Abstract: System for changing the read side on a transparent carrier carrying information recorded on both sides. Reading is carried out by means of an optical device focusing a light beam onto one preselected side, incorporating a feedback loop servomechanism which maintains constant the distance between the optical device and the recorded surface of the disk. The servomechanism is attached or connected by the detection of the high frequency electrical signal representing the recorded information. The system opens the feedback loop when, after the read side change control, the high frequency signal drops below a predetermined threshold. A side jump control pulse which imparts an accelerated movement towards the other side to the focusing device is generated synchronously with the loop opening. The high frequency signal again rises above the predetermined threshold when the light beam focusing point reaches the opposite side. At this time, the loop is closed again and a decelerating pulse is generated.

Abstract: In an audiovisual signals diffusion apparatus, a digital coding process for protecting coded digital sound signals alternately recorded with video signals against alterations or deteriorations encountered during the transcription process onto a recording carrier or support, comprising the steps of selectively protecting signals representing low analog levels against large erroneous variations, transmitting several times the thus protected signals and garbling the different bits of successively transmitted digital signals, said process being compatible with the multiplexed recording of several sound channels.

Abstract: The invention concerns the reading by optical means of data recorded along a track on a disc; an address code, which increases one unit at each step, is recorded on the disc at the same time as the data. The optical reader contains a device for the fast movement of the reading head in a direction radial to the disc, a device for counting the number of track grooves thus crossed, a device for automatic access to some given data which contains a device for detecting addresses recorded and a programmed control circuit which triggers fast movement or a step by step movement of the reading head depending on whether the reading head is far from the track groove whose address has been recorded or is near to this track groove.

Abstract: The invention relates to devices for obtaining color television signals conforming to one given standard from color television signals conforming to another given standard. The invention consists in using a single balanced modulator which is associated with a delay line, this modulator being fed by an alternating sequence of two sub-carriers in quadrature.

Abstract: A coder designed to receive color television audio video signals where a carrier wave is frequency modulated by the luminance signal and a sub-carrier wave is modulated by time multiplexed chrominance signal and audio signal; the carrier and the sub-carrier waves are linearly mixed and the resultant signal is converted into a multiplex wave formed by a train of length modulated pulses; the sub-carrier frequency is higher than the highest frequency of the luminance signal and the lowest instantaneous frequency of the carrier minus the highest frequency of the luminance signal is at least equal to the sub-carrier frequency; the multiplex signal may be transmitted and registered on a data carrier; and a decoder adapted for cooperating with the coder, for decoding the multiplex signal coming from the transmission channel or the read out data carrier and delivering the audio video signals.

Abstract: The present invention relates to a method and apparatus for detecting defects in signals produced by the read-out of information recorded upon a data carrier. The defects correspond either to an abnormally high frequency or to an abnormally low frequency. Detection is achieved by means of one, two or three monostable switching circuits supplied with trigger pulses originating from squared read-out signals. The signal produced by the last monostable switching circuit is used for controlling a defect correcting circuit.

Abstract: The invention relates to the recording of television signals upon an optically readable data carrier. The invention provides a method which consists in recording video information line by line on each track element. A revolution of the recording involves an even number of equal recording sections alloted to a sequence of signals items representative of the line succession.

Abstract: The present invention relates to a method of detecting defects in the signal furnished by the head used to read-out information recorded upon a data carrier. The read-out signal is converted by two voltage comparators whose thresholds are respectively lower and higher than the mean peak amplitude of the carrier signal in two squarewave signals which, applied to an assembly of monostable switching circuits associated with logic gates, are responsible for the production of a defect signal capable of controlling a defect correcting circuit, which is fed with the read-out signal.

Abstract: The invention relates to the multiplexed transmission of television audio-visual signals which comprise, for example, a luminance signal successive chrominance signals and at least one audio signal. The method in accordance with the invention utilises a subcarrier wave f, frequency modulated, on the one hand, by the chrominance signals, and on the other, by a train of isochronous pulses emitted during the line blanking intervals of the luminance signal and amplitude modulated by the audio-frequency signal. The multiplex signal which will subsequently be decoded, is obtained by frequency modulating a carrier wave by a signal which is the sum of the luminance signal Y and the above mentioned frequency modulated subcarrier.