JPH0771306B2 - Digital magnetic recording / reproducing method of video signal - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for digitally recording and reproducing a video signal, particularly NTSC.
The present invention relates to a method for efficiently digitally recording and reproducing signals, PAL signals and SECAM signals on a magnetic tape.

2. Description of the Related Art As a video signal recording / reproducing apparatus, many systems and apparatuses such as a magnetic tape recording medium and an optical disk recording medium have been studied and put into practical use.

By the way, in such a video signal recording / reproducing apparatus, a method of digitally processing a video signal and directly recording / reproducing digital data has been actively researched and developed in recent years.

The following is a discussion of what is called a digital VTR (hereinafter referred to as "DVTR"), which is a device for digitally recording and reproducing data on a magnetic tape.

Now, a conventional example of the DVTR will be described with reference to the drawings. Third
The figure is a block diagram showing a conventional example of a DVTR. In the figure, 5 is a recording amplifier, 10 and 11 are switches, 12 and 13 are reproducing amplifiers, 8 and 9 are magnetic heads, 7 is a rotating cylinder, and 6 is a magnetic tape. The video signal to be recorded is digitized and then guided to the recording amplifier 5 through a predetermined digital signal processing. During recording, the switches 10 and 11 are closed on the recording amplifier side, and a data string is recorded on the magnetic tape 6 via the magnetic heads 8 and 9. The magnetic heads 8 and 9 are fixed to the rotary cylinder 7, and by rotating together with the rotary cylinder 7, the magnetic tape 6 is scanned and recorded.

On the other hand, at the time of reproduction, the switches 10 and 11 are closed to the reproduction amplifier side 12 and 13, and the data string recorded on the magnetic tape 6 is reproduced via the magnetic heads 8 and 9.
Each is led to 13. The reproduction amplifiers 12 and 13 amplify the weak signals extracted via the magnetic heads 8 and 9 to a predetermined amplitude. The outputs of the reproduction amplifiers 12 and 13 are restored to analog signals through predetermined digital signal processing.

FIG. 4 shows a recording pattern on the magnetic tape 6 when recording is performed in this manner. In the figure, 6 is a magnetic tape,
52 to 57 are trucks. Magnetic tape 6 in FIG.
Moves slowly on the circumference of the rotary cylinder 7, and at the same time the rotary cylinder 7 rotates at a high speed to perform a helical scan, so that licked tracks 52 to 57 are formed on the magnetic tape 6. The tracks created by the magnetic head 8 are 52, 54, 56 ..., and the tracks created by the magnetic head 9 are
53,55,57 …….

Next, the relationship between FIGS. 3 and 4 will be described with reference to the timing chart of FIG. In the figure, 22 to 36 are NTSC signals (hereinafter referred to as "525/60 system"), 37 to 44 and 58 to 62 are PAs.
The case of L signal or SECAM signal (hereinafter referred to as "625/50 system") is shown. 22 is a frame pulse, 23 is a field pulse, 24 is a video signal, 26 to 29 are valid signals, 30 is a valid period, 25 is a vertical period signal (actually, it should be a complex period signal, but the drawing and explanation are simple For synchronization, only the vertical synchronizing signal is shown), 31 and 34 are magnetic heads 8 and 9, respectively.
Timing of tracing on magnetic tape 6, 32 and 33
Indicates a period in which the magnetic head 8 is in contact with the magnetic tape 6, and 35 and 36 indicate a period in which the magnetic head 9 is in contact with the magnetic tape 6. The rotary cylinder 7 has a field pulse 23
(Or frame pulse 22) and rotates in synchronization with the phase. In this example, the rotating cylinder has an apex of 180 ° during one field
The case where it rotates is shown. Vertical sync signal 25 of video signal 24 and video signal of valid period 30 excluding blanking period
24 is digitized and subjected to predetermined digital processing, and is recorded on the magnetic tape 6 through the magnetic head 8 in a period 32. As a result, the track 52 is formed. The next valid signal 27 is also processed in the same manner through the magnetic head 9 for a period 35.
Are recorded on the magnetic tape 6 to form tracks 53. The same operation will be repeated thereafter.

Note that the reproduction is the reverse of the above-described processing, but the description thereof is omitted.

Next, the case of the 625/50 system will be described. In FIG. 5, 37-44 and 58-62 show the case of 625/50,
37 is a frame pulse, 38 is a field pulse, 39 is a video signal, 41 to 43 are valid signals, 44 is a valid period, 58 and 61 are trace timings of the magnetic heads 8 and 9, and 59 and 60 are magnetic tapes from the magnetic head 8. 6, a period 62 in which the magnetic head 9 is in contact with the magnetic tape 6, and a period 40 is a vertical synchronizing signal. 37-44 and 58-62 correspond to 22-36, respectively, and thus detailed description thereof will be omitted.

Problems to be Solved by the Invention By the way, the problems in the case where both the 525/60 system and the 625/50 system are supported by sharing the mechanical part will be described below.

