[time-nuts] Re: Where do people get the time?

[Lux, Jim]

On 1/1/22 8:48 PM, Tom Van Baak wrote:
> Hal Murray wrote:
> > where do you get the time?
>
> The new years celebrations last night remind me of another source of 
> time: time balls.
>
> Although a bit of nostalgia these days or even a joke, time balls were 
> clever, precise, and a critical part of naval infrastructure in the 
> 19th century, lasting well into the 20th century, and still 
> operational daily in Greenwich (not right now due to refurbishment). 
> It falls into the category of "time dissemination"; you know, WWV, 
> GPS, UTC, NTP, and all.
>
> The sound of church bells gave approximate time, partly because their 
> use case didn't require high precision and partly because sound 
> travels only one foot per millisecond. Related: starter pistols at 
> track events; clapperboards on movie sets; timing thunderstorms with 
> lightning. 


Clapper  boards even automatically compensate for the acoustic time 
delay, especially in a multi channel recording scenario. The board is 
placed near the people being recorded, the camera and sound gear is 
started (Rolling, Speed,...)

Then the clapper board is actuated (electronically today, with timecode 
displayed on an electronic board) (a process called "slating"). So the 
*sound* of the clap has to propagate to the sound recording equipment 
(some ten miliseconds away if the mic is on a fishpole or boom).  In 
editing, the sound and picture are lined up, (i.e. the sound is started 
later) using the sync from the clapper.

Obscure note - if they forgot to slate at the beginning, or they 
couldn't do it for some reason (focus, zoom, blocking), they do it at 
the end of the take, and hold it upside down.

Slating is done even if there's no sound, so you can identify the piece 
of film. And, if there's multiple cameras, there will be multiple slating.

I sort of left the business before modern digital cameras were 
universal, I assume they still do it, even if there's no need to 
physically identify a piece of film.