Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!att!occrsh!uokmax!mflawson
From: mflawson@uokmax.ecn.uoknor.edu (Michael F Lawson)
Newsgroups: sci.electronics
Subject: Re: automatic commercial deletion
Summary: Some stations use DTMF
Keywords: DTMF, commercials, VCRs, satellite programming
Message-ID: <1989Sep21.010603.26604@uokmax.ecn.uoknor.edu>
Date: 21 Sep 89 01:06:03 GMT
Expires: 10/1/89
References: <6428@ingr.com> <11213@fluke.COM> <1680@ns.network.com>
Reply-To: mflawson@uokmax.UUCP (Michael F Lawson)
Followup-To: sci.electronics
Distribution: usa
Organization: University of Oklahoma, ECN
Lines: 33

In article <1680@ns.network.com> logajan@ns.network.com (John Logajan) writes:
>
>I've often noticed, however, some touch-tone like sounds on cable
>tv broadcasts, such as from WTBS Atlanta, CNN etc.  I don't know what
>sort of information is being sent -- but it doesn't coorelated with
>the time commercials appear.
>

The signals being sent are ordinary DTMF codes (like you get on your touch-
tone phone).  Each network which uses them has its own code.  Their purpose
is to signal local cable companies' insertion equipment that a slot is
available.  Usually one or two slots per hour are available for local
insertion.  There is one code which signals the beginning of the slot,
and one which signals the end.  For example, on ESPN the start code is 048#
and the end code is 048* (from what I can remember).  The code transmissions
don't appear to be correlated with the commercials because the VCR's need
an eight second preroll time to get up to speed.  So the next time you hear
one, count eight seconds, and a commercial spot should begin.  Lots of the
time it is network promos or public service announcements that go here if
locals aren't inserting their commercials.  The preroll time is, I believe
the exact reason Headline News has their little (~8 sec) "around the world
in 30 minutes, this is Headline News" clip during the commercial breaks
at the end of each half hour.  Several networks, though, are now switching
to tones on a different audio channel (or inaudiable, I forget which).
That's why you don't hear the tones on several stations anymore (CNN and
Headline News, for instance). I suspect we will hear less and less DTMF
as the years go on.

Even if you built a circuit to intercept these codes, though, you would only
cut out maybe 4 minutes of commercials per hour, hardly worth the effort.

Mike Lawson
mflawson@uokmax.uucp