Gordon:

'HD Radio' is the trade name of the digital modulation scheme
developed for use on AM/FM broadcast stations in the USA by Ibiquity,
Inc.

This is also known as "in-band, on-channel" or 'IBOC' [radio] and
allows the AM and FM stations we're all familiar with to add to their
existing 'channel' a digital modulation signal, the benefits of which
a

(In the case of FM stations) provide a more 'robust' primary channel
signal (generally free from multi-path and other distortions that can
degrade an analog FM signal) as well as adding one-to-several
'additional' 'channels', known as "HD-2", "HD-3", etc. That is, let's
say your favorite FM station is WXYZ, the program format of which is
polka music. If you're equipped with an HD capable receiver, you'll
hear the polka music with 'near' CD quality. Then, if you push the
"tuning" button up, you may then hear WXYZ's HD-2 channel, which may
be a jazz format, for example. Push the tuning button up once again,
and you may find WXYZ's talk programming. In other words, HD Radio
provides an FM station with multiple channel streams, which has
heretofore not been possible with traditional analog modulation.

AM stations can also participate in HD radio, though to a lesser
extent. On AM, the digital modulation noticeably increases the
fidelity of the signal, most noticeable on music programming. Because
of the limited bandwidth allocated to AM broadcasting, no 'additional
channels' are possible (as they are on FM, as described above).

DRM is the digital modulation scheme developed by a consortium on
European broadcasters - Digital Radio Mondiale. Unlike HD Radio, DRM
does not allow for the simultaneous transmission of both the
traditional analog and new digital modulation. It is simply digital
modulation on the frequencies traditionally used by AM/FM
broadcasters.

The real question is: where do you live? If you're in the USA, then
a new HD Radio may be right for you. In the USA, a DRM receiver would
be worthless, since US radio broadcasters are not permitted to use
digital modulation exclusively.

If you're in Europe, then a new DRM capable receiver would be the way
to go (assuming your local telecom governing board has allowed DRM
transmissions in your Country).

Mike Worrall
Los Angeles