Abstract: A method of recording a digital audio signal in association with a digital video signal which is to be recorded in oblique tracks on a magnetic tape using a rotary head the rotational frequency of which is locked to the digital video signal, comprises the steps of assembling incoming audio data words which correspond to successive samples of an audio signal into groups nominally of N audio data words where N is the number of audio samples corresponding to the digital video signal to be recorded in one oblique track, allowing the number of audio data words in each group to vary preferably over the range N-1 to N+1 to maintain synchronism of the audio signal with the rotational frequency of the rotary head, coding the audio data words into error-correcting blocks for recording by the rotary head, and associating with each error-correcting block a status code for use on reproduction and which indicates whether the number of audio data words in the corresponding group is N-1, or N+1.

Abstract: Apparatus for concealing errors in a digital television signal comprises delay elements for deriving a current sample value and a first group of the sample values spatially closest to the current sample value in the same frame of the television signal and delay elements for deriving from the preceding frame of the television signal a delayed sample value corresponding in position to the current sample value and a second group of sample values respectively corresponding in position to the sample values. The current sample value and the delayed sample value are checked for error, and subtractors check pairs of sample values corresponding in position in the current and preceding frames of the television signal for error, derive a measure of the difference in the levels of the sample values in each pair, and combine the results of these checks to provide an output signal which is a measure of the number of the errors and of the sum of the differences.

Abstract: Digital video tape recorder apparatus comprises a recording head assembly having 2n heads, where n is an integer, preferably one, two or three, a demultiplexer for demultiplexing the video samples of an incoming digital television signal sample-by-sample, into 2n channels for supply to the 2n recording heads, and a switching arrangement for switching the connections between the channels and the heads line-by-line and also possibly field-by-field or frame-by-frame of the television signal.

Abstract: A sequential data block address processing circuit for deriving address signals in dependence on incoming data representing, for example, a digital television signal and formed by sequential blocks of data each including a block address which changes cyclically from block to block and which is formed of three address words respectively representing block, line and segment numbers which change cyclically, the circuit comprising a read-only memory operative for each incoming block address to increment the block number and if this incrementing involves a carry to increment the line number and so on up to the segment number, and further operative for each incoming block address to form a predicted next block address which is formed of three address words each representing the respective block, line or segment number or incremented number as appropriate, and a comparator to compare each predicted next block address with the next incoming block address and to supply a correct address indication only if there is ide

Abstract: A method of correcting errors in binary data which may represent a digital television signal, comprises assembling the data into a plurality of first blocks, each first block comprising a first plurality of, say sixty, data words and a second plurality of, say six, check words and further assembling the first blocks into arrays of first blocks and deriving first and second check blocks for each array of the first blocks. Each check word is derived in dependence on all the data words in the first block and each other check word in the first block. One check word may be derived by modulo-2 addition and the remaining check words may be derived by respective primitive polynomial generators. The first check block is derived by modulo-2 addition and the second check block is derived by a primitive polynomial generator.

Abstract: A digital PAL color television signal demodulator for demodulating the U and V color component signals from an input chrominance signal derived from a PAL color television signal which has been digitized by being sampled a predetermined number of times per horizontal line comprises a first memory storing values representing the phases of the sub-carrier signal, on which the U and V color component signals have been modulated, at the first sample position of each of the successive lines of four fields of the television signal, a second memory storing values representing the relative phases of successive sample positions along a horizontal line, means for deriving from the memories values representing the phases of successive sample positions of each of the successive samples in eight fields of the television signal, means to derive from the values derived from the memories quadrature amplitude values of the sub-carrier in synchronism with a sample frequency of the input chrominance signal, and multipliers and

Abstract: A television frame signal synchronizing circuit comprises a presettable cyclic counter and a maximum count detector, a clock pulse generator for supplying clock pulses to the counter, a store for storing the count of the counter, and a source of reference frame pulses to which input frame pulses are to be synchronized, each reference frame pulse causing the count stored in the store to be loaded into the counter. A television signal processor is capable of adjusting the timing of television signals passed therethrough in dependence on a reverse frame pulse, the carry signals from the counter forming reverse frame pulses for supply to the television signal processor for adjusting the phase of the television signal passed therethrough, the television signal including the input frame pulses at least some of which are derived and supplied to the store which thereupon stores the count of the counter.

