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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

#41

Post by ssl-3 »

d332 wrote: post #36
ssl-3 wrote: post #27

Earlier quoted context omitted.

Audio CDs were never ripped/transferred as ISO files. ISO-9660 is a filesystem that came years later, and Redbook audio CDs simply do not contain files. If you want to look at the structure of a whole audio CD, then one way is to rip it with a decent tool (perhaps cdrdao or EAC) and generate a bin/cue file pair as an output.

But that's not my goal. I'd like to be able to observe every grove, the physical encoding of data, and see if I could implement decoding from scratch. First problem is though that I don't know how to get a microscopic image of the disc.

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 akin to (although opposite of) how a single-track vinyl record is physically laid out. The entire CD -- whatever it contains -- is just a continuous string of pits and lands.

And to observe that string as it appears on a real disc, all you need to get started is a regular old-school CD player and some appropriate data acquisition gear, and maybe an oscilloscope to help figure out what you're looking at.

The optics and basic motor controls are already solved problems, and it doesn't even have to be particularly fast data acquisition gear by today's standards to record what is happening.

Re: How CD pregaps gained their hidden track superpowers

#42

Post by kevin_thibedeau »

ssl-3 wrote: post #37
kevin_thibedeau wrote: post #35

Earlier quoted context omitted.

My personal CD ripping script is configured to leave all pregaps after track one at the end of the preceding track when splitting them out as individual files. It gets ripped in one DAO pass for guaranteed preservation of all samples when using gapless playback on live recordings. Track navigation then works just like a real CD without having to listen to an incongruous section of audio meant to link the previous tra…

That's probably the best way to do it, given common toolsets and players. I also rip pregaps as lead-outs (rather than the lead-ins that the structure may appear to suggest). It's things like this that make me wish that we'd landed on on a good, popular way to store albums (with metadata!) instead of individual tracks -- or to at least reassemble individual tracks' files properly into whole albums without glitches an…

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 forgotten curiosity like the typewriter or rotary phone.

Re: How CD pregaps gained their hidden track superpowers

#43

Post by op00to »

kevin_thibedeau wrote: post #35
ssl-3 wrote: post #29

One less-secretive way I've seen pregaps used is for live recordings. The crowd noise betwixt songs can be contained in a pregap, so that it is only ever heard when listening to the album straight-through (instead of in shuffle or track-program mode). --- Another fun feature of audio CDs is indexes. A disc can have 99 tracks, and each track can have some pregap (including track 1, as the article discusses). And each…

My personal CD ripping script is configured to leave all pregaps after track one at the end of the preceding track when splitting them out as individual files. It gets ripped in one DAO pass for guaranteed preservation of all samples when using gapless playback on live recordings. Track navigation then works just like a real CD without having to listen to an incongruous section of audio meant to link the previous tra…

> At least until their perpetually cruddy remotes eventually failed.

For me, Sony remotes were made of the same stuff as early Nokia phones - indestructible! Surprised to hear someone thought they were cruddy.

Re: How CD pregaps gained their hidden track superpowers

#44

Post by hunter2_ »

ssl-3 wrote: post #41
d332 wrote: post #36

Earlier quoted context omitted.

But that's not my goal. I'd like to be able to observe every grove, the physical encoding of data, and see if I could implement decoding from scratch. First problem is though that I don't know how to get a microscopic image of the disc.

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

Re: How CD pregaps gained their hidden track superpowers

#45

Post by kevin_thibedeau »

op00to wrote: post #43
kevin_thibedeau wrote: post #35

Earlier quoted context omitted.

My personal CD ripping script is configured to leave all pregaps after track one at the end of the preceding track when splitting them out as individual files. It gets ripped in one DAO pass for guaranteed preservation of all samples when using gapless playback on live recordings. Track navigation then works just like a real CD without having to listen to an incongruous section of audio meant to link the previous tra…

> At least until their perpetually cruddy remotes eventually failed. For me, Sony remotes were made of the same stuff as early Nokia phones - indestructible! Surprised to hear someone thought they were cruddy.

