Abstract: The invention provides a process for manufacturing optical disks by pressing and disks obtained by such a process, for improving the inherent flatness of the optical disk of the thick type, obtained by a process of pressing between a recorded master and another master, recorded or not depending on whether it is a question of a single or double side disk, this latter being formed from a stack of at least two thin sheets of thermoformable material subjected to a pressure-temperature cycle after which bonding together of the sheets and duplication of the information from the masters for information recording are obtained.

Abstract: A digital process for controlling the correct reproduction of a composite television signal and in particular of a composite color television signal comprising sequential-type chrominance signals, transmitted or recorded on an information-carrying medium such as a videodisk in which binary-coded pulsed signals are inserted during available intervals of the line scanning return, the binary value of these pulsed signals representing a particular state to be controlled. This value is detected during the process reproducing the composite television signals to make the particular state to be controlled dependent on this value. A first coded pulsed signal may be used for identifying the two components of the chrominance signals. A second coded pulsed signal may be used for identifying the face read of a transparent videodisk having information recorded on both its faces.

Abstract: Process for coding binary image numbering signals to be stored on a recording medium and device for reading these signals. The process aims at protecting these signals from variations encountered during the transcription process onto a recording medium. This protection is obtained by selective inversion and repetition of predetermined parts of the binary signals.Application more specifically to an audio visual signal transmission apparatus incorporating a track jump pulse generating system, the images and the binary numbering signals of these images being recorded on a video disk.

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: A process for recording on a video-disc a television signal comprising a luminance signal, a chrominance signal, and a sound signal, wherein these three signals modulate respectively three carrier-waves. The three modulated carrier-waves are added and then optically recorded onto said video-disc along a spiral track. The level of these three modulated carrier-waves are each processed according to their own correction parameters related to the distance of the recording point from the center of the video-disc, thus allowing the disc to be later read without any correction processing during reading out.

Abstract: The present invention relates to the read-out of a data carrier having a track along which there is transcribed an angularly modulated carrier wave. In accordance with the present invention, there is provided a system for processing the read-out signal, which uses a feedback loop correcting the duty factor of a restored rectangular waveform when its value deviates from the value 0.5.

Abstract: The optical reader, for information discs of which the items of information are locatable by addresses previously recorded on each of the grooves forming the track, comprises a device for counting the number of grooves traversed during search phases which simultaneously uses the envelope of the reading signal and the signal representing the radial error in the position of the head relative to the nearest track, for algebraically counting the number of tracks traversed. After comparison with the number of grooves to be traversed, the counting device controls the deceleration of the radial advance when the spot is at a predetermined distance from the groove to be reached and also its total stoppage and the closure of the radial servocontrol loop when the groove is reached.

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 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.