Abstract: Digital video tape recorder apparatus comprises, at the recording side, a field store controlled by a programmable read-only memory to shuffle samples making up a digital television signal prior to recording, the shuffling alternating between a first and a second predetermined manner field by field of the television signal. At the reproducing side of the apparatus a reverse de-shuffling process is carried out.

Abstract: A method of concealing errors in a digital television signal formed by a plurality of sample signals corresponding respectively to sample positions along a horizontal scan line of a television picture made up of a plurality of such lines, comprises, in respect of each sample signal which is in error, selecting from a plurality of algorithms a preferred algorithm for correcting the error sample signal, calculating a corrected value of the error sample signal using the preferred algorithm, and substituting the corrected sample signal for the error sample signal so as to conceal the error. The algorithms may be four in number and use sample values located along the horizontal, vertical and two diagonal directions respectively to predict the known sample values at sample positions adjacent to the position of the error sample signal, the algorithm giving the best result being selected.

Abstract: A method of correcting errors in binary data which may represent a digital television signal, comprises dividing the data into a plurality of first blocks, each first block comprising a first plurality of, say sixty, data words and a second plurality of, say six, check words, and further deriving a parity check block for a plurality of the first blocks. Each check word is derived in dependence on all the data words in the first block and each other check word in the first block. One check word may be derived by modulo-2 addition and the remaining check words may be derived by respective primitive polynomial generators.

Abstract: Apparatus for regenerating a clock pulse signal from a stream of data derived from a variable-speed digital video tape recorder and lacking a strong clock pulse component, comprises a first phase-locked loop circuit to which the incoming data is supplied and which includes a loop filter of relatively wide bandwidth and a first voltage controlled oscillator. The first voltage controlled oscillator supplies a regenerated clock pulse signal to a second phase-locked loop circuit which includes a loop filter of relatively narrow bandwidth and a second voltage controlled oscillator which supplies a regenerated output clock pulse signal. The first and second voltage controlled oscillators are controlled by a preset control signal derived by a preset control signal generator arrangement in dependence on the direction and speed of a magnetic tape from which the video tape recorder is reproducing the stream of data.

Abstract: A digital random error generator for generating burst errors comprises a first digital random error generator arrangement including a first pseudo random generator and a static random number generator for generating burst start signals at random times, a second digital random error generator arrangement including a second pseudo random generator and a second static random number generator for generating burst errors of random duration, and a flip-flop circuit receiving the outputs of the digital random error generator arrangements whereby the output of the second digital random error generator arrangement is enabled in dependence on the output of the first digital random error generator arrangement, so that the digital random error generator supplies a burst error of random duration starting at each above-mentioned random time.

Abstract: A method of correcting errors in binary data comprises associating with each block of data words a plurality of check words for use in error detection and correction, each check word being derived in dependence on all the data words in the block and each other check word associated with the block. One check word may be derived by an exclusive-OR addition and the other or others may be derived using a primitive polynominal generator.

Abstract: A magnetic tape recording and reproducing arrangement comprising a rotary drum, helical scan digital video tape recorder including first and second head assemblies mounted diametrically on a rotary drum, the first head assembly including first and second heads having gaps of opposite azimuth angle, and third and fourth heads having gaps of opposite azimuth angle to the first and second heads respectively, the second head assembly including fifth and sixth heads having gaps of opposite azimuth angle, and seventh and eighth heads having gaps of opposite azimuth angle to the fifth and sixth heads respectively, tape guides to wrap a tape more than 180.degree.

