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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 6th Oct 2006, 2:26 pm   #1
oldeurope
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Default FotH TV System / Converters Discussion

Quote:
Originally Posted by m1ecy View Post
Excellent Stuff!

Looks like the PC wins again!

...

Cheers
Sean
Aurora?

Darius
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Old 6th Oct 2006, 2:44 pm   #2
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Default Re: FotH TV System / Converters Discussion

Hi,
Quote:
Originally Posted by oldeurope View Post
Aurora?
Hmm... I'd love one, actually; but as I'm stuck out of work on state benefits the cost of a DVD player, hard disk recorder, two digital TV set-top boxes and an Aurora (what I'd need to do somewhat less, and none of which I have already) is a bit beyond reach.

I'll stick with a pile of free and cheap old PC parts and free software for now. Total outlay for two networked MythTV PVR systems is still less than 100 spread out over several months. Most of that outlay was the two digital TV tuner cards in the master backend machine...

Regards, Kat
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Old 6th Oct 2006, 3:20 pm   #3
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Default Re: FotH TV System / Converters Discussion

Hi again,

I just thought I'd add that making comparisons between the FotH TV System and standards converters is a tricky area - they're just not the same thing.

There's no standards conversion - in the sense of converting analogue video in one standard to analogue video in another standard - happening anywhere in the computer system.

It's not a standards converter

Regards, Kat.
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Old 6th Oct 2006, 7:45 pm   #4
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Default Re: FotH TV System / Converters Discussion

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Originally Posted by Kat Manton View Post
Hi,

... the cost of a DVD player, hard disk recorder, two digital TV set-top boxes and an Aurora (what I'd need to do somewhat less, and none of which I have already) is a bit beyond reach.

Regards, Kat
Actually the PC can be used as the source for a conveter still retaining any of it's existing functionality, so a seperate DVD, DVR or tuner are not required. I even use my video iPod as a source! Now that's quite a sight with an iPod feeding a 1930's television

Darryl

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Old 7th Oct 2006, 7:25 am   #5
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Default Re: FotH TV System / Converters Discussion

Hi,

I've started this new thread and moved the above posts into it in order that a potentially interesting discussion can continue without drifting off-topic in the thread where the discussion started.

Regards, Kat
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Old 7th Oct 2006, 8:20 am   #6
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Default Re: FotH TV System / Converters Discussion

Hi Darryl,
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Originally Posted by tubesrule View Post
Actually the PC can be used as the source for a conveter still retaining any of it's existing functionality, so a seperate DVD, DVR or tuner are not required.
It could, but would seem strange to me to do this when a simple change to the graphics configuration means the computer outputs directly in the standard required.

It'd also increase the amount of processing going on, possibly compromising picture quality.

At present, when using digital sources already within the PC, the images are scaled once then output via the DAC in the chosen standard.

Without building additional hardware and using the TV output on the graphics card together with a converter, the following takes place.
  • Image is scaled to a 'standard' resolution, more often than not 800 x 600 is used.
  • Image is scaled again by the scaler in the TV encoder to a resolution appropriate for 625-line PAL.
  • Image is output via DAC as S-video or composite.
  • Image passes through an ADC in the converter.
  • Image is scaled a third time.
  • Image is output by the DAC in the converter, finally in the chosen TV standard.
So I think it'd be counter-productive to consider setting up such a system.

As I see it, standards converters and the system I've come up with are two very different things. Both achieve a common goal of "getting pictures on vintage television sets" but there the similarities end.

A standards converter, particularly one with a built-in modulator, offers an easy, true "Plug and Play" solution, and there lies one distinct advantage.

To set up the PC system, you've first got to dedicate a whole PC to it; this isn't really a good system to set up on a machine you ordinarily use as a desktop general-purpose machine.

Then you need the right bits inside it. Only nVidia graphics cards have the control over pixel-clock frequency required. You need enough processing power and RAM. Digital sources work best hence for off-air television a digital cable/satellite/terrestrial card is needed, along with a DVD drive.

Then there's the fun and games installing the software; it's fairly straightforward but still needs a certain amount of knowledge to get it all installed and running correctly. For example, it took me weeks before I got the infra-red remote-control to work properly.

There's still a requirement for additional hardware, you're going to have to build an RGB/sync combiner as the TV output can't be utilised. Then you still need to build or buy a modulator appropriate to the TV system you wish to generate.

