Re: question about sound?
- From: "J. T. Laurie" <taylor-sedai@xxxxxxxxxxx>
- Date: Wed, 31 Jan 2007 15:07:16 -0600
these are good questions. in the split second I am conscious when an EAS
test is running, when the data bursts are sent and the silence before the
audio message I assume when the crawl is going on, yes it is much much
louder and higher. I don't know. we do have digital cable, but I've also
noticed the whine over the radio as well. Could it be something with the EAS
equipment at the sttion itself?
"Doug Smith W9WI" <w9wi@xxxxxxxxxxxxxxx> wrote in message
Tadeusz Krzeminski wrote:
As I'm living in Europe and had no idea that such an alert system is used
U.S. (apart from that it's interesting idea and I'm reading about it
I'm afraid I won't be able to help you.
As far as the video is concerned, the Emergency Alert System (EAS)
of a text crawl, created by a standard character generator. Stations have
considerable latitude to decide what the text crawl should look like.
Audio is more important to the EAS: six data bursts (similar to old 1200
baud modem tones, but not at the same data rate or frequency) are
transmitted, sometimes with a brief steady two-tone signal and/or a voice
announcement. The data bursts total out to maybe 2-3 seconds in length
(in two groups), if the two-tone signal is transmitted ISTR it's supposed
to be 8 seconds, +/- quite a bit.
Weekly tests of EAS are required both of terrestrial over-the-air stations
(both radio and TV) and of cable TV systems. Once a month, a special test
(which usually includes a voice announcement) is transmitted.
Many stations also activate EAS for severe weather.
J.T., when you have the problem with the emergency alert tests, does it
happen on *all* channels, or just *some* channels? Do you have cable TV?
Have you notcied the whine is worse when a station is transmitting a
title - i.e., some text on the screen?
I'm wondering if the TV is sensitive to sharp transitions as are commonly
found in titles? Or if there's a level problem with a character generator
at your local cable system? (that would affect all channels that aren't
available by antenna. A character generator problem at one of the
stations would only affect that channel. If you're using an antenna, and
it affects all channels, then it's a problem with your TV.)
Does it happen *every* time an emergency alert test is run, or only for
Doug Smith W9WI
Pleasant View (Nashville), TN EM66