Meeting Report - Feb 23, 2010
For a moment in time, 40 members and guests gathered on February 23, 2010, in the auditorium at Dolby Labs in Burbank, CA to hear a talk by SMPTE Fellow Al Kovalick of Avid Technology. He presented "A Brief History of the Second". Al developed several themes centered on the second and its relationship to media systems. Although we often take for granted the tick of the clock, the second has deep mechanical, electrical, atomic, relativistic, astronomical, and poetic meaning. The talk was divided into several parts: the basics of timekeeping; defining "the second, Einstein's theory of Special and General Relativity as relates to time dilation; atomic clocks; time systems and their applications to video production and distribution.
The discussion included "Greenwich time balls", the all-important work to navigation of clock inventor John Harrison, who strove to win the Longitude Prize of 1712, Cesium clocks, ensemble clocks, UTC/TAI, GPS, and their ultimate connection to video systems timing.
The audience had fun with an interactive demo of the physical "ensemble clock" or paper clock. At a known reference time, Al asked 8 people to write on cards the exact time displayed on their wrist watches. Paul Chapman, section Chair, averaged the results and derived a new "ensemble time", an average that was nearly the same as the target time and more improved, on average, than any individual wrist watch time value. Instructive.
Al discussed that leap seconds are necessary to align atomic clocks to the actual rotation rate of the earth. The earth does not rotate precisely at 24 hours (solar mean time) but rotates, instead, on its axis every 86,400.002 seconds, slightly more than 24 hours. So in a given year, this 2 Ms offset
adds up to ~730 Ms. Hence, leap seconds are needed to keep earth time and atomic time in alignment. There is always a small known offset between atomic and earth time, but less than one second.
SMPTE has been in the "time business" for half a century. Al described the recent work of the SMPTE/EBU Task Force on Timing and Synchronization. SMPTE has formed a new Standards Committee (33TS) to create a new sync signal and time label. The current black-burst reference signal will be replaced with a new sync signal locked to GPS time. Any framing signal, regardless of
frame rate and resolution, can be created within the media facility with precise horizontal and vertical timing relationships.
Al Kovalick serves as a Strategist and Fellow with Avid Technology, and is also the author of "Video Systems in an IT Environment".
Paul Chapman - Chair, Hollywood Section.
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