OldGringo said:
Nobody listens to adjacent channel stations under the shadow of a primary local. There is no loss
So I'm 'nobody'? IBOC supporters who make statements like "sacrifices need to be made" are just making excuses for why their incompatible, flawed and destructive system should be allowed to operate. They justify this by making claims that all listening occurs in areas local to stations, and therefore fringe and secondary coverage area listeners aren't being lost. Then you'll hear them go on about how IBOC is so wonderful because it eliminates the pops, hisses, and static associated with analog.
Now let's just assume for the moment that the first claim (local listening only) is true. Then why is the second statement (eliminating pops, hisses, and static) even an issue? If listening occurs only in LOCAL areas, we're dealing with STRONG analog signals, which sound pretty darn good and are mostly static-free. Static isn't a problem until you get into the fringe and secondary coverages.
Now let's change direction and assume that the first claim is NOT true. Digital broadcasting could, in theory, clean up some of those weak signals. Only problem is IBOC causes so much destructive interference that it would prevent anyone from listening in these areas in the first place, hence the reason IBOC supporters keep standing behind the first claim.
So whether your claims about local listening are correct or not, IBOC offers zero benefit.
Digital signals have another problem. Note that I said it would be nice IN THEORY to clean up those weak signals. Unlike analog, which will fade out and gives plenty of warning when it does, digital signals will cut out without warning, a much hated occurrence to anyone who's ever used a cellphone. There were some studies done that involved delays on computers (they were varying how long after you hit a key it takes for the input to show up on the monitor). When the machine was 'busy', the delay could be in the one second or more range, while it could be instantaneous when the machine was not busy. Now obviously the best you can do, on average, is to have the machine respond as quickly as possible given its current conditions. But what they found was that people preferred consistent delay, even if that meant slowing down the response time when the machine was not 'busy', rather than unpredictable delays. I think the same is true for radio, people would be very annoyed by having their stations drop out suddenly and unpredictably because they drove into a grove of trees. Note that this is different from the situation from HDTV because in TV most of the time the receivers and antennas
don't move
Because it is analog compatible, and does not obsolete all analog radios. It adds digital, rather than substituting digital for analog as in DRM.
It is not analog compatible. A compatible system would not be so destructive by violating the interference rules, especially on AM. On FM you can use, to some extent, the built-in guard bands but the iBiquity system does it poorly. On AM, the only solution is to not do hybrid mode AT ALL, due to overlapping channels with no guard bands to speak of, there is simply no space. It must be done on all stations at once, by operators flipping a switch, on a day that there are enough digital receivers out there, if that day ever comes.
The only way manufacturers will keep putting AM on radios and add digital AM is if ther eis one chip and one license. With the small amount of listening to AM today, they really would like to totally eliminate AM from all radios, like the new Microsoft MP3 player which has no AM but does have FM.
Sure, just have a single chip that can do hybrid/full digital FM and full analog/full digital AM. At some point in the future, convert both bands to full digital overnight. Just ditch the destructive iBiquity system. There are plenty of other ways to implement this that won't cause destructive interference. Particular attention needs to be paid to the full digital AM side so that skywave fadeouts don't become 30-60 second signal dropouts. You want to design the modulation so that in the presence of a weaker signal, the receiver can "fall back" to a lower bitrate (but still listenable) signal by making approximations. I'm sure you can do something like separate the most significant bits in symbols most distant from each other in the constellation diagram, so that when you get noise that makes the different points difficult to discern you can throw away only the least significant bits (and use the receiver to approximate them).
