Digital television tape recording

Abstract

The present invention relates to digital television tape recording and more particularly to such recording using helical scan apparatus of the segmented type i.e. where one field of video is recorded by a plurality of rotations of the headwheel. The invention also provides apparatus for recording or playing back a digital television signal comprising a helical scanning device including a drum which may be a rotatable headwheel provided with a plurality of recording/playback heads, guide means for wrapping a magnetic recording tape around a portion of the circumference of the drum, means for rotating the headwheel, and means for moving the tape around the surface of the drum whereby one field of a television video picture is recorded or played back by a plurality of rotations of the headwheel, characterized in that the recording/playback heads are disposed on the headwheel.

I claim: 
     
       1. Apparatus for recording or playing back a digital television signal comprising a helical scanning device including a drum which may be rotatable, a rotatable headwheel provided with a plurality of recording/playback heads, guide means for wrapping a magnetic recording tape around a portion of the circumference of the drum, means for rotating the headwheel, and means for moving the tape around the surface of the drum whereby one field of a television video picture is recorded or played back by a plurality of rotations of the headwheel, characterised in that the recording/playback heads are disposed on the headwheel and the degree of wrap of the tape around the drum is such that for one complete revolution of the headwheel there is a period of time during which there is no head in operative contact with the tape, and storage means are provided for receiving information in the form of digital words to be recorded or played back for altering the timing of the information whereby on recording all the information received is recorded and on playback the information on the tape is recovered and returned to the timing relationship existing for the original information. 
     
     
       2. Apparatus according to claim 1, wherein all the heads are clustered together over one segment of the headwheel and the degree of wrap is from 180° to 330°. 
     
     
       3. Apparatus according to claim 2, wherein there are at least three heads and the degree of wrap is between 240° and 300°. 
     
     
       4. Apparatus according to claim 1, wherein there are diametrically opposed heads or head groups, and the rotation of the heads in which they are active for video is less than 180°. 
     
     
       5. Apparatus according to claim 1, wherein storage means comprise a plurality of stores for storing the digital words in the form of blocks of words, each block corresponding to a predetermined number of lines of a video signal and the stores being written into at one speed and read from at a second speed different to the first. 
     
     
       6. Apparatus according to claim 5, wherein each store is capable of storing information relating to 51 lines of a television video signal or a sub-multiple thereof. 
     
     
       7. Apparatus according to claim 5, wherein, for recording means are provided responsive to timing signals in the digital information to be recorded for controlling the writing in of digital information into the desired one of the stores, and means indicative of the position of the headwheel are provided for controlling the reading of digital information from a desired one of the stores. 
     
     
       8. Apparatus according to claim 1, wherein means are provided for supplying signals indicative of the audio information associated with the video to at least one of the heads for recording on the tape in the gaps between adjacent blocks of video information. 
     
     
       9. Apparatus according to claim 8, wherein said means is arranged to time compress the audio information. 
     
     
       10. Apparatus for recording or playing back a digital television signal comprising a helical scanning device including a drum which may be rotatable, a rotatable headwheel provided with a plurality of recording/playback heads, guide means for wrapping a magnetic recording tape around a portion of the circumference of the drum, means for rotating the headwheel, and means for moving the tape around the surface of the drum whereby one field of a television video picture is recorded or played back by a plurality of rotations of the headwheel, characterised in that the recording/playback heads are disposed on the headwheel diametrically opposite each other, storage means are provided for receiving information in the form of digital words representing video signals to be recorded or played back for altering the timing of the information whereby, for one complete revolution of the headwheel there is a period of time during which there is no head recording or playing back said digital words, thereby to record the video signals in blocks on the tape with gaps therebetween, and means are provided for supplying signals indicative of the audio information associated with the video signals to at least one of the heads for recording audio information on the tape in gaps between adjacent blocks of video information. 
     
     
       11. Apparatus according to claim 10, wherein there are diametrically opposed head groups, and the rotation of the heads in which they are active for video is less than 180°. 
     
     
       12. Apparatus according to claim 10, wherein said storage means comprise a plurality of stores for storing the digital words in the form of blocks of words, each block corresponding to a predetermined number of lines of a video signal and the stores being written into at one speed and read from at a second speed different to the first. 
     
     
       13. Apparatus according to claim 12, wherein, for recording means are provided responsive to timing signals in the digital information to be recorded for controlling the writing in of digital information into the desired one of the stores, and means indicative of the position of the headwheel are provided for controlling the reading of digital information from a desired one of the stores. 
     
