Dynamic magnetic information storage or retrieval – Manual input recording
Patent
1984-06-08
1986-01-07
Richardson, Robert L.
Dynamic magnetic information storage or retrieval
Manual input recording
358339, 358341, 360 39, 360 191, H04N 5008, H04N 576
Patent
active
045637105
DESCRIPTION:
BRIEF SUMMARY
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.
In this specification the expression "plurality of rotations" means more than one rotation and includes fractional rotations in excess of one, e.g., one and one half rotations.
Digital television tape recording has already been the subject of considerable attention, but most work has been concentrated on the problems of high bit rates and packing densities and on error correction and concealment. While many of the problems have been largely solved, there is still a need for a format for digital television recording which will provide for improved error concealment or correction. Further, the requirements for recording the sound channel associated with the video has been largely ignored.
The present invention provides 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 on playback the information on the tape is recovered and returned to the timing relationship existing for the original information.
An advantage of this apparatus is that it records the video information on the tape in such a way as to leave gaps into which the audio information can be inserted. Further, at least one of the video heads can also be used for audio.
In order that the present invention be more readily understood, embodiments thereof will now be described by way of example with reference to the accompanying drawings, in which:
FIG. 1 shows diagrammatically a head arrangement and degree of tape wrap according to the present invention;
FIG. 2 shows a diagram representing how digital information relating to one line of video is recorded and played back according to the present invention;
FIG. 3 shows a diagram similar to FIG. 2 for another proposal according to the invention;
FIG. 4 shows a diagram similar to FIG. 2 but forthe audio signal associated with the line of video;
FIG. 5 shows a block diagram of apparatus for recording a video signal according to the present invention.
In the description which follows, it is assumed that segmental helical scan recording is well known and it will therefore not be described in detail. Further, the description is given in relation to recording one field of a television signal, it being understood that a television frame is made up to two interlaced fields.
Referring now to FIG. 1, for the purpose of this consideration it has been assumed that the source data rate for video will be 216 Mbit/s. This corresponds to sampling the luminance at 13.5 MHz and each colour difference channel at 6.75 MHz. These particular frequencies are integral multiples of both 525 and 625 horizontal frequencies.
Further assumptions are that a 200:1 ratio between head and tape speed will be used under normal conditions, for example 1600 and 8 in/s respectively, and also that picture in shuttle is required at 30 times normal speed. The data rate recovered from tape under these conditions will be as if t
REFERENCES:
patent: 4283744 (1981-08-01), Melwisch et al.
patent: 4353098 (1982-10-01), Heinz et al.
Masahiko Morizono et al., "Digital Video Recording-Some Experiments and Future Considerations" in SMPTE Journal, vol. 89, No. 9 (9/80), pp. 658-662.
Katsuya Yokoyama et al., "An Experimental Digital Videotape Recorder" in SMPTE Journal, vol. 89, No. 3 (3/80), pp. 173-180.
Ampex, "Labor-Experimentieranlage fur Digitale Video-Magnetbandaufzeichnung," in Fernsehtechnik, vol. 51, No. 25 (12/79), pp. 72-74.
Independent Broadcasting Authority
Richardson Robert L.
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