Abstract: A system for block encoding words of a digital signal achieves a maximum of error compaction and ensures reliability of a self-clocking decoder, while minimizing any DC in the encoded signal. Data words of m bits are translated into information blocks of n.sub.1 bits (n.sub.1 >m) that satisfy a (d,k)-constraint in which at least d "0" bits, but no more than k "0" bits occur between successive "1" bits. The information blocks are catenated by inserting separation blocks of n.sub.2 bits therebetween, selected so that the (d,k)-constraint is satisfied over the boundary between any two information words. For each information word, the separation block that will yield the lowest net digital sum value is selected. Then, the encoded signal is modulated as an NRZ-M signal in which a "1" becomes a transition and a "0" becomes an absence of a transition. A unique synchronizing block is inserted periodically.

Abstract: An arrangement for the transmission of audio signals, comprising a delay line (1) provided with 5, 7 or 9 tappings situated at equal time intervals along the delay line. The tappings are each connected to a common adding circuit (16) via an amplitude control device (9 to 13). The ratios between the amplitudes of the output signals of the amplitude control devices, viewed from one end of the delay line (1) to the other end are 1:2n:2n.sup.2 :-2n:1 for five tappings, 1:2n:2n.sup.2 :n.sup.3 -n:-2n.sup.2 :2n:-1 for seven tappings, and 1:2n:2n.sup.2 :n.sup.3 -n:1/4(n.sup.4 -1)-2n.sup.2 :-(n.sup.3 -n):2n.sup.2 :-2n:1 for nine tappings. This yields an arrangement having a flat frequency response from the input (2) to the output (15). The invention also relates to a plurality of delay lines (for example 31 to 35) connected in series and to a reverberation unit provided with such a transmission arrangement.

Abstract: An artificial reverberation device comprising first, second, third and fourth delay lines and first and second adder circuits with at least a part of said first, second, third and fourth delay lines connected in a cascade arrangement with the first and second adder circuits. First and second feedback circuits and first and second transmission paths are coupled to the cascade arrangement so as to produce a multiple reverberation effect with a minimum number of components.

Abstract: An optical read unit is described for scanning a record carrier with a radiation-reflecting trackwise-arranged information structure. The read unit utilizes a diode laser which generates the read beam and also detects the information stored on the record carrier. The read unit is also provided with an opto-electronic system for detecting the position of the read spot relative to a track to be read and the position of the plane of focussing. The diode is mounted in a housing and the unit includes electromechanical apparatus for moving the housing in two perpendicular directions so as to correct the position of the read spot. The objective system for the formation of the read spot is of simple construction.

Abstract: Disclosed in an apparatus for optically scanning a record carrier in which the scanning beam is focussed on the record carrier by a focussing system. For automatically correcting an incorrect control point of the focussing system, the apparatus is provided with a phase detector to which are applied the focussing error signal generated by the focussing system and a signal corresponding to the amplitude of the information signal being read. The output signal supplied by the phase detector is applied to the focussing system a correction signal so as to automatically correct for an incorrect control point of the focussing system.

Abstract: A focusing system for focusing a radiation beam onto an object, in particular an optical disc. The focusing system comprises focusing-error detection means and two control elements for correcting the focusing depending on the detected focusing error. The detection means are constructed so that via one of the two control elements a feedback servo system is obtained while via the other control element a servo system without feedback, i.e. a feed-forward system, is obtained.

Abstract: A control loop provided with a control unit for realizing a transfer characteristic having a number of peaks at a fundamental frequency and harmonics thereof. The control unit comprises a memory device for digitally storing a number of samples of the error signal appearing in the control loop during a cycle period equal to the period corresponding to the fundamental frequency. Furthermore, there are provided means for comparing the sample stored in the memory device with the value of the error signal one cycle period later and, depending on this comparison, correcting the memory content of the relevant memory location. The variation of the error signal stored in the memory device is furthermore cyclically employed as a control signal for the control device included in the control loop.

Abstract: A tachometer system for supplying a control signal indicative of positional and/or speed errors of a rotatable element comprises a tachometer on which marks are arranged in a closed track and a detector responsive thereto to produce n tacho-pulses per revolution of the tachometer. The tachometer system further comprises a memory device with n locations in which n correction signals are stored. The correction signals are obtained by driving the tachometer at an accurately constant speed, measuring the phase difference between the tacho-pulses and the reference signal, and storing the phase-error signals related to the consecutive tacho-pulses in separate locations of the memory device. When the tachometer system is used in a servo control loop these correction signals are used to correct the phase-error signals then measured, yielding a correction in respect of the deviations in these phase-error signals owing to positional tolerances of the marks on the tachometer.

Abstract: An optical read unit for reading radiation-reflecting video discs comprises a semiconductor laser which with the aid of a scan wobbler and a focussing wobbler is moved at high frequency in two directions relative to the video disc, a radial direction for tracking purposes and a direction normal to the disc for the purpose of automatic focussing. The semiconductor diode laser is mounted on a metal radiation source carrier which is connected to a heat sink for carrying off the heat with a low temperature gradient, and is driven by piezo-electric plates.

Abstract: An optical scanning device which scans a rotary video disc with the aid of a light beam comprises an objective which performs focussing movements, for focussing a light spot on a recording surface of the video disc, as well as tilting tracking movements and time-error correction movements. Near its lower end the objective is suspended in an impregnated corrugated loudspeaker diaphragm of fabric fibre which enables the various movements of the objective to be made without giving rise to annoying resonant effects. The tracking movements and the time-error correction movements are obtained with the aid of coils which are connected to the objective near the upper end and which are disposed in air gaps of associated permanent magnetic stators.