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!”

SECTION B.3.1    

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