Abstract: A system and method for recording multi-level data to a multi-amplitude recording channel encodes binary data to form multi-level data. The multi-level data are recorded to the storage media for later recall. The system utilizes linear, multi-amplitude recording media which allows data to be stored as multi-level data--requiring fewer `bits` to represent the same number of symbols. To obtain greater data density in the storage media, a diffraction limited write laser is utilized, resulting in a smaller write-spot size. Because the read laser is of a longer wavelength, its diffraction limited spot size is larger. As a result, more than one mark is read at a given read time resulting in a inter-symbol interference. Trellis coded modultation techniques are adopted to convert the binary input data into M-ary data having M levels. Further coding is then performed to compensate for the effects of the inter-symbol interference. This is accomplished by precoding the data using a Tomlinson-Harashima precoder.

Abstract: A system for encoding and decoding binary data in a data transmission system, such as a magnetic or optical data storage channel. The encoding process is implemented as a two-step RLL coding procedure wherein the original user bit data are first encoded as an asymmetric RLL code signal at a reduced clock rate and then translated to a second even-spaced RLL code signal suitable for recording to a data storage medium at a full-speed clock rate. The system also provides for recovering suitable even-spaced RLL codes recorded at a full-speed clock rate, translating the recovered even-spaced RLL code signal to an asymmetric RLL code signal at a reduced clock rate, and then decoding the asymmetric RLL code signal to recover the original user bit data. A preferred embodiment uses a rate 2/5 (2, 16, 2) even-spaced RLL code at a full-speed clock rate and a rate 4/5 (0,7; 1,8) asymmetric RLL code at a half-speed clock rate.

Abstract: An apparatus for converting source data into modulation data includes a compressed look-up table based on a conversion correlation, a non-effective data discriminator, a group discriminator, an output flag generator, a flag modulator, a control signal generator and an output compensator. A first address having the source data and a original input flag and a second address having the source data and a modulated input flag are sequentially applied to the look-up table which in turn generates first tentative data and a first tentative flag with respect to the first address, generates second tentative data and a second tentative flag with respect to the second address, and produces unique non-effective data when non-effective data is applied.

Abstract: A coding method and apparatus convert a data word of m.times.r bits into a code word of n.times.r bits (m<n) with regard to a predetermined number r. The basic data word length m is made two or three bits, basic code word length n is made five bits and the predetermined number r satisfies the relation 1.ltoreq.r.ltoreq.4 or 1.ltoreq.r.ltoreq.2 respectively, the data word of m.times.r bits is converted into a code word of 5r bits, and coding is performed in such a manner that the run number of "0"s is greater than four and less than 19, or greater than one and less than five respectively. Further, a decoding method and apparatus decode perform decoding in accordance with the logical expressionsY.sub.1 =X.sub.13 +X.sub.14 .multidot.(X.sub.19 +X.sub.20)+X.sub.9 .multidot.X.sub.10 .multidot.X.sub.15 +X.sub.9 .multidot.X.sub.10 .multidot.X.sub.11 .multidot.X.sub.12 .multidot.X.sub.13 .multidot..sub.14 +(X.sub.4 +X.sub.5).multidot.X.sub.10 .multidot.X.sub.15Y.sub.2 =X.sub.12 +X.sub.13 +X.sub.14 +X.sub.15 +X.sub.

Abstract: A method for constructing trellis codes and an apparatus for providing trellis codes with increased minimum distance between output sequences of partial response channels with constrained inputs. A Viterbi detector expands a conventional trellis structure for the channel incorporating additional states interconnected such that a preselected function associates each state in the trellis with an algebraic evaluation of a polynomial at a particular element of a finite field. The detector trellis is time-varying such that only certain values of the preselected function are allowed every m bits. The time-variation assures that there are no minimum distance extensions of erroneous sequences beyond a predetermined length in the trellis. Reliability of storage channels is desirably increased, because more noise is required to overcome the additional distance and cause an error in distinguishing the correct encoded sequence.

