From the DRM website:

The DRM on-air system will propel the AM broadcasting bands below 30 MHz -
short-wave, medium-wave and long-wave - to the next level.

DRM is the only universal, non-proprietary digital AM radio system with
near-FM quality sound available to markets worldwide.

The quality of DRM audio is excellent, and the improvement upon analogue AM
is immediately noticeable. DRM can be used for a range of audio content,
including multi-lingual speech and music.

Besides providing near-FM quality audio, the DRM system has the capacity to
integrate data and text. This additional content can be displayed on DRM
receivers to enhance the listening experience.

Unlike digital systems that require a new frequency allocation, DRM uses
existing AM broadcast frequency bands. The DRM signal is designed to fit in
with the existing AM broadcast band plan, based on signals of 9 kHz or10kHz
bandwidth. It has modes requiring as little as 4.5kHz or 5kHz bandwidth,
plus modes that can take advantage of wider bandwidths, such as 18 or 20kHz.

Many existing AM transmitters can be easily modified to carry DRM signals.

DRM applications will include fixed and portable radios, car receivers,
software receivers and PDAs. Several early prototype DRM receivers have been
produced, including a software receiver. The DRM system uses a type of
transmission called COFDM (Coded Orthogonal Frequency Division Multiplex).
This means that all the data, produced from the digitally encoded audio and
associated data signals, is shared out for transmission across a large
number of closely spaced carriers. All of these carriers are contained
within the allotted transmission channel. The DRM system is designed so that
the number of carriers can be varied, depending on factors such as the
allotted channel bandwidth and degree of robustness required.

The DRM system can use three different types of audio coding, depending on
broadcasters' preferences. MPEG4 AAC audio coding, augmented by SBR
bandwidth extension, is used as a general-purpose audio coder and provides
the highest quality. MPEG4 CELP speech coding is used for high quality
speech coding where there is no musical content. HVXC speech coding can be
used to provide a very low bit-rate speech coder.

The robustness of the DRM signal can be chosen to match different
propagation conditions.

http://www.drm.org/system/globtechnical.htm