Abstract: In a digital phase detector arrangement, the combination of a digital phase detector for deriving a digital output signal representing the phase differences between two input clock signals supplied to the phase detector, and a circuit for reducing jitter in the output signal; the circuit comprising a differentiator for differentiating the output signal to produce a differentiated signal, a low-pass filter for low-pass filtering the differentiated signal to produce a filtered signal, and an integrator for integrating the filter signal to produce a further digital output signal from which at least some jitter has been removed by the low-pass filter.

Abstract: A television standards converter for converting an input digital video signal from one television standard to another, comprises a high-pass filter (36) for filtering the input video signal horizontally and vertically, a pluraity of parallel processing channels comprising respective circuits (43 to 58) for determining pixel by pixel of the high-pass filtered video signal the correlation magnitudes for a range of horizontal and vertical pixel offsets, low-pass filters (59) for filtering the resulting correlation magnitudes, a selecter (62) for determining for each pixel of said video signal, from the relationship between motion vector magnitude and the correlation magnitude, the motion vector corresponding to the maximum correlation magnitude, and a temporal interpolator (FIG. 14) for deriving interpolated fields or frames by combining sample values offset by the motion vectors.

Abstract: Apparatus for demultiplexing an input 4:4:4:4-standard digital video signal into first and second output 4:2:2-standard digital video signals comprises a demultiplexer for separating the input video signal into a luminance input signal, two chrominance input signals, and a key input signal; for each said chrominance input signal, a first low-pass filter for low-pass filtering said chrominance input signal with a cut-off frequency preferably equal to 7/16 the Nyquist frequency of the input chrominance signal, a sub-sampler for sub-sampling the signal from the first filter at a ratio of 2:1 to provide a first chrominance output signal, a subtracter for subtracting the signal from the first filter from the input chrominance signal, a demodulator for demodulating the signal resulting from the subtraction with a signal preferably of 3/8 the Nyquist frequency, and a second low-pass filter for low-pass filtering the resulting demodulated signal with a cut-off frequency equal to half the Nyquist frequency, the sub-sa

Abstract: A MAC signal encoder, for encoding a video signal into MAC format, includes vertical sub-samplers for vertically sub-sampling color difference signals of the video signal, vertical filters that vertically filter the color difference signals prior to their vertical sub-sampling so as to limit their spectra to a band below the vertical Nyquist frequency of the sub-sampled color difference signals, a multiplexer that multiplexes together the filtered and sub-sampled color difference signals and luminance information of the video signal to produce a signal in MAC format, and a marker detector responsive to the video signal containing marker information indicating that the signal has previously been MAC encoded to inhibit the vertical filtering of the color difference signals by the vertical filters.

Abstract: In an apparatus and method for deriving gradient vectors for use in the spatial interpolation of an input digital video signal; the scan lines of a field of the input digital video signal are high pass filtered so as to provide a high pass filtered video signal which is supplied to a plurality of parallel processing channels in which the high pass filtered video signal is differently low pass filtered so as to form respective low pass filtered video signals, the correlation for a range of pixel offsets is determined pixel-by-pixel for the video signal outputs from the channels so as to form a plurality of gradient vectors for each pixel of the input digital video signal, and the gradient vector is selected, for each pixel of the input digital video signal, which corresponds to the maximum correlation value therefor. The apparatus for deriving gradient vectors is also applicable to a television standards converter.

Abstract: In a video signal clamping circuit, a FIFO register stores a sequence of digital samples of an input video signal taken during a portion of a horizontal blanking interval of the signal during which the signal is at a black level. A black level error PROM generates a digital error signal representing any deviation between a digital sample from the FIFO register and a reference black level. An accumulator accumulates digital error signals supplied thereto by the PROM to produce an accumulated digital error signal which is converted to analog form by a digital-to-analog converter. A clock controls the supply of the stores samples in sequence from the FIFO register to the PROM such that the samples are supplied, during a line-active period that follows the horizontal blanking interval, at a clock frequency which is less than the sampling frequency.

