Developing a analogue capture card with in built tbc

[dellsam34]

ADLLT meets my criteria for line TBC since it corrects horizontal line timing errors. Issue is it is only known to to be actually implemented on the TBS800 by Snell and Wilcox. See post #13 here for samples which show the actual correction it performs:
https://forum.videohelp.com/threads/402431-New-Device-Tested-for-TBC-Functionality

I was shocked at that time when I found out it addressed baked in timing errors in the second gen dub, It can also be compounded with the built in VCR line TBC unlike some consumer DVD recorders. But not just this ADLLT feature, overall the frame stability of the device is outstanding, It has a ton of other features that I haven't tested, so basically I'm just using as an analog to digital converter, Yes it is bulkier (1/2 rack size) compared to other devices that use similar chips but performance wise is the best I've tested so far.

[mountaincabbage]

All I'll tell you is this: an idiot chooses to "make his own mistakes", a wise person learns from the mistakes/experiences of others.

Why do you think I posted on this forum? To be honest, I wasn't expecting members to have drilled into the A2D chips, else I would have posted before the chip selection.

Has anyone heard of Intersil TW6865 being used?

Tapes have a 35-65 years shelf life (something I chemically calculated in the 2000s, contrary to the 10-20 years BS at the time). We're only now seeing mass degradation (such as early 80s BASF breaking down en masse, at about the 45 mark in that 35-65 range). I'm sure many will hit 65, and some even 10-20 beyond that.

That's good news, much more in line with what we're seeing.

So far, it appears the most important factors for a capture card are:
- Color and sharpness performance - The TW6865 has the following features:
10-bit ADCs: High-resolution digitization (page 9) preserves color/luma accuracy.
Adaptive 4H Comb Filter: Superior Y/C separation for NTSC/PAL, minimizing cross-color
Color Transient Improvement (CTI): Enhances color edges without overshoot
Clamping/AGC: Sets pedestal (7.5 IRE NTSC-M, digital 60, page 11) and prevents highlight clipping
Programmable Controls: Brightness, contrast, saturation, hue, and sharpness
So hopefully will see some good results from this.

- Ideally some form of TBC, the presence of which in analogue devices chip is debated, the functionality of previous TBCs is deemed unfeasible to reproduce.
- We're pretty nerdy with software, so I'm interested to see what can be done that side if we can control the A2D chip.

Hundreds of devices contain chips that are ADLLT capable, but virtually none have the additional (and always separate) RAM required to actually use it. So while the ubiquitous Blackmagic Analog to SDI converter has an ADLLT capable chip, that feature cannot be active because the Blackmagic hardware lacks the supporting RAM for that feature to work.

Perhaps this is something we can explore if we choose to use this chip at some point.

[johnmeyer]

ADLLT meets my criteria for line TBC since it corrects horizontal line timing errors. Issue is it is only known to to be actually implemented on the TBS800 by Snell and Wilcox. See post #13 here for samples which show the actual correction it performs:
https://forum.videohelp.com/threads/402431-New-Device-Tested-for-TBC-Functionality

I looked at the captures in post #13, and the TBS800 results are quite impressive. I am not a TBC aficionado, but I would be extremely happy owning that unit.

[dellsam34]

If you are willing to pay a premium, I think the CVR900 is a sister product from Grass Valley after they took over Snell, But user manual should be available online, Sorry for going off topic.

Back to the subject, Whatever route you decide to pursue keep us updated.

[mountaincabbage]

Back to the subject, Whatever route you decide to pursue keep us updated.

Will do

[aramkolt]

Datasheet kind of suggests that the TW6865 chip is composite only, probably wouldn't bother with that personally, but it does have the 4 channels of video you are looking for I guess.

[pandy]

So far, it appears the most important factors for a capture card are:
- Color and sharpness performance - The TW6865 has the following features:
10-bit ADCs: High-resolution digitization (page 9) preserves color/luma accuracy.
Adaptive 4H Comb Filter: Superior Y/C separation for NTSC/PAL, minimizing cross-color
Color Transient Improvement (CTI): Enhances color edges without overshoot
Clamping/AGC: Sets pedestal (7.5 IRE NTSC-M, digital 60, page 11) and prevents highlight clipping
Programmable Controls: Brightness, contrast, saturation, hue, and sharpness
So hopefully will see some good results from this.

Nothing spectacular i would say - OK but hardly innovative.

