[time-nuts] PC clock generator without 14.318MHz
artgodwin at gmail.com
Tue Oct 18 19:50:56 EDT 2016
How about the Apollo launches ?
On Wed, Oct 19, 2016 at 12:40 AM, jimlux <jimlux at earthlink.net> wrote:
> On 10/18/16 4:25 PM, Magnus Danielson wrote:
>> On 10/19/2016 12:51 AM, jimlux wrote:
>>> On 10/18/16 2:30 PM, Tom Van Baak wrote:
>>>> Hi Vladimir,
>>>> Some of these numbers survive to the present. I'm typing this post on
>>>> an XP laptop where QueryPerformanceCounter() has a Frequency.QuadPart
>>>> of, you guessed it, 3579545 Hz, which is why my Win32 laptop's
>>>> high-res clock has ~279 ns resolution.
>>>> For more fun with time, frequency, oscillators, and prime numbers,
>>>> see: http://www.poynton.com/PDFs/Magic_Numbers.pdf
>>> and this is why clocks in film movies on TV run slightly slow<grin>..
>>> because the film was shot at 24 fps, and it's converted to 29.97 frame
>>> rate (in the US) by a 3:2 pulldown scheme.
>>> I am sure that all the time nuts here notice that 0.1% rate difference.
>>> Over a half hour TV program it adds up to almost 2 seconds of offset.
>>> (that's just because we watch things like movies shot of counters
>>> Hmm.. there's probably film footage of things with a running counter in
>>> the scene counting tenths or hundredths of a second (sporting events,
>>> nuclear bomb tests, etc.) I wonder if you could see that difference by
>>> single framing something like a filmed 100 meter race where they have an
>>> onscreen timer.
>> The time-code of TV and film production runs with a frame-counter.
>> Now, since the 30/1.001 factor is uneven, to get things into shape the
>> factor is compensated using the drop-frame method.
> SO that compensates in the "big sense" so that "timecode" and "wall clock"
> line up..
> But when they do the original telecine, they're basically running a 30fps
> (interpolated from 24 fps) sequence of frames at 29.97. Over the air,
> there will usually be a commercial break and they can add/drop any
> arbitrary number of frames to get it to line up (should they even care
> about whether the on-screen clock ticking the seconds actually lines up)
> So I was thinking about something where you get a broadcast (or maybe a
> video conversion on DVD/tape/online) that is a continuous piece of film.
> Seems that something like 100 meter race, which lasts 10 seconds, and will
> have an on screen timer to hundredths isn't quite long enough to see the
> 1.001 error (and would it be one continuous shot, or would they have edited
> film together from different viewpoints).
> What about a filmed rocket launch with a countdown timer or similar? they
> might have one continuous piece of film long enough.
> Partly, its going to be limited by the magazine size of the camera: a 400
> ft magazine is a bit more than 6 minutes (1 ft = 1 second in rough terms),
> so that's plenty long to see the difference.
> What you really want is continuous footage lasting, say, a minute, of some
> event (motivating the coverage) where there's an accurate clock visible in
> the scene, where the film was originally shot at 24fps, and has been
> converted to video.
> An interesting quest....
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