Abstract: The present invention relates to a method of recording and reproducing data on a recording medium, wherein original data is recorded on a recording medium by converting it into a code having more than one "0" between bits "1" such as MFM code and RLL (1,7) code, and a timing of a zero-cross of a reproductive signal or a second order differential signal from the recording medium is detected to obtain a bit "1" and reproduce the original data. The method allows to avoid affect of interference between marks and to record and reproduce data at high recording density and with high reliability.

Abstract: A recording method and apparatus for an optical disk employs a data format having a fixed pattern sync portion in which a minimum run length of zeros and a maximum run length of zeros are not adjacent to each other. As such, temperature difference caused during recording the optical disk may be made smaller, thermal stress applied upon the medium may be reduced, the deterioration thereof may be restrained, and the repetitive frequency of the medium may be improved.

Abstract: A pilot signal is superposed and recorded on data at the beginning of each track. The beginning portion of the track is constituted only of codewords having a disparity of each 10 bits which is +2, 0 or -2. Also, the cumulative value of the disparities of every 10 bits may fluctuate in a period coinciding with the period of the pilot signal to be superposed. Therefore, the frequency spectrum in the beginning part of the track has a peak at the frequency of pilot signal, and using this peak as the pilot signal, tracking is controlled during reproduction.

Abstract: Systems, apparatus and methods for recording or reproducing from a re-recordable record carrier digital signals, representing a digital audio signal, containing information which results in concealment of a portion of a replica of the digital audio signal during its reproduction to prohibit audio distortions resulting from a boundary between two digital signals, wherein one of those digital signal is newly-recorded over a previously-recorded other digital signal. The concealment information can also be included in auxiliary signals recorded on reproduced from the record carrier along with the digital signals. In a recording apparatus, a digital signal including audio information (i.e.

Abstract: An encoding apparatus for constructing an asymptotically optimal coding scheme for second order DC-constrained channels is disclosed. A first encoding function block breaks an input data stream into equal sized vectors of length m bits. A sign designation bit is then attached to each vector to make vectors of length m+1 bits. r redundancy bits are added to each vector, to produce balanced vectors of length m+1+r bits. A first moment is calculated for each vector. A determination is made whether the addition of this vector's first moment value to an accumulated running sum of all the vectors' first moments effectively drives the running sum in the direction of zero. If is does then that vector's first moment is added to the accumulated running sum of first moments and the vector is added to the output array.

Abstract: M sets of digital data obtained by adding a control bit to an n-bit data string are collected to generate 2.sup.m kinds of m(n+1)-bit data strings, with I-NRZI modulation being applied to these data strings to generate m kinds of I-NRZI modulated data strings and the I-NRZI modulated data strings are subject to spectrum analysis for the desired frequency components, in order to supply one of the I-NRZI modulated data strings as a recording signal based on the result of the spectrum analysis.

Abstract: A digital video recording system for digitizing analog video signals and recording the digital signals on video tape and for reading digital video signals from video tape and producing an analog video signal. The recording system comprises an A/D converter, a data compressor for compressing digital video signals at a data rate of 1/N (N an integer greater than 1), an encoding and modulating mechanism that provides digital data segments, and a control mechanism for controlling the system such that recording data for one field, which is normally recorded in M tracks (M: an integer greater than N) in ordinary recording mode, is recorded in about M/N tracks in a long recording mode.

Abstract: A synchronous read channel having a single chip integrated circuit digital portion which provides digital gain control, timing recovery, equalization, digital peak detection, sequence detection, RLL(1,7) encoding and decoding, error-tolerant synchronization and channel quality measurement is disclosed. The integrated circuit accommodates both center sampling and side sampling, and has a high degree of programmability of various pulse shaping and recovery parameters and the ability to provide decoded data using sequence detection or digital peak detection. These characteristics, together with the error-tolerant sync mark detection and the ability to recover data when the sync mark is obliterated, allow a wide variety of retry and recovery strategies to maximize the possibility of data recovery.

