Robert Boschgmbh

Bts Broadcast Television Systems Gmbh

Jurgen Heitmann

Rolf Loos

Hans-Peter Maly

Roland Mester

Jurgen Muller

Rudolf Wilhelm

Peter Wagner

Michael Hausdorfer

Gerhard Illetschko

Reiner Noske

Hans-Peter Richter

Hannfried Preissler

Horst Rickenbrock

For reducing the d.c. component of a digital signal in which a good many data words are put together in data blocks each having the same number of words, a supplementary word is derived and is transmitted or stored along with the data words. The bit mix of the supplementary word contains information for shifting the word bit-mix range, defined in accordance with the d.c. component of various words of the data words in the data block. The bit-mix value of the supplementary word is derived by evaluation of the weighting of ASE-coded data words in the data block, this being done in a manner dependent on the standard deviation and an expected value or center of gravity of the data block. A difference value determined with respect to the center of gravity and the value of a middle level value of a data word represents the value of the supplementary word with which, by the use of the modulo-2 addition the digital signal is shifted in bit-mix value range. The supplementary word is transmitted or recorded with each data block and is used in an operation which is the inverse of what is done before recording or transmission so that the original digital signal will be available again.

Coding method for reducing the D.C. component in the data stream of a

As many as three of the four heads spaced at 90.degree. intervals around the periphery of a head wheel may be in contact with the magnetic tape of a video recorder and reproducer at the same time. Oblique tracks are recorded on the tape record video date in blocks corresponding to sectors, each composed of the same numbers of lines, each track beginning with a video sector and ending with another video sector with small audio blocks inbetween. Four different sector designations succeed each other in turn. The video data of each block is preceded by an identification signal of which the two most significant bits designate the sector. The sector designations are separated from the outputs of each of the magnetic heads and control a PROM, the output of which controls a crosspoint switch to direct data blocks in accordance with the sector identification to four memories and the audio blocks to an audio memory. When reproduction is performed at a speed faster or slower than the recording speed, the control data for the switch normally still has enough redundance for correct switching but when the control data becomes inconsistent with the track pattern, an error is detected and the previous setting of the switch is preserved. Errors can be reduced by taking into account head wheel pulses on the tape or data from a longitudinal track on the tape.

Method and apparatus for reproducing video data stored on a magnetic

A pulse code modulation process converts an analog video signal into a digital signal to be passed through a recording or transmission channel. The digital signal includes a digital words of a given number of bits, and each digital word represents an amplitude level of the video signal. The digital words are allocated to a given set of graduated amplitude levels such that the sum ##EQU1## has a minimum value whereby

Pulse code modulation system

In playback scanning of oblique tracks the jumps of velocity errors in the transition from one head to another are found to be substantially constant, but the magnitude of the velocity error as a whole is subject to statistical fluctuation and the like. Within a track a velocity error determined for one line is used for correction in the following line, while for the first line the magnitude of a jump from a previous magnetic head changeover in the same sense is utilized. With the help of a value from the last line or next-to-last line of the earlier track, a correction value is provided for the first line of the after next track. A ramp signal is inserted in each horizontal blanking interval ahead of the color synchronization signals, raising the latter to the top of the ramp level. The inserted signals are digitized along with the video signal. Samples of the digital ramp signal which pass through a magnitude window (70-73), which is set for passage of not more than two samples in a narrow range symmetrical with respect to the ramp midpoint, address a PROM which converts those magnitudes into timing error values of the pulse generator which provides sampling rate pulses for the converter that digitizes the video signal. The timing error values are used to correct the phase of that pulse generator.

