Re: [IRCA] IBOC 8- SECOND DELAY

[Scott Fybush <scott@xxxxxxxxxx>]

Pete Taylor wrote:
> KPLU-88.5 Tacoma has a repeater near Seattle on 88.1 and the  
> repeater's audio is 8 seconds ahead of the mother signal  presumably  
> because 88.5 is IBOC. I have seen many comments relating to the  
> limited range of the IBOC signal on AM but I don't recall seeing  
> anyone comment on what must happen with an IBOC station as you  
> approach its fringe area. Does the audio pop back and forth between  
> the digital and analog signals as you alternate between them?  
> Obviously I am referring to a potential situation while driving. I  
> would think this would make maintaining continuity very challenging...

That's the reason for the 8-second delay. A properly-adjusted IBOC 
signal will have its analog audio delayed to match up with the digital 
audio, thus providing for a smooth transition in fringe signal areas. In 
theory, this "time diversity" should also eliminate the "bridge effect" 
when listening to MW signals, since the hit to the data stream (digital 
audio) from passing under a bridge and losing the signal won't result in 
a loss of audio for another three or four seconds (that's how long it 
takes the radio to decode the compressed audio it's receiving). By then, 
you'd be out from under the bridge and, in theory, would have a clean 
analog audio signal to revert to while waiting for the digital signal to 
lock in again.

Obviously, this can be highly disconcerting when the delay between 
analog and digital isn't matched properly. I heard that today while 
demo'ing an IBOC receiver on the WOWO digital signal, which apparently 
has no delay on the analog. It wasn't pretty!

s, in Fort Wayne
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