Grand Illusions Baird Televisor

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Grand Illusions Baird Televisor

Postby ljmayes » Wed Jul 17, 2019 8:17 pm

I've come across this:

https://www.grand-illusions.com/televisor-kit-c2x24326293

From Grand Illusions (cost: £43 + p&p).

I wonder if anyone has bought one of these. Anyone know exactly what the signal format is?

Regards,

Lawrence
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Re: Grand Illusions Baird Televisor

Postby Dave Moll » Thu Jul 18, 2019 6:02 pm

The "Grand Illusions" incarnation seems to be new, but a number of us have bought this under its MUTR/Mindsets incarnations. It is not a bad low-cost introduction to mechanical NBTV. It uses the the "club standard" 32-line format recorded on one channel of the stereo signal and mono audio on the other.

One thing to note when using the NBTV signal is that some CD players invert the signal they output. This does not matter for audio applications, but the NBTV waveform does not work with an inverted signal, so would require a second inversion to re-establish the correct form.
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Re: Grand Illusions Baird Televisor

Postby Klaas Robers » Thu Jul 18, 2019 6:12 pm

I bought one years ago and it simply works. However it is amazing how good the video on this website is. This guy should have done quite some clever tricks to eliminate the strong flicker that the picture in real life has.

The format of the video is the NBTVA-format, 32 lines, 12.5 frames per second. If you look on the webstite of the club: http://www.nbtv.org, you will find al details. The video (and the audio) signal fit in the bandwidth of Compact Disc. You get an audio-CD with the "televisor" with the shown phragment and many more. But that "sound" can be found as well in the form of .wav files on the website of the NBTVA. Go to http://www.nbtv.org/kit.htm and you will get more information on the MUTR televisor.

On that page you will find a link to the content of the MUTR-CD. This is a lot of .wav files that you can down load. You will see that the files are there twice, in normal polarity and in inverted polarity. You can even make a CD with as well the program in normal polarity as well as in inverted polarity.
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Re: Grand Illusions Baird Televisor

Postby ljmayes » Thu Jul 18, 2019 8:14 pm

Thanks for the feedback. I was wondering what the line standard was. It's good to know that it conforms to the NBTV club standard.

Regards,

Lawrence
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Re: Grand Illusions Baird Televisor

Postby Andrew Davie » Fri Jul 19, 2019 1:37 am

Given the clip used in the video, I think it's a useful comparison to look at this...


youtu.be/GM1C3cLfelk

Filming a flicker-free image is not actually THAT difficult. I do it with a dirt-cheap Android phone and creative lighting. I've discussed elsewhere on the forum. Interesting to see the clip used, as I am fairly sure this clip was converted by yours truly... quite the surprise to see it used on the MUTR.

Cheers
A
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Re: Grand Illusions Baird Televisor

Postby Klaas Robers » Fri Jul 19, 2019 6:51 am

Yes Andrew, I converted indeed all the MUTR-files from CD-ROM-files into audio-files. When doing so the line frequency was made exactly 400 Hz, I have a kind of time base corrector in software. If the samplefrequency of your CD-player is correct, and most of them are, the video is also correct in timing. Also this film fragment has undergone that procedure. Then also the beginning and the end were made precise. If you record an audio CD from the .wav files in the correct way, disc at once, then you end up with a video + sound CD that is one uninterrupted NBTV stream. Only in the middle, where the switch from upright video to negative video is situated, there is a strange thing happening. For a short time there is positive and negative sync present at the same time.

It was a pleasure to do that. The disc has more TV-phragments that are a pleasure to watch. They all are from the very beginning of TV transmissions, say 1937 in England.
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Re: Grand Illusions Baird Televisor

Postby Klaas Robers » Fri Jul 19, 2019 7:57 pm

When looking again to both recodings I see that the picture quality, sharpness and so on, is visibly better on Andrews. Also in the recording of Grand Illusions the frame sync is 3 or 4 lines out of phase. You see at the left side of the picture 3 or 4 lines that should be at the right side, so you mis there a stroke. I know that the MUTR televisor tends to mis-synchronise for one line, + or -, but I never saw this large amount. I fear that the paper label with sync information (the black squares) was not glued in the right position.

