17 comments

  • ssl-3 15 days ago
    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 of these 99 tracks can be further subdivided with 99 index markers.

    This gives a CD the theoretical ability to have 9,801 selectable audio segments.

    Although realistically, I've only owned a couple of CD players that even displayed index numbers and exactly one CD player (a Carver TL-3300) that allowed a person to seek to a given index number within a track.

    (And I've only known one CD to actually make use of indexes in any useful manner, which was a sound effects CD from the early 1980s that had a lot more than 99 sounds on it -- all organized by tracks, and sub-organized by index marks. I just can't think of the name right now.)

    • kevin_thibedeau 15 days ago
      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 track on sequential play or, even worse, missing it altogether.

      I have a classical CD from the 80's with index marks for different movements within within the individual compositions represented by a handful of tracks. My understanding is that DG was the only publisher routinely using them. That required some manual intervention to convert the indices to separate tracks. Sony was pretty good about providing index nav. on their full size stereo players. At least until their perpetually cruddy remotes eventually failed.

      • op00to 15 days ago
        > 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.

        • kevin_thibedeau 15 days ago
          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.
          • alliao 14 days ago
            Japanese called it Sony Timer...some call it urban legend but this seems like yet another independently verified data point
      • ssl-3 15 days ago
        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 and weirdness. (FLAC/cue can do some of this, but hardware player support is nearly nonexistant.)

        I've been told that this is a stupid thing to want, and I want it anyway.

        I'm old enough to remember listening to albums the whole way through by default since anything else would take extra steps, and perhaps fortunate-enough to have generally preferred listening to albums where that is a thing that is also worth doing intentionally.

        (And yet, I am young enough to still be bitter about Lars killing Napster. My dissatisfaction is multifaceted.)

        • kevin_thibedeau 15 days ago
          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.
          • ssl-3 14 days ago
            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 this way, which is perhaps less expected.

            (And sure, I can rip an album as an album and convert that to a singular MP3 that I can play as an album almost anywhere, and it needs to be a single file since MP3s can't be perfectly concatenated. But then, I can't easily skip around on that singular album when it behooves me to do so.

            I could do both things when it was still in CD format.)

            • caf 14 days ago
              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...)
              • ssl-3 14 days ago
                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.

        • qingcharles 14 days ago
          I'd love a new solution that wasn't "break the CD data into pieces."

          I've never looked inside a CUE file, but it's just text and I don't think it supports meta data, right?

          We need like a new CUE file to go with the FLAC, right?

          p.s. https://news.ycombinator.com/item?id=40923646

          • ssl-3 14 days ago
            Ideally, I think I'd want a singular container (of whatever sort) that has the album's audio, the music-related timing metadata (as applicable), and whatever other metadata may be appropriate (lyrics? liner note graphics? music videos? sure!).

            The audio should be able to be FLAC. But it should also be able to be anything else, like Vorbis or MP3 or AAC or IDK. It needs to be able to be played continuously without aberration (which can't actually be done with a group of MP3 streams).

            The audio needs to be able to be seekable, like a CD is also seekable. By track. By index. (With pregaps, where appropriate -- because CDs also have pregaps.)

            Other potential metadata must be able to include whatever subcodes are involved in things like CD+G[0] and HDCD and CD Text, since all of those are supersets of the regular datastream and playback is compatible with any CD player.

            And it needs to be a singular container file because...well, that's just easier to keep track of as the years go by and data migrates.

            Only then, will we have the beginning of a valid archive format for audio CDs as they actually still exist on [some] store shelves today.

            (Some stuff can be optional, just as lots of things are optional inside of an MKV container for a film.)

            [0]: Almost nobody ever used this outside of the 1990s karaoke world, but Information Society's self-titled album includes an illustrated sequence, with lyrics, that is completely implemented in CD+G and that runs for the entire length of the album. And I should be able to render that locally here in 2024 from a container on my pocket supercomputer instead of watching a bad rip from a Sega Genesis: https://www.youtube.com/watch?v=b89sSa8QlLg

          • kevin_thibedeau 14 days ago
            Cue is a bodge that should never have become a defacto standard. Joerg Schilling's cdrdao tool has its own TOC format that faithfully captures everything including index marks, various flags, and multilingual CD text but it was ignored by everything else in the heyday of the ripping era. Nowadays we'd be better off with a standard yaml/json format that duplicates what cdrdao provides.
    • cainxinth 15 days ago
      > 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)#T...

      • egypturnash 15 days ago
        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
    • pseudosavant 14 days ago
      I mastered a CD in 2000 for a band that wanted a secret track at the end. I came up with a novel way to do it.

      There were a dozen regular tracks. A bunch of empty ones. And the final track over about a dozen tracks of varying length with no gap. Used all 99 tracks.