When sampling a video signal, the sampling frequency is often set to an integer multiple of the color subcarrier frequency ( _sc ). For example, for an NTSC signal, 14.3MHz ( _4sc ... 3.58MHz
Of 4-fold), in the PAL signal 17.7MHz (4 · _sc ...... 4.43MHz
4 times) is often adopted. It is common knowledge that the number of bits per pixel is 8 bits. Therefore, the magnetic tape 6
The data rates recorded above are often related to _sc . Therefore, the ratio of the data rates of the 525/60 system and the 625/50 system is often the ratio of the color subcarriers, whether the straight PCM or the band compression is adopted.

Therefore, the data rate in the 525/60 system is R ₅ , the data rate in the 625/50 system is R ₆ , and the color subcarrier frequency of the NTSC signal is
_If the color subcarrier frequency of the _scn and PAL signals is _scp , then R ₅ : R ₆ = _scn : _scp = 3.58: 4.43 (1). On the other hand, since the rotary cylinder 7 rotates in synchronization with the frame timing, the relative speed and the frame frequency in the 525/60 system are S ₅ and the relative speed and the frame frequency in the 5,625 / 50 system are S and _{5 respectively} . ₆ and ₆ Becomes Therefore, 1 on the magnetic tape 6 in the 525/60 system
Assuming that the bit length is λ ₅ , the 1-bit length on the magnetic tape 6 in the 625/50 method is λ ₆ , then from equations (1) and (2) Becomes

By the way, since the data rate is high in DVTR, one of the issues is how to reduce the consumption of magnetic tape, and high density recording is indispensable. Therefore, as a matter of course, short wavelength recording is forced. In such short wavelength recording, a slight difference in recording wavelength greatly affects the C / N characteristics and error rate during reproduction. As in formula (3), there is a large difference in the recording wavelength between the 525/60 system and the 625/50 system, and it is not possible to efficiently record and reproduce both of these systems.

Therefore, the present invention eliminates the above-mentioned drawbacks, and the 525/60 system and 62
It proposes a method that can efficiently record and reproduce both 5/50 methods.

Means for Solving the Problems In the present invention, the data rate is set to a times the color subcarrier frequency, and the rotation speed of the rotary cylinder is set to b times the frame frequency (= b · ₅ ) in the 525/60 system. In the 625/50 system, the recording wavelength is set to be 1.5 × b times (= 1.5 · b · ₆ ) so that the recording wavelength is substantially equal in both the 525/60 system and the 625/50 system.

By setting as above, the recording wavelength can be made almost the same with any signal system, and as a result, 625/50 can be obtained with the 525/60 system.
However, it is possible to record and reproduce efficiently.

EXAMPLES Next, examples of the present invention will be described below.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is an input terminal, 2 is an A / D converter, 3 is a recording side processor, 4 is a modulator, 5 is a recording amplifier, 10 and 11 are switches, 8 and 9 are magnetic heads, 7 Is a rotating cylinder, 6
Is a magnetic tape, 12 and 13 are reproduction amplifiers, 14 and 15 are equalizers, 16 is a head switch, 17 is a detector, 18 is a demodulator, and 19
Is a reproducing side processor, 20 is a D / A converter, and 21 is an output terminal.
The video signal to be recorded is input to the A / D converter 2 via the input terminal 1.
And digitized. The output of the A / D converter 2 is subjected to various digital processes (time axis conversion, error correction coding, band compression, etc.) in the recording side processor 3 and then digitally modulated in the modulator 4. The output of the modulator 4 is applied to the recording amplifier 5. During recording, the switches 10 and 11 are closed on the recording side, and data is recorded on the magnetic tape 6 via the switches 10 and 11 and the magnetic heads 8 and 9.

On the other hand, during reproduction, the switches 10 and 11 are closed on the reproduction side, and the information recorded on the magnetic tape 6 is reproduced through the magnetic heads 8 and 9 and the switches 10 and 11 to the reproduction amplifier 12 and
Applied to 13. The output of the reproducing amplifiers 12 and 13 is inversely corrected for the transmission distortion in the tape head system in the equalizers 14 and 15, respectively. The head switch 16 switches the outputs of the equalizers 14 and 15 at a predetermined timing to obtain a continuous reproduction signal, which is applied to the detector 17 to restore the output of the modulator 14. The output of the detector 17 is digitally decoded by the demodulator 18, and the reproduction side processor 19
Then, the signal is subjected to a predetermined digital processing at and is led to the D / A converter 20. Restore the original analog video signal with the D / A converter 20,
It is output via the output terminal 21.

