Appendix d: performance considerations, Testing, one two, Imag and latency – NewTek TriCaster TC1 (2 RU) User Manual
Page 325: D.2.1, Relativity and the speed of light, D.2.2, Latency and your audience
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APPENDIX D:
PERFORMANCE CONSIDERATIONS
In this section, we’ll consider the most common questions
you may have (and of course
we’ll provide the answer, too). Answers are
intentionally brief
–
perhaps just a
reminder of one or two steps required to perform some operation. For this reason,
we’ll also point you to explanatory information elsewhere in this manual whenever
that would be useful.
D.1
TESTING, ONE TWO …
Professionals simply do not leap into new environments blindly. They prepare, plan, plan some more, and
then
–
most importantly
–
they test. This allows them to tackle the really tough jobs with confidence.
D.2
IMAG AND LATENCY
What’s IMAG? It’s a
compression of the expre
ssion “I
mage MAG
nification.” 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 ven
ues 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.
D.2.1
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 po
sition 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 actu
ally “A Good Thing!”