Abstract: In apparatus for spatially interpolating between lines of a digital video signal, to produce interpolated lines, a supersampler horizontally interpolates between samples of the signal to produce a supersampled signal consisting of the original samples and interpolated samples located between them. Block matching circuits each determine, for each sample of the supersampled signal, the extent of matching between two blocks of N.times.M samples (N=number of lines and M=number of samples), the blocks being vertically offset in opposite directions with respect to a line to be interpolated, and being horizontally offset in opposite directions with respect to a predetermined sample position. Each block matching circuit produces a matching value for a respective different horizontal offset.

Abstract: A composite digital video signal encoder comprises crosstalk measuring filters for measuring crosstalk between luminance and chrominance components of a composite digital video signal, a vertical comb filter and a vertical/temporal filter each operative to separate one of the luminance and chrominance components from the composite signal, a mixer for mixing output signals produced by the vertical and vertical/temporal filters, and a mixer control means responsive to the measured crosstalk to control the mixing ratio of the mixer in a sense to reduce cross effects in the mixed output signal resulting from the crosstalk.

Abstract: Apparatus for coding a digital component video signal, comprising first means for modulating a first carrier signal with one of the component chrominance signals, the first carrier signal having a four-field sequence such that the phase of the first carrier signal is inverted at every line interval, second means for modulating a second carrier signal with the other of the component chrominance signals, the second carrier signal having a two-field sequence such that the phase of the second carrier signal is inverted at every field interval, and means for combining a luminance signal with the modulated chrominance signals to thereby reduce the bandwidth of the combined component video signal.

Abstract: In a system in which a digital video signal is transmitted with differential pulse code modulation, a predetermined number of samples alternate in a horizontal line of the digital video signal are grouped, and the center sample of the grouped samples of the digital video signal is transmitted with the original number of bits, while the other samples of a group are differentially modulated with reference to the respective center sample and are transmitted with the center sample as a cluster of samples.

Abstract: A method of processing timecode data in a recorded digital video signal comprises assigning a first timecode to a first timecode location in the signal during recording, assigning the first timecode to a second timecode location and assigning a current second timecode to the first timecode location during a first editing step, and in subsequent editing steps sequentially changing the timecode locations of the timecodes so that the current timecode is assigned to the first timecode location and the previous timecodes are shifted sequentially through the other timecode locations.

Abstract: A digital video tape recorder comprises a head drum, four transducer heads mounted in pairs on the head drum for recording oblique tracks on a magnetic tape, a demultiplexer for distributing digital data to be recorded and corresponding to a video signal such that each field of the video signal is divided into 50-line segments, the digital data corresponding to each field are evenly distributed between all four of the heads for recording, and each track comprises a block of digital data relating to one 50-line segment and a block of digital data relating to another 50-line segment, the two blocks of digital data being separated by an edit gap.

Abstract: A video replay store for a multi-channel digital video tape recorder, comprises a respective channel store for each channel, each channel store comprising a plurality of field stores which are written in and read from cyclically, a respective field boundary detector for each channel, each field boundary detector supplying a first pulse in response to each field boundary where an odd field changes to an even field, and a second pulse in response to each field boundary where an even field changes to an odd field, in the off-tape data in the respective channel, and a replay store controller for supplying write requests and read requests in a predetermined sequence to all of the channel stores, the replay store controller stepping on to the next state in the predetermined sequence in response to each first first pulse following a second pulse and each first second pulse following a first pulse.

Abstract: A method of decoding digital synchronizing signals each of which consists of a plurality of bits in a predetermined pattern, the intervals between the starts of successive synchronizing signals in an input digital signal being variable over a range, comprises ascertaining the bit period distance between the starts of two successive synchronizing signals, subsequently searching the input digital signal for the pattern using a window comprising the bit period distance, which window is varied in position if the bit period distance changes, and supplying an output synchronizing pulse in synchronism with subsequent synchronizing signals found in the window.

