lauren@vortex.UUCP (06/19/83)
The audible tones that you hear on CATV services are simple touch-tone sequences used to pass various sorts of programming control information to local cable systems. Several cable industry publications list most of these sequences, including "Satellite Program Guide" (the "TV Guide" of the satellites). The sorts of information passed by touch-tone includes: 1) Local insertion opportunity control. Some services guarantee local systems a certain number of minutes per hour (or day) of local insertion time. During these intervals, the local systems may replace the service's programming with their own local message generators or other locally generated commercial/ non-commercial programming. These intervals are typically one or two minutes in length, and use different tone sequences to signal the beginning and end of the insertion segment. 2) Programming start/stop control. Some satellite transponders are shared by several different (often unrelated) programming services. Tone sequences are often used to indicate when one service ends and the next begins, so that local cable systems who are licensed to transmit some services on the transponder (but not others), may switch the particular cable channel off of or on to the correct transponders at the appropriate times. Many cable systems use special timers for this same purpose, but tone control is more reliable when non-uniform scheduling is in use. This gets pretty important when "dissimilar" services share a single transponder. For example, until very recently, Dr. Gene Scott's satellite religious feeds shared space with "The Playboy Channel"! [Dr. Scott has now taken over TPC's time on that transponder (NCN). I'll have to devote an entire message to Dr. Scott someday. He is an absolutely fascinating character. He's the guy who recently lost the license for KHOF-TV (30) here in the L.A. area after a LONG battle with the FCC. He's still around though -- not only on satellite for 10+ hours/day but in long blocks on several local stations as well. Truly a UNIQUE individual. But I digress...] A similar tone use involves separating "real" programming from promotional feeds and testing. Some services run multiple promos for cable systems to tape (and use at a later time) before regular programming begins. Tone sequences may indicate these promo periods so that cable systems can avoid sending them out directly to subscribers and boring them to death. Tones may also be used to indicate when the day's programming is ending (and testing or "dark" time is about to start), or when the day's activity is beginning (and/or testing is ending). This information allows cable companies to avoid running color bars all night on a particular channel, and can free the local channel for other use as the cable company desires. In some cases, a programming service may run the same programming TWICE (one after the other) -- once for the Eastern time zones and once for the Western. Tone sequences may indicate the start/stop of these periods to allow cable systems the option of not repeating the programming. Note that many cable systems don't even bother to decode these tones, and just run whatever the transponder is sending. Most smaller systems, for example, never bother to take their local insertion opportunities, and just run the commercials (or other programming) that are sent by the services during that interval. As I mentioned above, when control *is* necessary, many systems use timers to avoid running the "wrong" services. Occasionally a service will neglect to properly signal the "end" of an insertion opportunity, or will believe that the tones were "mangled" with other audio. In these cases, it may insert the tones even after regular programming has already resumed, to make absolutely sure that they've gotten all of their cable systems back! Some services run some of the more "important" tone sequences two or three times to make sure that they are received properly. While many of the "older" services (CNN, ESPN, USA, HBO, etc.) use touch-tone signals for control, some of the newer services use non-audible signals for various purposes. MTV, for example, uses a non-audible subcarrier "flag" to indicate the two minute insertion opportunities that they provide most hours (these are the periods where MTV runs rather bizarre edited "collages" of strange visual material accompanied by music.) SNC (Satellite News Channel) uses data inserted in the video signal's "vertical interval" to control both local insertions and the switching of local systems to alternate transponders (at various times) for "regional reports". Obviously, more specialized equipment is needed to detect such "non-audible" signals, which is sometimes provided for free (or very cheaply) to participating cable companies by the services. --Lauren-- P.S. Essentially *ALL* cueing of cable companies by programming services is done via one or another of the above mentioned "within-channel" techniques. There is virtually NO use of separate "cueing" channels (the technique used by the major "establishment" TV networks). Of course, the variety of cueing techniques that the cable companies ARE using provide many of the same services that network cueing channels typically provide. --LW--