Video being only 1Vp-p in level means only small (20mV or so), levels of mains hum (due to ground loops etc.) are visible in the picture and by keeping the frequencies the same, the hum bars appear stationary or very slowly drifting through the picture and so much less intrusively visible.
Originally yes. To my understanding these problems have been long gone (due PSUs) so choice of 50Hz for HDTV makes little sence - especially when it comes to digital broadcasting. Most likely the decision was based on history and politics.
I also agree, but I can be very ignorant on this. HDTV is a 'computer' display. And don't see any banding on my computer monitor which runs with 50Hz mains and 85Hz VGA. Or should I see, and what I should look for?
Also majority of HDTV displays are non-tube based (if hum bars are tube-based problem). Generally Plasma, TFT/LCD or DLP is the main choise for high definition. And all those tend to sample input signal (if analog), run some algorithms (deinterlace, pulldown det. and inv. telecines) and store frame into internal framebuffer and output it for your pleasure.
Best regards, Jori
jori.hamalainen@teliasonera.com wrote:
Video being only 1Vp-p in level means only small (20mV or so), levels of mains hum (due to ground loops etc.) are visible in the picture and by keeping the frequencies the same, the hum bars appear stationary or very slowly drifting through the picture and so much less intrusively visible.
Originally yes. To my understanding these problems have been long gone (due PSUs) so choice of 50Hz for HDTV makes little sence - especially when it comes to digital broadcasting. Most likely the decision was based on history and politics.
I also agree, but I can be very ignorant on this. HDTV is a 'computer' display. And don't see any banding on my computer monitor which runs with 50Hz mains and 85Hz VGA. Or should I see, and what I should look for?
As the poster just above said, these issues are almost irrelevant due to technological advances in various areas.
To the decision being based on history and politics, I would also add legacy. It will take some time before stations have enough HD native originated material to fill 100% of their schedules and what about re-runs of pre HD material? Keeping the frame rate the same means standard definition material just needs upscaling, rather than interpolating to a different frame rate as well. Look critically at material that has been NTSC->PAL standards converted to see the compromises the latter involves.
Regards,
Richard
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jori.hamalainen＠teliasonera.com -
Richard Scobie