      I could only pull it off with this CD burning software that didn’t have a UI. It took a text file as input at the command line. But it could do everything from almost every color of spec (Red Book, Blue Book, etc) for CDs.

      • chaboud 14 days ago
        The Nine Inch Nails “Broken” EP had a couple of tracks at the end of 99, though the middle tracks were all 1-second blanks.
      • ssl-3 14 days ago
        I've had visions of putting a CD together that was that way, but with pregaps and indexes utilized as well.

        "WTF? The time counter keeps going forward, and then sometimes it goes backwards! And using the track seek buttons completely eliminates some parts that I can hear if I don't touch anything!

        It's a whole different song entirely when you program tracks 39, 40, and 52 in a loop, and IDFK what it is with this Index number that only always showed "1" before.

        Oh wait. Srsly? From tracks 71-93, it's using the index to count beats...and the track number to count measures? No, that can't be it. Except...."

  • afavour 15 days ago
    One memorable album using this was Queens of the Stone Age’s Songs for the Deaf. If you rewound from the start of the first track you got 90 seconds of strange sounding (but tuneful) rumbles and bleeps and bloops.

    When I looked it up online I found out it was called “The Real Song for the Deaf”. It was literally a song for deaf people, the idea was that if they turned it up enough they’d be able to hear the vibrations forming a song.

    For those interested to listen via a more accessible method: https://www.youtube.com/watch?v=XEU01LrnWng

  • LeoPanthera 14 days ago
    Semi-related: "Minidisc" is an album by Gescom (who are really Autechre in disguise) released, as the name suggests, only on Minidisc, containing 88 tracks which are designed to be played on shuffle, because Minidisc, unlike CD or any other physical format, can be shuffled with no audible gap between tracks.

    Each track is designed to segue into any other so the album is different every time you play it.

  • MOARDONGZPLZ 15 days ago
    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.
    • mikepavone 15 days ago
      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 sector).

      If a CD is properly following the Red Book standard, index 0 will point to a 2 second pre-gap of silentce and index 1 will point to the actual start of audio of the track (additional indices are allowed, but not common). The purpose of the pregap is to make life easier for less sophisticated players that aren't able to seek to a precise frame on the disc. They just have to be able to hit a 150 frame region. However, just because the standard says the pregap is supposed to be 2 seconds and silent doesn't mean it actually has to be. Players generally don't care and by the time the format was popular, even inexpensive players could seek precisely. This allows you to stick audio data before a track that will be skipped by the player when it's trying to seek to that track. If you stick it before track 01, it will be skipped even when just playing the disc through unless you rewind.

      • kevin_thibedeau 15 days ago
        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 faithfully reproduced.

        Some players permitted you to skip back from 1.1 to 1.0 to hear the lead-in as a hidden pseudo-track. Typically this was only possible with hardware index nav. buttons rather than the track nav. buttons, further obfuscating the presence of the hidden track.

        The other means of "hiding" tracks is to have a bunch of short silent tracks until you get to track 99 (inconvenient to reach on a player without numeric track entry) or to have a long section of silence starting on the last track from index 1.

        • crtasm 15 days ago
          >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.

    • monocasa 15 days ago
      Basically cd audio tracks have a base sector and a start specified. That allows sectors representing audio before timestamp 0:00 to be represented the track. The reason for this originally was probably to allow the drive to get synchronized before the track started. Enterprising cd masterers put actual hidden audio data in that area which would allow you on some CD players to rewind past 0:00 and then play the hidden audio at the negative timestamp.
      • crazygringo 15 days ago
        How much hidden audio could be stored?

        Was it limited to something negligible like a couple of seconds?

        Or could you store a whole five-minute recording in there or something?

        • boomboomsubban 15 days ago
          There doesn't seem to be a limit, this https://en.wikipedia.org/wiki/List_of_albums_with_tracks_hid... mentions a 27 minute live recording.
          • jvan 15 days ago
            Incredible! Songs in the Key of X was the only album I ever knew to do this, and it wasn't even the first. I had no idea so many others did the same thing.

            Edit: Son of a *, I've had a copy of Sister Machine Gun's Burn for almost 30 years and never knew there was a hidden track!

            • ChrisArchitect 15 days ago
              Classic X-Files album is the one I think of too. And how they hinted to everyone that there even was a hidden track on the sleeve: "'0' is also a number". (and the technical fineprint about the disc possibly not being Redbook compliant)
    • dylan604 15 days ago
      Oh good, so I'm not the only one that thought the article failed to actually state what the superpower was. Some lame ass patent was granted?
    • add-sub-mul-div 15 days ago
      As the article says its like an easter egg, putting a hidden song before the first track of a CD. If the song wasn't in the pregap it wouldn't be hidden. It's just for fun.

      (Sometimes songs can also be hidden in tracks at the end of the CD like 99, but that feels less mysterious.)