The easy bit is changing the graphics card configuration so it natively produces a reasonable approximation of the chosen TV standard. That's only easy, though, if I've already worked out the modeline and published it.

And note that it's only a reasonable approximation - due to the limitations of the graphics card it's not possible to generate exactly the chosen standard, to specification. The total line length and horizontal/vertical timings will be very close - as that's my primary aim when working out the modelines. But sync timing won't be quite right, and the waveform will generally be crude compared to most standards.

This will remain true when using crude and simple methods of combining RGB and syncs, improvements can be made at the cost of increasing the complexity of the circuitry needed.

But, my aim is to get pictures on vintage television sets - if the set locks to the signal and you get a picture then the video waveform is "close enough"

An area where the computer system is weak and where a stand-alone standards converter beats it hands-down is true standards conversion. If I feed analogue video into a capture card and try to use the system as a true standards converter the results are not likely to be too good. There's no synchronisation between the capture card and graphics card. Using the MythTV system, the captured video is encoded to MPEG, buffered to hard disk, read from disk, decoded, scaled... It's not going to work too well as a standards converter hence I claim it isn't one; it could be used like this but I wouldn't recommend it.

I've never seen my solution as competition, and as it's such a different approach there's a place for both types of system side-by side.

I have an extensive library of VHS tapes and a decent enough VHS machine; as I'd like to watch these on vintage sets I'm likely to buy an Aurora as soon as my disposable income allows as it's the best option. Anyone else wishing to watch analogue source material on vintage sets would be advised to do the same.

Regards, Kat
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Old 7th Oct 2006, 8:26 am   #7
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Default Re: FotH TV System / Converters Discussion

As a reasonably neutral observer I think that Kat's summary in the last post gets the arguments about right.

Darryl isn't going to stop selling Aurorae anytime soon because of FotH TV. Conversely the availability of the Aurora isn't going to stop ardent experimenters having a go at FotH TV.
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Old 7th Oct 2006, 9:20 am   #8
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Default Re: FotH TV System / Converters Discussion

Exactly the point - Once more work is done on the PC more standards will become available.

I do not know of any standards converters that incorporate a tuner, mpeg decoder, or indeed a dvd player - hence, it is much more than a standards converter in that respect, but as Kat mentions it has limitations that a properly designed converter - Aurora, or Darius does not have

All three systems stand on their own merits - I am far more likely to get away with a converter in the front room!

Cheers
Sean
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Old 7th Oct 2006, 9:40 am   #9
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Default Re: FotH TV System / Converters Discussion

Quote:
Originally Posted by m1ecy View Post
All three systems stand on their own merits - I am far more likely to get away with a converter in the front room!
Indeed they do, and I can well appreciate that most people probably wouldn't want a computer sitting in their lounge, next to the TV or whatever... I mean, we instituted a "no computers in the lounge" rule, several years ago - only problem is, this is a rather geeky household and so the rule has been practically impossible to hold to Well no... totally impossible, if I'm being honest - there are four running machines in here as I write! The main MythTV box, my main PC (which is supposed to be hiding upstairs but is currently home to a heard of lego horses- don't ask!), and two laptops (one mine, the other Herself's)!

Mind you, the MythTV system does have the advantage that you can split the backend and frontend functionality across more than one machine: have the noisy machine with hard-drives and tuner cards and everything hiding away somewhere, and have, say, a fanless mini-itx machine in the lounge as the frontend. Perhaps a way to get the idea past some Significant Others?

But then, I suspect I'm probably one of a rather special group of SOs who are actually not unhappy to have old TV sets in the lounge in the first place... so what do I know?

Regards,

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Old 7th Oct 2006, 10:24 am   #10
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Default Re: FotH TV System / Converters Discussion

Hi,
I only thing wanted to point out that Darryl made the first 819 I know.
So the race, if there was one, who gets first 819 is won by Darryl's Aurora.

At the monent I have trouble to get 625 from my grafic card video out and it
is made for 625. If I want to playback pictures from my computer, I am recording them on CDROM and playback the CDR in my DVD player via converter. So I am far away from getting 819 or 405 from the computer.

I am very impressed that it is possible to make 819/405 etc from a grafic card.

