DRM is the world's only, open standard digital radio system for short-wave, AM/medium-wave and long-wave. It has been endorsed贊同 by the ITU, IEC and ETSI. While DRM currently covers the broadcasting bands below 30 MHz, the DRM consortium國際團體voted in March 2005 to begin the process of extending the system to the broadcasting bands up to 120 MHz. The design, development and testing phases are expected to be completed by 2007-2009.
DRM is the only universal, open standard digital AM radio system with near-FM quality sound available to markets worldwide.
The quality of DRM audio is excellent, and the improvement upon analogue類似 AM is immediately noticeable顯著. DRM can be used for a range一系列 of audio content, including multi-lingual多國的 speech演說 and music.
Besides providing near-FM quality audio, the DRM system has the capacity to integrate data合併資料 and text. This additional content can be displayed on DRM receivers to enhance the listening experience.
Unlike digital systems that require a new frequency allocation流量管制, DRM uses existing AM broadcast frequency bands. The DRM signal is designed to fit in with the existing AM broadcast band plan, based on signals of 9 kHz or10kHz bandwidth. It has modes requiring as little as 4.5kHz or 5kHz bandwidth, plus modes that can take advantage of wider bandwidths, such as 18 or 20kHz.
Simulcast同步 testing is underway.
Many existing AM transmitters基地台 can be easily modified修改 to carry DRM signals.
DRM applications will include fixed and portable攜帶型 radios, car receivers, software receivers and PDAs. Several early prototype標準 DRM receivers have been produced, including a software receiver. The DRM system uses a type of transmission發送 called COFDM (Coded Orthogonal直角 Frequency Division分割 Multiplex多路傳輸). This means that all the data, produced from the digitally encoded轉碼 audio音頻信號 and associated data signals, is shared out for transmission across a large number of closely spaced carriers傳送者. All of these carriers are contained within the allotted指定 transmission channel. The DRM system is designed so that the number of carriers can be varied, depending on factors such as the allotted channel bandwidth and degree of robustness健壯 required.
The DRM system can use three different types of audio coding, depending on broadcasters’ preferences. MPEG4 AAC audio coding, augmented增加 by SBR bandwidth extension, is used as a general-purpose audio coder and provides the highest quality. MPEG4 CELP speech coding is used for high quality speech coding where there is no musical content. HVXC speech coding can be used to provide a very low bit-rate speech coder.
The robustness of the DRM signal can be chosen to match different propagation 宣傳conditions.
我覺得DRM這個是能夠保護數位加密技術，是對音樂創作者的一種保護，他能夠讓音樂的版權獲得保障，但是JOBS的想法也沒有錯，他希望音樂能夠更加快速的互通有無，流通性更好，讓這個大餅更能廣闊，不然透過IPOD或ITUNES所下載的音樂不能分享給其他使用者，這樣對IPOD或ITUNES的使用者或其他人也是不公平的。
參考資料:http://www.drm.org/system/technicalaspect.php
http://www.vtplc.com/communications/ (這是國外專門在研究DRM的機構之一)
http://www.drmrx.org/ (這是我下載的DRM)
參考圖片: 下圖是我從網路下載DRM的介面
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