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Open source VHS: how would you do it?

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Spehro Pefhany
Guest

Mon Aug 15, 2016 4:35 pm   



On Mon, 15 Aug 2016 20:21:26 +1000, the renowned Sylvia Else
<sylvia_at_not.at.this.address> wrote:

Quote:
On 14/08/2016 9:40 PM, Aleksandar Kuktin wrote:
As a budding member of the Obsolete Interfaces Mafia, I'm always on the
lookout for ways to implement things no-one is using anymore.

Some time ago, I found a video on YouTube of someone driving around
Tokyo. The video has a vague VHS-like feel to it, and since I watched it
many times (I like modern architecture), I got a crazy idea of maybe
implementing a tape storage device. Open source, because if more people
(around me) use it, then my life would be better, since I would be able
to share.


The recorders used precision machined heads. Few would have the required
skill.

Sylvia.


The signal was transferred through a rotary signal transformer as
well.

Finding an old VHS recorder and rehabilitating it would be a couple of
orders magnitude easier than making one.

--sp


--
Best regards,
Spehro Pefhany
Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8

Tim Williams
Guest

Mon Aug 15, 2016 5:14 pm   



<tabbypurr_at_gmail.com> wrote in message
news:4bb7a3b3-10a2-47d5-8a52-c34596826556_at_googlegroups.com...
Quote:
On Monday, 15 August 2016 10:34:34 UTC+1, Tim Williams wrote:

Conventional analog grooves are probably not the way to go. Maybe a
dot-matrix impact tool would be better. It'd be fine for plain digital
(e.g. CD-ROM) encoding.

painfully slow.


Well, yeah. But you snipped the part about it being archival quality
daydreaming, and the part about wondering how fast something can go.

I would wager that conventional dot-matrix heads are /not/ at the absolute
speed limit for a magnetomechanical component. Your out-of-hand rejection
is neither useful nor justified...

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com

Don Y
Guest

Mon Aug 15, 2016 9:21 pm   



On 8/15/2016 2:34 AM, Tim Williams wrote:
Quote:
"Don Y" <blockedofcourse_at_foo.invalid> wrote in message
news:noqbd6$l7b$1_at_dont-email.me...
The folks interested in (REALLY) long term data storage think in terms
of nickel and tungsten disks (for thousands to billions of years,
respectively).

Hmm, curious...

I wonder if one could make an archival record-RW, with inert atmosphere, plasma
torch and cutting lathe. Torch the track to erase it flat, then cut a new
one. Has to be plasma to be precise enough (or laser or e-beam, but come on,
now..), so as not to obliterate multiple tracks at a pass.


I think part of the criteria behind the mentality these folks have is
that you can't rely on any *technology* to read/write the medium.
Those devices (and the *instantiations* of the "algorithms" to operate
them) are just as tenuous as the non-robust storage technologies.

Instead, they rely on your *eyes* to decode the information -- a magnifying
glass.

When you think about it, that's how all of our oldest "recordings" have
survived. Papyrus, hieroglyphs, etc.

Quote:
It would be nice to recast the groove rather than cut it, but I don't see an
immediately obvious way for that to be effective. It's not like nickel is wax
that can be smooshed into with a hot needle (and not like that gives good high
frequency response anyway). Cutting of course necessitates limited erasures,
or added material to replace it (which would make erasure a full-disk
flame-spray process, or something like that).

Conventional analog grooves are probably not the way to go. Maybe a dot-matrix
impact tool would be better. It'd be fine for plain digital (e.g. CD-ROM)
encoding. You could make something like a dot-matrix centerpunch. I wonder
how fast the head can actually write, without getting crazy hot (so basically,
if it's magnetic, it'll have to be in the <2T field range, so steel pole pieces
are reasonable and copper wire doesn't completely melt away).

Interesting unit conversion: a 1T field works out to about 4atm pressure, so a
magnetic solenoid is comparable to a pneumatic one in force-to-size ratio.

Tim



Guest

Mon Aug 15, 2016 10:35 pm   



Quote:
"Finding an old VHS recorder and rehabilitating it would be a couple >of
orders magnitude easier than making one. "


Still not very practical. There are probably a few high end five motor decks out there that do not use belts that actually still work.

But the main reason disks took over is that there is no physical contact and therefore no wear. Every time you play a tape it gets worn out and so do the heads. With CDs, every time you play a burned one the LASER does actually degrade the signal just a little bit, but not stamped CDs. However, the plastic does degrade over time. When it is not transparent enough for that LASER to focus it is over.