- We're pretty nerdy with software, so I'm interested to see what can be done that side if we can control the A2D chip.

Then do everything in software - just use single or two channel general 12..14 bit ADC and decode video in software so you can control every aspect how video is processed and you can develop full and proper TBC in software. Signal processing can be done in framework such as GNU Radio - perhaps this can be inspiration https://wenku.csdn.net/answer/00221e35d50648bb880ce58f11fe729e but there is more activity on this area - just search for sdr pal ntsc .

[mountaincabbage]

Datasheet kind of suggests that the TW6865 chip is composite only, probably wouldn't bother with that personally, but it does have the 4 channels of video you are looking for I guess.

- we've planned a method to convert s-video to composite, so you can select which input you'd like.

Then do everything in software - just use single or two channel general 12..14 bit ADC and decode video in software so you can control every aspect how video is processed and you can develop full and proper TBC in software. Signal processing can be done in framework such as GNU Radio - perhaps this can be inspiration https://wenku.csdn.net/answer/00221e35d50648bb880ce58f11fe729e but there is more activity on this area - just search for sdr pal ntsc .

Can you elaborate on this please? Are you suggesting vhs-decode + additional signal processing to reduce the computation/data workload computer side?

[aramkolt]

Mixing S-Video to composite is easy enough to do, it's just never the best quality result and it'll make most people here question why bother with making a custom card if it can't do what basic and already available hardware can do.

There are entire forums about how to get the best out of a composite-only source like laserdisc and what they came up with was a whole different method (RF capture) to avoid using it at all. So when you can start with an S-Video signal and then mix it to composite, that's a huge step backwards. I guess if you use a low enough bitrate or the end result is going to be posted to YouTube where the compression may make them look pretty similar either way, it may not visually matter in some cases. Much depends on how good the comb filter is on the ADC, but there's no such thing as a perfect comb filter, so if you can just stick to "never mixed" S-Video, that's the better choice since it avoids the main limitation of composite - interference between chroma and luma.

How many tapes do you typically capture at once and how many of these 4 channel cards would you actually be making for internal use? What is the final delivery format and bitrate to your customer? I guess if the final bitrate is low enough, composite may be fine, but it won't be the best that it can be. Seems your goal might be more to save space/complexity (fewer physical separate components in each video chain) and have readily available new hardware rather than getting the best quality if you aren't planning on using S-Video?

[dellsam34]

I agree, Working around existing low quality multi-channel composite CCTV card is a backward step in quality, One should work around high quality single channel YC cards and try to multiply it, The cost of having multi capture rig is not the $50 capture cards themselves, but rather the VCRs, the fast computer needed with high capacity storage and a proprietary software to go along with it.

[mountaincabbage]

Seems your goal might be more to save space/complexity (fewer physical separate components in each video chain) and have readily available new hardware rather than getting the best quality if you aren't planning on using S-Video?

Currently we do capture with s-video if available, all our vhs/8mm tapes are done through s-video. If s-video > composite significantly reduces the quality noticeably, then we'll have to figure out a different route for that. Quality is a priority. The ideal card for us would be multi channel, great quality, stable that we can interface completely with software side.

Just for clarification - Are you saying that the s-video is processed in a way that avoids that in other cards, e.g. the ADV7802?:
https://www.analog.com/en/products/adv7802.html

[pandy]

Then do everything in software - just use single or two channel general 12..14 bit ADC and decode video in software so you can control every aspect how video is processed and you can develop full and proper TBC in software. Signal processing can be done in framework such as GNU Radio - perhaps this can be inspiration https://wenku.csdn.net/answer/00221e35d50648bb880ce58f11fe729e but there is more activity on this area - just search for sdr pal ntsc .

Can you elaborate on this please? Are you suggesting vhs-decode + additional signal processing to reduce the computation/data workload computer side?

This is simple - project vhs-decode trying to remove issues with analog signal processing in typical VCR - as video on tape is stored trough FM modulation then all you need is something called RF so raw signal from video head (probably after amplification) - such signal is sampled and later demodulated in software, firstly from FM modulation to voltage and later all steps to recover chroma and luma into something that can be decoded (NTSC/PAL). This is area where you can use higher precision than analog electronics can offer (SNR for common VCR analog circuitry rarely exceed 45..48 dB at best, 16 bit integer precision offer at least 90dB and usually 32 bit float is used for calculation so your signal can be processed with precision beyond analog electronics capability).

