Rca Inc.

John Gordon Amery

James H Wharton

Michael E Miller

Dennis Michael Schneider

Thomas W Bursus

In video recording apparatus a luminance signal is doubly preemphasized by a cascade connection of two networks prior to clipping and application to a frequency modulator. One network has a non-linear phase characteristic and an amplitude response which increases by a predetermined amount over a lower portion of the luminance band and is substantially constant otherwise. The other network has a substantially linear phase response, and a rising amplitude response within the upper portion of the luminance band. The relative amplitude responses of the networks are in a predetermined relationship such that the combination exhibits a frequency dependent variation dominated by the one network over the lower portion of the luminance band and dominated by the other network over the upper portion of the luminance band whereby the luminance signal receives an increase in preemphasis over both portions of its bandwidth and clipping distortion under transient signal conditions is reduced. In video reproducer apparatus, a combination of deemphasis networks imparts a complementary deemphasis characteristic to the preemphasized luminance signal thereby effecting a signal-to-noise ratio enhancement.

Video disc systems with plural preemphasis/deemphasis networks

A filter separates a composite video input signal into luminance and chrominance signal components. DC signals are combined with the luminance signal to produce four control signals, first and fourth ones of which have an AC component inversely proportional to the luminance signal, second and third ones of which having an AC component directly porportional to the luminance signal, each having a respective DC component. The DC components of the first and third control signals are regulated in proportion to a first reference voltage, V1, and the DC components of the second and fourth ones of the control signals are regulated in proportion to a second reference voltage V2. Cascade connected complementary non-additive mixers limit excursions in a first sense of the chrominance signal to the lesser in that sense of the first and second control signals and limits excursions in a second sense of the chrominance signal to the lesser in that sense of the third and fourth control signals to thereby provide a limited chrominance output signal. The luminance and chrominance signals are combined to provide a composite video output signal limited to a range defined by the reference voltages V1 and V2 and in which the chrominance component of the output signal is limited symmetrically with respect to the luminance signal level, thereby reducing even order harmonic distortion of the chrominance signal under limiting conditions.

Chrominance signal limiter

A transcoder useful in a video disc player includes a single multiplier in a chrominance signal path supplied with conversion signals which cause the multiplier to simultaneously frequency translate, conjugate and timebase correct a recovered chrominance signal in one format, such as NTSC, to produce a chrominance signal of another format such as PAL.

Chrominance transcoder

Improvement of the signal-to-noise ratio for a wideband video signal is effected by subtraction from the wideband video signal of a signal which follows low-amplitude excursions of the video signal's high frequency component. The latter signal is formed by a circuit arrangement which includes a high pass filter, of a C-R differentiator form, coupled to the input of an amplifier. A negative feedback path, coupled between the amplifier output and the junction of capacitive and resistive elements of the differentiator includes threshold devices which permit activation of the negative feedback path only during input signal excursions which exceed selected close-to-axis limits. The threshold device disposition relative to the high pass filter elements is such that negative feedback path activation also serves to introduce an appreciable reduction in the effective time constant of the differentiator, whereby a rapid return from a large input signal excursion beyond one of the selected limits may be followed at the amplifier input. In an illustrative use, the noise reduction circuitry is advantageously employed to process a luminance signal component separated by comb filtering from a composite signal recovered during playback of a video disc, with the subtraction step being effected in apparatus also serving to recombine separated luminance and chrominance components for formation of the disc player's output composite signal.

Noise reduction apparatus

One type of video disc reproducing system senses the capacitance between a stylus and a disc record to reconstruct the video information. The stylus includes a thin conductive element or electrode and rides in a groove of the record, which is rotated at high speeds. The record includes a conductive layer covered with a thin dielectric material. A velocity correction system comprising a closed-loop feedback system provides an advantageous means to vary the position of the pickup means relative to the moving record. This positioning maintains the relative velocity between the two substantially constant for a given radius from the center of rotation, thus correcting for residual velocity errors. There is disclosed a transducer apparatus which is mechanically coupled to the signal pickup means and electrically coupled to circuitry providing a velocity error signal. The transducer has a stationary portion which includes means for generating a magnetic flux. The transducer also has a second portion which is coupled to the pickup stylus and which is movable with respect to the stationary portion. The stationary and movable portions are intercoupled by compliant members. An electrical winding is disposed on the movable portion and is coupled by the magnetic flux such that an electrical current passed through the winding imparts motion to the movable portion. Electrical damping is provided by a closed-loop conductive member on the movable portion which is coupled by the magnetic flux and is operative to oppose motion of the movable portion.

Velocity correction system with damping means

Circuits are disclosed for processing color encoded video signals, encoded per a format wherein a chrominance signal in the form of a modulated subcarrier is buried in spectrum 'troughs' in the midband of a wider band luminance signal, an illustrative use of the encoding format being in video disc recording. The processing circuits serve, in use with composite signals developed during video disc playback, to convert an input composite signal of buried subcarrier format to an output composite signal of NTSC format. Carrier waves are amplitude modulated in accordance with composite signals developed during video disc playback, and applied to the input of a 1H delay line. Subtractive combination of the modulated carrier waves from both input and output of the delay line effects a first comb filtering action to develop a chrominance signal output in the highband location desired for output use. The delay line output is applied to an amplitude detector. The detected signal is additively combined with the input composite signal to effect a second comb filtering action, developing a luminance signal output free of chrominance components and also lacking vertical detail components. A phase inverted version of the detected signal is also additively combined with the input composite signal to effect a third comb filtering action, and the sum is low pass filtered to provide a vertical detail signal. Combining of the products of the three comb filters provides the output composite signal. The output of the amplitude detector is also used as a substitution signal input to the carrier wave modulator under defect pickup conditions.

Color image signal processing circuits

In a video disc player, an FM signal recovered from the disc is subject to frequency demodulation to obtain a composite color video signal. In the composite signal, chrominance information appears in the form of a modulated subcarrier buried in spectrum troughs in the midband of a wider band luminance signal. The composite signal is applied to a modulator to develop amplitude modulated carrier waves, which serve as the 'normal' signal input to a 1H delay line. Comb filter circuits respond to the delay line input and output to obtain separated chrominance and luminance signal components, which are suitably processed for delivery to color image display apparatus (e.g., color television receiver). The amplitude modulated carrier wave output of the delay line is also utilized as a 'substitution' signal input to the delay line, replacing the normal signal input when a defect detector, monitoring the output of the FM demodulator, indicates the onset of a picture defect. The substitution signal path includes a network providing respectively different amounts of phase shift at the carrier frequency, and at the sideband frequency associated with the color subcarrier. In a variant of the aforesaid arrangement, switching between normal and substitution signals is effected in the video domain. A composite signal from the output of the FM demodulator is normally supplied to the amplitude modulator input, but, upon defect detection, a detected version of the amplitude modulated carrier wave output of the delay line is substituted.

Defect compensation systems

A composite video signal recorded in a non-standard encoding format is rearranged in a format which can be decoded by standard television circuitry. Simplified circuitry utilizing a relatively inexpensive, narrow band delay line is provided for separating the luminance and chrominance signal components from the non-standard signal. Additional circuitry recombines the separated signal components into a desired composite signal format. Filters are incorporated for providing attenuation to particular frequency regions of the luminance and chrominance signals for effecting a relatively uniform frequency response in the resultant composite signal.

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Indianapolis, IN, United States of America

John Gordon Amery