Richard,
In the early 1970s, I was Chief Engineer of Charles River Broadcasting in
Boston. AT&T was developing the diplexed audio system that you mention. They
wanted to make a preliminary field test of it and asked if they could use
our FM station, WCRB-FM, to make the first-ever field test. They wished to
use the Metropolitan Opera broadcast for the test. We had spare 15 kHz
stereo lines from Toll-Test, so the test was easy to setup. I did not know
at the time that we would alpha-testing the system.
A senior engineer from AT&T Long Lines in New Jersey came up for the test.
We met at the station on Saturday. I was enthused about the system, because,
if it worked, we would get the MET Opera in full-fidelity stereo for the
first time ever. Outside of NYC, the MET feed was mono and often low
fidelity. Note that the underlying video for this test was unrelated to the
MET Opera. They used a convenient video cable from NYC to Boston, probably
one of the TV network feeds.
The test seemed to be going well, until I got a call from a listener. The
voices had disappeared in mono. Although I had checked the phase before the
broadcast, it had flipped. I quickly flipped phase with a patch cord and
began to monitor in mono. A few minutes later, the phase flipped again.
Consternation broke out in the control room. I had to constantly flip phase.
It was later determined that certain video level peaks on the underlying
video carrier would cause the phase flips in the audio.
During this fiasco, I had a long discussion with the AT&T engineer. I
complained about the levels and clipping on peaks. I told him that VU meters
wouldn't work on their system, that they should use PPM meters, to show the
real peaks. He thought I meant the ratio of peak to rms, which was only 3
dB. I explained in depth about VU meter ballistics. He was completely
unaware of this. VU meters can be off by as much as 12 dB on human voices.
He left after the broadcast, with his tail between his legs. It was a year
or more before they got the system working. I gather from your remarks that
they still had level problems.
--Kevin Mostyn
-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]] On Behalf Of Richard L. Hess
Sent: Thursday, September 30, 2010 5:43 AM
To: [log in to unmask]
Subject: Re: [ARSCLIST] Lost recordings
<snip>
I recall working at ABC-TV in the 1970s and we celebrated the day that ATT
made diplexed audio available (TV program audio running on the video link on
a subcarrier). While they had problems with it at first--and didn't
understand broadcast audio level--it certainly sounded better than the
separate audio circuits. In my early days there, I recall--on typical TV
fare, not concerts--the loss of sound quality on the "Round Robin" which
went out from New York and then returned passing only as far west as
Chicago, I believe, and then returning via Washington DC>
Now, for ABC (and CBS in 1963) the economies of running the good lines you
refer to might have been judge unwarranted, so that may have been a factor.
Cheers,
Richard
--
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.
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