[HN Gopher] Error correction and concealment in the Compact Disc...
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Error correction and concealment in the Compact Disc system (1982)
[pdf]
Author : mmastrac
Score : 60 points
Date : 2023-10-01 21:27 UTC (1 days ago)
(HTM) web link (www.pearl-hifi.com)
(TXT) w3m dump (www.pearl-hifi.com)
| dylan604 wrote:
| I don't remember which specific audio CD ripper software it was,
| but one of my most favoritist features ever was the "Try really
| hard" checkbox. This was used if you had a disc which was hard to
| read from either scratches or dirty or whatever. I never looked
| into exactly what it did, but I had assumed that a normal read
| just read, but try really hard would make use of the error
| correction which the math caused the slower reads.
|
| To this day, I've been known to write functions called
| tryReallyHard() even if I haven't made a UI option explicitly for
| it, yet.
| TacticalCoder wrote:
| CD rippers have progressed a lot. Now most audio CDs' hashes
| are stored in public databases and you can rip a CD in a 100%
| bit-perfect way and if a single bit is off, your checksum won't
| match the hash other people got in the database.
|
| And CD rippers do check the online DB automatically.
|
| Many people do archive their CD collection in a bit perfect way
| nowadays and you know when your rip is perfect (and it usually
| is).
| ben7799 wrote:
| Yes, and it's been this way for at least 10 years at this
| point.
|
| My first wave of ripping CDs in the early 2000s this stuff
| wasn't around yet.
|
| But I redid everything around 2013 and ripped them all as
| FLAC, and by that point EAC and the databases were very good.
| mrguyorama wrote:
| I don't think many computer CD drives have ever exposed the
| error correction to the computer. It's usually handled entirely
| internally, as the link shows on the last page. What that
| program was probably doing was trying a bunch of times to read
| the same area from a bunch of different starting points to see
| if it could tease out the data with a little luck.
|
| >math caused the slower reads.
|
| The error correction was ALWAYS being done, and that math was
| done on a dedicated circuit.
| OfSanguineFire wrote:
| cdparanoia[0], still the standard Linux command-line
| application for CD ripping, took its name from the fact that it
| goes heavy on error-correcting. However, among the filesharing
| community the Windows-only application Exact Audio Copy[1]
| always enjoyed a stronger reputation for accuracy, and several
| major private torrent trackers and DC++ hubs required EAC to
| have been used for rips, which sadly prevented Linux-only users
| from contributing to the scene.
|
| [0] https://en.wikipedia.org/wiki/Cdparanoia [1]
| https://en.wikipedia.org/wiki/Exact_Audio_Copy
| dylan604 wrote:
| those may be apps that use error correction, but these are
| not the apps I was thinking. i don't run Linux desktops. It
| was most likely a Mac program, but at that time I was still
| forced to use Windows for some work tasks. I'm thinking it
| was Nero Burning ROM.
| userbinator wrote:
| The picture on the last page makes a great illustration of how
| dense electronics integration has become over the years --- all
| of that, and more, are now possible in a single IC:
|
| https://www.nxp.com/docs/en/data-sheet/SAF784X.pdf
|
| There was an article here with a good graphical description of
| CDs a few years ago:
| https://news.ycombinator.com/item?id=21185897
|
| Unfortunately that site is gone, and the archive doesn't have a
| copy.
| snerbles wrote:
| Maybe this copy?
|
| https://web.archive.org/web/20200322151217/https://byuu.net/...
| dfox wrote:
| Well, it is certainly a prototype. In the early consumer CD
| players the whole CD decoding datapath was split into chip with
| the analog part (servo amplifier, which also produces an error
| signal that contains the read data) and digital chip with its
| associated DRAM that does the rest of the decoding. It is
| somehow surprising how empty the single layer PCB in these
| early CD players is. Obviously, this level of integration was
| required for the technology to be commercially viable. The CD
| somewhat coincides with the time of cost-effective VLSI ASICs,
| which made this possible.
|
| On the other hand, the modern CMOS logic runs so fast and can
| be so densely integrated, that the 15 years old SAF784x
| apparently implements the "complex analog RF" part of CD player
| by using DSP techniques. And the process it is made in is
| apparently mature enough that it can accommodate various analog
| functions including high-powered ones so you end up with a
| complete CD/MP3 player on one ASIC (if you can fit what you
| want to do into 64kB of ARM7TDMI code and can tolerate the
| sound quality and EMC implications of the integrated audio
| output DAC)
| ben7799 wrote:
| I still love CDs. I started buying them around 1990-1991. I
| started with MP3 in 1996 but kept buying CDs. I think I got an
| iPod in 2003, I digitized all my CDs by 2004-2005 and I did go
| through a period from about 2005-2013 where I bought almost all
| my music as digital files.
