Developing a analogue capture card with in built tbc

[johnmeyer]

As I read back through these posts, the problem I have is that it is not clear what problem the VHS-Decode project is trying to solve.

You obviously still need a VCR, so it doesn't solve the problem of VCR shortages, and VCRs which are not fully functioning.

I still need hardware to get the video/audio into my computer, so it doesn't solve the problem of obtaining quality capture hardware, and making sure I get something that works well.

The one, somewhat vague, promise is that I can get a higher-quality, better-looking video. The theory is very intriguing, but so far I haven't seen any solid test that shows this to be true.

Don't get me wrong, I am totally open to the idea, and do not in any way dismiss it out of hand.

The one other thing that is also a little off-putting is the workflow. Having to hot-wire my VCR is a little worrisome, even for me (i.e., someone quite comfortable with soldering), but then having to do all the extra steps to convert the "capture" into usable video (and audio which, apparently, requires some extra steps) makes it sound like it could create real workflow problems when having to capture 50 tapes for a project.

[Cornucopia]

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.scienced...b4DOzkb_lR66PB

That was in 1999, so I expect improvements have been made since then.

With non-contact scanning as a possibility, I could envision a much simpler, more streamlined tape transport mechanism that just played the tapes linearly and scanned the entire tape linearly, then using a high enough bitdepth multiple oversampling of the tape, the rest should be able to be done in software. Track alignment & V + A + Control/TC separation, track segment stitching, the rf & fm decode, etc.


Scott

In fact, the transport & A/D could be one device, with perhaps a Thunderbolt 5 interface.

[dellsam34]

... unmolested SD will be the challenge, especially in NTSC. The SD is generally force-processed, be it deinterlace, scaling, or otherwise. Tapping into chips is also suspect, as some lock/encrypt code.

I was referring to some DVD recorders from the 2000-2010 era where the digital output from HDMI is conform to the standard, Not referring to any modern analog to HDMI scaler.

[dellsam34]

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.scienced...b4DOzkb_lR66PB

That was in 1999, so I expect improvements have been made since then.

With non-contact scanning as a possibility, I could envision a much simpler, more streamlined tape transport mechanism that just played the tapes linearly and scanned the entire tape linearly, then using a high enough bitdepth multiple oversampling of the tape, the rest should be able to be done in software. Track alignment & V + A + Control/TC separation, track segment stitching, the rf & fm decode, etc.


Scott

In fact, the transport & A/D could be one device, with perhaps a Thunderbolt 5 interface.

Chances are nothing happened to that idea since 1999, There is nothing wrong with scanning the tape with a spinning drum, there is nothing to be gained doing otherwise, As a matter of the fact scanning the video tracks the same way they were laid down during recording may yield better results than any other scanning technology, There is no need to re-invent the wheel.

[mountaincabbage]

Perhaps a more realistic approach than these half drafted software solutions is to get few DVD recorders with S-Video input and HDMI lossless SD output and use them as capture devices, Multi HDMI recording is easier to achieve nowadays, and being digital it should be well supported by major software and hardware companies. If you have the knowledge you can be creative and see if you can remove the DVD drives and other unnecessary boards not needed for the purpose.

This could work in terms of optimising workflow and scalability, but we'd still be relying on high end VCRs which are dwindling. The goal here is to learn in depth different methods of analogue capture, and see if improvement can be made.

You obviously still need a VCR, so it doesn't solve the problem of VCR shortages, and VCRs which are not fully functioning.

If it can produce the same quality as a high end VCR, on a lower end VCR, then it helps by increasing the pool of VCRs available for transfer. The immediate issue is that the top end decks are now hard to come by. There is still plenty of normal VCRs out there.

I'll dig into the vhs-decode project and see if I can get some decent comparisons with a typical analogue capture setup.

[dellsam34]

This could work in terms of optimising workflow and scalability, but we'd still be relying on high end VCRs which are dwindling. The goal here is to learn in depth different methods of analogue capture, and see if improvement can be made.

You would be wrong, The sole purpose of using such DVD recorders is to take advantage of their TBC capability because low end VCRs lack it. The DVD recorders I referred to have HDMI out so no need to an analog to digital capture card, you just need a HDMI acquisition card or device.

[lollo]

The DVD recorders I referred to have HDMI out so no need to an analog to digital capture card, you just need a HDMI acquisition card or device.

Nice! You start to think about the "German" approach has alternative (with the drawbacks we all know, I personally do not use it).

Just as curiosity, what made changing your mind about the HDMI output from such machines not being strictly compliant with Analog SD specifications ?

