|
Eight-to-fourteen modulation (EFM) is a data encoding technique – formally, a ''channel code'' – used by compact discs (CD), laserdiscs (LD) and pre-Hi-MD MiniDiscs. EFMPlus is a related code, used in DVDs and SACDs. EFM and EFMPlus were both invented by Kees A. Schouhamer Immink. European Patent Office President Benoît Battistelli: "Immink's invention of EFM made a decisive contribution to the digital revolution."〔(【引用サイトリンク】title= Pioneering the digital revolution: Kornelis Schouhamer Immink, developer of CD, DVD, and Blu-ray Disc coding named finalist for the European Inventor Award )〕 == Technological classification == EFM〔, EFM Patent, applied in Compact Disc, CD-R, MiniDisc.〕 belongs to the class of DC-free run length limited (RLL) codes; these have the following two properties: * the spectrum (power density function) of the encoded sequence vanishes at the low-frequency end and * both the minimum and maximum number of consecutive bits of the same kind are within specified bounds.〔(【引用サイトリンク】title='Runlength-Limited Sequences', Proceedings IEEE, vol. 78, no. 11, pp. 1745-1759, Nov. 1990. )〕〔(【引用サイトリンク】title=Codes for Mass Data Storage Systems, Second fully revised edition, Shannon Foundation Publishers, Eindhoven, The Netherlands, Nov. 2004. ISBN 90-74249-27-2. )〕 In optical recording systems, servo mechanisms accurately follow the track in three dimensions: radial, focus, and rotational speed. Everyday handling damage, such as dust, fingerprints, and tiny scratches, not only affects retrieved data, but also disrupts the servo functions. In some cases, the servos may skip tracks or get stuck. Specific sequences of pits and lands are particularly susceptible to disc defects, and disc playability can be improved if such sequences are barred from recording. The use of EFM produces a disc that is highly resilient to handling and solves the engineering challenge in a very efficient manner. 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「Eight-to-fourteen modulation」の詳細全文を読む スポンサード リンク
|