Records are very easy to understand. Even without a microscope, you can see periodic patterns on test vinyls with beeps. And sound being periodic motion is also obvious from string and percussive instruments.
You can even see tracks starting and ending on pressed CDs under the right lighting with your own eyes. I wonder, is the encoding of silence (approx. 2 seconds) really that different or does the density of grooves or pit/land pattern intentionally differ to help the player seek there faster? I know that uncompressed audio naturally results in a repeated pattern when silence is encoded but given the 8-to-14 modulation and other error correctiion techniques, I find it hard to believe it would result in significantly different density unless they specifically added a special mode just for encoding silence that makes the track brighter-colored for easier coarse seeking.
Theres a graphic somewhere I’ll try to find that shows a bird call as a sound wave then a picture of record topography of the same call that makes it fairly obvious.
Gramophones are also fairly illustrative given that the needle directly acts on a diaphragm that is directly connected to a bell shaped horn.
Long runs of no changes is generally undesirable because it makes it harder to know where the reader is. So you’d want some type of coding to make sure you see changes occasionally regardless of where you are. For CDs, it seems like each byte is converted into 14 bits, where the longest run of zeroes is 10.
I know, among other things there is a time code inserted very frequently between audio data, without which seeking would not be possible at all. However, the audio uses over 90 % of the data so it’s largely responsible for the overall appearance of the track.
Records are very easy to understand. Even without a microscope, you can see periodic patterns on test vinyls with beeps. And sound being periodic motion is also obvious from string and percussive instruments.
You can even see tracks starting and ending on pressed CDs under the right lighting with your own eyes. I wonder, is the encoding of silence (approx. 2 seconds) really that different or does the density of grooves or pit/land pattern intentionally differ to help the player seek there faster? I know that uncompressed audio naturally results in a repeated pattern when silence is encoded but given the 8-to-14 modulation and other error correctiion techniques, I find it hard to believe it would result in significantly different density unless they specifically added a special mode just for encoding silence that makes the track brighter-colored for easier coarse seeking.
Theres a graphic somewhere I’ll try to find that shows a bird call as a sound wave then a picture of record topography of the same call that makes it fairly obvious.
Gramophones are also fairly illustrative given that the needle directly acts on a diaphragm that is directly connected to a bell shaped horn.
Would love to see that
Long runs of no changes is generally undesirable because it makes it harder to know where the reader is. So you’d want some type of coding to make sure you see changes occasionally regardless of where you are. For CDs, it seems like each byte is converted into 14 bits, where the longest run of zeroes is 10.
I know, among other things there is a time code inserted very frequently between audio data, without which seeking would not be possible at all. However, the audio uses over 90 % of the data so it’s largely responsible for the overall appearance of the track.
It doesn’t seem like there’s a pseudorandom coding applied, so repeated patterns should show up visibly. I’ve never really examined it myself though.
Welp, I remembered this post and it’s most likely valid CD-audio, just with awful noise.
Cool! Good to know this software is out there.