[BC] Blending issue

[Skoog, Arne W]

Mike,

Here in Seattle, we have three Harris type installs and use the factory
recommended set up and haven't had any problems. I do remember a Dexstar
upgrade that changed the character of the blend, a dip in level, but not
silence. 
AES I like to think of this way, it is a carrier (think of Telco stuff),
so swapping the polarity of the AES cable won't do you any good. The
polarity swap that is needed is prior to the audio being encoded on the
AES stream.
Inside an audio processor this could really be impossible to get at. If
you have a pair of "Bit Buddy's" or some other type of  AES test
equipment you can experiment for yourself.

Arne 

-----Original Message-----
From: broadcast-bounces at radiolists.net
[mailto:broadcast-bounces at radiolists.net] On Behalf Of Mike McCarthy
Sent: Thursday, November 17, 2005 12:28 PM
To: Broadcast Radio Mailing List
Subject: RE: [BC] Blending issue

No, this is a real issue.  Not sure what to do yet.  I recall having
heard about swapping the AES polarity. But does THAT invert the analog
signal?

MM

At 01:53 PM 11/17/2005 -0600, Jeff Welton wrote
>Barry commented:
>
> > There has been some recent discussion about a phase problem with the

> > audio when IBOC receivers "blend" to analog.
> >
> > Apparently there are cases where the analog and the "decoded
digital"
> > are out of phase to each other, and the radio goes "quiet" for a 
> > moment.  Some have attributed this to a recent software upgrade on 
> > some IBOC exciters.
> >
> > Another person told me this week that this issue has been known for
> > some time, and pointed to a specific processor.   I won't name it
> > here, because I am not in position yet to verify that.
> >
> > However, it may be useful for anyone running IBOC to verify the 
> > blend is without "dropout."
>
>Barry - if I was the person to whom you're referring, I misled you 
>(sorry!).  I'm going to plead that I didn't completely understand the 
>question over the phone (bad Jeff, go to corner, write, "understand, 
>then respond" 100 times).
>
>While I haven't really been following the topic, the above sounds like 
>primarily an issue of synchronization.  Folks, it is CRITICAL that you 
>synchronize the analog and digital audio signals - even if (in the case

>of
>FM) the analog audio does not go through the HD generator.  In the case

>of FM, not synchronizing the audio can definitely cause dropouts when 
>blending between analog and digital.  In AM, lack of synch will also 
>cause dropouts and can, on occasion, cause the HD generator to lock up 
>if the two signals meander far enough out of phase.  Our NE-IBOC 
>generators (I assume the rest, but don't know for sure) have a couple 
>of ways with which you can synch the audio.  First, there's a sample 
>rate converter provided in the auxiliary unit that is part of the 
>NE-IBOC package.  This can be connected to the output of the STL (or 
>whatever receives the program audio at the transmitter site) and used 
>to drive both the analog and digital processors.  Alternately, the 
>NE-IBOC main unit has three 10MHz clock outputs which can be used to 
>synchronize external devices, or one of the sample rate converter 
>outputs could also be used to synchronize the processors, if the 
>processor has the ability to synch to an external input.  There are 
>other options, don't hesitate to call your manufacturer for additional 
>information
>
> > ... that is ... IF you have a receiver.  Amazingly, I still hear of 
> > stations installing digital without even having one receiver on
hand.
>
>I've been to a few where the only digital receiver was in the GM's car 
>- not available at installation time - or in the regional DOE's car - 
>also not available.  I've only installed two that I can think of where 
>we actually had a receiver done up so that we could listen in the site 
>to what we were putting on the air.
>
>Just some thoughts from the rainy, foggy North East (I'm not 
>complaining, a customer in Tennessee just told me it was 20 degrees 
>there (near
>Knoxville) this morning - the lowest temperature we've seen so far 
>recently has been about 40).
>
>Best,
>
>Jeff Welton
>Customer Service Dept.
>Nautel Limited
>Tel: +1-902-823-3900, ext. 127
>Fax: +1-902-823-3183
>jwelton at nautel.com
>
>
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>
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