binary-to-decimal conversion which, I assume, would have been quite costly at the time.

tclancy 8y ago

Wait a minute, you mean the guy in the mall audio store in 1982 or so who claimed you could break the disc and still play it might have been lying to a kid?!