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:[EMAIL PROTECTED] 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? _______________________________________________ Swprograms mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/swprograms To unsubscribe: Send an E-mail to [EMAIL PROTECTED], or visit the URL shown above.