But in Andrews recording there is a slight instability in the synchronisation, the picture is somewhat moving up and down. I know, it is difficult to get that better, my monitor also suffers from that, however this is not visible in the Illusions recording. And I saw in your recording Andrew, some small black dots moving slowly up or down. Any idea where they are generated?

I have the feeling that you recorded picture and sound separatedly and you joined them afterwards again, because I see in the singing no coincidence in sound and picture, especially at the end. As far as I remember, this was not in the original video and sound.
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Re: Grand Illusions Baird Televisor

Postby Andrew Davie » Fri Jul 19, 2019 8:06 pm

Klaas Robers wrote:When looking again to both recodings I see that the picture quality, sharpness and so on, is visibly better on Andrews. Also in the recording of Grand Illusions the frame sync is 3 or 4 lines out of phase. You see at the left side of the picture 3 or 4 lines that should be at the right side, so you mis there a stroke. I know that the MUTR televisor tends to mis-synchronise for one line, + or -, but I never saw this large amount. I fear that the paper label with sync information (the black squares) was not glued in the right position.

But in Andrews recording there is a slight instability in the synchronisation, the picture is somewhat moving up and down. I know, it is difficult to get that better, my monitor also suffers from that, however this is not visible in the Illusions recording. And I saw in your recording Andrew, some small black dots moving slowly up or down. Any idea where they are generated?

I have the feeling that you recorded picture and sound separatedly and you joined them afterwards again, because I see in the singing no coincidence in sound and picture, especially at the end. As far as I remember, this was not in the original video and sound.



This was an in-progress recording as I was building my televisor. It is now rock-solid on the synchronisation. But yes, it does appear to be much sharper and better quality. Also, it's quite possible I had the sound out of synch too in this demo. The small black dots (or, the white band too) are artefacts caused by the frame rate of the phone camera and its synchronisation with the rate of the disc spinning. The frame rate on the camera is auto-adjusting, and I was eyeballing the resultant image and shifting slightly in my whole body in front of a light behind me, thus affecting the total avalable light detected by my camera - and hence the resultant exposure/frame rate it employed when auto-adjusting these things. That's just my screwy way of recording with my phone camera and (mostly) avoiding the black bands. Another way of putting this; the black dots are the very edge of the black bands - just on the threshold of the timing/frame rate where they would be seen. And the white bands are on the other side of things - timing is wrong in the other direction (too slow an exposure on the camera).

I think you are probably right that I recorded picture and sound separately and rejoined. Again, this was just an in-progress build of my televisor and a test image and I never expected to be discussing the hows and wherefores a few years later!!
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Re: Grand Illusions Baird Televisor

Postby Klaas Robers » Sat Jul 20, 2019 7:48 pm

This explained a lot to me. I was already wondering how you forced the camera to have an exposure time of exactly 1 / 12.5 sec. Because that is what you need. And even better, there should be a synchronisation between the video signal and the exposure moments of the camera.

Long ago, in 1972, I made something special to synchronise an Arriflex 16 mm film camera with the CCIR 625 lines video signal. I was lucky that this film camera had an exposure time of 50% and had a DC-motor. So I made a DC-signal strong enough to drive the film transport of the camera and I made a sensor on the rotating mechanical shutter of the camera. Some simple electronics kept the shutter in sync with the V-sync of the video signal. The camera than ran on 25 frames per second, so just one of the two interlacing fields was "taken". Beginning and end of the exposure was kept within the vertical blanking. For 16 mm film this was sufficient, especially because the usual black or white bar was absent.

I don't know if these tricks are possible with the current electronic cameras, where you have no access to the internal processes. So I admire people that get done with these problems, like you and the Grand Illusion camera man.
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