Comment by Suppafly
12 days ago
>Whenever I saw a CRT running at 60 Hz, I'd be immediately be able to tell. Always used at minimum 75 Hz but preferably 85 Hz at home (early 2000s, Windows).
Same, I remember installing some program that would let you quickly change the display settings on basically every computer I ever interacted with. It was especially bad if the crt was in a room with fluorescent lighting.
If your lighting and display have flicker at mathematical ratio you will notice unless the frequency is extremely high. 1:1 is most likely because it is easy to sync lights and the CRT to the AC line frequency which is 60Hz in the US (50Hz in Europe). 1:2 (used to be somewhat common) or 4:5 ratios would also cause issues.
Though now that I think of it, the CRT should be syncing with the signal and there is no reason that sync needs to be related to the AC line, but it does anyway (all the computers I know of generate their own sync from a crystal, I have no idea where TV stations get their sync but I doubt AC line frequency).
Wikipedia for NTSC alludes to a couple reasons why you'd want your refresh rate to be based on your power line frequency:
> Matching the field refresh rate to the power source avoided intermodulation (also called beating), which produces rolling bars on the screen. Synchronization of the refresh rate to the power incidentally helped kinescope cameras record early live television broadcasts, as it was very simple to synchronize a film camera to capture one frame of video on each film frame by using the alternating current frequency to set the speed of the synchronous AC motor-drive camera.
(I suspect shows that were pre-recorded and telecined for broadcast would've also been filmed at 30fps using a synchronous AC motor.)
> In early TV systems, a master voltage-controlled oscillator was run at twice the horizontal line frequency, and this frequency was divided down by the number of lines used (in this case 525) to give the field frequency (60 Hz in this case). This frequency was then compared with the 60 Hz power-line frequency and any discrepancy corrected by adjusting the frequency of the master oscillator.
I think later TVs would've just synchronized to the received signal.
https://en.wikipedia.org/wiki/NTSC#Resolution_and_refresh_ra...