Anyway, tape is another concern. I wonder if anyone is making any more. I got a nice big reel of Ampex R2R tape just opened last year and the oxide comes off it so fast that it is unusable. With a helical scan system, you beat on the tape much more.

As much as I would like to have a reel to reel because I like the looks of it and the sound quality is extremely good, and I could get one off my buddy, a really nice four track Teac, tape is so ridiculously expensive it just ain't worth it in light of the fact I got DVD burners in my computers.

Somewhere in DC they have the original Constitution in a thing filled with pure nitrogen. It has lasted a while but one day it will also be gone. (along with the shit stains from them wiping their ass with it) Nothing lasts forever. They got those new DVDs supposed to last billions of years, but who is going to be around to complain if they don't ?

Lasse Langwadt Christense
Guest

Mon Aug 15, 2016 10:59 pm   



Den mandag den 15. august 2016 kl. 22.35.33 UTC+2 skrev jurb...@gmail.com:
Quote:
"Finding an old VHS recorder and rehabilitating it would be a couple >of
orders magnitude easier than making one. "

Still not very practical. There are probably a few high end five motor decks out there that do not use belts that actually still work.

But the main reason disks took over is that there is no physical contact and therefore no wear. Every time you play a tape it gets worn out and so do the heads. With CDs, every time you play a burned one the LASER does actually degrade the signal just a little bit, but not stamped CDs. However, the plastic does degrade over time. When it is not transparent enough for that LASER to focus it is over.

Anyway, tape is another concern. I wonder if anyone is making any more. I got a nice big reel of Ampex R2R tape just opened last year and the oxide comes off it so fast that it is unusable. With a helical scan system, you beat on the tape much more.

As much as I would like to have a reel to reel because I like the looks of it and the sound quality is extremely good, and I could get one off my buddy, a really nice four track Teac, tape is so ridiculously expensive it just ain't worth it in light of the fact I got DVD burners in my computers.

Somewhere in DC they have the original Constitution in a thing filled with pure nitrogen. It has lasted a while but one day it will also be gone. (along with the shit stains from them wiping their ass with it) Nothing lasts forever. They got those new DVDs supposed to last billions of years, but who is going to be around to complain if they don't ?



another future problem will finding equipment that can actually play those
DVDs or what ever it will be, the myriad of different codecs and even worse
DRM could make that a nightmare

years ago I saw an article on how the national TV station was still working on transferring old tapes to modern media, there was one semiretired guy that knew how to run the tape machine and there was only two still existing one of them used for spares


-Lasse

whit3rd
Guest

Tue Aug 16, 2016 6:23 am   



On Sunday, August 14, 2016 at 4:40:43 AM UTC-7, Aleksandar Kuktin wrote:
Quote:
As a budding member of the Obsolete Interfaces Mafia, I'm always on the
lookout for ways to implement things no-one is using anymore.

I've read a bit about VHS and I'm aware of its basic design, but I'm
short on knowledge about all the various implementation problems you
encounter with it.

How would seasoned veterans attack such a problem?


The tensioning, tilting of the drum, correction of azimuth due to tape variation,
and such, are relatively hard to do. So is the manufacture of read heads for
close contact with the tape. Two for stereo, two for video, one for control,
not sure about VHS HiFi.

So, I'd leave those technologies out. The VHS scheme didn't have any frame memory,
it had to operate real-time; we don't. So, I'd scan to a buffer, repeatedly, then analyze.

A T120 tape holds 247 meters, half a minute or so of video per meter.
Hold the tape against a transparent medium that exhibits Faraday rotation, use polarized
light to scan it (lasers, maybe galvanometers, image sensors, the whole works) to read
the magnetic field. Patch together scan data and read out the audio tracks, the video
tracks, and the 'control signal' tachometer track. VHS HiFi will take some extra work, though.


Guest

Tue Aug 16, 2016 11:01 am   



On Monday, 15 August 2016 21:35:33 UTC+1, jurb...@gmail.com wrote:

Quote:
"Finding an old VHS recorder and rehabilitating it would be a couple >of
orders magnitude easier than making one. "

Still not very practical. There are probably a few high end five motor decks out there that do not use belts that actually still work.


belt drive decks should be workable. For smaller belts you can use stationery rubber bands, so it's not costly to re-belt.


> Anyway, tape is another concern. I wonder if anyone is making any more. I got a nice big reel of Ampex R2R tape just opened last year and the oxide comes off it so fast that it is unusable.

Fit a wiping pad to keep loose oxide off the heads & record the data to something else.

> With a helical scan system, you beat on the tape much more.

IIRC the read head on vhs/beta didn't touch the tape, it flew above the surface. The tapes seemed to take it no problem, even years after VHS was obsolete.

