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

[Joe Buch <josephbuch@xxxxxxxxx>]

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?

--- SaulBro@xxxxxxx wrote:

> Huh?   The FCC requires identical programming on digital and analog? 
>   Here 
> in Philadelphia, I listen to classical music on the HD radio from
> WHYY-HD, 
> while listening to talk on WHYY-FM.    In Washington, DC, WAMU-FM is
> regular NPR 
> news/talk/features, while one of their HD channels is strictly
> bluegrass 
> music.   Am I misunderstanding what you're saying, Joe?
> 

No.  Sounds like the predicted transition is already happening at least
for public radio stations.  It would be enlightening to know if you
hear anything other than simulcasting on the primary digital channel
and the analog channel on any commercial stations.

Joe



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