4 ms·

Only tangentially related, but are there any projects out there that modify CD or DVD readers to make it possible to read the raw (analog) pits and lands from t

Only tangentially related, but are there any projects out there that modify CD or DVD readers to make it possible to read the raw (analog) pits and lands from the disc? When I was rescuing the last batch of burned CDs from my teen years a few years ago I unsurprisingly had some with lots of read errors. Googling around only lead me to forum threads where people recommended certain drives that would be very good at error recovery, but I thought it might be even better if you could get the raw stream from the disc and then do all the EFM reversal etc in software with more advanced analysis, brute forcing etc. But nothing of this kind seemed to exist.

londons_explore 6y ago
A major issue is that tracking (ie. Getting the laser to follow the route of the written data) is usually the thing that fails when reading disks. Even if you had access to raw laser data, you can't fix the tracking after reading it...
- agumonkey 6y ago
  side note, the magnetic adjustment coils on laser lenses are a thing of beauty..
flotzam 6y ago
On https://web.archive.org/web/20090318021921/http://club.cdfreaks.com/f52/offsets-handling-syncing-audio-data-vs-q-channel-111913/#post726955 https://web.archive.org/web/20090318021921/http://club.cdfre... someone writes: 'I used an oscilloscope to find a sweet spot in the analog signal path of an audio CD player (an old Sanyo - the older the better, for this kind of stuff...) where a pre-filtered and amplified version of the laser readout is available - in this particular player, this is basically a test header marked "EFM" (which provides a good hint to its function - it's the last analog stage of the signal, just prior to entering the digital Fourteen-to-Eight demodulator). This point is probed and fed into a high-speed AD converter (12 bit res, 50 Msamples/sec) that is hooked to an FPGA. I implemented a flank detector and a run-length encoder in VHDL.' And later in the thread: 'Old audio CD players are so amazingly stupid, they will happily "play" CD-ROM discs if you feed it with one. This is truly ideal for analysis purposes.'
NKCSS 6y ago
From waaaaay back, I remember CDRWin by Golden Hawk was the best piece of software out there to rip CD's, with their error recovery, options to re-read the same thing > 50x, alllowing the whole process to take hours but produce results. Not sure if you tried that one yet? Not what you are looking for, but probably the best off-the shelf solution that exists (though state of the art may have changed in the last decade)...
grishka 6y ago
I was just thinking of doing the reverse: defeating game console DRM by artificially generating the analog signals normally picked up by the photodiode array.
- rasz 6y ago
  this is how https://shop.terraonion.com/en/home/17-Terraonion_MODE_Dreamcast_Saturn_ODE.html https://shop.terraonion.com/en/home/17-Terraonion_MODE_Dream... works Its so trivial someone managed to implement it in a $3 ESP32, you can download firmware for free at https://www.fenrir-ode.fr/firmware/ https://www.fenrir-ode.fr/firmware/
  - rasz 6y ago
    forgot there is also playstation one using ESP32 https://github.com/x-station/xstation-releases https://github.com/x-station/xstation-releases
rasz 6y ago
After having watched "Dissecting the CD Player: How to Turn Shiny Plastic into Music" by Technology Connections https://www.youtube.com/watch?v=3yJqlD9RxD4 https://www.youtube.com/watch?v=3yJqlD9RxD4 and https://www.youtube.com/watch?v=7olNiMCz9to https://www.youtube.com/watch?v=7olNiMCz9to I went on a CDROM research binge. Found this on my way https://debugmo.de/2007/07/read-your-dvds-the-raw-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"). There is also LaserDisc preservation by capturing raw rf signal https://www.domesday86.com/?page_id=978 https://www.domesday86.com/?page_id=978

londons_explore 6y ago

A major issue is that tracking (ie. Getting the laser to follow the route of the written data) is usually the thing that fails when reading disks. Even if you had access to raw laser data, you can't fix the tracking after reading it...

agumonkey 6y ago
side note, the magnetic adjustment coils on laser lenses are a thing of beauty..

flotzam 6y ago

On https://web.archive.org/web/20090318021921/http://club.cdfreaks.com/f52/offsets-handling-syncing-audio-data-vs-q-channel-111913/#post726955 https://web.archive.org/web/20090318021921/http://club.cdfre... someone writes: 'I used an oscilloscope to find a sweet spot in the analog signal path of an audio CD player (an old Sanyo - the older the better, for this kind of stuff...) where a pre-filtered and amplified version of the laser readout is available - in this particular player, this is basically a test header marked "EFM" (which provides a good hint to its function - it's the last analog stage of the signal, just prior to entering the digital Fourteen-to-Eight demodulator). This point is probed and fed into a high-speed AD converter (12 bit res, 50 Msamples/sec) that is hooked to an FPGA. I implemented a flank detector and a run-length encoder in VHDL.' And later in the thread: 'Old audio CD players are so amazingly stupid, they will happily "play" CD-ROM discs if you feed it with one. This is truly ideal for analysis purposes.'

NKCSS 6y ago

From waaaaay back, I remember CDRWin by Golden Hawk was the best piece of software out there to rip CD's, with their error recovery, options to re-read the same thing > 50x, alllowing the whole process to take hours but produce results. Not sure if you tried that one yet? Not what you are looking for, but probably the best off-the shelf solution that exists (though state of the art may have changed in the last decade)...

grishka 6y ago

I was just thinking of doing the reverse: defeating game console DRM by artificially generating the analog signals normally picked up by the photodiode array.

rasz 6y ago
this is how https://shop.terraonion.com/en/home/17-Terraonion_MODE_Dreamcast_Saturn_ODE.html https://shop.terraonion.com/en/home/17-Terraonion_MODE_Dream... works Its so trivial someone managed to implement it in a $3 ESP32, you can download firmware for free at https://www.fenrir-ode.fr/firmware/ https://www.fenrir-ode.fr/firmware/
- rasz 6y ago
  forgot there is also playstation one using ESP32 https://github.com/x-station/xstation-releases https://github.com/x-station/xstation-releases

rasz 6y ago

After having watched "Dissecting the CD Player: How to Turn Shiny Plastic into Music" by Technology Connections https://www.youtube.com/watch?v=3yJqlD9RxD4 https://www.youtube.com/watch?v=3yJqlD9RxD4 and https://www.youtube.com/watch?v=7olNiMCz9to https://www.youtube.com/watch?v=7olNiMCz9to I went on a CDROM research binge. Found this on my way https://debugmo.de/2007/07/read-your-dvds-the-raw-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"). There is also LaserDisc preservation by capturing raw rf signal https://www.domesday86.com/?page_id=978 https://www.domesday86.com/?page_id=978