I don't yet own a HD radio mostly because what is available on
AM and FM, here, ranges from positively rotten to barely
tolerable, in my opinion, but that truly is just one person's
opinion.
The AM stereo that Lynn mentioned in a previous message
is kind of an interesting story. I am too lazy to look up exact
dates and system names, but we tried AM stereo in the United
States back in the eighties and it was a total flop. The FCC had
the same rules for AM stereo that they have always used for
improvements in broadcast technology such as the introduction of
stereo to FM around 1960 and color television in 1954 and then
stereo sound to television in the early eighties. The rules say
that the new improvements must not make a radio or television
channel occupy any more spectrum space than an existing channel
and that they must be compatible with existing technology so
that every existing radio or television set doesn't become a
paper weight the day the new technology comes on air.
They also said that after a trial period in which the
private market could experiment with several technologies, only
one would be chosen as the national standard.
That last rule was bent a bit with AM stereo so we got
4, yes, 4 incompatible systems during the eighties. All 4 sort
of worked and a few high-end tuner manufacturers built AM and FM
tuners that could receive them all.
Most people settled for buying a set that would receive
any stereo AM stations in their area if they even cared at all.
The chances were good that not all the stereo stations
receivable used the same format so it was a mess from Day 1.
AM stereo in North America quietly died with not so much
as a whimper and may all that expensive AM equipment rest in
pieces.
The IBOC system we use in North America now also bends
the rules a bit in that it does cause AM stations to take up
more room on the dial, so to speak. There is only one digital
system approved for the United States and that is a system
licensed by the iBiquity Corporation to piggy back digital
information on AM channels.
iBiquity also licenses a similar, but much wider-band
signal processing system for the FM broadcast band that also
causes a FM station to occupy a little more spectrum space, but
it's not quite as disruptive to adjacent channels as is the AM
system.
The iBiquity system delays the analog sound by 8 seconds
because there are 8 seconds of audio stored in the digital
buffers in a HD radio. The idea is that if your HD radio looses
the digital signal and switches to analog mode, you will still
hear a seemless switch over.
If you were listening to a digital broadcast in your car
or on a portable radio and carried the radio in to a weak spot,
the 8-second delay would make the digital audio and analog audio
come out exactly at the same instant. I hope all this makes
sense.
People who have listened critically say that AM digital
sounds like very good FM analog stereo today. FM digital is
CD-quality sound.
When I looked up iBiquity, I was sent to a wikipedia
article and a quick read of that indicates that this system is
actually a fairly versatile system in that it may one-day not
share the channel with analog audio. If you run the AM version
without analog audio, it only takes up the spectrum space of one
normal AM broadcast channel but older AM radios would just hear
noise, there.
The argument as to whether or not we should plan to
scrap analog radio for a clean new digital system like the UK,
Australia and Canada are doing is still going on, here, but one
problem in North America is distance and the fact that everybody
and their dogs want pieces of spectrum for all kinds of new
digital services. As some of you have already mentioned, not all
frequencies are equal so nature and the laws of physics dictate
who goes where to a large extent.
We may, someday, end up with digital broadcast radio on
frequencies used by the old analog TV channels, but I am betting
that in North America, analog broadcasting may slowly disappear
from the AM broadcast band and one day, 40 or 50 years from now,
that band will either go dark or be full, end to end, with
digital hiss. AM analog radio is the electronic equivalent of an
oil lamp. At night, here, the AM broadcast band is end-to-end
noise that does nobody any good at all. If a thunderstorm is
anywhere nearby as in a few hundred miles, you can stick a fork
in it. It is done.
IBOC on FM does work well so there is no push to turn
off the analog service. A digital signal theoretically goes
anywhere the analog signal goes so, in my opinion anyway, the
technology we are using here on FM broadcasting to send digital
radio is sensable for the near future.
This definitely is not a "My toy is better" argument,
but a case that one size doesn't fit all. There are huge areas
of the United States, Canada and Australia where you can drive
for hundreds of miles and not meet another soul. satellites are
about the only affordable way to get television and high-quality
radio and data services to those few who live ther. The only
other choice for audio is AM short and medium-wave signals. We
should probably be using the AM broadcast band for a few
regional power houses and forget the rest.
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