The modulation method employed in the Compact Disc CD) digital audio system codeveloped by Philips N.V. (Eindhoven, The Netherlands) and Sony Corporation (Tokyo, Japan) is described. This method, called eight-to-fourteen (EFM), is an 8 (data bit) ( 14 (channel bit) conversion block code with a space of 3 channel bits for every converted 14 channel bits which is used to connect the blocks. These 3 channel bits, called merging bits, are selectable, enabling the suppression of the low-frequency contents of the frequency spectrum.: First some of the major conditions are listed which are required of the modulation method used for recording/reproducing digital audio signals on an optical disk. The various parameters of EFM as a modulation method are explained in the second part, proving the suitability of EFM for optical disks. An actual example explains the method in detail; a frequency spectrum is also given to enhance understanding.: EFM is well matched with the error-correction method CIRC employed in the CD. The combination of these two methods plays an important role in stably reproducing a 2-channel 16-bit audio signal on a 12-cm-diameter optical disk for more than playing time, single sided.
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