Re: [Swprograms] HD radio audio delay problems...

["Rob de Santos" <rdesantos@xxxxxxxxx>]

As I understand the current regulations, on AM, no multiplexing is permitted and
the sole digital signal must be the same program feed as the analog signal.
Back at the SWL Fest, I had one bullet point in my briefing that mentioned my
own testing which showed back then (testing not yet repeated!) that most of the
signals I had heard on HD were out of sync.  Some by as much as several seconds
(not milliseconds!).  I'll probably retest the local signals before the next
'Fest. 

On FM, the first digital channel has to be identical to the primary analog
signal feed but the rest may be almost anything.  Stations whose ownership is
part of the HD Alliance (or whatever they are now called) have agreed to submit
their alternative channel programming to the alliance for coordination and
approval to minimize duplication in any market.  My own observation is that, in
practice, this is more PR than reality since minor changes can result in two
formats being largely the same in all but name and a few songs or hours of
programming being different.  

--
-Rob de Santos 

-----Original Message-----
From: Joe Buch [mailto:josephbuch@xxxxxxxxx] 
Sent: Tuesday, October 23, 2007 6:54 AM
To: Shortwave programming discussion
Subject: Re: [Swprograms] HD radio audio delay problems...

Originally the FCC required stations to broadcast the same material on
analog and digital channels.  Because the range of the digital
transmissions were predicted to not cover the entire service area of a
station's analog service, it was mandated that receivers soft switch
back to the analog service when the digital service became erratic. 
That is why it is necessary to time sync the two streams so, as the
soft transition blends from digital to analog, the transition would be
transparent to the listener.  

The article points out that if there is as little as a fraction of a
millisecond of error in the sync process, notches in the recovered
audio spectrum would appear during the blending of the two signals.  If
that error was 1 millisecond, article author observed notches at 500
Hz, 1500 Hz, etc. This is due to the phase of those frequencies being
180 degrees out of phase with a 1 millisecond delay.  

I have been away from developments in this area recently.  You
obviously have an advantage on me in that you have an HD receiver.
WHYY-FM and WETA-FM are both public radio stations.  Maybe FCC has
given them authority to run separate programs in order to raise more
public funding and offload the need for government subsidy.  I wonder
if any commercial stations have separate programs?


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