Abstract: A method for identifying a disk loaded in a digital disk player as being either a single layer disk or a dual layer disk, and for setting a predetermined servo gain with respect to reproduction from each of two signal recording layers of a dual layer disk to achieve accurate servo control. The player counts the number of S curves occurring in a focus error signal generated during a focus search, and a system controller identifies the disk as being a dual layer disk or a single layer disk on the basis of the number of S curves or, alternatively, on the basis of the amplitude of the focus error signal. After a dual layer disk loaded in the player, the system controller determines servo gain coefficients with respect to first and second signal recording layers of the disk on the basis of signal amplitudes read from the signal recording layers, and stores the servo gain coefficients in a memory.

Abstract: A communication device wherein leader pulses which continue for a predetermined time period are transmitted prior to the transmission of data from its transmitter; its receiver is rendered intermittently operative at a cycle shorter than half the continuation time of said leader pulses by means of a cycle operation controlling means to thereby become operative for a short time at a duty lower than 1/10; while the receiver is operating, it is detected by a detector means whether or not the leader pulses are transmitted; and when the transmission of the leader pulses is detected by the detector means, the receiver is kept operative for a predetermined time period by an operation holder means.