Sub-$250 Receivers Coming for Digital Radio Mondiale Broadcasts
Showgoers can expect plenty of DRM announcements at the IFA fair in Berlin later this month-- not just digital rights management but Digital Radio Mondiale, the digitized AM system already in use by 20 broadcasters worldwide. Take-up has been limited so far due to the dearth of popularly priced radios, but that’s set to change this holiday season with the availability of sub- $250 receivers, 1/4 the current price, based on a tuner module by TI and RadioScape.
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More than 10 European broadcasters are expected to announce their DRM plans at IFA (Berlin, Sept. 1-7) along with the DRM Consortium, in 2 separate exhibit areas. Also on hand at each, several manufacturers will showcase DRM multi-standard radios that use the RS500 module from U.K.’s RadioScape, whose software-based decoding algorithms run on a new DSP from TI. The radios will be multi-standard, able to receive DRM, DAB (Digital Audio Broadcast), as well as analog FM and long-, medium- and short-wave AM.
DRM is the only non-proprietary global standard for digitizing AM short-wave, medium-wave and long-wave broadcasts. Other digital radio systems vary from country to country, such as Europe’s DAB, IBOC in the U.S., and various satellite formats. DRM’s supporters tout its ability to cover great distances and provide FM-like audio quality using lower transmission power and compatible channel allocations. More than 20 broadcasters are using it to reach local, national and international audiences, including the BBC World Service, Deutschlandradio, Deutsche Welle, DRF, Littoral AM, Radio de la Mer, Radio Netherlands, RTL Group, Truckradio and Voice of Russia, who'll exhibit at IFA.
None of the existing digital radio systems provide the coverage options available from the AM bands below 30 MHz. Medium-wave, popularly called “AM” in the U.S., gives local area coverage by direct transmission. Long- wave covers wider areas by direct transmission, and is how travelers from Britain hear BBC Radio 4 across Europe. AM shortwave transmits worldwide at very low power by upper atmosphere reflection. It’s how travelers get home news anywhere in the world, and how emergency services communicate from disaster zones. But all analog AM suffers from interference and poor audio fidelity. Shortwave use in particular is dwindling, because of the very poor sound quality and annoying need to keep re- tuning for the best frequency at different times of day and locations in the world.
In comparison, DRM radio can be pre-programmed to tune itself to the best frequency for time of day and place in the world. DRM works side by side with ordinary AM in the same band, giving FM-like sound and better resistance to interference because of its digital error correction. The DRM signal is designed to fit in with the existing AM broadcast band plan, based on signals of 9 kHz or 10kHz bandwidth. It has modes requiring as little as 4.5 kHz or 5 kHz bandwidth, plus modes that can take advantage of wider bandwidths, such as 18 or 20 kHz. Many existing AM transmitters can be modified easily to carry DRM signals, according to the DRM Consortium. Unlike existing AM, several DRM transmitters round the country can all use the same frequency. As with DAB, the receiver just picks up the best signal available.
The FCC will allow DRM if U.S. broadcasters want to use it. The transmission uses Coded Orthogonal Frequency Division Multiplex. 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, and all these carriers are contained within the allotted transmission channel. The number of carriers can be varied, depending on factors such as the allotted channel bandwidth and degree of robustness required. The DRM consortium recently voted to begin the process of extending the DRM system into the broadcasting bands up to 120 MHz.
Broadcasters can use 3 different types of audio coding for DRM, depending on their preference. MPEG-4 AAC audio coding, augmented by SBR bandwidth extension, is used as a general-purpose audio codec and provides the highest quality. MPEG-4 CELP coding is used for high quality speech coding where there’s no musical content. Finally, HVXC speech coding can be used to provide a very low bit-rate speech coder.
The DRM standard offers more than just listening. The existing 9-10 kHz AM channel can carry a data rate between 20- and 40 kbps, and this can hold up to 4 components. Choices include digital audio, text, multimedia, software updates for hardware and even for car engine operating systems. For text, a standard coding format called UTF8 handles all languages. Several channels can be ganged together for higher data rates. Additionally, DRM receivers can download data overnight and store text, such as for a newspaper, it for reading on their LCD displays the next day.