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Digital Audio Broadcasting (DAB) is a digital radio technology for broadcasting radio stations, used in several countries across Europe and Asia Pacific. The DAB standard was initiated as a European research project in the 1980s.〔(【引用サイトリンク】title=DAB Eureka-147: a European vision for digital radio )〕 The Norwegian Broadcasting Corporation (NRK) launched the very first DAB channel in the world on 1 June 1995 (NRK Klassisk),〔(【引用サイトリンク】title=St.meld. nr. 30 (2006-2007) )〕 and the BBC and SR launched their first DAB digital radio broadcasts in September 1995. DAB receivers have been available in many countries since the end of the 1990s. DAB may offer more radio programmes over a specific spectrum than analogue FM radio. DAB is more robust with regard to noise and multipath fading for mobile listening, since DAB reception quality first degrades rapidly when the signal strength falls below a critical threshold, whereas FM reception quality degrades slowly with the decreasing signal. Audio quality varies depending on the bitrate used and audio material. Most stations use a bit rate of 128 kbit/s or less with the MP2 audio codec, which requires 160 kbit/s to achieve perceived FM quality. 128 kbit/s gives better dynamic range or signal-to-noise ratio than FM radio, but a more smeared stereo image, and an upper cut-off frequency of 14 kHz, corresponding to 15 kHz of FM radio.〔(S. Holm, "Audio quality on the air in DAB digital radio in Norway", in Proc. 31st Audio Engineering Society International Conference, London, UK, June 2007 ), AES〕 However, "CD sound quality" with MP2 is possible "with 256…192 kbps".〔(harmoniccycle.com ), Fraunhofer: MPEG Audio Layer-3〕 An upgraded version of the system was released in February 2007, which is called DAB+. DAB is not forward compatible with DAB+, which means that DAB-only receivers are not able to receive DAB+ broadcasts.〔(DAB/DAB+/DMB Receivers ), worlddab.org〕 However, broadcasters can mix DAB and DAB+ programs inside the same transmission and so make a progressive transition to DAB+. DAB+ is approximately twice as efficient as DAB due to the adoption of the AAC+ audio codec, and DAB+ can provide high quality audio with bit rates as low as 64 kbit/s.〔(EBU Tech 3264 )〕 Reception quality is also more robust on DAB+ than on DAB due to the addition of Reed-Solomon error correction coding. In spectrum management, the bands that are allocated for public DAB services, are abbreviated with T-DAB, where the "T" stands for terrestrial. More than 20 countries provide DAB transmissions, and several countries, such as Australia, Italy, Malta, Switzerland, The Netherlands and Germany,〔(Nationales Digitalradio erfolgreich gestartet ), digitalradio.de〕 are transmitting DAB+ stations. See Countries using DAB/DMB. ==History== DAB has been under development since 1981 at the ''Institut für Rundfunktechnik'' (IRT). In 1985 the first DAB demonstrations were held at the WARC-ORB in Geneva and in 1988 the first DAB transmissions were made in Germany. Later DAB was developed as a research project for the European Union (EUREKA), which started in 1987 on initiative by a consortium formed in 1986. The MPEG-1 Audio Layer II ("MP2") codec was created as part of the EU147 project. DAB was the first standard based on orthogonal frequency division multiplexing (OFDM) modulation technique, which since then has become one of the most popular transmission schemes for modern wideband digital communication systems. A choice of audio codec, modulation and error-correction coding schemes and first trial broadcasts were made in 1990. Public demonstrations were made in 1993 in the United Kingdom. The protocol specification was finalized in 1993 and adopted by the ITU-R standardization body in 1994, the European community in 1995 and by ETSI in 1997. Pilot broadcasts were launched in several countries in 1995. The UK was the first country to receive a wide range of radio stations via DAB. Commercial DAB receivers began to be sold in 1999 and over 50 commercial and BBC services were available in London by 2001. By 2006, 500 million people worldwide were in the coverage area of DAB broadcasts, although by this time sales had only taken off in the United Kingdom and Denmark. In 2006 there were approximately 1,000 DAB stations in operation world wide.〔(World DMB forums list of benefits ), worlddab.org〕 The standard was coordinated by the European DAB forum, formed in 1995 and reconstituted to the World DAB Forum in 1997, which represents more than 30 countries. In 2006 the World DAB Forum became the World DMB Forum which now presides over both the DAB and DMB standard. In October 2005, the World DMB Forum instructed its Technical Committee to carry out the work needed to adopt the AAC+ audio codec and stronger error correction coding. This work led to the launch of the new DAB+ system. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Digital Audio Broadcasting」の詳細全文を読む スポンサード リンク
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