Dynamic magnetic information storage or retrieval – Converting an analog signal to digital form for recording;...
Patent
1991-10-29
1995-01-24
Hajec, Donald
Dynamic magnetic information storage or retrieval
Converting an analog signal to digital form for recording;...
360 331, G11B 509, H04N 578
Patent
active
053846664
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for recording a digital picture signal such as a digital video signal on a magnetic tape, more specifically, relates to a magnetic recording apparatus of a digital picture signal which can record the signal for a long time by selecting the azimuth angle of the magnetic head to particular values.
BACKGROUND ART
A D1 format component type digital VTR and a D2 format composite type digital VTR both of which are used in broadcasting stations have been practically used as digital VTRs for digitalizing color video signals and recording them on a recording medium such as a magnetic tape.
In the former D1 format digital VTR, a luminance signal and first and second color difference signals are A/D converted with sampling frequencies of 13.5 MHz and 6.75 MHz, respectively. Thereafter, the signals are processed in a particular manner and then recorded on a tape. Since the ratio of sampling frequencies of components is 4:2:2, this system is also named the 4:2:2 system.
On the other hand, in the latter D2 format video digital VTR, a composite video signal is sampled with a signal with a frequency 4 times higher than the frequency fsc of a color subcarrier signal and then A/D converted. Thereafter, the resultant signal is processed in a particular manner and then recorded on a magnetic tape.
Since these VTRs are designed for use in broadcasting stations, the top priority of them is in picture quality. In these VTRs, a digital color video signal where one sample is A/D converted into for example 8 bits is recorded without substantially being compressed.
As an example, the data amount of the former D1 format digital VTR will be described in the following.
When each sample is A/D converted into 8 bits with the above mentioned frequency, the information amount of a color video signal is approximately 216 Mbps (megabits per second). When the data in the horizontal an vertical blanking intervals are removed, the number of effective picture elements of the luminance signal per horizontal interval and the number of effective picture elements of each color difference signal per horizontal interval become 720 and 360, respectively. Since the number of effective scanning lines for each field in the NTSC system (525/60) is 250, the data amount Dv of picture signal per second can be expressed as follows.
Even in the PAL system (625/50), since the number of effective scanning lines for each field is 300 and the number of fields per second is 50, it is obvious that the data amount in the PAL system is the same as that in the NTSC system. By considering the redundant components necessary for error correction and format with respect to such data, the bit rate of picture data becomes approximately 205.8 Mbps in total.
In addition, the data amount of audio data Da is approximately 12.8 Mbps while the additional data Do such as a gap, a preamble, and a postamble used in editing is approximately 6.6 Mbps. Thus, the information amount of overall record data can be expressed by the following equation. ##EQU1##
To record the above mentioned information amount, with respect to the D1 format digital VTR, a segment system having a track pattern with fields of 10 tracks in the NTSC system, and with fields of 12 tracks in the PAL system has been employed.
In addition, a recording tape with a width of 19 mm is used. There are two types of recording tapes in thickness, which are of 13 .mu.m type and 16 .mu.m type. To house these tapes, there are three types of cassettes, which are of large type (L), middle type (M), and small type (S). The information data is recorded on such tapes in the above mentioned format. Thus, the data recording density is approximately 20.4 .mu.m.sup.2 /bit. When the recording density is high, an error tends to take place in the playback output data due to interference between codes or non-linearity of electromagnetic conversion system of the head and tape. Thus far, even if the error correction encoding was performed, the above mentioned value was the limit a
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Design Considerations for the D-2 NTSC Composite DVTR, pp. 182-193, SMPTE Journal, Mar. 1988, Richard Brush.
Chiba Kazunobu
Inoue Hajime
Kanota Keiji
Kawaguchi Moriyuki
Kubota Yukio
Forbus Jr. T. N.
Frommer William S.
Hajec Donald
Sinderbrand Alvin
Sony Corporation
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