|
| I never got rid of my CDs though, and in recent years I started
| listening to them again just like Vinyl LPs. There's still
| something fun about listening to them, and they always sound
| great and work really well. I've never had a CD get damaged
| enough to hear any artifact. It is still a good way to support
| artists you like, and prices have inverted to the point CDs are
| affordable and Vinyl LPs are quite ridiculous a lot of the time.
| tverbeure wrote:
| It's really amazing how many fallback layers there are in a CD to
| work around errors.
|
| There's a first Reed-Solomon layer that can theoretically correct
| 2 errors per 28 byte frame, but they actually only fix 1 error
| and use the remaing error detection as an erasure code (instead
| of an error correction code) to make a second layer of Reed-
| Solomon correction much better due to interleaving.
|
| If that fails, they have the audio samples swizzled in a way so
| that you can do interpolation between neighboring samples, and if
| that fails, there was yet another mechanism (that I forgot the
| details about) for a final effort.
|
| I reminds me a bit of spacecraft, where there's so much
| redundancy and flexibility to make things still work in case of a
| catastrophic failure.
|
| The Galileo spacecraft comes to mind, where they reprogrammed the
| whole communication mechanism (adding compression etc) after the
| main antenna failed.
| (https://en.m.wikipedia.org/wiki/Galileo_project#High_gain_an...)
| OfSanguineFire wrote:
| I still feel awe at the compact disc. When I was a teenager in
| the mid - late 90s, scanning microscopic pits with a freaking
| laser beam, and storing hundreds of megabytes on a storage
| medium, still seemed like a big deal, real cutting edge stuff.
| And yet that format had been invented well over a decade before.
|
| I'm also surprised that if the CD was already invented by the
| early 1980s and widely sold commercially for music, it took until
| the early 1990s for applications in computing with CD-ROM. Was
| the bottleneck here CPUs, RAM, and graphics cards, which would
| not have been able to handle the amount of data that a CD-ROM
| could store?
| RetroTechie wrote:
| CD drives were expensive at first.
|
| That, and a mismatch between the huge capacity of a CD, and
| typical software back then.
|
| Remember, popular games like Doom fitted on a couple of 3.5"
| floppies. 3D graphics was just coming. PC's with the cpu to
| process many MB's of game data (or decode full screen video)
| were often business machines with limited graphics
| capabilities. Homecomputers like the Amiga or Atari ST were in
| similar price range as a CD drive. Harddisks were like 1 or 2
| GB.
|
| CD _writers_ were much more expensive. So out of most people 's
| reach as backup medium.
|
| Only when prices came down _and_ PC 's gained in cpu, storage &
| graphics (and software ballooned with that), it made sense to
| add a CD drive.
|
| I do kind of miss the days where you'd buy a magazine with
| cover CD, and spend weeks playing 100s of shareware games. Then
| buy the full box for the best-of those. Or try a Linux distro
| without needing to download 100s of MB's over a 33k modem.
|
| And it's a shame those mini-CD's (similar to GameCube discs)
| weren't more popular. I always liked those. Almost impossible
| to find these days (whether used for music, software, or as
| -R/RW media).
| HPsquared wrote:
| Ah, downloading hundreds of MB on dial-up... those were the
| days
| bluedino wrote:
| The first CD-ROM connected to a computer that I ever remember
| was Grolier's (Compton's?) encyclopedia we had in the school
| library. It was a DOS program that ran on an IBM 286,
| external caddy-loading CD-ROM, and then a laser printer. Was
| probably an expensive and amazing setup at the time.
|
| https://twitter.com/Foone/status/1308257334603337728
| mcpackieh wrote:
| > _That, and a mismatch between the huge capacity of a CD,
| and typical software back then. Remember, popular games like
| Doom fitted on a couple of 3.5 " floppies. 3D graphics was
| just coming._
|
| I think this is why encyclopedias were one of the first
| "killer applications" for CD-ROMs. Wikipedia didn't yet
| exist, paper encyclopedia sets cost several hundred dollars
| at least, and floppy disks weren't really big enough for it.
| Having a whole encyclopedia on one or two CDs was a game
| changer.
| justsomehnguy wrote:
| > was a game changer
|
| The game changer was _multimedia_ encyclopedia. You can
| have a lot of text on compressed 3.5 ", but having a
| digital sound _and video_ was the main selling point.
