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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

#101

Post by albrewer »

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…

I had a set of cds that went with an intro to music theory textbook around ~2009. It did also made heavy use of indices in tracks to do exactly the same thing. My car stereo listed each index as a track.

I wish I could remember the name of the textbook because I really liked a lot of the baroque music on the CDs and can't remember who they were by or the titles of the songs...

Re: How CD pregaps gained their hidden track superpowers

#102

Post by AkBKukU »

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…

I'm curious if you have a specific example of an album with the crowd noise between tracks like that? I collect and rip hundreds of CDs and am always on the look out for edge case discs to further hone my tools.

On your pregap + 99 indexes remark, the "pregap" is the space between index 00 and 01 which continues on up to index 99. Players seek to index 01 as the start point of the track. There is no separate pregap designation. I've paid special attention to this because it is a difficult problem to solve as many discs have space between tracks stored in index 00-01 but rarely is there anything audible in there after the first track. The only example I have of this is a specialty music sample disc, Rarefaction's A Poke In The Ear With A Sharp Stick, that has over 500 samples on the disc accessed by track + index positions.

As a sidebar based on the later comments in the thread, I've made it a habit to rip and store every audio CD as BIN/CUE+TOC using cdrdao. This allows me to go back and re-process discs I may have missed something on. But that is imprecise even because it usually breaks bluebook discs with multiple sessions to store data due to absolute LBA addressing. Also the ways different CD/DVD drives handle reading data between index 00-01 on track 1 is maddening. Some will read it, some will error, and the worst is those that output fake blank data.

Re: How CD pregaps gained their hidden track superpowers

#103

Post by WarOnPrivacy »

barrkel wrote: post #81
MOARDONGZPLZ wrote: post #2

I read this whole thing twice and I now know what pregaps are and the history but still have no idea why people would put them on a CD or why they’re useful for hidden tracks.

The writing is not good; I gave up part way through. It's weirdly elliptic and almost autistic in its focus on details and an almost complete absence of a big picture. It could do with some kind of proper context-setting introduction, at the very least.

This mirrors my experience. It's good content but I'd barely land on one splainer before being segueded into the next one. I kept thinking I missed the part they delved into hidden tracks.

Re: How CD pregaps gained their hidden track superpowers

#104

Post by mikepurvis »

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…

This is an issue for movie discs too. Some mkv rips will preserve chapter data (though player support is spotty), but in the end it's still a big linear file— menus, intros, trailers, optional features, etc are all gone once it's ripped unless you rip that stuff to separate video files.

Which I get on the one hand, but it's a bummer that in all these cases (CD, DVD, Blu-Ray) the metadata for the larger structure of the production got inextricably tied to the specific physical media implementing it, such that the only real way to preserve that data was to rip a full disc copy.

Re: How CD pregaps gained their hidden track superpowers

#106

Post by AkBKukU »

thristian wrote: post #58
d332 wrote: post #23

This inspired me to read up on the low-level details of CD structure. I'm curious if anybody scanned an entire CD and shared the results, so that we could work with a raw image of disc that contains all its quirks, as opposed to the typical .iso format?

It's really difficult. Unlike floppy disks, where you tell the drive to seek and get back raw magnetic pulses (so you can produce raw flux images), or hard disks where you tell the drive to read an arbitrary sector and get a blob of data (so you can produce sector-level images), the protocol for talking to a CD ROM involves asking for track/sector addresses, which means you have to trust the drive to interpret all th…

Even BIN/CUE is not enough. It cannot store subchannel data like CD+G and is only able to hold a single session which breaks bluebook CDs with audio and data.

We do not currently have a widely supported CD standard for storing data from a CD that can properly hold all data. Aaru [0] is close, but still has to output back to other formats like BIN/CUE to use the contents of the disc.

[0] https://www.aaru.app/#/

Re: How CD pregaps gained their hidden track superpowers

#107

Post by meindnoch »

AkBKukU wrote: post #102
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…

I'm curious if you have a specific example of an album with the crowd noise between tracks like that? I collect and rip hundreds of CDs and am always on the look out for edge case discs to further hone my tools. On your pregap + 99 indexes remark, the "pregap" is the space between index 00 and 01 which continues on up to index 99. Players seek to index 01 as the start point of the track. There is no separate pregap d…

>I'm curious if you have a specific example of an album with the crowd noise between tracks like that? I collect and rip hundreds of CDs and am always on the look out for edge case discs to further hone my tools.

E.g. the Japanese version of Flying Lotus' album "Until The Quiet Comes" has a pregap of 5 seconds before the 19th track, to separate it from the rest of the album, as it's a Japanese-exclusive bonus track.

Re: How CD pregaps gained their hidden track superpowers

#108

Post by AkBKukU »

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…

Look into the Domesday Duplicator project for Laserdiscs as an example of how what ssl-3 is talking about can be done using a high sample rate input. That exact process is possible and with enough storage and processing power can be used to get the most "low level" access to the data. It is not for the faint of heart though, and can take around 1TB of storage and hours of CPU time to process full movies in this way, I know because I've done it.

I believe I've seen there is work being done to attempt this on CDs but it would have still been in the exploratory phases and not yet ready to start archiving with. It might seem like overkill to do this to something meant to be digitally addressed but I've experienced enough quirks with discs and drives when ripping that I would 100% be willing to switch over to a known complete capture system to not have to worry about it anymore. Post process decoding also allows for re-decoding data later if better methods are found.

Re: How CD pregaps gained their hidden track superpowers

#109

Post by benjaminpv »

albrewer wrote: post #101
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…

I had a set of cds that went with an intro to music theory textbook around ~2009. It did also made heavy use of indices in tracks to do exactly the same thing. My car stereo listed each index as a track. I wish I could remember the name of the textbook because I really liked a lot of the baroque music on the CDs and can't remember who they were by or the titles of the songs...

Do you remember if the textbook was orange (possibly with a two-tone cover design)? I had a really good textbook in college that had a... 4? CD set (with the big jewel case) that had a bunch of tracks and like you I really enjoyed it.

Re: How CD pregaps gained their hidden track superpowers

#110

Post by egypturnash »

ssl-3 wrote: post #84
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

Was this better with the crazily fast-loading chonka-chonk slam-slam nature of a Pioneer 6-disc cartridge changer, or with something slower and perhaps more-civilized like a period-correct Technics 5-disc changer, with its nearly-silent and relatively exquisite, seemingly-careful demeanor? (Both have their merits, but I unfortunately have neither at hand. And I only have one of these 2 albums. And one of those albums…

Presumably Spotify has glommed all the Fingertips into one file. On the original CD release it was twenty-one separate tracks; there was a bit in the liner notes that explicitly encouraged you to put it on shuffle. https://tmbw.net/wiki/Fingertips

I could not tell you what brand the all-in-one turntable/radio/tape deck/cd player I had at the time was. There was a big tray with room for five CDs and I have absolutely no memory of how much noise it made when switching from one disc to another, and every physical object involved in this affair is long gone in a hurricane.

I suspect both CDs should be easy to find used copies of, if you have the appropriate hardware and want to experience the tension of not knowing if the next song you hear is going to be Trent bitching, a brief moment of silence, a Fingertip, or whatever else you put in the player. Given my tastes at the time this would have probably been Skinny Puppy, Ozric Tentacles, and Björk, but do whatever feels like the most interesting possible choice; I have a disc lying around now that’s nothing but forty iterations of Satie’s Vexations and that would have certainly been a prime choice for this little game.

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