[dellsam34]

I've never changed my mind about proper HDMI method, maybe it was a misunderstanding on my end about that German website. On the TBC side I still think a DVD recorder does not replace a proper VCR with line TBC and a capture device built in frame sync. But for the OP's purpose of running a business it might be just ok as long as he properly process the lossless files.

[lollo]

On the TBC side I still think a DVD recorder does not replace a proper VCR with line TBC and a capture device built in frame sync

Sure. (A specific device) Just replaces a DVD-Recorder used as external TBC in a workflow (example ES10 or ES15) and the chained capture card

[pandy]

NP - not sure what kind of price is on Amazon but probably cheapest Pluto is on ADI site (195$).

Wow, that is a LOT cheaper than the $495 on Amazon for a "kit."

Pandy, thanks for the SDR and ADALM2000 links. I just recently bought a cheap Hantek digital oscilloscope, and while it has a few functions found in the ADALM, it sure doesn't have them all, and it is not directly programmable. I have used the Hantek as a frequency counter and, through its very crude FFT, as a spectrum analyzer, but both are extremely marginal and barely usable. Something like the ADALM might be very useful. Thanks!

ADALM is suggestion from Sharc (btw it is a good candidate for VHS decode - 12 bit, 100MHz ADC is more than enough). I had this kind of suggestion earlier in thread - some DAQ supporting at least two channels (preferably 4 simultaneous sampling so Y, C and L, P - 12 bit or more, by adding large amount of noise to 12 bit over usable audio signal bandwidth and later decimating easily 90dB++ SNR can be achieved)

[pandy]

if you sample signal with sufficient sample rate and sufficient accuracy then you can later do whatever you want

If, if, if. Archivists, orgs, studios, and even "normal people" deal in known knowns. Not "let's spend time and money on this now, and then hope software works magic later".

Nope this is math i.e. science - something exactly opposite to what are trying to do - we know haw VHS signal is stored, there is no magic there - if you have 3..4MHz signal bandwidth then sampling it 4..8 times more (oversampling) is more than enough (but you can oversample more - 16 times if you wish - we are still on safe, sane <100MHz sample rate). 10..12 bit provide around 50..60dB SNR - way more than you need to demodulate FM - one of many examples https://www.nsf-shrec.org/sites/default/files/2024-03/On-FM-demodulators-in-software-d...sing-fpgas.pdf

There is lot of science there despite some nuts claiming best

Yes, pseudo-science is always "crazy + science". If it were a sundae, science scoop on bottom, nuts of top.

Well... you sounds like nutty audiophile...

I'm also quite old so you can call me conservative one but still i observe how truly amazing progress is in electronics

I agree, but we didn't get Star Trek. We largely got inventions and progress that were not planned. So to say "this will be big someday" is naive. It may be small, or nothing/vaporware, or not even needed later. That's the natural course of science, lots of "eureka!" moments, not "next, we will do this".

We not talking on WARP drive but we talk about real life solutions - nowadays you have ADC with SFDR 80dB+ and bandwidth around GHz - this is science (read once tape, demodulate in HW/SW to avoid old analogue electronics).

This is not emulation

It's also not an aardvark. But it was an example of tech not always being able to recreate the past. As another example, the Antikythera device took 100 years to be recreated, and people are still not 100% in agreement on how it works.

Pure sophism - we talking about FPGA - it is not emulation, this is HW using software description to perform data processing - in theory you can build discrete circuitry (for example using SRAM) to act like FPGA, from electronic perspective it is (FPGA) just smaller and more flexible approach between hard logic (like ASIC or VLSI) and pure software - you can reprogram HW (FPGA) multiple times but it is not emulate anything - it perform exactly same algorithm as real digital gates and registers made from transistors.

[pandy]

As I read back through these posts, the problem I have is that it is not clear what problem the VHS-Decode project is trying to solve.

From my perspective it is to replace old (deteriorating) analogue circuitry - VCR signal processing is quite complex so naturally analogue processing is affected by series of compromises - even latest generation of VCR's using very complex, partially hybrid (like discrete time analogue processing but still not digital signal processing where signal is sampled in time and voltage axis) IC's are affected by technological limitations - analogue memory (like CCD/BBD) allow to implement some algorithms in more efficient way but still are unable to provide sufficient signal to noise ratio - let say TBC can be made as analog delay line but probably you will not get SNR higher than 40dB, also you will be limited by "memory size" i.e. how many samples are stored and can be later used. In software this is not problem - you can store many frames so perform statistical processing over huge amount of samples and perform highly sophisticated processing not possible in typical VCR.
So use mediocre mechanics to deliver highest possible quality limited only by VCR system itself.

[johnmeyer]

ADALM is suggestion from Sharc ...