Depends on point where you perform digitization you may perform in software FM demodulation (so using so called RF) or software video decoding (decode NTSC/PAL). IMHO modern computers should be capable to perform demodulation and decoding in real time so if vhs-decode is slow this is outcome of only early stage - simply this is too early to optimize software if still lot of developments in basic areas is done.

Once when optimal algorithm will be established then there is nothing against to translate this algorithm to FPGA board so it can be performed in hardware.

[lordsmurf]

project vhs-decode trying to remove issues with analog signal processing in typical VCR

It's really not trying to "remove" anything as much as recreate better quality VCRs (like JVC S-VHS and Panasonic S-VHS, with line TBC). But using cheap junk VCRs.

Once when optimal algorithm will be established

This is really the crux. There are some intrinsic seemingly-uncorrectable problems to the current algorithms, and a "fix" is not a given. Remember, multi-billion dollar corporations had high-paid engineers develop VCRs. The perfection of VHS may be a feat that is lost to time, and all we get is a shadow of that quality. Not everything matures as some hope (tech, medicine, etc).

The biggest issue against the project is trying to use wildly variable junky decks. But if ever a certain deck (or decks) was "blessed" as best for it, those would quickly rise in costs (due to demand, and limited supply). So that confronts this misplaced/misguided desire to be cheap above all else.

So:
- If the project focused on quality, with a smaller menu of viable decks, then it might happen.
- If it continues to focus on "free", then it may be vaporware longer term.

Then the question becomes: is it really that much better than current S-VHS > TBC workflows? Probably not.

The project is in a "catch 22". I saw this years ago, even if they did not.

[pandy]

project vhs-decode trying to remove issues with analog signal processing in typical VCR

It's really not trying to "remove" anything as much as recreate better quality VCRs (like JVC S-VHS and Panasonic S-VHS, with line TBC). But using cheap junk VCRs.

Disagree - signal is signal - more expensive VCR may use additional circuitry to improve some signal aspect yet they are unable to go beyond analog circuitry limitations - let say - you need low pass filter or band pass - in analog domain you always need to stay within limits described by costs (electronic parts accuracy and their number), overall complexity, physical limitations - for example you can use or gentle but more phase linear filters (lets say Bessel type) or sharper but less phase linear filters (such as Butterworth or Chebyshev) - the more tighter characteristic then higher precision elements required. In digital domain you can use or IIR or FIR with very different types of frequency and phase responses or shift radically by using FFT. FIR theoretically can't be recreated in analog domain so this is your benefits from using digital domain. You can in analog domain use CCD/BBD to introduce analog delay and try to recreate some digital domain blocks but still you are limited by analog signal accuracy - real physics can be nasty - software is free from this.

Once when optimal algorithm will be established

This is really the crux. There are some intrinsic seemingly-uncorrectable problems to the current algorithms, and a "fix" is not a given. Remember, multi-billion dollar corporations had high-paid engineers develop VCRs. The perfection of VHS may be a feat that is lost to time, and all we get is a shadow of that quality. Not everything matures as some hope (tech, medicine, etc).

To perform software vcr decode you need to understand signal flow but in detailed way - some things may be trade secrets so unless you understand electronics in deep level (sometimes at very primitive basic which seems to be most difficult) then this looks mostly like blind search with some positives and more frequently fails. But as i'm electronics engineer then i see this direction as most complete and obvious way to excel vcr decoding beyond what is possible in analog domain world. So this project not delivering expected quality mostly because people lack very detailed hardware knowledge - please don't take this as criticism but rather observation based on many discussions present also on this forum - people having endless disputes on basics such as amplification, impedance and termination - for hw people this is obvious, things to solve once and go to more demanding areas.
So my impressions is enthusiasts project where lot of effort is spent on trivial things and everything of course need to be hyped similarly to audiophile world where gold plated wall socket made miracle with power current and you can hear this in audio...

The biggest issue against the project is trying to use wildly variable junky decks. But if ever a certain deck (or decks) was "blessed" as best for it, those would quickly rise in costs (due to demand, and limited supply). So that confronts this misplaced/misguided desire to be cheap above all else.

So:
- If the project focused on quality, with a smaller menu of viable decks, then it might happen.
- If it continues to focus on "free", then it may be vaporware longer term.