They were physically robust but the carbon button contacts always became dodgy for me. I tried to avoid Sony products for this reason because I encountered it so often in other people's gear. I have a remote from the late 00's that saw virtually zero use and it conked out with age alone.

Re: How CD pregaps gained their hidden track superpowers

#46

Post by egypturnash »

cainxinth wrote: post #31
ssl-3 wrote: post #29

One less-secretive way I've seen pregaps used is for live recordings. The crowd noise betwixt songs can be contained in a pregap, so that it is only ever heard when listening to the album straight-through (instead of in shuffle or track-program mode). --- Another fun feature of audio CDs is indexes. A disc can have 99 tracks, and each track can have some pregap (including track 1, as the article discusses). And each…

> Broken was re-released as one CD in October 1992, having the bonus songs heard on tracks 98 and 99 respectively, without any visual notice except for the credits, and tracks 7–97 each containing one second of silence. https://en.wikipedia.org/wiki/Broken_(Nine_Inch_Nails_EP)#Pa... Amarok (1990) by Mike Oldfield is a single hourlong track with 53 index marks. https://en.wikipedia.org/wiki/Amarok_(Mike_Oldfield_album…

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

Re: How CD pregaps gained their hidden track superpowers

#47

Post by zarmin »

ssl-3 wrote: post #33
snvzz wrote: post #32

Earlier quoted context omitted.

It's abusing the standard, which can break compliant implementations. Especially bad since most Audio CD players are opaque hardware without update-able firmware.

Has this been shown to be actually-problematic in the three decades since Willy Nelson's album contained a song in the pregap of track 1?

of course not.

Re: How CD pregaps gained their hidden track superpowers

#48

Post by zarmin »

snvzz wrote: post #32
ssl-3 wrote: post #28

Earlier quoted context omitted.

Why? Are easter eggs like this harmful to consumers or something?

It's abusing the standard, which can break compliant implementations. Especially bad since most Audio CD players are opaque hardware without update-able firmware.

You're right. We should start a letter-writing campaign to President Bush. Maybe it will make the nightly news.

Sent from my Discman

Re: How CD pregaps gained their hidden track superpowers

#49

Post by sho »

d332 wrote: post #36
ssl-3 wrote: post #27

Earlier quoted context omitted.

Audio CDs were never ripped/transferred as ISO files. ISO-9660 is a filesystem that came years later, and Redbook audio CDs simply do not contain files. If you want to look at the structure of a whole audio CD, then one way is to rip it with a decent tool (perhaps cdrdao or EAC) and generate a bin/cue file pair as an output.

But that's not my goal. I'd like to be able to observe every grove, the physical encoding of data, and see if I could implement decoding from scratch. First problem is though that I don't know how to get a microscopic image of the disc.

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

Re: How CD pregaps gained their hidden track superpowers

#50

Post by crtasm »

kevin_thibedeau wrote: post #40
mikepavone wrote: post #30

Earlier quoted context omitted.

An audio CD is mostly arranged like a single continuous recording. Tracks are added on top of this via the Q subcode channel that gives information about the current location and the ToC stored in the lead-in area (also using the Q subcode channel). In the ToC, each track will have one more indexes that points at a specific location on the disc by minute, second and "frame" (represents 1/75 of a second, basically a s…

The key for a hidden track at the beginning is that players usually start playing track 1 from index mark 1 (1.1) rather than index 0 as with continuous play through all subsequent tracks. The lead-in area for 1.0 is a holdover from grooved phonorecordings never meant to be played. It's a way for the primitive hardware of early CD players to acquire the start of the data stream in a safe area that doesn't have to be…

>Typically this was only possible with hardware index nav

Holding the previous track button would "rewind" playback and get you into the pregap on all the CD players I remember using, but these would have been late 80s models onwards.

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