Comment by byuu | Hacker News Reader

Comment by byuu | Hacker News Reader

Emulator development has cross-sections across many diverse fields of computer science, and I'm trying to share my experiences with all of them. If anyone here has suggestions for future articles for my site, I'm all ears ^-^

While folks are thinking about CDs: I've not been able to get an F2/F3-frame CD image. If anyone has such a thing (not copyrighted, just a CD containing a text file or public domain music piece is fine), I'd love to get it so I can implement a CIRC encoder/decoder! My GitHub repository (linked in the article) has an RSPC Reed-Solomon encoder/decoder, a disc scrambler/descrambler, and Q-subchannel encoder/decoder. I'm trying to build up a comprehensive ISC-licensed C++ library for working with every frame level of CD data.

For folks interested in the lead-in / lead-out data, to my knowledge only very few drives allow reading this raw data, namely older Plextor drives with the 0xd8 (READ_CDDA) command. If there are any hardware engineers who want to save an entire generation of CD history in a more exacting archival format, we could desperately use either hacked drive firmware for a modern CD drive, or custom CD reading hardware to preserve this data. Time is really of the essence.

The vanguard of CD preservation right now, to the best of my knowledge, is Claunia's DiscImageChef project: http://discimagechef.claunia.com/

I'm also working with the Game Preservation Society in Japan ( https://www.gamepres.org/ ), which has archives of thousands of rare and obscure Japanese CD media, so by all means if anyone reading this can help, please let me know.

> While folks are thinking about CDs: I've not been able to get an F2/F3-frame CD image. If anyone has such a thing (not copyrighted, just a CD containing a text file or public domain music piece is fine), I'd love to get it so I can implement a CIRC encoder/decoder!

I don't know if you've already seen this, but I've heard of someone getting an image like this. They used it to discover what the AccurateRip drive offset values mean in terms of the physical location of the subchannel data and interleaved main channel data on the disc. There's a vague description of their process in there as well.

https://club.myce.com/t/offsets-handling-syncing-of-audio-da...

> Using my neat hardware setup I now have captured a precious 0.1 seconds worth of 588-bit channel data frames from a pristine audio CD, each frame containing, among other things, a subchannel byte and 24 bytes of audio data.

> I can reproduce the CIRC, get the de-interleaved audio data, and also do the Reed-Solomon C1/C2 stuff in software from my analog laser readouts - showing an error-free read, identical to what I get with my Plextor using somewhat more conventional methods.

That is exactly what I need, but unfortunately the post is from 2004, and he didn't link to that precious sample of data =(

Still, some very interesting info there. It looks like if and when I get this data, I may need a follow-up article that goes even deeper.

Hmm, poking around on that website, there's some more:

https://club.myce.com/t/announcing-laser2wav-a-software-only...

That tarball seems to have fallen off the internet, but there's also this. Check out laserbits.txt. I wonder if that's the data.

https://github.com/sidneycadot/Laser2Wav/tree/master/python

After having watched "Dissecting the CD Player: How to Turn Shiny Plastic into Music" by Technology Connections https://www.youtube.com/watch?v=3yJqlD9RxD4 I went on a CDROM research binge. Found this on my way https://debugmo.de/2007/07/read-your-dvds-the-raw-way/ Its about DVDs (has data dump plus code), but you can use same mechanism to easily modify CDROM drive using $4 piece of hardware (ebay "EZ-USB fx2lp cy7c68013a board").

I saw something online where a scanned high-resolution image of a record could be played by simulating the record needle. Is it possible to scan or photograph a CD at such a high resolution that the pits become visible? Then you have all 2.5GB of the raw EFM right there. If the CD is scratched the lacquer layer could be removed somehow I imagine.

That might be the best option anyway.

I heard rumors that the original PlayStation copy protection involved introducing an intentional wobble into the tracks who's frequency is reported back to the application by the CD-ROM controller. Full preservation may necessitate your scheme.

Is it important to preserve what cannot be read today, and could not be read anytime during the heyday of the CD-ROM media?

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