Abstract: A decoder-recoder arrangement for decoding a composite digital television signal for recording on a digital video recorder and for subsequently recoding the reproduced signal, the arrangement comprising a decoder including filters for separating two chrominance components from the composite digital television signal, demodulators for demodulating the chrominance components, sample rate reducers for reducing the sample rates of the demodulated chrominance components, interpolators for interpolating samples into the sample-reduced demodulated chrominance components to restore the sample rate to the original value, modulators for remodulating the interpolated chrominance components, an adder for adding together the modulated interpolated chrominance components, and a subtractor for subtracting the output of the adder from the input composite digital television signal; and a recoder including interpolators for interpolating samples into said sample-reduced demodulated chrominance components to restore the sample

Abstract: An error-correction format for transmitting digital television signals comprises segments of data, which segments may for example represent 48 successive horizontal lines of a television field. The segment comprises, for example, data groups n to n+23 and a final group n+24 which forms a vertical parity check group. Each of the data groups n to n+23 comprises m blocks, and each block comprises a synchronization and address sub-block followed by s data sub-blocks, each data sub-block being followed by respective inner code protection bits for providing error protection for the immediately preceding data sub-block, and finally followed by a cyclic redundancy check code for providing error protection for the s data sub-blocks in the block. The vertical parity group n+24 is just the same in format as the other groups n to n+23, but each sub-block thereof is made up of vertical parity check words which form an outer error correcting code in place of data words.

Abstract: A method of concealing errors in a digital television signal formed by a plurality of sample signals corresponding respectively to sample positions along a horizontal scan line of a television picture made up of a plurality of such lines, the method comprising, in respect of each sample signal which is in error, selecting from a plurality of algorithms a preferred algorithm for correcting the error sample signal, calculating a corrected value of the error sample signal using the preferred algorithm, and substituting the corrected sample signal for the error sample signal so as to conceal the error. The algorithms may be four in number and use sample values located along four different directions respectively, such as the horizontal, the vertical, and the two diagonal directions of the television raster, to predict the known sample values at sample positions adjacent to the position of the error sample signal, the algorithm giving the best result being selected.

Abstract: Frame information is recovered from a stream of binary data formed at a transmitter from a block of m.times.n information bits comprising m groups of n bits plus m parity bits, one for each said group of n bits, these parity bits having then been scrambled by performing an exclusive-OR operation in a gate on each parity bit with a respective bit of an m-bit parity scrambling code, said block of bits together with the scrambled parity bits forming a frame for transmission over a transmission link. At a receiver new parity bits are produced in a parity bit generator at the incoming bit rate from the incoming stream of binary data by forming a new parity bit from each successive moving group of n+1 incoming bits. The new parity bits are cyclically distributed to n+1 m-bit shift registers and a framing signal is produced when one of the shift registers holds m bits substantially corresponding to the m bits of the parity scrambling code.

Abstract: A method of concealing errors in a composite PAL or NTSC digital television signal formed of sample signals corresponding respectively to sample positions along horizontal scan lines of a television picture made up of a plurality of such horizontal lines, comprises, in respect of each sample signal the steps of, using a first algorithm to calculate a first expected value of the sample signal, the first algorithm using actual values of adjacent sample signals in the same horizontal line as the sample signal, using a second algorithm to calculate a second expected value of the sample signal, the second algorithm using actual values of adjacent sample signals in the same horizontal line as the sample signal and actual values of adjacent sample signals in the horizontal lines preceding and following the horizontal line of the sample signal, continuously monitoring which of the first and second algorithms gives expected values closer to the actual values, and on occurrence of an error sample signal using the algor

Abstract: A composite PAL television signal decoder comprises a first delay device for delaying an input PAL television signal A by one horizontal line scan period minus one quarter of a period of the color sub-carrier signal to produce a first delayed signal B, a second delay device for delaying the signal A by one half of a period of the color sub-carrier signal to produce a second delayed signal C, a third delay device for delaying the signal C by one horizontal line scan period minus one quarter of a period of the color sub-carrier signal to produce a third delayed signal D, means to derive a luminance component Y as one half (A+D), means to derive a chrominance component U as one quarter (B+D) minus one quarter (A+C), and means to derive a chrominance component V as one quarter (C+D) minus one quarter (A+B).