Baird 240 line Operation

[peter scott]

Hi Jeffrey,

I'm not convinced. Watching my father's 16 mm cine films is very much more acceptable and they run at 16 frames / second if memory serves me correctly. This would be the type of thing the public would use to judge the Baird transmissions.

Peter

[ppppenguin]

Peter, although cine film was shot at low frame rates there's a multiblade shutter in the projector that flashes each frame on the screen 2 or 3 times. So although motion will be (even more) badly aliased the large area flicker will be greatly improved.

A refresh rate (to use modern terminology) of 16fps would be really horrible. Baird used 12.5fps in his 30 line work but that was with a very tny screen. Coming back to modern times, LCD displays have zero order hold, so there's no large area flicker regardless of refresh rate.

[peter scott]

But returning to the question of public acceptability, I suspect that the Baird transmissions would not only have been compared with the 405 line but also with such other home "video" sources as cine film.

Peter

[Murphyv310]

Hi Peter.
In my view the flicker is what killed the system stone dead. Ok we are aware of the static cameras and the the use of film for part of the process, these were factors but it's how the end user enjoys the experience.
I've tried 240 on a few sets that are able to resolve it. The TV22 with the thorn 950 line transformer is very good and bright, the flicker is horrible, even at very low brightness and contrast its the same, my eyes don't like it and I get a headache. The Decca 1000 with the big screen in some ways is worse even though you need to watch it in a dark room, the flicker is all around you and the peripheral vision you have enhances the flicker which is distracting. The 1946 Ekco is possibly the best with its soft tube and ion burn but still unacceptable.

[ppppenguin]

If we'd gone for a system with low refresh rate I'm pretty sure people would have come up with ideas to reduce the problem. Nowadays it's trivial with framestores to flash each frame on the screen 2 or more times. Cinema did it with a multiblade shutter. You can do it with longer persistence phosphors at the expense of motion blur. Perhaps this is more acceptable than motion judder? Perhaps somebody might have come up with a clever phosphor with non-exponential decay characteristics. As it is, I thnk most phosphors have a complex decay that isn't true exponential.

Many things killed the Baird system, not least because it was almost impossible to produce good programmes with it. Without those nobody would watch.

TV took the "live broadcast" route", akin to radio. Paul Marshall has argued that it needn't have gone that way. Baird's backers had massive cinema interests so it could have been a way to deliver movies to the home, a bit like like we now have with Netflix. Baird's telecine was well suited to that.

[peter scott]

Previously in this thread I had been using the crude voltage addition for line and frame syncs. I've now tried using the composite sync generated by the graphics card and the modeline editor. The syncs are still not as per the EMI 405 standard but are an improvement regarding interlace.

Below are images of the modeline editor with the two standards and screen shots taken from the HMV901 with 405 and 240 respectively. I had previously been using the 1680x220 for 240 line 

The 240 image is now using a new modeline of 1200x220 suggested by Jeroni Paul that uses the minimum horizontal resolution available from my graphics card and requires a less extreme aspect ratio adjustment of the source image.

Peter

[peter scott]

It has taken me a bit of time to get the source material aspect ratio corrected for video playing but I've now discovered that you can set user defined playback ratios in VLC Player. There are some standard ratios offered under the "Video" tab but to get user defined you need to run VLC from the command line.

So: In Windows hit Start and type "cmd" without the quotes into the search box then hit return.

In the command window you might see:

C:\Users\User>

At the prompt type "cd .."
to get up one level or type it again to get up to C:>

Then at the prompt type:
"C:\Program Files\VideoLAN\VLC\VLC.exe" --aspect-ratio=14:5

Exactly as above including the quotes. This will start VLC Player and when you select the video it will have the 14:5 aspect ratio needed for 240 line operation.

To display this you will need to download WinModelines from:
http://www.geocities.ws/podernixie/htpc/...ne-en.html

and copy the modelines.
For 405:
Modeline "664x377_25 10.1kHz 50.0Hz" 8.100 664 680 702 800 377 378 395 405 interlace +hsync -vsync

For 240 / 25:
Modeline "1200x220_25 6.0kHz 25.0Hz" 8.020 1200 1217 1291 1336 220 221 233 240 +hsync -vsync

and tick the "Composite" box for VGA2.

and hit "Save Changes" The PC will reboot to incorporate the changes.

Then in Control Panel, Display select the second window select the 1200x220 for 240 line.

The VGA output from your graphics card will need to be connected to your 240 line television via an appropriate modulator (e.g. Aurora with switch 6 selected) and you can now use your PC mouse to slide the VLC player off to the right side of your PC display and into your television display. To fill the screen you need to hit f on your keyboard whilst the mouse pointer is in the VLC window on your television screen. (Esc returns from full screen mode.)

The same procedure can be used for 405 lines but only requires a 20% increase in the aspect ratio width.

Peter

[Murphyv310]

Good result Peter.
Thing is I'm not into all this computer jiggery pokery. I also use Linux mint and using terminal and command lines is even more complex to me than DOS!!!!
Oh well maybe one day.

[peter scott]

Hi Trevor,

You don't actually need to use the command line. What I've done is to create two extra short cuts on my desktop for the VLC player. Just hit Properties on the icon and change the Target.

Instead of the normal link address:"C:\Program Files\VideoLAN\VLC\vlc.exe"

My 405 VLC player address is:"C:\Program Files\VideoLAN\VLC\vlc.exe" --aspect-ratio=8:5

and the 240 line oneis:"C:\Program Files\VideoLAN\VLC\vlc.exe" --aspect-ratio=14:5

Peter

[peter scott]

With a few more suggestions by Jeroni Paul the process of running 405 line or 240 line or what have you lines is now very simple.

Download the Modeline Editor for Windows here:
http://www.geocities.ws/podernixie/htpc/...ne-en.html

Having loaded the Modelines using Jeroni Paul's editor as in the first picture below, you don't need to use the Modeline Editor from now on. If you want to switch line rates then you use your Windows Control Panel, Display, Change Display Settings then select your Number 2 display and select the resolution you require.

If you want display video material the freeware application VLC Player works very well. You do need to make a little change to the pixel aspect ratio and so I have two shortcut icons on my Windows Desktop both pointing to VLC Player.

As normally loaded the Target in the shortcut might read:
"C:\Program Files\VideoLAN\VLC\vlc.exe"

For my 405 line shortcut to VLC Player I changed the Target to read:
"C:\Program Files\VideoLAN\VLC\vlc.exe" --monitor-par=11:14

And for my 240 line VLC Player the Target is:
"C:\Program Files\VideoLAN\VLC\vlc.exe" --monitor-par=11:45

Now if I want to display a DVD on a 405 line receiver I connect my Number 2 VGA port on the PC to my Channel 1 modulator and click on my 405 VLC Player. I select Media, Open Disc.. then in the new window "Play" and the DVD menu comes up in the window. I then drag that window over to the right and off my PC screen and into my TV screen. Then hit f to get full screen then position the cursor over the video to play and hit return.

The Sony 9-90 has next to no dc restoration hence the dreadful picture but it looks better on less contrasty material e.g. Test Card C also displayed from the graphics card + modulator.

Peter