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Actually, 60 lines at a frame rate of 37.5 fps is very possible with no increase in bandwidth. Take a look at John Logie Baird's patent for increasing line count and frame rate at http://www.taswegian.com/NBTV/forum/viewtopic.php?t=163 . The specific example shown in Figures 1 through 4 is for a 24 line system, but all that you have to do for a 60 line system is substitute 20 square apertures for the 8 square ones shown and 10 rectangular ones for the 4 rectangular ones shown.DrZarkov wrote:That is very interesting! I wonder where the technical limits are of CD-players, or maybe we can use PCs with a good soundcard, a little bit more than 20 kHz should be possible, maybe it is possible to add the left and right audio channel to get more bandwidth, if necessary. If you have such good results, I think 60 lines/25 frames could be possible? (I would then switch to landscape format.)
Don't forget that 20 kHz is the maximum of a common CD, but in reality we never transmit a checkboard with every pixel in black and white contrast, so I think 60 lines could be possible.
Of course such a monitor would be more difficult to make, but it is interesting to find the limits.
Sorry, after I thought it through, I realised that this is not true. The particular combination of 60 lines at 37.5 fps to give a 60 by 70 pixel image with Mr. Baird's embodiment would require a bandwidth of about 39 kHz. However, if each line represents 40 instead of 70 pixels, then the bandwidth of such a 60 line 37.5 fps system with a 60 by 40 pixel image would fall to about 22 kHz.Stephen wrote:Actually, 60 lines at a frame rate of 37.5 fps is very possible with no increase in bandwidth.
I always tend to think in terms of vertical scanning, but let us consider lateral scanning instead. If one modifies the Baird system as shown in the patent for lateral scanning with a 4:3 aspect ratio and 64 lateral lines at 25 fps, that would provide a laterally scanned 80 by 64 pixel "landscape" image. The bandwidth would be 40 kHz.DrZarkov wrote:My soundcard does 44 kHz, I think a video driver for something between 20 and 40 kHz should not be more difficult than those we are already using. I think mechanical skills are more important than electronic skills for "HD-NBTV".
Thanks, GL. Actually, I was wondering the same thing about Volker's sound card. Volker, do the specifications for the sound card indicate a frequency response up to 44 kHz, or is that the sampling frequency? As GL points out, if the bandwidth of the sound card is 44 kHz, the sampling rate would have to be just over twice that at a minimum.AncientBrit wrote:Stephen,
In fact whilst the sound card samples at 44.1kHz, the actual signal B/W after filtering is nearer to 20kHz.
This has ramifications when recording NBTV at rates other than 48kHz as the number of samples per line (even if a fraction as in 44.1kHz) varies over time.
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