Abstract: A tape drive subsystem discloses that variable length symbols can be used to reliably identify data stored on the tape. Machine controlling procedures are disclosed to encode and decode data for the reliable sensing of the serial number of a media, especially tape cartridges, having different track densities. The subsystem detects the serial number of the media and corrects, or at least detects, error patterns. A variable length symbol code is encoded in a plurality of groups with each group having a "one" being represented as an erase gap ERG signal covering a first two units of a group, and a "zero" is represented as one unit of an ERG signal, both followed by four units of an Inter Block Gap IBG signal.

Abstract: A disk file subsystem is disclosed which utilizes a track address decoding circuit which converts the track address which is recorded on the magnetic media in Gray code according to a 1/6 (2,8) run-length-limited recording code to its corresponding binary track address.

Abstract: A recovery routine enables data to be read from a sector of an optical data disk in the presence of damaged or missing syncs. If a sync is found, a "sync found" signal is generated to designate a normal read operation, and blocks of data read from the sector are aligned to resyncs distributed in the data stream. If a sync is not found, a pseudo sync is generated to designate a data recovery operation, and blocks of data are aligned to resyncs found in the data stream during a single pass or during separate passes through the sector at the user's option. The syncs and resyncs are searched using windows of programmably variable size for the read and recovery operations.

Abstract: A digital signal magnetic recording/reproducing apparatus subjects a digital signal to a digital amplitude phase shift keying and records and reproduces the modulated signal thus obtained on a magnetic recording medium. Use of the digital amplitude phase shift keying technique makes it possible to remove the direct-current component in the recording signals, and to improve the utilization efficiency of the recording frequency band, thus making high density recording possible. In addition, since a plurality of modulated signals are frequency-multiplexed and recorded, almost the entire frequency band recordable on a magnetic recording medium can be utilized, resulting in an increase in recording density. Further in addition, a pilot signal produced by frequency-converting a carrier is frequency-multiplexed with a modulated signal and recorded and reproduced and the carrier is reproduced from the reproduced pilot signal, so that a redundant part for reproducing the carrier is not necessary.

Abstract: An optical data storage system records pulse width modulated data as a series of contiguous and overlapping circular marks. A minimum number of circular marks are used to record the desired run length. Circular marks which overlap by greater or equal to one half the diameter of the circular mark are recorded using two different laser power levels. The result is that thermal buildup in the medium is kept to a minimum and the edge transitions are accurately positioned.

Abstract: A data word of 8 bits is code-transformed into a code word of 12 bits, for an 8/12 code which is suitable for high density recording such as d=2 and k=10, two kinds of synchronous pattern which never appear in data can be respectively provided for the video and audio uses while keeping the limitation with respect to d and k. Accordingly, decision error between the video data and audio data resulting from reproducing error can be significantly decreased, leading to an improvement in error probability and yet it is realizable with an extremely practical circuit structure. In addition, a pilot signal can be generated digitally with an extremely simple circuit, being suitable for home-use digital VCRs or the like which requires a stable pilot signal. As a result, the error rate of a super high density recording apparatus such as, for example, a digital VCR can be significantly decreased, and thus, its practical effects are very large.

Abstract: A digital adaptive finite impulse response filter circuit is provided for a PR4,ML sampled data channel including an analog to digital sampler for providing raw digital samples of data to the filter circuit and a sampled data detector for detecting coded data from conditioned digital samples received from the filter circuit. The filter circuit comprises a multi-tap transversal filter structure wherein each tap is connected to receive a selected coefficient, a source of a plurality of coefficients for each tap, a coefficient selector connected to the source to receive the plurality of coefficients and to provide a selected coefficient to each tap of the transversal filter structure, and a control circuit for controlling the coefficient selector and the source for providing each of the selected coefficients to a corresponding tap of the transversal filter structure. Training and adaptation methods and circuits for adapting the filter structure are also described.