Then the question becomes: is it really that much better than current S-VHS > TBC workflows? Probably not.

The project is in a "catch 22". I saw this years ago, even if they did not.

Once again - mechanics of VCR is important but only to some point - beyond this there is gray land where digital domain may deliver better quality than possible in analog domain.
You need to have solid knowledge on DSP (luckily this one is easier than before) on very deep trough knowledge on how VCR works (this is something difficult due age of the VCR technology).

[johnmeyer]

Once again - mechanics of VCR is important but only to some point - beyond this there is gray land where digital domain may deliver better quality than possible in analog domain.

I'm afraid you are off in your thinking. The mechanics (and the electronics) of each VCR design were wildly different and produced significantly different results on the screen. What you get from a cheap VCR cannot be tuned or recovered later with computer processing, no matter how many GPUs, CPUs, or AI you throw at it. I know this not only from my EE training but also from my practical experience. I still own seven working VCRs and five camcorders. Two of those VCRs are really low-end models I bought from "Value America" in the earliest days of the Internet, when online retailers were selling at a loss in order to get clicks and customers so they could get a big valuation and go public. I think I paid $49 for one of these VCRs.

When I put a tape in the cheap VCR I get a nice stable picture, but because of the cheap head, tolerances, and minimal circuitry, there is very little detail in what shows up on screen.

What isn't there cannot be later replaced.

[pandy]

Once again - mechanics of VCR is important but only to some point - beyond this there is gray land where digital domain may deliver better quality than possible in analog domain.

I'm afraid you are off in your thinking. The mechanics (and the electronics) of each VCR design were wildly different and produced significantly different results on the screen. What you get from a cheap VCR cannot be tuned or recovered later with computer processing, no matter how many GPUs, CPUs, or AI you throw at it. I know this not only from my EE training but also from my practical experience. I still own seven working VCRs and five camcorders. Two of those VCRs are really low-end models I bought from "Value America" in the earliest days of the Internet, when online retailers were selling at a loss in order to get clicks and customers so they could get a big valuation and go public. I think I paid $49 for one of these VCRs.

When I put a tape in the cheap VCR I get a nice stable picture, but because of the cheap head, tolerances, and minimal circuitry, there is very little detail in what shows up on screen.

What isn't there cannot be later replaced.

Sorry but this is exactly same what you can read/hear in audiophile world - VHS (and other systems to store video signal on magnetic tapes) using set of rules so from mechanical perspective some standardization is mandatory to provide interoperability between units and also vital part of commercial video tapes market.

Video signal is stored on magnetic tape not directly but as FM modulated signal - there is few reasons behind choosing FM - one of the most important is immunity to amplitude fluctuations - in fact FM demodulator to remove amplitude modulation pass signal to some form of comparer - limiter where AM is removed and later FM demodulated can be performed as such FM signal stored on tape carry complete video signal information - this is what heads and amplifier do in VCR - this is "RF" signal for demodulation.

I agree about remaining circuitry - it may be better (more complex) in expensive VCR's but it is no longer used by software FM processing so irrelevant form overall picture.

So your point may be valid but not for extracting FM signal from tape (to be later processed in software).

[johnmeyer]

My first job was at Hewlett-Packard in their microwave test equipment division. It was there where I learned all about modulation, including AM, FM, PM, PSK, etc.

Proper mechanics and circuitry are essential to recovering usable information from an analog FM-encoded signal, regardless of what information is in that signal. FM is, quite literally, an infinitely more difficult modulation scheme than AM. I say "literally" and "infinitely" because frequency modulation produces an infinite number of sidebands which extend from zero to infinity. By contrast, AM produces only a single set of sidebands for each frequency. Therefore, with FM, different circuits will produce a different level of fidelity, depending on their bandwidth, phase shift with frequency, etc.

As one example, there are all sorts of phase issues which can completely screw up what you recover when you demodulate. Almost everyone reading this has experienced this with FM radio where, when the phase gets screwed up, the 19 kHz pilot signal that is used to recover the 38 kHZ L-R subcarrier doesn't track and you get all sorts of static and hiss. This can be fixed by turning off the stereo and only listening to the L+R mono that is in the original audio below 19 kHz. It will usually be free from static and noise.

While the artifacts and problems in video are different from the problems with commercial FM radio, some of the same ideas apply.

