Digital Radio Mondiale
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.
Digital Radio Mondiale is also the name of the international non-profit consortium that has designed the platform and is now promoting its introduction.
The inaugural broadcast took place on June 16, 2003, in Geneva, Switzerland, at the ITU's World Radio Conference.
A few manufacturers have introduced DRM receivers which have thus far remained niche products due to limited choice of broadcasts.
It is expected that the transition of national broadcasters to digital services on DRM, notably All India Radio, will stimulate the production of a new generation of affordable, and efficient receivers.
[5] The General Overseas Service of Akashvani broadcasts daily in DRM to Western Europe on 9.95 MHz at 17:45 to 22:30 UTC.
[8] The BBC also trialed DRM+ in the FM band in 2010 from the Craigkelly transmitting station in Fife, Scotland, over an area which included the city of Edinburgh.
[10] RTÉ has also run single and multiple programme overnight tests during a similar period on the 252 kHz LW transmitter in Trim, County Meath, Ireland which was upgraded to support DRM after Atlantic 252 closed.
USAC is designed to combine the properties of a speech and a general audio coding according to bandwidth constraints and so is able to handle all kinds of programme material.
Given that there were few CELP and HVXC broadcasts on-air, the decision to drop the speech-only coding formats has passed without issue.
Opus is an open-source codec not included in the DRM standard, but commonly supported by popular software implementations.
Aside from perceived technical advantages over the MPEG family such as low latency (delay between coding and decoding), the codec is royalty-free and not subject to patent licensing.
The larger the guard interval, the greater the resistance to long multipath propagation errors (delay spread).
It can run in simulcast mode by switching between DRM and AM, and it is also prepared for linking to other alternatives (e.g., DAB or FM services).
The Dream software will receive the commercial versions and also limited transmission mode using the FAAC AAC encoder.
However, DRM+ (DRM Mode E) as designed and standardized only provides bitrates between 37.2 and 186.3 kbit/s[19][20] depending on robustness level, using 4-QAM or 16-QAM modulations and 100 kHz bandwidth.
