On Tue, 08 Jun 2004 14:45:41 GMT, Jon Noring wrote:

On FM, especially among alternative FM stations, one often finds very
unusual musical programs being broadcast of music which the listener
does not have in their collection (it helps them to expand their
horizons and maybe go out and purchase said music on CD/vinyl.) In
addition, there are sometimes live broadcasts of concerts which will
never appear on CD/vinyl. (In Salt Lake City, the alternative FM
station I am thinking of is KRCL, http://www.krcl.org/ . Really a fun
station to listen to, especially the late Sunday night program
broadcasting 1920's to 1940's era recordings.)

It's very true that the level of audio postprocessing varies a great
deal around the world. In the UK all FM commercial broadcasters use
very high levels of compression (including Classic FM, a national
classical music station) because they like to sound 'loud'. Only the
BBC's classical station uses reasonable levels of compression and
limiting. This heavy compression is also used on digital feeds, where
it is completely unnecessary.

On AM there are certainly broadcasts which interest different people
for different reasons at different times. Live sports events not found
elsewhere, news, of course the venerable talk radio, and for some of
us, we like to spin the dial at night and see what distant stations we
can pull in.

Yes Jon, but that's not audiophile listening, it's using radio as it's
always been used for 80 years. You would do just as well to plug a
1970s Grundig Yacht Boy into your system (which is what I do :-) )

Well, maybe in the U.S. most stations cutoff at 3.5khz. Then that's
where they cutoff. However, the AM tuner design is intended for the
world, and as Patrick Turner noted, in Australia many broadcasters
have a much higher rolloff because of the "open highway" they have
on the BCB -- fewer stations spread farther apart.

Modern AM transmitters have a very sharp rolloff above a certain
frequency. Broadcasting above this would just waste transmitter power,
since (almost all) radios wouldn't be able to receive it because of
their IF selectivity characteristics. The 9kHz or 10kHz AM channel
width is just a convention, but once it has been adopted there's no
point in trying to receive a wider bandwidth - you'll just get
interference from adjacent stations.

There's nothing wrong with building your own high quality AM tuner,
either solid state or tube, but no matter how many gold lettered
Telefunken ECC83s you use it won't sound very good.

Agreed in principle. The AM tuner must deliver the highest possible
fidelity as broadcast, that's all. It must have very low distortion.

One question to ask is in various areas of the world (including the
U.S.) what is the distribution of HF cutoff among the many broadcast
stations? I doubt in the U.S. every broadcaster rolls off HF at
3.5khz, but maybe most do -- are there any AM stations in the U.S.
which have a much higher HF rolloff than 3.5khz? Note again Patrick's
comment on Australian AM broadcasters.

In the US and Canada, AM stations are allocated 10kHz bandwidth,
giving a theoretical 5kHz treble cutoff. In most other place that's
9kHz/4.5kHz. Stations transmit a more restricted frequency range than
this though, for a number of technical reasons. That's where my rough
and ready 3.5kHz figure came from.

Best regards, Paul
--
Paul Sherwin Consulting http://paulsherwin.co.uk