[BC] DTV Capacity - Digital Radio, too?

[Bob Tarsio]

Rich:

It depends on what you really call HD and the encoding format. It is
possible to do two HD type services with the terrestrial over the air system
with a couple of caveats. One it would be preferable if the content on at
least one of the services was 24 frame capture such as film. Live video need
more bandwidth and the encoders need to crunch more when processing 30 frame
capture stuff. When I was a DTV development engineer at Viacom we did tests
with film captured material and we could actually resolve 1080i down to
about 8 MB/sec with film capture. In theory you could do two of these
services and get away with it. The problem is that the encoders really
crunch up the video during scene changes and with rapid motion. Showtime
found this out the hard way when they elected to go with a low bit rate and
then tried to do live boxing events. The pictures looked like in a word
crap. Most of the testing I did for them assumed film capture as that was
the bulk of their output at the time. It can be done but should it? The
pictures tell the story. 

Realistically you can do one fairly good quality HD service and a couple of
SD services with 8 - VSB over the air. Cable is a different story. You get
about a 2 to 1 increase in payload because you can control noise, gain etc.
where off air is subject to path anomalies. So for cable, you can do two HD
services in a 6 MHz block without too much difficulty. We tested just about
every encoder on the market back then for these kinds of configurations.
Harris/Lucent, General Instrument - now Motorola, SA - now Cisco, NDS - now
Tandberg, and Tiernan. The GI stuff looked the best at the time and that's
what we went with for Showtime HD. We also were the first cable premium
service to offer the full Dolby 5.1 output. HBO beat us by about a year with
an HD service but didn't offer 5.1 audio until after we did it. Another
interesting note is that we evaluated line doubling up converters a lot too.
The conventional wisdom was that a lot of older content would be line
doubled instead of pan and scanned all over again in HD. I am not sure how
that worked out. I guess classic films will eventually be converted over
time. 

Bob Tarsio
President
 
www.Broadcast-Devices.com
 

 
Tel. (914) 737-5032
Fax (914) 736-6916
 
 

-----Original Message-----
From: broadcast-bounces at radiolists.net
[mailto:broadcast-bounces at radiolists.net] On Behalf Of Rich Wood
Sent: Tuesday, February 20, 2007 10:45
To: Broadcasters' Mailing List
Subject: [BC] DTV Capacity - Digital Radio, too?

------ At 01:10 PM 2/19/2007, Dennis Cope wrote: -------

>Our local CBS station (WBOC-HD) has FOX on their secondary, works great.
>One of their engineers told me the other day they are working a way to get
>the secondary to get HD on it.  It appears that have an experimental
>Flexi-coder at the station.  The only thing I asked them to do was put grey
>panels when they went SD for the local news so by plasma screen would not
>burn in.

It's my understanding that you can only get one HD channel. The PBS 
station here runs all SD during the day (4 channels) and one HD and 
one SD at night and weekends. Is there enough bandwidth for 2 HD 
signals? CBS is 1080i and FOX is 720P.

Rich


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