Abstract: A data recording/reproduction method and apparatus uses an optical disk equipped with wobbling track guide grooves disposed in a track scanning direction and minutely wobbled. The apparatus uses a circuit for detecting and correcting displacement of an optical spot position from the wobbling track, and a system for allowing data to correspond to front and rear edges of recording pits as a recording system, and includes a circuit for independently handling reproduction pulses obtained from reproduction signals of the recording pits on the front and rear edge sides and for generating reproduction clocks. A circuit resynthesizes the two series of reproduction pulse trains by a specific pattern portion in the data. Another optical disk apparatus divides each track into zones, and switches a rate of revolution each zone to attain a substantially equal linear velocity. A servo signal reproduction clock generation circuit and a data signal recording/reproduction clock generation circuit are disposed separately.

Abstract: A recording and reproducing apparatus includes a rotatable rotating assembly and a fixed assembly disposed opposite thereto. The apparatus also includes a plurality of recording and reproducing heads and an erasing head mounted on the rotating assembly and first and second rotary transformers, having primary windings mounted on the rotating assembly and secondary windings mounted on the fixed assembly. A control signal generator is mounted on the rotating assembly and receives signals via the primary winding of the second rotary transformer. A first signal processor is mounted on the rotating assembly and connects the plural recording and reproducing heads to the primary winding of the first rotary transformer and a switch connects the erasing head with primary winding of the second rotary transformer. A recording and reproducing processor is connected the secondary winding of the first rotary transformer while a modulation signal generator is connected to the second winding of the second rotary transformer.

Abstract: In a method for recording and/or reproducing digital data, such as digital audio signals recorded simultaneously with video signals, dividing sampling data composed of a plurality of bits into higher order bits and lower order bits, constituting error correction coding blocks by only the higher and lower order bits of the sampling data of a plurality of samples respectively, thereby making it possible to easily realize adaptive error checking in the course of the block-by-block error checking in association with, for example, data criticality.A sync word and a block address are affixed to the error correction coding block constituted in that manner. Since one block address is formed using the address data of two or more blocks, a broader address space can be obtained even when the bit number of the address area of each block is few.

Abstract: Disclosed are a video signal recording apparatus for dividing digital video signal into blocks, transforming orthogonally, quantizing, coding in a variable length, and recording always in identical data quantity in a unit of specific number of blocks, and a video signal reproducing apparatus for decoding the recorded signal in variable length, quantizing inversely, transforming inversely and orthogonally, and reproducing the original digital video signal. The coding data in the specific number of blocks in the identical data quantity is divided in two code rows, the individual low frequency components are assigned to separate sync blocks, and high frequency components are also assigned to separate sync blocks, and recorded. When reproducing, if the sync block of high frequency components is wrong, it is possible to decode only with low frequency components, and the screen is reproduced at high fidelity to the reproducing speed at the time of high speed reproducing.

Abstract: A modulator circuit is constructed such that an input signal is code converted, after an error code correction code is added thereto, into a channel bit pattern suitable for characteristics of a recording and reproducing system for recording and reproduction of digital data. Margin bits are inserted between adjacent channel bit patterns in order to limit the lengths of the channel bit patterns. One or ones of a plurality of predetermined margin bit patterns which are to be inhibited from being inserted between particular two channel bit patterns are determined in accordance with a predetermined algorithm referring to the second last, the last and the present channel bit patterns and the last margin bit pattern. The output of an integrating circuit for measuring a digital sum variation of a channel bit pattern signal and a channel bit pattern is provided with a saturation characteristic so that the output may not diverge.

Abstract: A magnetic tape for the recording of digital video signals is constituted by a nonmagnetic base having thereon a magnetic layer of at least one thin magnetic metal film which has an energy product of at least 100 G.cm.Oe, and with the surface roughness of the magnetic tape being at most 0.003 .mu.m in center line average height. Such tape, when used with magnetic heads each having a gap defined between portions of the respective head having a saturation magnetic flux density of at least 14 kG., contribute to the maintenance of an acceptable raw error bit rate below 1.times.10.sup.-4 when recording with a recorded bit area of no more than 1.25 .mu.m.sup.2 /bit.

