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Old 6th Jul 2018, 5:57 pm   #1
smally_uk
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Join Date: Jul 2018
Location: Birmingham, West Midlands, UK.
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Default Newbie - Laserdisc / BBC Domesday Project / Software decode of video

Hi All,

I have just joined up and would like to say Hi.

Bit of a background on me and why I am here.

I am a big laserdisc fan and have a full working BBC Domesday System and am working with a few people on how to archive Laserdiscs with all of the information stored (Audio / Video / VBI / Syncs / Data / Digital Audio).

The team have designed and built a very high speed USB3 data acquisition card that samples from the RF test point on a laserdisc player. This allows the recording of the optical pickup in its rawest form. There is currently ongoing work to software decode the signal on a laserdisc back into video with a software based demodulation and time base corrector that is producing fantastic results so far.

By picking up the signal from the optical pickup you bypass the 20-30 year old electronics that all have the effect of filtering and attenuating the signal in different ways. We already have a signal to noise ratio of 45dB which is higher than any laserdisc player manufactured right upto the 2000s

What may be of interest to people is there is possible scope for software decode of VHS/Beta in the future but as yet currently only preliminary tests have been done.

I have attached a software decoded testcard so that people can see the progress. (Sorry needed to be a JPEG for size)

If anyone wants to know more Im happy to answer questions but I didn't want to post links on my first post.

Thanks

Ian
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Old 6th Jul 2018, 7:00 pm   #2
cmjones01
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Default Re: Newbie - Laserdisc / BBC Domesday Project / Software decode of video

That's very impressive. I knew there was work going on to preserve the Domesday data but had no idea it was going so deep in to the technology. Where can we find out more?

Reading about the Domesday discs has now got the tune 'Pigbag' rattling around in my head. Anyone else remember the bottling plant clip?

Chris
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Old 6th Jul 2018, 11:18 pm   #3
smally_uk
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Default Re: Newbie - Laserdisc / BBC Domesday Project / Software decode of video

Thanks.

There have been a few attempts in the past to recover the discs. The main one is that the original masters tapes were recovered by the BBC but this did not include the data portion of the discs or any disc lead-in or VBI (Vertical Blanking information which is unique to the discs). The computer based data was recovered from the discs and then run in a very basic emulator as part of the CAMiLEON project.

This project although proved the possibility of emulating the system was very unstable and would only run sections of the Domesday discs and would not run any of the other BBC Advanced Interactive video discs (EcoDisc, Countryside and Volcanoes). This was seen by ourselves as the emulator was not complete. After investigations into how a real system worked it was discovered that the original project had so many flaws that it was worth starting again with a different tact.

If we can emulate the original SCSI card to the logic level and then emulate a player to work on the original hardware then it must be correct. This was a hell of a task for the SCSI implementation as even the original schematics had errors and there was no documentation about the extra layer of SCSI protocol for LV-ROM (LaserVision ROM). This was slowly reverse engineered and we now have an emulator that works with real hardware. It is not yet complete as it does not have video mixing but is well on the way. Our emulator uses frame captures taken from the original discs, but as you can imagine these are not perfect after going through 30+ year old player electronics that are out of calibration.

The next stage was to try and get a copy of the analogue disc (Yes Laserdiscs are analogue) and we came across a project to software decode laserdiscs, This project was a fantastic piece of work but the hardware it was using for doing the captures was nowhere near ideal. This is where Simon decided to build a custom data acquisition capture device for capturing the full RF spectrum in one go. (Related to SDR but DC-20MHz / 40MSPS) This had a custom RF front end for dealing with the specific frequencies involved and removing the upper harmonics.

Over the past few months we have been in a development loop of customising the software decode (with lots of help from the original developer) with the new hardware. The quality of the images is now stunning and better than we thought possible and almost approaching broadcast.

Projects and links (All open source)

SmallyMouse - Quadrature mouse emulation with a native USB mouse.
https://www.domesday86.com/?page_id=245

BeebSCSI - Hard disc and Videodisc Emulation for the BBC Micro
https://www.domesday86.com/?page_id=689

Domesday Duplicator - 40MSPS 10bit ADC streaming to disc
https://www.domesday86.com/?page_id=978

We do have a facebook page with more up to date developments, just search for 'domesday86' and you will find it.

Thanks

Ian
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Old 7th Jul 2018, 11:24 am   #4
TonyDuell
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Default Re: Newbie - Laserdisc / BBC Domesday Project / Software decode of video

What exactly did the original hardware consist of? Make/model of the laservision player, what SCSI card, etc? What documention (schematics, etc) exists for it?
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Old 7th Jul 2018, 12:07 pm   #5
smally_uk
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Default Re: Newbie - Laserdisc / BBC Domesday Project / Software decode of video

The original hardware was...

BBC Master 128 (AIV) with
...65c102 Second processor - https://www.domesday86.com/?page_id=1962
...Acorn AIV SCSI Card - https://www.domesday86.com/?page_id=64
...Acorn VFS (Video Filing System ROM) - https://www.domesday86.com/?page_id=70
...Marconi Trackball - https://www.domesday86.com/?page_id=61

The laserdisc player is a custom player for the project which is a Philips VP415
https://www.domesday86.com/?page_id=316

After about 10 years of digging we now have schematics and rom dumps of everything that we know of within the player and computer.

The interesting thing about the player is that it is the Only SCSI Laserdisc player and it stores the data on the audio tracks using a similar encoding to CDs (EFM modulation within a FM modulated band) and there are only about 25 working worldwide.

We have gone to a lot of trouble to scan or reverse engineer as many schematics as possible from the original hardware and they are all available on the website where possible.
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Old 7th Jul 2018, 12:11 pm   #6
electronicskip
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Default Re: Newbie - Laserdisc / BBC Domesday Project / Software decode of video

Welcome to the forum Ian.
Nice to meet a fellow Laserdisc enthusiast.
Impressived you have a Doomsday set ,something ive always wanted myself!
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Old 7th Jul 2018, 12:20 pm   #7
smally_uk
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Default Re: Newbie - Laserdisc / BBC Domesday Project / Software decode of video

I have three complete Domesday setups.
1 working complete
1 for repair in Sweden (Only person who can fix them is Simon ) and part of Domesday86 team.
1 that needs a service as very temperamental

As you can see from the site we have every set of discs available for the system except the City Discs (Nobody has them not even museums but we have seen a photo)

Simon Also has two complete setups.

We are looking to sample the discs and do error correction over the different copies of the same pressing to remove any of the scratches that have been introduced over the years.

But first we need to calibrate the laserdisc players to get the best possible captures. Not as easy as it sounds as all of the calibration discs are NTSC and the Philips VP415 is a PAL only player. We are yet to find a PAL calibration laserdisc.

Our capture hardware will work with almost any laserdisc player so that is good but repairing the original Domesday players is fun!
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