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How CD pregaps gained their hidden track superpowers

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Re: How CD pregaps gained their hidden track superpowers

#71

Post by hunter2_ »

ssl-3 wrote: post #51
hunter2_ wrote: post #44

Earlier quoted context omitted.

The "unmolested data" would still have undergone error correction though, wouldn't it? I don't think a bin/cue rip would contain the redundant stuff, which GP seems interested in, nor the subcodes (of which some are represented in the cue file, while the bin file is PCM audio). And at the risk of taking us well beyond the rainbow books, I'll just leave this here: https://www.psxdev.net/forum/viewtopic.php?f=70&t=1266

There is a layer betwixt the optical reflection and the audio output that exists only as raw signals, before any molestation/error correction occurs. There cannot not be this layer. (And with a sufficiently-old-school CD player, it is probably not even challenging to get to it. The less-integrated the parts are, the better.)

Ah, I see. So what kind of capture hardware could read from that point? I assume it's a digital signal taking the form of 2-voltages, flipping on the order of 3.6 MHz (16 billion pits to read over 74*60 seconds). With Red Book audio at 1.4 Mbps, more than half of the raw data must be devoted to things like redundancy and other non-PCM stuff, if my interpretation that pits==bits isn't far off.

Aside: is your username inspired by Secure Socket Layer or Solid State Logic?

Re: How CD pregaps gained their hidden track superpowers

#72

Post by banish-m4 »

hunter2_ wrote: post #44
ssl-3 wrote: post #41

Earlier quoted context omitted.

You don't need a microscopic image of a disc to do that; a two-dimensional photograph is of essentially no advantage here. All you need is the unmolested data from that disc. The data is arranged on a singular spiral groove starting from the center and slowly winding its way towards the outside. The data is completely linear: It begins at the beginning, and continues to the very end without interruption. This is all…

The "unmolested data" would still have undergone error correction though, wouldn't it? I don't think a bin/cue rip would contain the redundant stuff, which GP seems interested in, nor the subcodes (of which some are represented in the cue file, while the bin file is PCM audio). And at the risk of taking us well beyond the rainbow books, I'll just leave this here: https://www.psxdev.net/forum/viewtopic.php?f=70&t=1266

Not necessarily. It depends if you're extracting data+subchannel data or corrected track data only.

Re: How CD pregaps gained their hidden track superpowers

#73

Post by banish-m4 »

qingcharles wrote: post #67
sho wrote: post #49

Earlier quoted context omitted.

this seems responsive: https://superuser.com/questions/140874/is-it-technically-pos...

I wonder if you could just tear the controller out of a CD/DVD drive and build a new one from scratch, kind of like the new floppy controllers being used now to read the raw magnetic data. You could just command the head to move to the center, find the beginning of the data and just keep reading until you hit the buffers.

Why? You can extract raw data and raw subchannel data directly from a CD/DVD drive. This isn't the case with how floppy drives work.

Re: How CD pregaps gained their hidden track superpowers

#74

Post by caf »

ssl-3 wrote: post #61
kevin_thibedeau wrote: post #42

Earlier quoted context omitted.

In addition to lossy compressed track files I also generate a FLAC with embedded cue as a master copy of the original. It's useful for recreating the whole recording for mass editing. I have a few discs mastered with preemphasis that needed correction. I too hope there will be a day when all FLAC players support track navigation. The reality is the music album has had its day in the sun and will largely be a forgotte…

You're not wrong. New music isn't frequently recorded with the intent for it to be heard in an album-oriented way. But the albums I like to listen to as albums will remain cohesive albums for an eternity. Lots of stuff from Roger Waters is cohesive in that way, which is perhaps something a person might expect me to say. But also lots of stuff from Maynard James Keenan, Trent Reznor, and even Marilyn Manson is also th…

Billy Eilish's latest is intended to be listened as a complete album (but of course the fact that this is known as an exception proves the general rule...)

Re: How CD pregaps gained their hidden track superpowers

#75

Post by caf »

Jedd wrote: post #25

This specification anomaly sounds like the polycarbonate equivalent of vinyl's multiple-groove capability. [0] I'd first heard of this for a Monty Python record (wikipedia notes this is in fact the most famous use case) but checked to see if people went for >2 grooves, and seemingly they did. I expect the casting for the pressing was horrendously expensive, which is why it didn't happen an awful lot. I suppose both m…

When I was very young, my parents had a game called 'wacky races' that was based on a multi-groove vinyl. It was a horse-racing game - I can't recall exactly how the gameplay worked, but the vinyl contained racing calls where the races would start the same way but the outcome would be somewhat random depending on which groove the needle ended up following.

Re: How CD pregaps gained their hidden track superpowers

#76

Post by ssl-3 »

caf wrote: post #74
ssl-3 wrote: post #61

Earlier quoted context omitted.

You're not wrong. New music isn't frequently recorded with the intent for it to be heard in an album-oriented way. But the albums I like to listen to as albums will remain cohesive albums for an eternity. Lots of stuff from Roger Waters is cohesive in that way, which is perhaps something a person might expect me to say. But also lots of stuff from Maynard James Keenan, Trent Reznor, and even Marilyn Manson is also th…

Billy Eilish's latest is intended to be listened as a complete album (but of course the fact that this is known as an exception proves the general rule...)

That.... that makes sense.

Her recordings are excellent. They generally sound simply fantastic. When turned up on the big stereo, they tickle every auditory input I have -- including the usually-strictly-tactile ones.