Quote:
As much as I would like to have a reel to reel because I like the looks of it and the sound quality is extremely good, and I could get one off my buddy, a really nice four track Teac, tape is so ridiculously expensive it just ain't worth it in light of the fact I got DVD burners in my computers.

Somewhere in DC they have the original Constitution in a thing filled with pure nitrogen. It has lasted a while but one day it will also be gone. (along with the shit stains from them wiping their ass with it) Nothing lasts forever. They got those new DVDs supposed to last billions of years, but who is going to be around to complain if they don't ?


that might be what makes them last a billion years :)

For archival a real key is simplicity of data extraction. Extracting data from a 78 is easy without any original equipment. Doing the same with bluray once the bluray players are all gone will likely be prohibitive. Time, lack of killed personnal & thus cost will prevent it being done.


NT


Guest

Tue Aug 16, 2016 9:32 pm   



Quote:
"The tensioning, tilting of the drum, correction of azimuth due to >tape variation,
and such, are relatively hard to do. So is the manufacture of read >heads for
close contact with the tape. Two for stereo, two for video, one for >control,
not sure about VHS HiFi"


It's a damn mess is what it is. Better quality is achieved with four video heads, the ones for SP being wider then the ones for EP. The video carrier is about 4.2 MHz and the chroma is about 629 KHz. The chroma also goes through a phase rotation to reduce crosstalk between the tracks. They used four phases and a COMB filter to reject the unwanted signal, as it does bleed being a lower frequency.

There is a difference between a discrete six head hifi and a DA hifi, and they will not track each other right. The audio and video will not peak at the same point on the tracking control because the DA heads (later models) do not have an offset between SP and EP speeds, and the hifi heads are something like 30 degrees away.

The hifi signal is depth multiplexed by using a larger gap head. It records deeper into the oxide and because of the larger gap is not picking up the higher video carrier. I remember that the azimuth of the two normally operating video heads is offset to reduce crosstalk, I think 7 degrees (?) but I don't remember about the hifi heads.

The whole damn thing was a mess, and hifi noticeably degraded the video quality. Bets hifi not so much because with their bigger head drum they had bandwidth to spare and didn't even require separate hifi heads. I had a few and the performance was noticeably better, even on old TVs. However most betas were an incredible bitch to align.

Between all these problems, as well as drum wear which screws with the alignment in ways that cannot be completely fixed, my recommendation about video tape is just get it running and rip it to your PC or DVD burner. Then put it away and don't wear it out anymore in case you lose the disks or your harddrive fails.

Even belts are ridiculous now. A belt kit used to be like five bucks, try ten times that now and that was last year FOR A CASSETTE DECK !


Guest

Thu Aug 18, 2016 12:34 am   



On Tuesday, 16 August 2016 20:33:01 UTC+1, jurb...@gmail.com wrote:
Quote:
"The tensioning, tilting of the drum, correction of azimuth due to >tape variation,
and such, are relatively hard to do. So is the manufacture of read >heads for
close contact with the tape. Two for stereo, two for video, one for >control,
not sure about VHS HiFi"

It's a damn mess is what it is. Better quality is achieved with four video heads, the ones for SP being wider then the ones for EP. The video carrier is about 4.2 MHz and the chroma is about 629 KHz. The chroma also goes through a phase rotation to reduce crosstalk between the tracks. They used four phases and a COMB filter to reject the unwanted signal, as it does bleed being a lower frequency.

There is a difference between a discrete six head hifi and a DA hifi, and they will not track each other right. The audio and video will not peak at the same point on the tracking control because the DA heads (later models) do not have an offset between SP and EP speeds, and the hifi heads are something like 30 degrees away.

The hifi signal is depth multiplexed by using a larger gap head. It records deeper into the oxide and because of the larger gap is not picking up the higher video carrier. I remember that the azimuth of the two normally operating video heads is offset to reduce crosstalk, I think 7 degrees (?) but I don't remember about the hifi heads.

The whole damn thing was a mess, and hifi noticeably degraded the video quality. Bets hifi not so much because with their bigger head drum they had bandwidth to spare and didn't even require separate hifi heads. I had a few and the performance was noticeably better, even on old TVs. However most betas were an incredible bitch to align.

Between all these problems, as well as drum wear which screws with the alignment in ways that cannot be completely fixed, my recommendation about video tape is just get it running and rip it to your PC or DVD burner. Then put it away and don't wear it out anymore in case you lose the disks or your harddrive fails.

Even belts are ridiculous now. A belt kit used to be like five bucks, try ten times that now and that was last year FOR A CASSETTE DECK !


