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

[Lux, Jim]

On 1/2/22 9:57 AM, Hal Murray wrote:
> jim at luxfamily.com said:
>> 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).
> How far off does the audio have to be before it doesn't look/sound right?  How
> accurately does the typical movie process get things aligned?
>
> We are used to a delay of several to low 10s of ms.  Somewhere in the 20-100
> ms range (depending on how good your eyes are) you can't see the speakers face
> well enough to help decode what they are saying.
>
> Are people sensitive to the sound being early?
>
>
I don't know today, but back in the day, probably 1/24th of a second, 
even though they're projected at 48 fps (each frame is projected twice, 
so the flicker frequency is higher).

A lot depends on the image size - you're used to a shorter delay when 
you're closer to the person (i.e. their image is larger), but when 
they're across the room you expect a longer delay.  This is one of the 
things that makes the audio sound different when watching a movie on a 
small screen up close rather than in a theater - the psycho acoustic 
cues are different.  As to how they do it - skilled editors use their 
judgement.

I'd say what people are sensitive to is lip movements not synced with 
sounds, whether early or late.  I suppose obvious simultaneous events 
(gunshot sound + flash) would be weird if the sound occurred before the 
image. But a bit late would just be like real life.  In fact, the 
simultaneous explosion and sound in movies is something that bugs me, 
because if you were actually there, the delay of, say, 100 ms, is very 
noticeable - and for big things like rocket launches (and, I suppose 
nuclear explosions) which you're watching from miles away it's very 
noticeable.  I watched a Titan IV launch from about 10km away. You saw 
the ignition, a 5-10 seconds later you felt the ground shaking, and the 
rocket was maybe 300-400 meters up and hitting the scattered clouds 
before the sound got to you 30 seconds later, and then you have the 
weird phenomenon of the rocket getting smaller and farther away, while 
the sound gets louder.