     
       14. Apparatus according to claim 13, wherein said means is arranged to time compress the audio information. .Iadd. 
     
     
       15.  Apparatus for recording or playing back digital signal information associated with television, comprising the combination of a helical scanning device including a drum which may be rotatable, a rotatable headwheel provided with a plurality of recording/playback heads, guide means for wrapping a magnetic tape around a portion only of the circumference of the drum, means for rotating the headwheel and means for moving the tape around the surface of the drum, the recording/playback heads being disposed on the headwheel, and storage means connected to the recording/playback heads and receiving the digital signal information in the form of digital words to be recorded or played back for altering the timing of the information represented by the digital words whereby on recording all the information received corresponding to the time for one field of a television video picture, such information is recorded on the tape in time-compressed fashion to define n successive blocks of digital word information and on playback the information recorded on the tape is recovered in time-expanded fashion. .Iaddend. .Iadd.16. Apparatus as defined in claim 15 wherein the digital signal information comprises audio information. .Iaddend. .Iadd.17. Apparatus as defined in claim 16 wherein the audio information represents sound channel output during a period of time equal to 1/n of the time for one field of the television picture. 
     
     
        .Iaddend. .Iadd.18.  Apparatus as defined in claim 17 wherein the audio information words are recorded and played back by different ones of the recording/playback heads. .Iaddend. .Iadd.19. Apparatus as defined in claim 18 wherein the audio information words defining the beginning and end of each gap are recorded during times which are substantially overlapping. .Iaddend. .Iadd.20. Apparatus as defined in claim 15 wherein each block of information comprises a central portion representing video information. .Iaddend. .Iadd.21. Apparatus as defined in claim 20 wherein the digital signal information comprises audio information and the digital words defining such audio information define the beginning and ends of taps between successive blocks of audio information. .Iaddend. .Iadd.22. Apparatus as defined in claim 21 wherein the audio information defining one end of each gap represents sound channel output during a period of time preceding such one end of the gap equal to 1/n of the time for one field of the television picture. .Iaddend. .Iadd.23. Apparatus as defined in claim 22 wherein the audio information defining the other end of each gap represents the sound channel output during a period of time preceding such other end of the tap equal to 1/n of the time for one field of the television picture. .Iaddend. .Iadd.24. Apparatus as defined in claim 23 wherein the audio information words defining the beginning and end of each gap are recorded and played back by different ones of the recording/playback heads. .Iadd.25. Apparatus as defined in claim 24 wherein the audio information words defining the beginning and end of each gap are recorded during times which are substantially overlapping. .Iaddend. .Iadd.26. Helical scanning recording or playing apparatus of the segmented type, comprising a helical scanning device including a drum which may be rotatable, a rotatable headwheel provided with a plurality of recording/playback heads, guide means for wrapping a magnetic recording tape around a portion of the circumference of the drum, means for rotating the headwheel, and means for moving the tape around the surface of the drum whereby one field of a television video picture is recorded or played back by more than a single rotation of the headwheel, storage means being provided for receiving information in the form of digital words representing video signals to be recorded or played back for altering the period of recording or playback of information on the tape, the disposition of the heads on the headwheel, the degree of wrap and the amount of alteration of the period of recording or playback being chosen so that the video signals are recorded in blocks on the tape with gaps therebetween, and further means being provided for supplying signals indicative of the audio information associated with the video signals of a program to at least one of the heads for recording audio information on the tape in the gaps in between adjacent blocks of video information, at least a portion of the audio information associated with each block of recorded video signal being duplicated and recorded at different locations on the tape. .Iaddend. .Iadd.27. Apparatus in accordance with claim 26, wherein the audio information is compressed in time prior to recording. .Iaddend. .Iadd.28. Apparatus in accordance with claim 27, wherein the duplicated audio information is recorded and played back by a different one of the recording heads which records and plays back the original audio information. .Iaddend. .Iadd.29. Apparatus for recording or playing back a digital television signal including video type and audio type of information, comprising a helical scanning device including a drum which may be rotatable, a rotatable headwheel provided with a plurality of recording/playback heads, guide means for wrapping a magnetic tape around a portion of the circumference of the drum, means for rotating the headwheel and means for moving the tape around the surface of the drum whereby one field of a television video picture is recorded or played back by a plurality n of rotations of the headwheel, the recording/playback heads being disposed on the headwheel and the degree of wrap of the tape around the drum being such that for one complete revolution of the headwheel there is a period of time during which there is no head in operative contact with the tape, and storage means are provided for receiving information in the form of digital words to be recorded or played back for altering the timing of the information whereby on recording, all the information received during n rotations of the headwheel is recorded in time-compressed fashion as n blocks of digital words in which successive blocks of the same type of information have gaps therebetween and on playback, the information recorded on the tape is recovered and returned to the timing relationship existing for the original information. .Iaddend. .Iadd.30. Apparatus as defined in claim 29 wherein the digital signal information comprises audio information and the digital words defining such audio information define the beginning and end of gaps between successive blocks of video type information. .Iaddend. .Iadd.31. Apparatus as defined in claim 30 wherein the audio information in each block thereof represents sound channel output during a period of time equal to 1/n of the time for one field of the television picture. .Iaddend. .Iadd.32. Apparatus as defined in claim 31 wherein the audio information words are recorded and played back by different ones of the recording/playback heads. .Iaddend.