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Concept
Digital Radio Mondiale
Summary
Digital Radio Mondiale (DRM; mondiale being Italian and French for "worldwide") is a set of digital audio broadcasting technologies designed to work over the bands currently used for analogue radio broadcasting including AM broadcasting—particularly shortwave—and FM broadcasting. DRM is more spectrally efficient than AM and FM, allowing more stations, at higher quality, into a given amount of bandwidth, using xHE-AAC audio coding format. Various other MPEG-4 codecs and Opus are also compatible, but the standard now specifies xHE-AAC.
Digital Radio Mondiale is also the name of the international non-profit consortium that has designed the platform and is now promoting its introduction. Radio France Internationale, TéléDiffusion de France, BBC World Service, Deutsche Welle, Voice of America, Telefunken (now Transradio) and Thomcast (now Ampegon) took part at the formation of the DRM consortium.
The principle of DRM is that bandwidth is the limiting factor, and computer processing power is cheap; modern CPU-intensive audio compression techniques enable more efficient use of available bandwidth, at the expense of processing resources.
DRM can broadcast on frequencies below 30 MHz (long wave, medium wave and short wave), which allow for very-long-distance signal propagation. The modes for these lower frequencies were previously known as "DRM30". In the VHF bands, the term "DRM+" was used. DRM+ is able to use available broadcast spectra between 30 and 300 MHz; generally this means band I (47 to 68 MHz), band II (87.5 to 108 MHz) and band III (174 to 230 MHz). DRM has been designed to be able to re-use portions of existing analogue transmitter facilities such as antennas, feeders, and, especially for DRM30, the transmitters themselves, avoiding major new investment. DRM is robust against the fading and interference which often plague conventional broadcasting in these frequency ranges.
The encoding and decoding can be performed with digital signal processing, so that a low-cost embedded system with a conventional transmitter and receiver can perform the rather complex encoding and decoding.
Official source
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