I just did a quick search on "VHS Decode" and "VHS RF Capture," and while the project is really interesting, and reminds me a lot of discussions back in the 1990s about how video was stored on laserdisc (I still have my player and library of 100+ LDs). Having now watched the results of those captures, I am not tempted to explore this method any further.

I think the fascination with this technique is being propelled by a certain amount of folklore mysticism about capturing the "original" signal before it gets processed by all that outdated analog signal processing circuitry, an idea that forgets that the "original" signal is also the result of analog signal processing circuitry.

I also think there is a certain digital mentality that has crept into peoples' thinking where they believe there is some sort of original bedrock of the original "bits" (even though the RF capture is an analog signal), and if you can get to those, you can get perfect fidelity.

That's just not the way analog works.

[dellsam34]

Both of you are kind of right, It is actually model dependent and the era the VCR was made.

For instance JVC has standardized the VCR manufacturing in late 90's with the introduction of 19 micron dual azimuth video heads, so they were putting mechanisms and heads that were interchangeable for both VHS and S-VHS, low and high end alike, The differences were just in electronics and signal processing and maybe minor hardware differences not related to playback such as a flying erase head.

The era the VCR was made is important as well, For instance a late model Funai from 2010's can outperform a top loading VCR from early 80's, it has nothing to do with the price of the VCR but rather the advancement of technology of mechanical assemblies, better motors, better motor control, direct drive vs belts ...etc. Manufacturing also improved by using modern technology and robots vs slow human labor which lowered the cost of parts and VCRs.

So building a new capturing workflow will still face the same challenges regardless if it's hardware based or software based, The common threat is the dwindling supply of cassette players, the parts and qualified technicians to maintain them, and the degrading tapes that need recovery.

[pandy]

My first job was at Hewlett-Packard in their microwave test equipment division. It was there where I learned all about modulation, including AM, FM, PM, PSK, etc.

Proper mechanics and circuitry are essential to recovering usable information from an analog FM-encoded signal, regardless of what information is in that signal. FM is, quite literally, an infinitely more difficult modulation scheme than AM. I say "literally" and "infinitely" because frequency modulation produces an infinite number of sidebands which extend from zero to infinity. By contrast, AM produces only a single set of sidebands for each frequency. Therefore, with FM, different circuits will produce a differently level of fidelity, depending on their bandwidth, phase shift with frequency, etc.

As one example, there are all sorts of phase issues which can completely screw up what you recover when you demodulate. Almost everyone reading this has experienced this with FM radio where, when the phase gets screwed up, the 19 kHz pilot signal that is used to recover the 38 kHZ L-R subcarrier doesn't track and you get all sorts of static and hiss. This can be fixed by turning off the stereo and only listening to the L+R mono that is in the original audio below 19 kHz. It will usually be free from static and noise.

While the artifacts and problems in video are different from the problems with commercial FM radio, some of the same ideas apply.

I just did a quick search on "VHS Decode" and "VHS RF Capture," and while the project is really interesting, and reminds me a lot of discussions back in the 1990s about how video was stored on laserdisc (I still have my player and library of 100+ LDs). Having now watched the results of those captures, I am not tempted to explore this method any further.

I think the fascination with this technique is being propelled by a certain amount of folklore mysticism about capturing the "original" signal before it gets processed by all that outdated analog signal processing circuitry, an idea that forgets that the "original" signal is also the result of analog signal processing circuitry.

I also think there is a certain digital mentality that has crept into peoples' thinking where they believe there is some sort of original bedrock of the original "bits" (even though the RF capture is an analog signal), and if you can get to those, you can get perfect fidelity.

That's just not the way analog works.

Ok, as you has technical background then first - i use AM as distortion for FM modulation (AM parasite modulation) in reception path you has one of first blocks - limiter so FM is not affected by parasite AM modulation. Bessel function is also fair point but tape and VCR design introduce unavoidable limitation so digital and analog domain face same issue related to VCR limitations.