Kind regards,
Darius
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Old 7th Oct 2006, 10:51 am   #11
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Default Re: FotH TV System / Converters Discussion

Don't forget we have also had viable 240 line from the PC, though Daryl has also done that with the Aurora.

Jim.
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Old 7th Oct 2006, 11:08 am   #12
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Default Re: FotH TV System / Converters Discussion

Hi Darius,
Quote:
Originally Posted by oldeurope View Post
I only thing wanted to point out that Darryl made the first 819 I know.
So the race, if there was one, who gets first 819 is won by Darryl's Aurora.
I've never made any claim to be the first to generate any of these standards. But, I've gathered using consumer computer hardware to generate obsolete standards has been something which has been discussed a lot over the years, but has never been done. That's where I come in...

I wasn't actually aware of how long this idea had been around as my interest in vintage television only really began after I'd managed to get 405-line video out of the PC. Now I have three TV sets and a broadcast monitor with 405-line capability along with one 819/625-line set. I doubt I'll stop at that...

I'm also aware that I'm not the first to generate 405-line video with a computer, I'm aware of two people who've reprogrammed the CRTC in a BBC model B computer to generate 405-line video. But that's a long way from being able to watch off-air or recorded television.

But as far as I'm aware I am the first to get good quality off-air or recorded moving pictures on 405-line and 819-line using little more than normal unmodified consumer computer hardware and readily available software. I'll take credit for that, if credit is due. Jim Beacon beat me to 240-line though...

I've proven it can be done and established what seems like a good way to do it. It still needs refining, but it's flexible and more standards will follow.

Quote:
At the monent I have trouble to get 625 from my grafic card video out and it is made for 625
If it involves Windows then I'm afraid I can't really help; I've not managed to get 625-line from a Windows system either, not that I've tried all that hard. I just don't get along with the operating system; it stops me doing what I want with the hardware.

Quote:
I am very impressed that it is possible to make 819/405 etc from a grafic card.
Thanks

What it all comes down to is that the hardware is capable of this; the "trick" is I'm using an operating system which doesn't hide low-level functionality and lets me access the capabilities of the hardware easily.

Regards, Kat
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Old 7th Oct 2006, 2:19 pm   #13
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Default Re: FotH TV System / Converters Discussion

Wow! You guys get a six hour head start, and look at all the fun I miss ;-)

Kat,
Going back several posts, you presented a well thought out description of each of the systems. I would have to agree with most everything you said. Each system has it's strengths and weaknesses. The stand-alone converters can produce accurate, high quality signals since they are hardware based, but this is also what makes them less flexible. While it is possible to make many firmware images, it's hardly practical to have users constanty flashing their units just to make it do something different.

The PC solution can, only becuase of the excellent work you have done since many of us didn't think this was even possible, provide a converted output with a lot of flexibility as to the actual output and features provided. This can be a huge factor when having all this functionality in one place is desirable, or the abilty to grow and change. This has always been the software solutions advantage over the hardware solution. With an FPGA, this converter is sort of a cross betweem the two with the "hardware" dictated by the firmware.

My comment about using the PC as a video source is based on what I do, and what a few others have relayed to me. It's really not that different than using a commercial DVR which is really just a stripped down computer/hard drive anyway, so the quality would be the same, potentially better in the PC since you could go all the way to full uncompressed recording!

You made a comment that you don't consider your system a standards converter because you can not effectively take an analog input and convert it do to the limitations of MythTV's lack of synchronization. I'm not familiar with the inner workings of MythTV, but if you were clever enough to coerce the graphics card into output other standards, I'll bet you could get this to work as well ;-) I know some graphics cards do have hooks for determining the vertical sync position, so perhaps this is something you could look into.

Regardless of the differences, all the efforts by all the people working on, providing feedback, and using conveters of all types has increased the interest in old telly's. The more people that realize they can have an old set, and not just have it be a piece of furniture in the corner of the room, but actually have it working, and transport them back to their youth, more sets will be save from the crusher!

Keep up the good work!!
Darryl

Not to go OT, but keep in mind that almost all video source available today started as analog somewhere along the chain, so even digital terrestrial or sattelite had to go through an A/D process. Unless it was shot in HD (even then the CCD had to go through an A/D), or is CGI, it was telecined from film. Surprisingly most eposidic television today is still shot on Super 16mm film and telecined before editing in an NLE!
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