Abstract: A system for playing back information recorded on a recording disc including a memory for storing a demodulated signal information. A read out clock signal generator produces a read out clock signal synchronized with a playback clock signal obtained according to information reproduced from the recording disc. The system is further provided with means for monitoring a memory utilization factor of the memory and a control signal is produced according to the result of the monitoring of the memory utilization factor. Thus, an overflow of the demodulated digital data in the memory is prevented.

Abstract: In a system for optically reading out information recorded on a recording medium, the focus servo device includes an object lens supported by a resilient support member and a focus servo loop. The focus loop includes a driving current generating means for generating a driving current of a cylindrical coil of a focus actuator connected to the object lens in accordance with an output signal of a pickup means which includes the object lens. The improvement is that the dc loop gain of the focus servo loop is substantially raised to infinity, so as to reduce the magnitude of the focus error signal which is required to produce the driving current of the cylindrical lens for moving the object lens against the resilient force of the support member. Further, the focus servo device is characterized by a phase retarding circuit for reducing the amount of the phase rotation at the higher frequency range so as to assure the stability of the operation of the focus servo loop.

Abstract: A tracking servo system of a video or audio disc player, wherein the control data signals extracted from the electric signals read out from an information-carrying face of a video or audio recording disc are inhibited from being delivered from the servo system when the servo loop forming part of the system is open.

Abstract: A video disc player featuring a signal correcting device capable of compensating for the attenuation of the signal level of high frequency components of the reproducing signal read out from an optically electromagnetically or electrostatically scanned video disc, a device for detecting the presence or absence of recorded information on a video disc being played back, or a tracking servo system which can be locked in reliably and in a stable condition when the servo loop is to be closed from an open condition.

Abstract: A two-way CATV system having a substantial number of terminals incorporates a central processor and transmitter system which continually interrogates the terminals at high speed, monitoring changes of usage of premium programs and other data while also permitting central control of access to restricted premium programs. For inexpensive but reliable intercommunication, short, fixed word length digital messages are frequency multiplexed onto the cable in both upstream and downstream directions, and subscriber groups are controllably selected in turn, with each subscriber being scanned in what may be an arbitrary order by transmission of unique private messages which are recognized at the terminal and in response to which previously prepared fixed length messages are immediately transmitted in return.