Alcorn Mcbride 1746-SMPTE, Руководство пользователя

Страница: 5 / 26

Welcome 1
Welcome
Welcome
Since the first V16 was introduced in 1986, Alcorn McBride has been providing
high quality show control solutions to the entertainment industry. The 1746-
SMPTE module brings that same power to the Allen-Bradley family of
programmable logic controllers. We at Alcorn McBride are pleased to provide
you with these tools. Good luck, have fun, and thanks for choosing
Alcorn McBride!
What is SMPTE Time Code?
Think for a moment about any recorded performance. It could be a stereo
recording of a symphony orchestra, a video of your child’s birthday party, or
your favorite motion picture. It would be very desirable to know the length of
the performance, and to be able to jump in to any point in the recording
accurately. Early systems provided such capabilities by linking a mechanical
counter to the tape or film reels. By counting revolutions of the reel, one could
return to the same point in the recording repeatably, and get some sense of the
overall length of the piece.
Mechanical or electronic counters work very well. In fact, they are still in
widespread use in much of today’s audio and video equipment. However, they
do have drawbacks, such as the lack of consistency from one machine to
another, and the fact that the counts can change when the tape gets edited or
copied.
A far more accurate system would encode the time information as a part of the
presentation itself, perhaps as an additional track of a multi-track audio
recording. This is exactly the technique that was standardized in 1981 by the
Society of Motion Picture and Television Engineers (SMPTE) and subsequently
adopted by the European Broadcast Union (EBU). The complete standard was
published as ANSI V98.12M-1981, and is generally known as the SMPTE/EBU
Longitudinal Time Code, or more simply, SMPTE Time Code.
To achieve film-like editing capability, SMPTE Time Code represents time in
hours, minutes, seconds, and frames. The common frame rates are 24 frames
per second for film work, 25 frames per second for European television, 30
frames per second for NTSC black and white television, and 29.97 frames per
second for NTSC color television. A typical SMPTE readout looks like
02:28:35:15, indicating 2 hours, 28 minutes, 35 seconds, and 15 frames.