Oops! Sorry Sharc. I edited that post so it reads correctly now.

[dellsam34]

The problem with these high frequency sampling software schemes is that they are not able to make it to a functioning, hassle free, easy, and ready to use product. we can fantasize about how great their capabilities are but cannot be used out of the box to replace a ready made capture card or device. I also read a lot of books about how to make a car that runs on water but does that mean I will include that option on my shopping list when I go buy a car next time?

[pandy]

The problem with these high frequency sampling software schemes is that they are not able to make it to a functioning, hassle free, easy, and ready to use product. we can fantasize about how great their capabilities are but cannot be used out of the box to replace a ready made capture card or device.

This is just beginning - what do you expect from project driven entirely by enthusiast sometimes with relatively low know how especially for old designs - they may excel in modern tools but old designs use some shortcuts known to older generations and lost in modern times - this is sometimes lot of effort to get something just work. But i'm sure that there is learning curve and additionally to learning also bit of luck.
Ready to use solutions are affected by compromise - they are designed in particular goal like consumer market and their are just fine for consumer but not for broadcast quality. Just check audio / video encoding tools and solutions - 20..30 years ago this was really knowledge of few people nowadays this no longer elite know how. I recall my first plays with jpeg or mp3 formats - on 386SX 20MHz decoding 800x600 jpeg by Image Alchemy took 26 seconds, i recall encoding audio wav to mp3 - Fraunhofer L3enc DOS encoding on 386DX 40MHz was like 8..10 times slower than real-time, decoding approx 2 .. 3 times slower - today cheap IC from China doing this in real time and it cost less than 2$ .

[dellsam34]

Not when you are running a business and want something better, faster and convenient, which what the OP is trying to achieve.

[pandy]

Not when you are running a business and want something better, faster and convenient, which what the OP is trying to achieve.

So i wrongly (obviously) get idea to create (develop) analogue cart to capture signal - all ready to use solutions are against idea to be "novel concept" and most of them is directly limited by series of compromises as they targeting two principal areas - consumer video and CCTV - so they goal is to satisfy mostly "price per capture port" with acceptable but not superb quality.
Also TBC is good question mark - real TBC is able to deal even with lost frame i.e. assumption is to store whole video frame in memory and output it with perfect timing (mostly for broadcast purpose - this is not so important for software encoding as computers may work with asynchronous stream of data usually).

[mountaincabbage]

Reading between the lines, it appears the general consensus hardware wise is that all the ICs developed for A2D have stopped progressing. VHS-Decode offers exciting potential as it's all software side.

At present I'm going to:
- Wait for the PCB of the TW6865 chip I've had designed, see if I can get that working, learn what I can and see if I have any additional control over the quality via parameter tweaking
- Learn about VHS-Decode, get it up and running and see how the quality compares with typical methods

Potential hardware route if TW6865 fails/deadends is the Analogue Devices chip mentioned.

Potential software route would be to investigate vhs-decode, improve processing speed and hardware so it is usable.

PS - thanks for everyone's comments so far

[pandy]

Reading between the lines, it appears the general consensus hardware wise is that all the ICs developed for A2D have stopped progressing. VHS-Decode offers exciting potential as it's all software side.

At present I'm going to:
- Wait for the PCB of the TW6865 chip I've had designed, see if I can get that working, learn what I can and see if I have any additional control over the quality via parameter tweaking
- Learn about VHS-Decode, get it up and running and see how the quality compares with typical methods

Potential hardware route if TW6865 fails/deadends is the Analogue Devices chip mentioned.

Potential software route would be to investigate vhs-decode, improve processing speed and hardware so it is usable.

PS - thanks for everyone's comments so far

Hypothetically there is software video decoding so between VHS decode and hardware video decoder - also TBC can be implemented at the software level easier. NTSC/PAL software decoding should be less complex and offer some benefits (as you have access to all lines so you can build statistic and decode more robust way even noisy video).

[lordsmurf]

Reading between the lines, it appears the general consensus hardware wise is that all the ICs developed for A2D have stopped progressing. VHS-Decode offers exciting potential as it's all software side.

That's the wrong takeaway.

The "software only" approach has already failed, because they keep adding in bits and pieces of hardware. Bandages, patches.

It's not so much that ICs have "stopped progressing", but rather that there's nothing really to progress. It's now mature and evergreen. It's like going to the grocery store, looking at the ears of corn, and asking "what new progress has been made?". Nothing, it's corn. Nothing, it's VHS.

[dellsam34]

The OP should know better, He worked for SingMai, If Daniel could not pull it off with all his knowledge and access to hardware and software chances are no one can, I hope I'm wrong.