The June meeting of the Detroit Section was held a week later than usual, but members' and guests' patience was rewarded with a brief, but informative presentation by Randy Conrod of Leitch. The topics of the evening were Universal Time Code and Time Division Multiplexing.
With the many means of transporting the variety of television signals in use, a need has been identified for assuring that Time Code attached to a particular program is still synchronous to that material when it arrives at its destination as well as with the reference time for that facility. One key reason for needing this is the 5 frame cycle of the NTSC television signal. Leitch has been working on a system of managing these differences which can be likened to a conveyor belt with a number of "wheels" of different sizes representing the various types of time. By understanding these differences in phase as well as the offsets from real time, as is the case with GPS time and TAI (atomic clock) time, an unknown time type can be derived from the relativ e position of the "wheel" representing it. There is currently a standard process underway at SMPTE (S22-16 is the working group) under the direction of Brooks Harris.
The second part of the program dealt with another proposed standard to Time Division Multiplex up to 18 interleaved program channels onto a single 1.22Gb/s signal. This would enable an entire family of signals to transported as one with a propagation delay of no more than 4 microseconds. Additional information can be embedded in the Horizontal ANCillary data area. A typical payload might consist of a single 1080i signal or 2x480p/60 or 4x480p/30 or 6xNTSC or 18xMPEG streams of no more than 68Mb/s each or any combination of these that fit into the 1.22Gb/s overall capacity. SDTI, although considered more economical, poses some limitations. Some key differences that were discussed are 1. SDTI latency is 1 field, TDM is a fraction of a line. 2. HANC data is needed for every frame of SDTI, where as in TDM required space is small. 3. With SDTI, multi-rate SDI cannot support multiple streams. The key advantages of TDM are that any standard can be delivered over a single piece of coax within a facility, TDM is more cost effective than Wave Division Multiplexing and TDM supports all formats, 4:0:0 to 8:8:8, uncompressed or compressed at the same time. Some interesting applications for TDM might be Stereo (3-D TV) on a single wire, medical and sports programming.
Finally, our group was given a tour of work in progress at our host's (WKBD) transmitter site where installation of their DTV transmitter is under way. Our thanks go to WKBD for their hospitality and refreshments and to Randy Conrod of Leitch for his informative presentation.