|
| An example of Encarta 94 video:
|
| https://youtu.be/mEySJkXezeg?t=500
| js2 wrote:
| Two other multimedia examples:
|
| _From Alice to Ocean_ :
| https://archive.org/details/CDAC-029000
|
| _Myst_ : https://en.wikipedia.org/wiki/Myst
| LocalH wrote:
| One of the earliest applications of "postage stamp size"
| video
| ben7799 wrote:
| I think some older than me may remember differently, but I'm
| slightly older than you and I'd actually say I think for people
| who could afford computers there weren't that many years
| between getting their first CD-ROM equipped computer and their
| first CD Audio player.
|
| It was within a year or two in my family, and my father was in
| the computer/internet industry by the mid-80s so had access to
| stuff pretty early. I think we got our first CD audio player in
| the family in 1990 and got a 486 with a CD-rom drive in late
| 1992.
|
| CD Audio was expensive at first too.
| thedougd wrote:
| My first CD-ROM drive used a printer parallel port. It worked
| well enough to run my first CD-ROM software purchase, Mad Dog
| McCree (1993). My PC was a microchannel PS/2 and it was
| difficult finding reasonably priced accessories.
| derefr wrote:
| CPU IO access speed and memory transfer delay, in a world
| before the advent of DMA.
|
| There's a reason that game consoles of the era had dedicated
| "Audio Processing Units" that rendered sound directly from
| sequencer instructions + a small set of loaded samples: trying
| to feed "one large continuous sample" (i.e. a raw PCM stream)
| through the CPU to a DAC, wouldn't have left any time for doing
| actual logic. If you compressed the audio, decompressing it
| would take the whole CPU too.
|
| Sure, CD-ROMs weren't usually _continuous_ streams of data in
| the way that audio CDs were; but the kinds of stuff that
| couldn't just be usefully fit into a floppy -- or a set of
| floppies installed onto a hard drive! -- was usually asset
| files that were individually large in the same way that PCM
| audio was individually large, in a way that would still choke
| either CPUs or RAM. No point in large image files you can't
| even display.
|
| There _were_ a few consumer use-cases for random access to
| individually large files -- mostly public databases, of the
| kind we'd expect to find online today. But people who really
| needed these, either _did_ use them "online" even back then (by
| dialing in directly to mainframe database services); or, if
| they were a more industrial consumer, they got these
| distributions on tape! These were the first things to be ported
| over to CD-ROM when CD-ROM drives did start becoming available.
|
| The whole "multimedia" hype took a bit longer, only really
| taking off once high-quality images and low-quality video were
| able to actually be displayed on PC (requiring PCs to first
| achieve display resolutions higher than 640x480; color depths
| higher than 256-color; at least 2MB of VRAM; and CPUs fast
| enough for MPEG1 decoding of at least small 100x100 video
| clips.)
| vel0city wrote:
| Speaking to the processing needed just to pass the PCM data
| around being a massive fraction of the overall processing
| power, you'll notice in a lot of early CD-ROM games they just
| completely sidestep this and just use the CD drive to read
| actual CD audio off the disk and have _it_ decode and play
| back the audio directly to the sound output device instead of
| going through the CPU. Essentially the computer would just
| tell the CD drive "play track 11" when you got to the 11th
| level of the game.
|
| And that was a decade past the creation of the audio CD that
| normal PCs (or _gaming PCs!_ ) still needed a lot of
| processing power just handling that data stream.
| justsomehnguy wrote:
| MPC standard gives a hint: The first MPC
| minimum standard, set in 1991, was: 16 MHz 386SX
| CPU 2 MB RAM 30 MB hard disk 256-color,
| 640x480 VGA video card 1x (single speed) CD-ROM drive
| using no more than 40% of CPU to read, with < 1 second seek
| time Sound card (Creative Sound Blaster recommended as
| closest available to standard at the time[2]) outputting 22
| kHz, 8-bit sound; and inputting 11 kHz, 8-bit sound
| Windows 3.0 with Multimedia Extensions.
|
| Though for a CD game you really wanted something in range of
| DX4/100 with 16MB RAM, which surpasses MPC-II specs.
|
| Also 4 incompatible CD interfaces _on the sound cards_ doesn 't
| bode well.
|
| https://en.wikipedia.org/wiki/Multimedia_PC
|
| https://commons.wikimedia.org/wiki/File:Mozart_16_(Oak_OTI60...
| ben7799 wrote:
| I think most people didn't get a CD-ROM drive till the 486
| was common.
|
| 386s did not come with CDs till late in their lifetime, by
| the time the 486 was becoming affordable most computers had a
| CD-ROM drive.
| RetroTechie wrote:
| > Also 4 incompatible CD interfaces on the sound cards
| doesn't bode well.