      • mattl 15 days ago
        Sometimes CDs would have a long piece of silence at the end of the last song and then another song on the same track.

        Other CDs really experimented with the shuffle feature. They Might Be Giants’ Apollo 18 had a bunch of very short tracks that would usually play between songs when shuffle was used.

        • gwbas1c 14 days ago
          I remember getting surprised by one of those. I was at a friend's house and forgot to turn off the CD at the end.

          It was funny at first, but when every other CD I bought had one, it became tacky.

        • add-sub-mul-div 15 days ago
          I had that CD and remember the short tracks but never thought of playing it on shuffle that way.

          I think it was nine inch nails' Broken EP that had the hidden tracks on 98/99 rather than after a long silence, but I could be wrong.

          • ssl-3 15 days ago
            Broken was first released as a 2-disc set. It was still in a many-fold Digipak case, but also included was a 3" mini-CD that had Suck and Physical (You're So).

            The regular-sized CD looked about identical to the 99-track version, but had only 6 tracks.

            (It was expensive to do this, and was never intended for long-term production. Later versions were generally as you describe.)

          • mattl 15 days ago
            I think it tells you in the liner notes that you should use the shuffle button.

            My copy in the UK at the time didn’t have the individual tracks. Just one track.

  • zdw 15 days ago
    I've been using https://github.com/whipper-team/whipper to digitize CD's, and it supports identifying Hidden Track One Audio (HTOA) when it exists and is not blank.

    Add in MusicBrainz Picard and Navidrome and you have a really nice solution.

  • dec0dedab0de 15 days ago
    I remember my friend accidentally found the negative track on a CD and called me up out of breath like aliens just landed. I think it was one of the early AFI albums.We spent the whole weekend checking for negative tracks on every CD we could find.

    The negatives between songs were also pretty cool sometimes, Mediocre Generica by Leftover Crack makes very good use of them. Listening to it over streaming or even mp3s ruins the effect, unless someone captured the entire album as one file.

    • Lammy 15 days ago
      > I think it was one of the early AFI albums

      I wouldn't call it an “early” album but I found one of these (untitled 18-second intro) on AFI - DECEMBERUNDERGROUND: https://i.imgur.com/XAsFMSR.png

      Some others I've run across in my CD collection include…

      — on Jonathan Katz - Caffeinated https://i.imgur.com/4ghQadv.jpeg

      — the track "Every Time Is The Last Time" on Bloc Party's Silent Alarm https://i.imgur.com/knhbZhA.png

      — a kid606 remix hidden in the first track pregap of The Locust's eponymous https://i.imgur.com/sXVFrQI.jpeg

      — the "Theme of Coon" (aka Riki) on the third disc of the SaGa Frontier soundtrack https://i.imgur.com/CqTTqpV.png

      > The negatives between songs were also pretty cool sometimes

      And one of these, the interlude at the end of “High Roller” on TCM's Vegas which is part of the pregap for “Comin' Back” https://i.imgur.com/G5PSCy3.jpeg

    • nammi 15 days ago
      AFI almost always had a "hidden" track after silence following the last track, I figured following the Misfits' tradition
      • xxr 15 days ago
        “Midnight Sun” at the end of Black Sails always gets me
  • Jedd 15 days ago
    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 mediums shared the less-well-hidden feature where a long silence separated the penultimate from the ultimate track.

    [0] https://en.wikipedia.org/wiki/Multisided_record

    • caf 14 days ago
      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.
    • alanfalcon 14 days ago
      This is supremely cool, thanks for sharing. I'm probably missing something obvious but why would the casting be any more expensive than any other pressing?
  • qingcharles 14 days ago
    I was responsible for some of the first digital content ingestion for the world's record labels back in the late 90s, which was all based around trucks filled with retail CDs being fed into CD-ROM drives and an army of young folks grinding hundreds of track names into a database. (what happens when a truck full of East Asian CDs turns up? what about all those albums by Aphex Twin and Sigur Ros with untypeable names? https://www.treblezine.com/wp-content/uploads/2014/08/aphex-... )

    I love these hidden tracks to death, especially the two hidden pregap tracks on Ash's first album, but they caused me unending pain and suffering.

    Not only are they an absolute nightmare to rip, often with more than one song per track (so the WAVs have to be edited), the names of the songs are often totally unknown, even to the record labels. What do you even number the things in the metadata?

    Added to that, you nearly always didn't even know they were there, so the negative numbered tracks would fail to get ripped and all the other ones in between or at the end would get ripped in weird ways and confuse all the data folk.

    https://www.discogs.com/release/984235-Ash-1977

    "Help, computer."

  • omar_alt 15 days ago
    I recall a CD of mine had hidden audio before track one circa 1997, a coffee table jungle breakbeat on a Symphonic Black Metal album:

    https://www.discogs.com/release/373044-Arcturus-La-Masquerad...