Abstract: A communication interface for interconnecting a computer with at least one other device has a link output circuit and a link input circuit. A link output on one device is connected to a link input on another device by a data line and a parallel strobe line. Data is transmitted on the data line in serial bit strings forming a succession of tokens of predetermined lengths. Signal transitions are provided on the parallel strobe line where no signal transition occurs on the data line. Each token includes a bit indicating the length of the token and a parity bit providing a check on bits in a preceding token.

Abstract: A digital video recording system for digitizing analog video signals and recording the digital signals on video tape and for reading digital video signals from video tape and producing an analog video signal. The recording system comprises an A/D converter, a data compressor for compressing digital video signals at a data rate of 1/N (N: an integer greater than 1), a selector mechanism for selecting between the compressed digital video signal and a non-compressed digital video signal, and a control mechanism for controlling the system such that recording data for one field, which is normally recorded in M tracks (M: an integer greater than N) in ordinary recording mode, is recorded in about M/N tracks in a long recording mode.

Abstract: A recording method and apparatus for an optical disk employs a data format having a fixed pattern sync portion in which a minimum run length of zeros and a maximum run length of zeros are not adjacent to each other. As such, temperature difference caused during recording the optical disk may be made smaller thermal stress applied upon the medium may be reduced, the deterioration thereof may be restrained, and the repetitive frequency of the medium may be improved.

Abstract: A data recording and/or reproducing apparatus records and/or reproduces file data by processing the file data on the unit of a predetermined block length, a data block and information data for identifying the data block on predetermined unit regions. A supplement data is recorded on a region other than the region recorded the file data, the block data and the information data for identifying within the unit regions. Thereby these data are recorded and/or reproduction processed at every predetermined units so that the bit error rate is remarkably improved.

Abstract: A data recording/reproducing device updates the identification data for identifying the recording data of recording track on the magnetic tape as the meaningless data. As a result, in a data recording reproducing device to be used for, such as an external memory device of the computer, the desired data can be erased easily.

Abstract: In a demodulation circuit for demodulating a pulse position modulation (PPM) signal, and a camera having the demodulation circuit, a change in PPM signal is counted by an up/down counter which is switched between count-up and count-down modes every time the PPM signal changes. When a carry signal is output from the counter, the carry signal is latched, and the PPM signal is demodulated into binary data on the basis of the presence/absence of the carry signal in the count-up mode and the carry signal in the count-down mode.

Abstract: A hard disk drive is disclosed wherein data is so recorded on the disk that a transducer puts out a waveform having a positive peak followed by a negative peak for each bit representative of a logic one of the data. For eliminating the read error that will arise when the disk is accidentally magnetized on its track gaps or other regions which should have been left unmagnetized, a read circuit connected to the transducer is constructed to recreate the recorded data by detecting the negative peaks, instead of the positive peaks, of the transducer output waveform.

Abstract: In a multi-channel data recorder, digital data for recording is converted to words of reduced length, and data for identifying the data channel is added to the reduced-length data words to produce a signal having a word length compatible for recording by a conventional data recorder.

Abstract: A multilevel encoding scheme for transmitted data that encodes data in a multilevel code wherein the amplitude of any transition is always exactly one level during any time interval. A single-level transition between any two adjacent levels during a time interval represents a logical "1"; no transition during a time interval represents a logical "0". In a specific embodiment, modulation is limited to three defined amplitude levels equally space in amplitude and encoding is according to a three-level code. A four-bit to five-bit encoding scheme may be used to distribute bits for minimizing d.c. offset. The input data is preferably further scrambled to minimize aberrations in the emissions spectrum of signal carried over unshielded media.