|
| Yeah, certainly in the beginning CD-ROM drives were marketed
| as a cornerstone to bring PC's into the "multimedia" age.
|
| And thus eg. bundled with an audio card that doubled as a CD
| drive controller.
|
| Only when they were more common, things like OSes, office
| suites etc came on CD by default.
|
| Oh and... encyclopedia. :-)
| justsomehnguy wrote:
| > bring PC's into the "multimedia" age
|
| Yep, office drones don't need this fancy-shmancy
| multimeedeeaa => no sound card => no CD interface.
|
| Only when ATAPI became _the_ standard (and MultiI /O became
| integrated) the support for the CD drives come to systems
| without a soundcard.
|
| > Oh and... encyclopedia. :-)
|
| That's multimedia.
| lizknope wrote:
| I got my first x86 PC in August 1994. It came with a 2X
| CD-ROM drive with the brand new ATAPI / IDE interface. I
| wanted to install Linux from CD but it was too new to
| have Linux support so I ended up using 10 floppies to
| install each Slackware disk set, back to the computer lab
| for the next set, and repeat.
| pgeorgi wrote:
| Pressing CDs was expensive, which worked for the audio mass
| market, but not for the PC niche market. That limited the
| appeal of buying an (expensive) CD drive, and they weren't even
| using a standard protocol (so: lots of issues).
|
| When CD creation became cheaper and the market grew, the
| economies started to work out in the mid-90s, until the
| late-90s saw computer mags with cover-CDs (a signal that
| everybody in that market had CD drives, and pressing CDs was
| cheap enough for one-off low-count productions like that)
| actionfromafar wrote:
| I think it was just too much data for (cheap) digital tech at
| the time, and the fact that Laserdisc games makers chose
| analogue LaserDisc over something digital on a CD is an
| indication.
| TerrifiedMouse wrote:
| Because LaserDisc could hold high quality video?
| actionfromafar wrote:
| Yes, that, but also that it was easier and cheaper to
| master and control an analogue signal than pushing that
| much video and sound data digitally through a computer.
| TerrifiedMouse wrote:
| You could store and playback video from a CD ... it
| looked like crap though. The best computers could handle
| back then was MPEG-1 video which it was really really
| blocky at CD bit rates. Double whammy of lack of storage
| and lack of processing power.
|
| Things finally got good enough with DVD that had 7x-13x
| the storage and MPEG-2 was available.
| CharlesW wrote:
| > _The best computers could handle back then was MPEG-1
| video..._
|
| Fun fact: MPEG-1 decode needed enough horsepower that
| software decode implementations shipped several years
| after popular-for-CD-ROM video formats like Cinepak1.
|
| The timeline: Cinepak shipped as part of QuickTime in
| 1992. Myst (a very popular CD-ROM title which used
| Cinepak) shipped in 1993. Apple shipped their MPEG-1
| QuickTime extension (PowerPC-only) in 1997.
|
| 1 https://en.wikipedia.org/wiki/Cinepak
| actionfromafar wrote:
| The CD came a decade before MPEG-1, though.
| FirmwareBurner wrote:
| Ah, back when Philips was at the forefront of cutting edge
| innovation.
| mitthrowaway2 wrote:
| Now the flag is carried by its spin-off, ASML.
| FirmwareBurner wrote:
| And NXP. Though it would have been nice if Philips would have
| evolved to be the "European iPhone" company instead of
| selling lights, shavers and food blenders.
| josephcsible wrote:
| > if Philips would have evolved to be the "European iPhone"
| company
|
| They've certainly nailed the evil and user-hostile bit of
| being an iPhone company. From just 2 weeks ago:
| https://news.ycombinator.com/item?id=37667266
| https://news.ycombinator.com/item?id=37594377
| extraduder_ire wrote:
| They also license the brand name to other manufacturers,
| making all kinds of dollar store tat. The first thing that
| clued me into this was reading the back of a set of airpod-
| like wireless headphones.
| nickdothutton wrote:
| Thanks to Philips, who produced such a tremendous range of R&D
| driven products.
| password4321 wrote:
| Related: yesterday's sub-discussion triggered RE:
|
| > _Yamaha 's old CD-Recorder, CRW-F1 really improved sound
| quality by abusing Red Book standard by lengthening the pits of
| audio CDs_
|
| https://news.ycombinator.com/item?id=37726359#37729766
| quercusa wrote:
| There's also some clever coding at the physical level with the
| way pits are arranged on the disc:
|
| https://en.wikipedia.org/wiki/Eight-to-fourteen_modulation
|
| https://spectrum.ieee.org/kees-immink-the-man-who-put-compac...
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