NewTek TriCaster 8000 - Manual (Page 490)

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B.3 IMAG AND LATENCY
What’s IMAG? It’s a compression of the expression “Image MAGnification.”
Typically in modern IMAG applications, video cameras supply live imagery to
projection systems, magnifying speakers and performers so that audience members
further back in large venues can still see what’s going on.
IMAG is a very tricky task at the best of times, one that calls for excellent planning,
and where possible, testing. Those designing an IMAG installation have, not just
one, but two inter-related broadcasts to consider – in the form of the audio and
video streams.
B.3.1 RELATIVITY AND THE SPEED OF LIGHT
Wouldn’t it be nice if audio and video travelled from their respective broadcast
devices at the same speed? Then, wherever you were seated in the audience, the
sound from hypothetically perfect speakers and the video image from huge video
displays co-located at the front of the auditorium would reach your ears and your
retinas at precisely the same moment!
This is not the case, however. Sound travels quite slowly – so slow, in fact, that even
in relatively small venues it reaches those in the rear of the audience noticeably
later than those in the front.
In loose terms, for a mid-size auditorium 600 feet long, it takes around a half-second for
the audio to reach those in the back.
For this reason, audio engineers often
position speakers throughout the ‘house’, then
introduce carefully considered delays by electronic means -
to ensure ‘late sound’ from
front speakers does not arrive after sound from the nearest speaker to those further back.
Light, on the other hand, travels so much faster that for all intents transmission can
be considered instantaneous in the same setting. So a person in the rear will see the
image on a screen at the front long before sound from a co-located speaker arrives.
If transmission of the video signal from the camera lens right through to the
projection screen were instantaneous (it’s not, mind you), we’d likely need to find a
way to delay it. Viewed in this light, a certain amount of latency is actually “A Good
Thing!”