    Also on the topic of trying to push the compact disc to its limits a Grindcore group who had a bonus track where "All efforts were made to exceed typical limitations of 16 bit linear digital technology compression, limiting, and equalization curves have been created to deliver maximum gain structure"

    https://www.discogs.com/release/4305023-Exit-13-Ethos-Musick

    I had a period of bad luck in my youth where I believed all these new enhanced CD's and shaped CD's were damaging the tracking of the lens on my CD player so I gave Exit-13 a swerve and started to listen to safer music ;)

  • kstenerud 14 days ago
    One compact disc extension I remember well is CD+G. It was pretty wild plugging an Information Society CD into a CDTV and watching the (admittedly crappy) graphics while you listened to music and samples of Leonard Nimoy and DeForest Kelley...
  • indus 15 days ago
    In the age of attention deficit infused dopamine—-who has the time for an Easter egg?

    Instead, engineers and product managers, slow roll quirkiness on social media.

  • exabrial 15 days ago
    I remember discovering “hidden tracks” on the Beastie Boys intergalactic album with my cousins… we were like what on earth is happening as the CD player display glitched out and played this stuff we hadn’t heard.
  • snvzz 15 days ago
    Abusing the standard to put songs in gaps was such a bad idea.

    I have no idea how they got a patent for such a thing and, even worse, anyone ever did it on actual commercial discs.

    • ssl-3 15 days ago
      Why? Are easter eggs like this harmful to consumers or something?
      • snvzz 15 days ago
        It's abusing the standard, which can break compliant implementations.

        Especially bad since most Audio CD players are opaque hardware without update-able firmware.

        • ssl-3 15 days ago
          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?
          • lampiaio 15 days ago
            Yes, there's been a serious issue recently reported. Apparently, it has triggered bureaucrats on the internet who can't acknowledge something innocuous that's never caused any problem for decades.
          • zarmin 15 days ago
            of course not.
        • zarmin 15 days ago
          You're right. We should start a letter-writing campaign to President Bush. Maybe it will make the nightly news.

          Sent from my Discman

  • RiverCrochet 15 days ago
    If you are interested in this topic, locked grooves may also interest you.

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

  • d332 15 days ago
    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?
    • thristian 14 days ago
      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 the track metadata and error-correction for you - you generally can't just dump the "raw" data and do the interpretation yourself.

      That's why the most robust CD image format is the BIN/CUE format. The BIN file contains all the sectors the drive allows us to read, the CUE file contains the disc metadata as interpreted for us by the drive firmware.

      There are some drives which support extra "raw read" commands, but they're incredibly rare and consequently in great demand by CD preservation projects like redump.org.

      Some people have used the contents of BIN/CUE data to reconstruct what should actually be on the disk, but that's not quite the same thing. Here's a great explanation of the CD structure in all its complexity:

      https://github.com/higan-emu/emulation-articles/tree/master/...

    • ssl-3 15 days ago
      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.

      • d332 15 days ago
        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.
        • ssl-3 15 days ago
          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.

          • hunter2_ 15 days ago
            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

            • banish-m4 14 days ago
              Not necessarily. It depends if you're extracting data+subchannel data or corrected track data only.
            • ssl-3 15 days ago
              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.)

              • hunter2_ 14 days ago
                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?

                • ssl-3 14 days ago
                  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-variable rotational speed.)

                  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)

        • sho 15 days ago
          • qingcharles 14 days ago
            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.
            • ssl-3 14 days ago
              Sorta, kinda? It's a bit of a different game.

              Floppies (most of them, anyway) have fixed track widths, and these tracks are arranged cylindrically, and these cylinders align with the steps of the stepper motor that is used to actuate the head assembly.

              It's relatively easy, with the right ratio betwixt step advancement and track width, to get the head moving properly on a new implementation of a floppy controller. Want to read track 1? Step to the head N times to reach track 1 from wherever it started, and read it. Next, want to read track 33? Step the head N times to track 33, and read that.

              But tracking the spiral groove of a CD is a very different problem to solve. Steps tend to lose their meaning. Instead of electromagnetic steps, it involves 3 different laser beams: Two to continuously keep the head centered where it needs to be on the ever-changing groove using a servo feedback loop, and a third to read the data from the pits and lands from the middle of that groove.

              Is it do-able? Sure! People with far less advanced tech than we on HN might have laying around did it 40+ years ago.

              It's just a very different nut to crack than reading a floppy is, even if the mechanical and optical bits are recycled.

              (And that's just head positioning. The pits and lands still needs to be read, and those reflect back from the disc as optical phase shifts, not as changes in magnetic polarity and/or amplitude.)

            • banish-m4 14 days ago
              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.
  • fortran77 15 days ago
    What's the "A.C." band?
  • fnord77 14 days ago
    that whole article went into a lot of detail about the history of pregaps, but never says what was actually put on the pregap