Cassette decks can usually be done with regular stationery rubber bands. Some types last well, some don't. But you get 99 free spares in the pack.


NT


Guest

Thu Aug 18, 2016 1:33 am   



I wouldn't. At least not for money. Things that don't last are bad news, and some them the disassembly to change the belts is no trivial matter.

I tell people "No, I don't want to do it right, I just don't want to do it again". Like if I paint something for you, there is only a warranty if I pick the paint. That would be Benjamin Moore. That is in the best class off paints. Down a shelf is like Sherwin Williams and the high end Sears that everyone thinks is so great but it isn't. At the bottom we got like Glidden and Walmart brand, though I have not used it I assume it is the cheap stuff. However, Walmart has surprised me with good quality on occasion. But I mean like the paint that was six bucks a gallon at Kmart. Part of the reason good paint costs ten times that is it has more titanium dioxide in it. Cheap paint cannot match the look of it, plus it is durable. You prep a wall right and but Benny Moore Aquaglow (IIRC) on it, after it dries for a week you can literally scrub it with steel wool ad it ain't coming off.

Also when doing wiring. Yeah, one time I bought a box of elcheapo light switches. Brand new, and by the time the drywall was up I had to replace three of them. When I got the call, the contractor (I worked for him this time but he has worked for me as well) sounded like he thought it was my fault. Well I showed him, bad switch, no continuity when turned on. From now on it's Leviton. And I won't replace any Federal Pacific. The box gets torn out and replaced either with Square D QO or GE if the customer wants it a bit cheaper. But Square D QO series is seriously top of the lie, in fact I think better than Seimens which is pretty damn good.

Now the nature of a DC coupled audio amp makes it possible for bad outputs to blow other parts. What do you think I am going to do ? I really don't want to have to do it again.

If you are over like 50 years old, put the good belts in the tape deck and it is likely you will never have to change them again. With rubber bands then gotta get the thing apart and not lose any screws or little gears and whatnot, not break any of the brittle plastic parts in the process, and unless you screw thepro way you wear out the holes.

By that I mean when you stick the screw in the hole you turn it backwards until it drops. That means it goes into the threads already there rather than making new ones. In plastic, you only get so many chances it you do that. In fact things are so flimsy now I no longer use an electric screwdriver or drill, at least during reassembly.


Guest

Thu Aug 18, 2016 1:37 am   



Oh, and that won't work for the capstan belt. It is supposed to flat. Using a rubber band the speed will be off and you'll have so much wow and flutter that it might make you dizzy.


Guest

Thu Aug 18, 2016 2:54 pm   



On Thursday, 18 August 2016 00:33:35 UTC+1, jurb...@gmail.com wrote:
> I wouldn't. At least not for money.

No-one would for money. So what. If you're fixing your own it's normally fine, like I said.

> Things that don't last are bad news, and some them the disassembly to change the belts is no trivial matter.

not usually.

I cba discussing the rest. Everyone knows the options.


NT


Guest

Thu Aug 18, 2016 2:55 pm   



On Thursday, 18 August 2016 00:37:12 UTC+1, jurb...@gmail.com wrote:
> Oh, and that won't work for the capstan belt. It is supposed to flat. Using a rubber band the speed will be off and you'll have so much wow and flutter that it might make you dizzy.

complete cobblers


NT

Aleksandar Kuktin
Guest

Sat Aug 27, 2016 3:59 pm   



On Sun, 14 Aug 2016 11:40:37 +0000, Aleksandar Kuktin wrote:

On Sun, 14 Aug 2016 11:40:37 +0000, Aleksandar Kuktin wrote:

Quote:
How would seasoned veterans attack such a problem? The problem being VHS
in particular and tape storage in general. Where to begin, especially if
you assume you have a blank slate and blue skies


I've been reading more and getting to understand the technology and what
it can accomplish. As several people have mentioned, it's probably not
worth trying to build the tape assembly, especially anything related to
helical scanning. Some success may be had using stationary heads, with a
scheme similar to compact cassettes, but I doubt one can put enough data
onto those things to make it worthwhile.

I made a rough approximation about the amount of raw data that could be
put to a VHS tape. I'm basing my calculations on System M (for reasons
that will become apparent in a moment), but giving it a lot of slack.
Assuming 400 scanlines, with 400 fields per scanline, 25 frames per second
and 8 bits per field ("pixel") gives us a bitrate of 32 Mbps. A 2.5 hour
tape can then be estimated to hold 33 GB of data. Such a tape would be
labeled "DF300", giving an easy approximation of the data you can put on
it. Same goes for DF360, DF420 and so on.