Abstract: A data processing system records information on magnetic disks in a format in which sector headers, which include embedded servo information, are radially aligned and recorded at a single frequency and data are recorded at various band-related frequencies. The system records sector headers at a frequency which is optimal for the recording of address information in the shortest sector and records the data at frequencies which are optimal for the recording of information in the disk space allocated to the data portion of the various lengths of sectors. The system synchronizes to the headers, using conventional embedded servo synchronization methods, and produces header timing signals. It can then use the same header timing signals to locate and interpret the headers on different tracks, since the header frequency and the location of the headers are the same in every track. The system may record the data portions of the sectors at frequencies which are related to the header frequency by ratios of small integers.

Abstract: A helical-scan tape storage device is operative to write computer data to tape according to a predetermined format in which the data is store in tracks arranged in groups. These groups are optionally separated by one or more amble track To enable auxiliary data, such as audio data to be stored within the format, the storage device is arranged to store a succession of N ambles into which the auxiliary data is written. Using the amble tracks to store auxiliary data permits storage devices that have been designed only with regard to computer data storage to read tapes containing both computer and auxiliary data, since the auxiliary-data-containing amble tracks are ignored by such a device. A storage device designed to extract auxiliary data from ambles can readily recover the auxiliary data.

Abstract: A magnetic recording and/or reproducing device uses a Viterbi decoding circuit wherein, when data falls within a predetermined range, the level of the reproduced signal is sensed and the level of the reproduced signal is corrected in a manner which reduces bit error caused by noise in the reproduced signal. Alternatively, the value of a previous video signal value is corrected in accordance with the amount of change in an instant signal value.

Abstract: An encoding circuit converts successive bits of the original data to successive bits of coded data at a coding rate equal to m/n, where m and n are each an integer satisfying m<n, in accordance with a rule of a run-length-limited coding system and contains an encoder which inputs parallel m bits of the original data, and outputs parallel n bits of coded data corresponding to the input. Successive bits of data which are to be encoded are cyclically divided into a plurality of groups, and the data in the plurality of groups are input in a plurality of shift registers, respectively. Each of the plurality of shift registers simultaneously supplied a part of the m bits of the input to the encoder, synchronizing with a clock. The n bits of the output of the encoder is received in parallel in another shift register, and are serially output from the shift register, synchronizing with a second clock.

Abstract: A memory system having a moving memory recording media. A sector in each track on the media includes recordings defining a synchronizing field and a start of data field. Selected bit signals of bit signals derived from the recordings are simultaneously combined in a plurality of differing bit signal combinations. The simultaneously validity of all of the bit signals in each of a predetermined number of the differing bit signal combinations, which predetermined number is less than the plurality of bit signal combinations, provides fault tolerant detection of the start of data field.

Abstract: A method and device for use in measurement and compensation of nonlinear bitshift in nonlinear communication media such as magnetic and optical recording devices. The method and device are based on special bit patterns constructed to eliminate at least one harmonic of the fundamental frequency of the data pattern if all bits are communicated without any nonlinear bitshift. The presence of nonlinear bitshift is manifested by the appearance of the harmonic. By measuring the magnitude of the harmonic, the amount of nonlinear bitshift is determined, and compensation adjustment is then used to offset its effect on the data detection scheme.

Abstract: A signal reproduction apparatus reproduces data from an information recording disc. The data is recorded for every data block and is modulated so that data in one data block has n (n is an integer) bits including arbitrary m (m is integer and less than the n) bits each having an active value. The signal reproduction apparatus includes, a reading circuit reading out the data from the information recording disc, a converter converting the data into a pulse signal for every data block, the pulse signal having an active pulse corresponding to the active value of the data and an inactive pulse corresponding to the inactive value of the data, a judgment circuit judging whether or not the pulse signal has m active pulses for every data block, and a correction circuit correcting the pulse signal so that the pulse signal has m active pulses in one data block when the judgment circuit judges that the pulse signal has a number of active pulses other than the m in the one data block.