Digital pulse generator phase-locked to color television video signals

The rotary headwheel device for scanning oblique tracks on an advancing magnetic tape is provided with normal playback heads which follow the recording heads and trace the path of the same oblique tracks and also with auxiliary playback heads which trace the path of the respective tracks which the normal playback heads trace but do so 6 and 1/2 revolutions in advance. In order to improve display of the content of recorded digital television signals in a slowed down or accelerated motion mode, the auxiliary playback heads are shifted axially to offset them by a half track width from their position useful for audio processing, whenever the magnetic tape playback speed is off-normal. At such times the outputs of the several normal playback heads are evaluated as to error rate and if any of these outputs exceeds a reference error rate, a switchover unit on the rotary scanning device switches the rotary transformers, which carry the playback outputs to processing channels, from the normal playback heads to the auxiliary playback heads. The error rates are then measured and evaluated for the auxiliary playback heads, and when one of them shows an error rate exceeding the reference error rate, the rotary transformers are switched back to the normal playback heads and so on. The mechanical shift of the relative offset between auxiliary playback heads and normal playback heads is made and maintained electromagnetically for the duraton of off-normal tape speed operation in playback.

Fast and slow playback method and apparatus for data recorded on

For slow motion playback operation with a digital video magnetic tape recording and reproducing equipment an intermediate memory system has four picture field memories of which there are always three available for writing into but only one of them at a time is in read-out operation. In a first reading operation of a particular picture field memory an AND correlation of a write flag and an error flag is necessary for providing an error recognition signal to following circuits and before a reading goes to the next address the write flag is erased by writing in a logic zero, but the correlated signal is used to rewrite the error flag in the error flag memory. In subsequent readings any error flag is transmitted and rewritten, but all write flags remain erased to signify that the memory has been read out at least once.

Intermediate picture field storage system for slow motion playback of

A rotary scanning device of a magnetic tape recording and playback equipment, which carries a set of recording heads and a set of playback heads on its periphery is provided with one rotary transformer in addition to the number equal to the number of recording heads and to the number of playback heads of said sets. The additional rotary transformer is used for cyclically connecting its rotor to the respective playback heads during a recording operation by means of a controlled transfer switch, so that a fraction of the signals recorded by each of the recording heads is made available for an after-check which can be performed without visual display because of the digital nature of the recorded signals, which are evaluated by error recognition and word count circuits.

Magnetic tape recording and playback equipment for automatic check of

A method of recording signals on a magnetic medium, in which a first magnetic head (1) blanks a wide track by recording signals at a first azimuth angle and a second magnetic head (2) records a narrower signal track (15) by recording signals at a second, differing azimuth angle. This permits feeding the same current or signal through the head windings (8,9) of both heads, thereby economizing on driving circuitry (10). Due to the differing azimuth angles, the reading head does not pick up any significant amount of noise from the border regions defined between the edges of the signal track and the wider blanking track. The width of the signal track and the widths of the border regions sum to equal the width of the blanking track.

Method and magnetic head for recording signals magnetically

In a video signal processor incorporating a reference clock pulse generator of highly precise frequency, two pulse generators, one preceding the drop-out corrector circuit which includes a picture memory and another following the drop-out corrector, are controlled in phase and frequency periodically in response to a horizontal synchronizing pulse. An addition circuit (101) the output of which is intermediately stored in a 20 place register (105) has a data input (104) to which bits of higher binary significance, for phase control, are supplied in response to the synchronizing pulse and thereafter bits of lower binary digit significance are supplied by a velocity error detection circuit for frequency control during the remainder of a television line interval. The output of the 20 place register is fed back to another input of the addition circuit, to produce a sawtooth wave resulting from the overflow of the addition circuit, which is a submultiple of the reference clock pulse generator frequency. A PROM, responsive to the 10 most significant output bits of the addition circuit, and subsequent processing circuits (114,118, 115) convert the sawtooth wave to an analog sinusoidal wave which is then frequency multiplied to a frequency approximating the frequency of the reference clock pulse generator.

Digital pulse generator of phase and frequency periodically controlled

The head wheel of a video recorder-reproducer is equipped with a set of four advanced read heads, in addition to the usual sets of four read and write heads, so that each advanced read head can read the contents of an oblique track on a magnetic tape on which one of the write heads will be able to record thereafter and which will be read still later by one of the normal read heads. The advanced read heads are so located that while one of them is reading a track, one of the normal read heads is out of contact with the tape. The advanced read heads are used for reading out audio sections of video tape tracks for processing and rerecording in accordance with a previously known processing procedure used in editing newly recorded video tapes for better audio recording. The normal read heads are available for an after-check of the rerecorded audio. A switching system timed by the rotation of the head wheel disconnects each of the normal read heads in a sequence during the periods in which they are respectively out of contact with the tape and at the same time the switches in one of the advanced read heads for scanning the mid-portion of the recorded tracks where the audio sections of the recording are located.

