DRM stands for Digital Radio Mondiale. It is a digital radio system designed to operate on the long, medium and short wavebands currently used for AM broadcasting. Like DAB, DRM uses COFDM modulation, splitting the signal between a series of low bit-rate carriers. This enables signals transmitted over different paths to be combined without interference. Unlike AM, DRM is not subject to fading and distortion as a reflection by the ionosphere. Thus, using DRM enables clear reception on short wave for the first time and allows clear medium and long range reception on medium wave at night. In addition, networks of DRM transmitters carrying the same programme can share a single frequency without interference. DRM and AM can operate side by side on the same wavebands. As DRM can operate with a lower signal to noise level, it can use frequencies not suitable for AM broadcasting in a given area.

Using a standard 9 or 10 kHz width channel in the AM bands, DRM can deliver audio at around 20-30 kbit/s, depending on the level of protection used. This is much lower than the bit rates used for DAB. However, DRM, being a much newer technology uses the much more efficient HE-AAC audio coding standard. Although only mono can be supported and the sound quality is poorer than FM, it is dramatially better than the sound quality offered by AM in Europe. If two channels are used, doubling the bit rate, DRM can deliver reasonable quality stereo. A channel may also be shared between AM and DRM, though this reduces the DRM bit rate and the AM audio bandwidth, though most AM receivers use a lower bandwidth than transmitted in order to limit adjacent channel interference.

A version of DRM for use in VHF broadcast bands I and II (the FM radio band) with 50 kHz channels and FM quality stereo audio is currently under development. As DRM will use narrower channels than FM and requires less power to attain a given coverage level, it can share band II with FM, making use of frequencies where new FM transmitters can not be accommodated, much in the same way that digital terrestrial TV in the UK currently shares broadcast bands IV and V with analogue TV. Band II DRM would provide an ideal opportunity for the smaller FM (and AM) stations, whose coverage areas do not match a DAB multiplex, to broadcast digitally.

DRM is not a competitor with DAB. In general, the two systems will carry different stations. DRM was developed by a consortium of electronics companies and international broadcasters, including the BBC World Service, so international broadcasters will be the first to use it. As well as the international public broadcasters, the international religious stations are also likely to take up DRM. European media giant RTL has announced plans to launch a series of commercial stations on DRM next year, including a short wave service for the UK. Over the next decade or so, DRM is likely to displace AM on short wave.

The future of DRM for domestic broadcasting is uncertain at the moment. Germany is conducting extensive DRM tests on medium wave. However, the BBC and the UK's major commercial broadcasters are committed to DAB, so demand for DRM is likely to be driven by the smaller independents, religious, ethnic minority and enthusiast stations. If DRM becomes a defacto standard for digital radio alongside DAB, with radios offering both systems (and FM), it will take off. However, if DRM is limited to premium radios, like short wave is at the moment, its use is likely to be limited largely to the international broadcasting sector.

Digital Radio Mondiale is the official international site for DRM. DRM Radio is the UK's DRM site and includes technical information.