30fps/60hz

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Was 30fps/60hz chosen for television since it could convert film
(24fps) well to TV using (3/60+2/60)/2 = 1/24, or was that just a
clever formula discovered after the fact.

 

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Tim923 wrote:
> Was 30fps/60hz chosen for television since it could convert film
> (24fps) well to TV using (3/60+2/60)/2 = 1/24, or was that just a
> clever formula discovered after the fact.

Our electricity in the US is 60Hz AC.

--
David G.

 

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Archived from groups: alt.tv.tech.hdtv (More info?)

Actually 24/50 works best as it is so close to film's 24/48. The use
of 50 and 60 was due to the powerline frequencies here and in Europe,
It was an attempt to avoid some nasty hum bars.
Some people comment on seeing a flicker in the image when they go to
Europe because of the lower field rate. I've been to England and
frankly I must not be sensitive to that particular problem as the
pictures looked fine.
The interlace scheme provides benefits although it violates Nyquist
sampling. Each field updates motion and thus TV looks more natural
than film where each frame is held and flashed on the screen twice.
(In some systems it's more than that.)
Years ago someone asked me about aliasing. I told them that instead of
watching the housewife holding the sponsor's product, to watch the
counter edges behind her vibrating like crazy. They cursed me because
once I'd caused them to see it, they couldn't not see it. That's why I
watch so little TV. I'm so tuned into such things. Although I must say
the continuity errors in films and the leaps of faith in the story
lines bug me more.
Roy
Tim923 <tws0923@verizon.net> wrote in message news:<j8hig0lhn67ejc3h9lb290hk9hag3ifk40@4ax.com>...
> Was 30fps/60hz chosen for television since it could convert film
> (24fps) well to TV using (3/60+2/60)/2 = 1/24, or was that just a
> clever formula discovered after the fact.

 

[Guest]

Archived from groups: alt.tv.tech.hdtv (More info?)

In article <7bidnTzYVJUE5pTcRVn-uw@comcast.com>,
david_please_dont_email_me@i_hate_spam.com says...
> Tim923 wrote:
> > Was 30fps/60hz chosen for television since it could convert film
> > (24fps) well to TV using (3/60+2/60)/2 = 1/24, or was that just a
> > clever formula discovered after the fact.
>
> Our electricity in the US is 60Hz AC.

Back when TV was being developed, there was a lot of concern that
60hz hub pickup from many sources (radiation, leaky capacitors,
poorly shielded transformers, et al) would a) interfere with the
ability of TV sets to maintain vertical sync, and b) cause horizontal
bars that rolled up or down the screen, if the vertical sync were not
exactly the same as the power line (60hz in the US, 50 hz in Europe).

That concern evaporated, and with the introduction of color (NTSC) in
the 50's, the vertical sync frequency was changed to approx. 59.94
Hz. (This wierd choice comes from dividing down the color subcarrier
frequency, again to minimize a diferent type of interference.)

The 3:2 pulldown is result of the 60Hz choice, not the other way
round.

/Chris, AA6SQ

 

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Chris Thomas <cthomas@mminternet.com> wrote in
news:MPG.1b73239cecbac78b98984c@news.mminternet.com:

> In article <7bidnTzYVJUE5pTcRVn-uw@comcast.com>,
> david_please_dont_email_me@i_hate_spam.com says...
>> Tim923 wrote:
>> > Was 30fps/60hz chosen for television since it could convert film
>> > (24fps) well to TV using (3/60+2/60)/2 = 1/24, or was that just a
>> > clever formula discovered after the fact.
>>
>> Our electricity in the US is 60Hz AC.
>
> Back when TV was being developed, there was a lot of concern that
> 60hz hub pickup from many sources (radiation, leaky capacitors,
> poorly shielded transformers, et al) would a) interfere with the
> ability of TV sets to maintain vertical sync, and b) cause horizontal
> bars that rolled up or down the screen, if the vertical sync were not
> exactly the same as the power line (60hz in the US, 50 hz in Europe).
>
> That concern evaporated, and with the introduction of color (NTSC) in
> the 50's, the vertical sync frequency was changed to approx. 59.94
> Hz. (This wierd choice comes from dividing down the color subcarrier
> frequency, again to minimize a diferent type of interference.)
>
> The 3:2 pulldown is result of the 60Hz choice, not the other way
> round.

Actually, I had a TV on the bench for two weeks back in 1967 that I could
NOT figure out. Turned out it was a bad filter cap in the power supply
that was JUST bad enough to cause the TV to sync to the power line
instead of the actual signals. Found it the minute I got frustrated
enough to stick a scope probe into it!


--
Dave Oldridge+
ICQ 1800667

A false witness is worse than no witness at all.