I've heard that her brother, who is probably (and perhaps obviously) her biggest fan, generally has a huge part in producing and mixing her music. It is apparent that they work well together.

Anyhow, thanks. That album is on the list for the next time the neighbors have left for the weekend.

Re: How CD pregaps gained their hidden track superpowers

#77

Post by TonyTrapp »

caf wrote: post #75
Jedd wrote: post #25

This specification anomaly sounds like the polycarbonate equivalent of vinyl's multiple-groove capability. [0] I'd first heard of this for a Monty Python record (wikipedia notes this is in fact the most famous use case) but checked to see if people went for >2 grooves, and seemingly they did. I expect the casting for the pressing was horrendously expensive, which is why it didn't happen an awful lot. I suppose both m…

When I was very young, my parents had a game called 'wacky races' that was based on a multi-groove vinyl. It was a horse-racing game - I can't recall exactly how the gameplay worked, but the vinyl contained racing calls where the races would start the same way but the outcome would be somewhat random depending on which groove the needle ended up following.

Techmoan has a video on a similar horse racing game (maybe it's even the same just with a different name) and how it works: https://www.youtube.com/watch?v=I5l75romOXY

Re: How CD pregaps gained their hidden track superpowers

#78

Post by ssl-3 »

hunter2_ wrote: post #71
ssl-3 wrote: post #51

Earlier quoted context omitted.

There is a layer betwixt the optical reflection and the audio output that exists only as raw signals, before any molestation/error correction occurs. There cannot not be this layer. (And with a sufficiently-old-school CD player, it is probably not even challenging to get to it. The less-integrated the parts are, the better.)

Ah, I see. So what kind of capture hardware could read from that point? I assume it's a digital signal taking the form of 2-voltages, flipping on the order of 3.6 MHz (16 billion pits to read over 74*60 seconds). With Red Book audio at 1.4 Mbps, more than half of the raw data must be devoted to things like redundancy and other non-PCM stuff, if my interpretation that pits==bits isn't far off. Aside: is your username…

I'm getting off into the weeds of what I know here, so take this all with a grain of salt. (I probably used to know more about all of this than I do right now.)

The difference between a pit and a land is an optical phase change. The pits and lands vary in length, and there are 9 valid variations in their lengths. This combined phase/temporal situation eventually (thanks, science folks from 1970-something!) turns into a serial binary electrical signal inside of a CD player.

This binary electrical signal can be recorded.

Recorded with what, you asked?

CDs have a lot more going on than just audio data: Remember, there's forward error correction at play and (by spec, IIRC) a player is supposed to be able to completely recover data even if there is a gap of 1mm due to a scratch or other interruption. (There's also room for tricks like CD+G to live in the background, and certainly what may seem like an inordinate amount of data used just for clocking: CDs are CLV, so playing them happens at a continuously-varying rotational speed in a tightly closed loop because buffer RAM was expensive to buy, and expensive to manage, and tight speed control was cheaper to implement. Remember, this was a finished digital product that was released in 1981.)

I find old references[0] that suggest that the raw data rate of a CD (it does not matter what kind) is 4.3218 Mbps.

So, to posit some example hardware: With careful loops and decent wiring, accurately capturing this seems like it would be well within the purvey of an RP2040's PIO's DMA modes to get that data into RAM, and also well within one of its 133MHz 32-bit ARM core's ability to package up and deliver that data over USB 2 to a host machine that can store it for later analysis -- plus or minus a transistor or two, or maybe a pullup resistor in just the right spot.

(But that's just my opinion as a home hacker who has dabbled in RP2040 PIO assembler, and who is at or a bit beyond their knowledge of compact discs. I may wake up tomorrow and decide that the above is all bullshit and wish I could erase all of it. If in doubt, Phillips datasheets for CD player chipsets from the first half of the 1980s can probably help a lot more than I can.)

---

As to the username: It's old. It predates Secure Socket Layer, but it's way newer than Solid State Logic. I was just a young kid with a new modem when I dialed into a Telegard BBS and started to sign up for an account, and got stuck at the prompt to enter a "Handle". I didn't know what a handle was in this new-to-me context.

The sysop saw that I was stuck and dragged me into chat, as good sysops (hi Shawn!) tended to do upon seeing such a thing. We chatted for a bit, and I wasn't feeling creative, so he suggested that maybe I could look around for inspiration since most people used a made-up handle on his particular BBS.

I found a 5.25" floppy disk on the desk that I'd borrowed from the local public library. It was labeled "Selective Shareware Library, Volume 3." (It was also almost certainly infected with the Stoned virus[1]).

Anyhow, that was sufficiently inspiring, so ssl-3 it was.

---

0: https://www.geocities.ws/columbiaisa/cd_specs.htm

1: https://en.wikipedia.org/wiki/Stoned_(computer_virus)

Re: How CD pregaps gained their hidden track superpowers

#79

Post by tecleandor »

eyelidlessness wrote: post #66
egypturnash wrote: post #46

Earlier quoted context omitted.

Broken was absolutely perfect to put into a multi-disc player along with TMBG's Apollo 18 , which contains "Fingertips", a suite of 21 very short songs. Set it to shuffle songs from everything in the player, and enjoy your sonic whiplash

If you want sonic whiplash without so much effort, you can also listen to a Fantomas album in its original order.

This could be fun :)

https://en.wikipedia.org/wiki/Short_Music_for_Short_People

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