Abstract: In a method of recording digital audio signals of four audio channels in association with a digital video signal in oblique tracks using a 4-head digital video tape recorder, the digital audio signals are assembled into error-correction blocks each comprising two audio data words and two error-correction code check words, each oblique track comprises in sequence first and second sectors at the beginning of the track, a central portion in which the video signals are recorded, and third and fourth sectors at the end of the track, the audio data words and the check words are distributed to the four heads to be recorded in the sectors, and the assembly, the error-correction code and the distribution are such that the four audio channels can be correctly reproduced even if, on reproduction, any two of the sectors are lost from each reproduced track, or any two of the four heads fail to supply a reproduced output.

Abstract: A component digital video signal is encoded such that first and second color components CB, CR are modulated on the lower sideband of a carrier at the Nyquist frequency of the luminance component Y. The encoding method involves alternately adding and subtracting the luminance and color component signals Y+C, Y-C, Y+C, Y-C, (etc) and changing the phase relationship between this addition and subtraction for the first and second color components every field, so that in each alternate field the addition and subtraction operations are in phase for both color components CB, CR and in every other field, the operations are out of phase. Upon decoding, the encoded video signal is comb filtered to recover the luminance component Y and color components CB, CR, and the correct phase for the color components (CB, CR) is restored by a phase alternation operation which is inverse to that applied during encoding.

Abstract: A method of and apparatus for reproducing digital audio data which have been recorded in oblique tracks on a magnetic tape in association with digital video data is provided, the audio data in each track having been assembled as blocks of audio data words for recording, and the audio data words having been shuffled in order over a predetermined distance greater than one block prior to recording. In the method, in a slow motion reproduction mode, the recorded audio data is reproduced at a speed lower than the normal reproducing speed, and on a first occasion that any given block of audio data words is reproduced in complete form, that block of audio data words is stored, and each stored block of audio data words is read out under control of a read clock signal the frequency of which is adjusted to correspond to the reproduction speed, whereby the audio data is reproduced with a change in pitch. In a fast motion reproduction mode fragments of the audio data are reproduced without a change in pitch.

Abstract: A method of and apparatus for reproducing digital audio data which have been recorded in oblique tracks on a magnetic tape in association with digital video data is provided, the audio data in each track having been assembled as blocks of audio data words for recording, and the audio data words having been shuffled in order over a predetermined distance greater than one block prior to recording. In the method, in a slow motion reproduction mode, the recorded audio data is reproduced at a speed lower than the normal reproducing speed, and on a first occasion that any given block of audio data words is reproduced in complete form, that block of audio data words is stored, and each stored block of audio data words is read out under control of a read clock signal the frequency of which is adjusted to correspond to the reproduction speed, whereby the audio data is reproduced with a change in pitch. In a fast motion reproduction mode fragments of the audio data are reproduced without a change in pitch.

Abstract: In a method of or apparatus for decoding incoming digital data which includes respective synchronizing codes and address codes associated with successive data blocks, the address codes including respective data block addresses which increase by one from data block to data block, the incoming digital data is checked to locate the positions of the synchronizing codes, successive address codes are checked to ascertain if the block addresses increase by one from one address code to the next, and if the block address does increase by one from one address code to the next, the incoming digital data is aligned using the synchronizing codes, for subsequent decoding of the data blocks.

Abstract: Concealing errors in a digital television signal, which has a plurality of component sample values corresponding respectively to sample positions along a horizontal scan line of a television picture made up of a plurality of scan lines, in respect of each sample value which is in error, by calculating a first concealment accuracy by determining the difference between two immediately adjacent sample values both in the scan line immediately preceding or following the scan line which the error sample is in, and one of which sample values is immediately adjacent to the error sample, calculating a second concealment accuracy by determining the difference between two immediately adjacent sample values both in the vertical line immediately preceding or following the vertical line which the error sample is in, and one of which sample values is immediately adjacent to the error sample, selecting from the available concealment accuracies a preferred direction of the television picture for concealing the error sample, c