Apparatus including a head wheel carrying advanced read, write and

Data blocks recorded on oblique tracks on magnetic tape are preceded by synhronizing signals and block identification signals. The serial data identification signals are converted to 8-bit parallel form and then are split between an undelayed channel and a channel delayed by one data block. Under control of a sync detector the parallel data are made to correspond with data words and are then decoded for comparison of the block numbers. Since the block numbering is consecutive, the delayed decoded block number is incremented by one for comparison. When a positive comparison is obtained the block number of the delayed decoded signals is made available to identify the data block. A counter in a so called fly wheel circuit assures provision of a new block start signal if a synchronizing signal is missed and prevents the timing of the circuit from being put off by a false detection of a synchronizing signal. A block identification output appears only if its block number is in sequence.

Method of cross-checking data block identification signals of data

Four picture field memories which contain storage places for luminance data, chrominance data, error flags and write flags are switchable from write in to read out by changeover switches controlled by an access control unit for connection of the address and control inputs of the memories either to a write in control circuit or a read out control circuit. The access control unit can be set for operation at normal speed, which is the recording speed of the tape from which signals are read out, below normal speed or above normal speed. The read-out control circuit is synchronized by a synchronizing signal that contains a vertical scan frequency reference pulse. The several picture field memories are cyclically interchanged, written into and read out from. One of the picture field memories is read out while the others are available for write-in. The incoming error flags are passed on. Use is made of write flags and error flags to improve operation at speeds different from the recording speed.

Intermediate picture field storage system for variable speed magnetic

A color television signal processor for signals reproduced from magnetic tape converts the signals to digital form at a sampling rate substantially equal to three times the color carrier frequency, incorporates a timing system that locks the sampling rate into step with the picked up synchronizing signals in which a digital pulse generator of high stability is utilized having other possible applications, an additional demodulator separately switched is used to recover synchronizing signals for the first line of each segment, a ramp signal is provided during the blanking interval to assist in accurate timing of the sampling pulses, velocity errors are corrected for each line by a measurement of the period of a previous line and discontinuities (jumps in alternating directions) related to the switching between heads are also measured and compensated for. A more economical scheme for dealing with signal dropouts makes use of a digital low-pass filter for separating luminance and chrominance signals for dropout compensastion that can be left in circuit without deterioration of picture quality during periods in which no dropouts are detected.

Processor for video signals obtained from an information carrier such as

Both the analog and the video component of a television signal are converted to digital form, the audio component being converted at a much lower sample rate with a word length which is an integral multiple of the video word length. The digital audio component is then compressed by use of a temporary memory and read-out therefrom at a rate that is half of the sample rate of the digtal video component, after which the word length is halved and the word rate doubled in a shift register circuit. In that form the audio component is inserted in horizontal blanking intervals of the video component in a compatible form by a multiplexer, the output of which is read into a single picture field or full picture memory under control of an address generator clocked in synchronism with the incoming video component. The buffer memory is read-out at a rate controlled by a reference signal such as is used for synchronism in a television studio. On the output side the digital video and audio components of the television signal are separated by a demultiplexer, the audio word length is doubled and the word rate halved and the still compressed audio signal is expanded, to make available a substantially continuous digital component. The audio component can then be converted to analog form and will be correctly timed for accompanying the digital video component converted to analog form at the output of the demultiplexer. Separate audio signal delay circuits are thus avoided by the use of relatively simple multiplexing circuits and audio processing circuits.

Method and apparatus for maintaining audio/ video synchronism in a

For transmission of serial digitally coded signals over a path having a high-pass frequency characteristic synchronizing signals are transmitted in synchronizing word pairs at the beginning of each data block in which the synchronizing words are either identical or else both have the same number of bits of each of the two binary logic levels, for reduction of d.c. and low-frequency components while permitting the choice of a synchronizing signal word which occurs at most rarely in a television video signal, for example.

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Alsbach-Hahnlein, Germany

Jurgen Heitmann