But ok - everything you wrote is correct but there is one remark - technology progress - hope you are aware of concept of SDR - next step - typical consumer equipment such as TV/cable box reception nowadays made so called Full Band Capture ( https://broadbandlibrary.com/full-band-capture-revisited/ ) where fast ADC acquire at once spectrum from few MHz to single GHz and demodulation is performed by DSP - this common consumer technology present in home since few years at least:
https://investors.maxlinear.com/press-releases/detail/128/maxlinear-debuts-mxl582-sate...-with-extended
https://www.maxlinear.com/news/press-releases/2015/maxlinear-launches-low-power%2c-ful...pectrum-captur
In technology there is fundamental change - paradigm shift - you have fast ADC offering SFDR around 70..90dB (12..16 bits) and 1..2GHz bandwidth.
Decoding VHS is trivial in terms of technology when compared to FBC.
FM Radio reception also changed - nowadays you can build worldwide radio receiver (various modulation and ranges with frequency up to 108+MHz) - check Si4732/4735 - single 16 pin IC all demodulation made by DSP... https://www.digikey.com/en/htmldatasheets/production/713403/0/0/1/si4735-c40-gur

So VHS decode in software is nothing special - nowadays it seems quite obvious.

[johnmeyer]

... hope you are aware of concept of SDR

Yes, but not until recently. After I found out about them, I did some research and am still planning on getting either one of these cheap SDRs, but only when I think I'll have time to do something with them:

Nooelec RTL-SDR v5

or

V3 R860 RTL2832U 1PPM TCXO SMA Software Defined Radio (Dongle Only)

My son-in-law got interested and purchased some antennas, radios, and several of these SDRs. I played around with them. They are absolutely fascinating, but having been around two-way radios for a long time (this is me in 1976 with a transceiver test system I created at HP with one other engineer)


[Attachment 87074 - Click to enlarge]

I found the SDR performance to be significantly inferior to a "real" radio. The flexibility is amazing, but the quality is not. This seems to match what I have seen in the VHS Capture videos posted on YouTube.

[lordsmurf]

Once again - mechanics of VCR is important but only to some point - beyond this there is gray land where digital domain may deliver better quality than possible in analog domain.

I'm afraid you are off in your thinking. The mechanics (and the electronics) of each VCR design were wildly different and produced significantly different results on the screen. What you get from a cheap VCR cannot be tuned or recovered later with computer processing, no matter how many GPUs, CPUs, or AI you throw at it. I know this not only from my EE training but also from my practical experience. I still own seven working VCRs and five camcorders. Two of those VCRs are really low-end models I bought from "Value America" in the earliest days of the Internet, when online retailers were selling at a loss in order to get clicks and customers so they could get a big valuation and go public. I think I paid $49 for one of these VCRs.
When I put a tape in the cheap VCR I get a nice stable picture, but because of the cheap head, tolerances, and minimal circuitry, there is very little detail in what shows up on screen.
What isn't there cannot be later replaced.

^ This.

Sorry but this is exactly same what you can read/hear in audiophile world

No. Those people are nuts. We're talking basic video science here, not audio pseudo-science.

Video signal is stored on magnetic tape

Recording varies as wildly as playback. The standard is really quite loosy-goosey, which is how/why we all run into problems.

I agree about remaining circuitry - it may be better (more complex) in expensive VCR's but it is no longer used by software FM processing so irrelevant form overall picture.
So your point may be valid but not for extracting FM signal from tape (to be later processed in software).

The entire internals matter, not just heads.

My first job was at Hewlett-Packard in their microwave test equipment division. It was there where I learned all about modulation, including AM, FM, PM, PSK, etc.

Proper mechanics and circuitry are essential to recovering usable information from an analog FM-encoded signal, regardless of what information is in that signal. FM is, quite literally, an infinitely more difficult modulation scheme than AM. I say "literally" and "infinitely" because frequency modulation produces an infinite number of sidebands which extend from zero to infinity. By contrast, AM produces only a single set of sidebands for each frequency. Therefore, with FM, different circuits will produce a differently level of fidelity, depending on their bandwidth, phase shift with frequency, etc.

As one example, there are all sorts of phase issues which can completely screw up what you recover when you demodulate. Almost everyone reading this has experienced this with FM radio where, when the phase gets screwed up, the 19 kHz pilot signal that is used to recover the 38 kHZ L-R subcarrier doesn't track and you get all sorts of static and hiss. This can be fixed by turning off the stereo and only listening to the L+R mono that is in the original audio below 19 kHz. It will usually be free from static and noise.

While the artifacts and problems in video are different from the problems with commercial FM radio, some of the same ideas apply.

I just did a quick search on "VHS Decode" and "VHS RF Capture," and while the project is really interesting, and reminds me a lot of discussions back in the 1990s about how video was stored on laserdisc (I still have my player and library of 100+ LDs). Having now watched the results of those captures, I am not tempted to explore this method any further.