Is the estimate valid? D-VHS, the digital variant, puts 31.7 GB onto a
DF300, 44 GB onto DF-420 and so on. In addition, comparisons to other
formats (LTO, DDS) all feature the same rough numbers and the same rough
timeframe (2000-2004). Therefore, I'd say the estimate is roughly valid.
In fact, the estimate may even be underestimating the amount of data. I
distinctly remember VHS having more than 256 colors, which means it
encodes more than 8 bits of data per "pixel", but the big question is
encoding and ECC. A few lines going wrong on a video don't mean much, but
if every 400th block of data comes out of the tape drive bad, that's a big
problem.

With that out of the way, the next big problem is usability and viability.
So I asked myself how well does a hypothetical tape system compare to
other external storage systems.

A big part of this is the cost of the medium. Where I am (Serbia), I can
get the tapes for prices that range from $5/GB to $12/GB, depending on
the deal offered. The competition, like external USB HDDs and thumb
drives are really stiff. You can get them at about $8/GB, and they pack a
theoretical transfer rate of 400Mbps with random access. That's hard to
beat. On the other hand, CDs and DVDs go for about $1/GB (and random
access) which is pretty much impossible to beat. I would basically need
to pack 8 times more per length of tape to get those kinds of prices,
which is a steep order. It's basically a three-generational improvement
over the "base case". If this were a commercial project, it would be dead
at this stage (but only buried after the next few paragraphs).

Fortunately, this is a "let's do something" project, so the insane price
competition by the optical storage is not a real issue.

I spent time researching the actual mechanism of storing and retrieving
data on magnetic media. I knew the basic principle involved, but not the
actual specifics. It seems ultra-precise electromagnetic assemblies are
used. I wasn't aware of the dimensions involved, but not that I am, hand
making these things is simply out of the question. If I had a precise
robot, it could make it for me, but I don't. Interestingly, it seems that
when reading, these heads rely on the movement of the magnetic medium to
induce the current (and voltage) in them that gets sensed. This poses a
whole new set of problems, because not only would I need to precisely
control the electronic component of the device, but I would also need to
worry about the mechanical component. In a linear scan device (like LTO
or compact cassettes), this can even be "faked" while relying on generous
tolerances, but a helical scan device may be too complicated.

All in all, if using a helical scan, the best option is probably finding
a device with working mechanical components and changing the electronics.

There is also an interesting business aspect of using ever-shrinking
magnetic heads, in that at some point they become critical components.
While not all of my numbers align, it seems the storage capacity of a
tape depends solely on the physical size of the "signal" on the tape,
which in turn depends on the size of the magnetic head. Depending on how
the business is organized (are you producing your own heads or not), your
profit margin could become hostage to the suppliers good will. Again, if
this were a commercial project, this is the point at which it would be
buried.

As for the rest, I saw an ad for an old VHS for 10 euros. The seller
guaranties the device turns on, but says he does not have a TV and can
not check if the device actually works. Smile It's just a question of
whether I want to do it or not.

If I actually do make something usable, I'll post some kind of a guide
here. But it won't be a fast project.

rickman
Guest

Sat Aug 27, 2016 8:20 pm   



On 8/15/2016 11:21 AM, Don Y wrote:
Quote:
On 8/15/2016 2:34 AM, Tim Williams wrote:
"Don Y" <blockedofcourse_at_foo.invalid> wrote in message
news:noqbd6$l7b$1_at_dont-email.me...
The folks interested in (REALLY) long term data storage think in terms
of nickel and tungsten disks (for thousands to billions of years,
respectively).

Hmm, curious...

I wonder if one could make an archival record-RW, with inert
atmosphere, plasma
torch and cutting lathe. Torch the track to erase it flat, then cut a
new
one. Has to be plasma to be precise enough (or laser or e-beam, but
come on,
now..), so as not to obliterate multiple tracks at a pass.

I think part of the criteria behind the mentality these folks have is
that you can't rely on any *technology* to read/write the medium.
Those devices (and the *instantiations* of the "algorithms" to operate
them) are just as tenuous as the non-robust storage technologies.

Instead, they rely on your *eyes* to decode the information -- a magnifying
glass.

When you think about it, that's how all of our oldest "recordings" have
survived. Papyrus, hieroglyphs, etc.


I think that is mainly because they didn't have batteries to power their
iPhones so they could store the data on the Flash 7000 years ago. They
got tired of hand cranking the generators on the base stations and gave
up on cell phones altogether and just used wooden or clay tablets.

--

Rick C

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