Abstract: A method and apparatus for generating high rate run length limited trellis codes and increasing minimum distance between output sequences of partial response channels with constrained channel inputs without requiring codes with spectral nulls. A Viterbi detector replicates a conventional trellis structure for the channel N times. The N copies of the channel response trellis are interconnected such that a preselected function associates each state in the trellis with a particular integer value modulo N. The number N is selected according to the channel detection and coding constraints so that diverging erroneous sequences of minimum distance lead to detector states which are distinct from the correct detector state. The detector trellis is time-varying such that only certain values of the preselected function are allowed every m bits. The time-variation assures there are no minimum distance extensions of erroneous sequences beyond a predetermined length.

Abstract: A zone-bit-recording disk drive has a rotating platter with a surface which is divided into at least two zones each having a respective different number of angularly spaced sectors therein. A method and apparatus for positioning the head relative to the platter surface involve maintaining a count of the number of sectors which pass the head after the platter passes a predetermined angular orientation, ignoring the count during a time interval when the head moves out of a first of the zones toward a second of the zones which contains the specified sector and until the head has entered the second zone and the platter thereafter passes a predetermined angular orientation, and thereafter determining when the count corresponds to the specified sector to be accessed.

Abstract: In an apparatus for detecting input digital data, for example, as derived by analog-to-digital conversion of a reproduced binary signal in analog form; a distributor circuit distributes the input digital data into at least two channels, a processing circuit in each channel processes the respective digital data in accordance with a predetermined formula, a decoder in each channel decodes an output of the respective processing circuit in accordance with the Viterbi algorithm, and the outputs of the decoders are composed or combined to provide therefrom a single sequence of digital data.

Abstract: A reader for a coded discontinuous security thread in a security document comprises a multiplicity of reading channels each coupled to at least one magnetic transducing means (11, 40) for sensing along a track across the document and including processing circuits for forming a channel signal which exhibits signal excursions in response to the passage of the ends of each length of magnetic material. First and second comparators (55, 56) compare the channel signal with relatively positive and relatively negative thresholds respectively and a bistable switching means (59) is coupled to the comparators to provide a digital signal. A reference comparator (64) controls an analog switch and diode pumps (70, 71) to adjust the thresholds in accordance with the amplitude of a signal excursion.

Abstract: A magnetic tape for the recording of digital video signals is constituted by a nonmagnetic base having thereon a magnetic layer of at least one thin magnetic metal film which has an energy product of at least 100 G.cm.Oe, and with the surface roughness of the magnetic tape being at most 0.003 .mu.m in center line average height. Such tape, when used with magnetic heads each having a gap defined between portions of the respective head having a saturation magnetic flux density of at least 14 kG., contribute to the maintenance of an acceptable raw error bit rate below 1.times.10.sup.-4 when recording with a recorded bit area of no more than 1.25 .mu.m.sup.2 /bit.

Abstract: A data signal reproducing apparatus has an envelope detector for detecting a DPSK-modulated data signal, a change point detector for detecting a point of change of the detected envelope, and a latch for inverting and holding an output signal every time the change point detector detects a point of change of the envelope. An electronic still camera incorporating the data signal reproducing apparatus has a magnetic head that reads a picture signal and a DPSK-modulated data signal which have been recorded on a recording medium in the form of a multiplex recording signal. An extracting device extracts the DPSK-modulated data signal from the multiplex recording signal read by the magnetic head.

Abstract: In a helical scan recorder, a sequence of n-bit first codewords (W.sub.1) and n-bit second codewords (W.sub.2) if any, are stored in second track parts (TP2) which form the beginning of the tracks (T.sub.1, T.sub.2 . . . ), these codewords having a form so that both a PR1 detection and a PR4 detection is possible on reproduction. The second codewords are the inverses of the first codewords. An optional form of the first codeword may be: 0001110001110000011100011.

Abstract: A digital data decoder is provided that combines Viterbi algorithms and a run-length code constraint. The combined Viterbi detection and code constraint does not limit the bits that can be analyzed in determining the binary state of the bit currently being detected. The logic associated with the code constraint is not enabled unless actual data is being decoded.