I think the fascination with this technique is being propelled by a certain amount of folklore mysticism about capturing the "original" signal before it gets processed by all that outdated analog signal processing circuitry, an idea that forgets that the "original" signal is also the result of analog signal processing circuitry.

I also think there is a certain digital mentality that has crept into peoples' thinking where they believe there is some sort of original bedrock of the original "bits" (even though the RF capture is an analog signal), and if you can get to those, you can get perfect fidelity.

That's just not the way analog works.

I humbly bow and salute you for that post.

Sometimes you posts are so richly informative that people should read them twice (or more).

My only point of disagreement would be with Laserdisc RF decoding, which does extract slightly more data, though mostly due to bypassing inferior LD player circuitry. That process is fairly mature now, after 15 years. (If you look at comments made in those early days, the output was rough quality, proof of concept. Just like vhs-decode. But there's also zero guarantees vhs-decode will ever hit maturity. It's not just about time.)

Both of you are kind of right, It is actually model dependent and the era the VCR was made.

For instance JVC has standardized the VCR manufacturing in late 90's with the introduction of 19 micron dual azimuth video heads, so they were putting mechanisms and heads that were interchangeable for both VHS and S-VHS, low and high end alike, The differences were just in electronics and signal processing and maybe minor hardware differences not related to playback such as a flying erase head.

The era the VCR was made is important as well, For instance a late model Funai from 2010's can outperform a top loading VCR from early 80's, it has nothing to do with the price of the VCR but rather the advancement of technology of mechanical assemblies, better motors, better motor control, direct drive vs belts ...etc. Manufacturing also improved by using modern technology and robots vs slow human labor which lowered the cost of parts and VCRs.

So building a new capturing workflow will still face the same challenges regardless if it's hardware based or software based, The common threat is the dwindling supply of cassette players, the parts and qualified technicians to maintain them, and the degrading tapes that need recovery.

^ This.

But I'd disagree about Funai having "advancements". More like "cheap components". I don't find those motors better, just newer. Longer term, I think those motors will fail more than 90s decks. Most 80s decks were pretty bad, on par with Funai in the 00s/10s.

But ok - everything you wrote is correct but there is one remark - technology progress -

That's never a given. Sometimes "progress" regresses. We see that all the time. It often (not always) becomes cheaper, but not necessarily better. I always find that to be a simpleton/naive view of technology.

Technology "advancing" is not a guarantee, just a goal.

The flexibility is amazing, but the quality is not. This seems to match what I have seen in the VHS Capture videos posted on YouTube.

Things like this remind me of emulation. I was into emulators in the early 1990s. For the most part, it was nifty "proof of concept", but that was it. Fast forward 30+ years, and it's overall better. And yet, some issues still have not been fixed. No amount of reverse engineering has yet recreated that piece of hardware.

[mountaincabbage]

Certainly the results on the VHS-Decode page look impressive, has anyone here got decent results themselves?

I think this summer we'll dig into testing that project out again. I spoke with someone on the project and it might be that the processing speed can be significantly improved by adding GPU support, which is something we could possibly help with.

[pandy]

... hope you are aware of concept of SDR

Yes, but not until recently. After I found out about them, I did some research and am still planning on getting either one of these cheap SDRs, but only when I think I'll have time to do something with them:

Nooelec RTL-SDR v5

or

V3 R860 RTL2832U 1PPM TCXO SMA Software Defined Radio (Dongle Only)

This best price/performance SDR on market https://www.analog.com/en/resources/evaluation-hardware-and-software/evaluation-boards...alm-pluto.html - it could be used with VHS decode project if upconverter involved. Also you have powerfull FPGA on board with ARM core on board of FPGA (so you can run Linux on FPGA to control FPGA algorithm so technically you should be able output on USB video).

I found the SDR performance to be significantly inferior to a "real" radio. The flexibility is amazing, but the quality is not. This seems to match what I have seen in the VHS Capture videos posted on YouTube.

This depends on SDR price - those cheap ones are inferior but expensive not - they offer usually SFDR over 100dB and additional analog part digitally controlled so in overall matching analog quality. RTL based dongles are very limited - narrow bandwidth and USB limitations made them very crude SDR - they are able to perform software demodulation of video but quality is inferior.

[pandy]

What isn't there cannot be later replaced.

^ This.

Nope and yes - if you sample signal with sufficient sample rate and sufficient accuracy then you can later do whatever you want - is this really important whether you sample FM baseband signal from VHS heads or PAL after FM demodulation and PAL decoding?

No. Those people are nuts. We're talking basic video science here, not audio pseudo-science.

Are you sure? You probably didn't read carefully enough some discussion where many people with oh and ah discuss in similar to audiophiles way.
For me video signal is signal, audio signal is signal - RF signal is also signal - some rules are universal for all signals and there is many special areas for each signal separately but at some point you going in one or another way - you can process signal badly or properly. Methods can vary, approach can vary but objective goal not.

Btw There is company named Accuphase, their Tuner (T-1000) is considered as one of the best if not the best - this is widely accepted opinion - do you know what kind of FM demodulator was used by Accuphase to convert FM signal into voltageso later it can be stereo decoded?
Or another example - this is more or less agreed in audiophile world - there was (not sure if their still exist) company named Tact - their pure digital amplifier is considered as the most neutral, objective amplifiers in audiophile world (some audiophiles don't like neutrality and objectivity).

There is lot of science there despite some nuts claiming best sound from ruthenium made cables (or graphite ones)

Video signal is stored on magnetic tape

Recording varies as wildly as playback. The standard is really quite loosy-goosey, which is how/why we all run into problems.

Then there is no market for commercial video tape distribution or tape rental but you and i know this is opposite - there can be some differences but in general standard is sufficiently well defined to be widely accepted and applied on market proving compatibility and interoperability.

I agree about remaining circuitry - it may be better (more complex) in expensive VCR's but it is no longer used by software FM processing so irrelevant form overall picture.
So your point may be valid but not for extracting FM signal from tape (to be later processed in software).

The entire internals matter, not just heads.

For demodulation and color decoding yes but if you process baseband FM signal then it is irrelevant.

Drum with heads, servo and head amplifier is something than count - if you replace servo then also servo begin to be irrlevant.
You need transform VCR circuitry in algorithm.

But ok - everything you wrote is correct but there is one remark - technology progress -

That's never a given. Sometimes "progress" regresses. We see that all the time. It often (not always) becomes cheaper, but not necessarily better. I always find that to be a simpleton/naive view of technology.

Technology "advancing" is not a guarantee, just a goal.

I'm also quite old so you can call me conservative one but still i observe how truly amazing progress is in electronics - when i was young fastest ADC offered 200..300MSps and up to 10 bit resolution - nowadays you may have ADC with 16..18 bit accuracy and few GHz sample rate - also cost for such electronics dropped significantly.
We observe constant progress not only in video/audio coding but also signal processing.

The flexibility is amazing, but the quality is not. This seems to match what I have seen in the VHS Capture videos posted on YouTube.

Things like this remind me of emulation. I was into emulators in the early 1990s. For the most part, it was nifty "proof of concept", but that was it. Fast forward 30+ years, and it's overall better. And yet, some issues still have not been fixed. No amount of reverse engineering has yet recreated that piece of hardware.

This is not emulation - this is freedom - you are no longer limited by physical limitation of components - and emulation nowadays is also different - people decaping IC's and mapping real HW into schematics so they can emulate every aspect, even HW design flaws.

[johnmeyer]

Thanks for the ADALM-PLUTO link. I found it on Amazon and have added it to my "wishlist" so I can evaluate it if and when I decide to explore SDR.

[pandy]

Thanks for the ADALM-PLUTO link. I found it on Amazon and have added it to my "wishlist" so I can evaluate it if and when I decide to explore SDR.

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

[Sharc]

Thanks for the ADALM-PLUTO link. I found it on Amazon and have added it to my "wishlist" so I can evaluate it if and when I decide to explore SDR.

John
If you are interested in SDR you might find this site and their products useful:
https://www.sdrplay.com/

Also, I am using the ADALM2000 as digital scope etc. It is quite handy.
https://www.analog.com/en/resources/evaluation-hardware-and-software/evaluation-boards...ml#eb-overview

[dellsam34]

@OP, 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.

[johnmeyer]

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, [edit: oops, Sharc] 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!

[lordsmurf]

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".

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.

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".

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.

Certainly the results on the VHS-Decode page look impressive,

Cherry-picked samples always are.

@OP, 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.

Interesting suggestion, but...

HDMI lossless SD output

... 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.