Next, an embodiment of the present invention will be further described with reference to the timing chart shown in FIG. In Figure 2, 22-36 is 525/60
In the case of the system, 36 to 51 are 625/50, and 22 to 36 are the same as 22 to 36 in FIG. Therefore, detailed description of 22 to 36 will be omitted, and 37 to 51 will be described below. 37 is a frame pulse, 38 is a field pulse, 39 is a video signal, 40 is a vertical synchronizing signal, 44 is a valid period, 41 to 43 are valid signals, 45 and 49 are trace timings of the magnetic heads 8 and 9, 46 to 48 are The period in which the magnetic head 8 is in contact with the magnetic tape 6 is 50 and the period in which 51 is the magnetic head 9 is in contact with the magnetic tape 6. In the present embodiment, in the case of the 525/60 system, the rotary cylinder 7 is set to rotate at an angle of 180 ° in one field period. That is, if the rotation speed of the rotary cylinder 7 is K ₅ , then K ₅ = b · ₅ (4) (where b = 1). On the other hand, in the case of the 625/50 system, the rotary cylinder 7 is set to rotate the apex by 270 ° in one field period. That is, when the rotation speed of the rotary cylinder 7 is K ₆ , K ₆ = 1.5 · b · ₆ (5) (where b = 1). Not surprisingly, the relative speed S ₅ in the 525/60 system
And the relative speed S ₆ in the 625/50 method is S ₅ = C ・₅ …… (6) S ₆ ＝ 1.5 ・ C ・₆ …… (7) where C is a constant (= [cylinder diameter] × π) Become. The video information 41 to 43 within the effective period 44 is recorded.
Information corresponding to the period 3 is recorded via the magnetic head 8 during the period in which the rotary cylinder 7 rotates 180 ° as indicated by 46. The information corresponding to the remaining 1/3 period of the effective signal 41 and the information corresponding to the front 1/3 period of the next effective signal 42 are shown via the magnetic head 9 as indicated by 50.
It is recorded during a period of 180 ° rotation. Further, the information corresponding to the remaining 2/3 of the valid signal 42 is recorded via the magnetic head 8 during the next 180 ° during which the rotary cylinder 7 rotates by 180 °. The same operation is repeated thereafter.

Now, the embodiment of the present invention shown in FIG. 1 will be further described by taking specific numerical values as an example.

Now, assuming that the sampling number wave number _{S5 in the} 525/60 system and the sampling frequency _S6 in the 625/50 system are four times the respective color subcarriers, _S5 = _4.scn = 14.3MHz (8) _S6 ＝ 4 ・_scp = 17.7MHz …… (9) Further, assuming that the bit allocation of 2 bits / pel per pixel is realized by introducing the band compression technology to the recording side processor 3, the data rate R _{5 in the} 525/60 system and the data rate in the 625/50 system R ₆ is R ₅ = 2 · _S5 = 28.6 Mbps (10) R ₆ = 2 · _S6 = 35.4 Mbps (11) As a matter of course, at this time, the expression (1) is satisfied. Next, assuming that the diameter D of the rotary cylinder 7 is 76 mm, the relative speed S _{5 in} the 525/60 system and the relative speed S ₆ in the 625/50 system are calculated from the formulas (6) and (7). Becomes Assuming that the NRZ system is adopted as the modulator 4, the 1-bit length λ ₅ on the magnetic tape 6 for the 525/60 system and the 1-bit length λ ₆ on the magnetic tape 6 for the 625/50 system. Is from equations (10) to (13) Therefore, the shortest recording wavelength on the magnetic tape 6 is about 0.5 μm even in the case of the 625/60 system, which is equal.

Next, regarding the number of tracks per unit time (1 second), 52
Let ₅ and ₆₀ and 625/50 be T ₅ and T ₆ , respectively. Becomes In order to equalize the recording time in the 525/60 system and the 625/50 system, the respective track pitches T _P5 and T _P6 are the formula (16),
From equation (17), it is necessary to set T _P5 : T _P6 = T ₆ : T ₅ = 1: 0.8 (18). In the case of formula (18), the playback C / N (ratio between the reproduced signal component and the noise component) loss due to the track width in the 625/50 system is L _TW compared to the 525/60 system. Is. Furthermore, the C / N loss L _BW in the 625/50 system due to the frequency bandwidth required for recording / reproducing via the magnetic tape 6, magnetic heads 8 and 9 is higher than that in the 526/60 system. Therefore, the C / N loss L of the 625/50 method against the 525/60 method is L = L _TW + L _BW 1.9 dB (21). On the other hand, since the 625/50 system has a higher relative speed even at the same recording wavelength, the C /
N gain G _S Therefore, the C / N loss shown in equation (21) can be compensated for. As a result, the 525/60 system and the 625/50 system have almost the same error rate.

In the above description, the rotation speed of the rotary cylinder 7 is 52
In the case of the 5/60 method, the frame frequency is made equal, and in the 625/50 method, the frame frequency is set to 1.5 times. This is the case where the constant b in the expressions (4) and (5) is 1, but it goes without saying that the present invention can obtain the same effect even when the constant b is other than 1.

Also, the case where a total of two magnetic heads are mounted on the rotating cylinder is shown, but depending on the data rate and cylinder diameter, multi-channel recording (recording on multiple tracks at the same time,
There may be a method of reproducing from multiple tracks at the same time), the tape winding angle may be other than 180 °, and the head location may be other than 180 ° on the rotating cylinder, but the present invention is applicable to any case. .

Furthermore, the SECAM signal does not have the same color width carrier as the PAL signal, but it is possible to create a sampling pulse approximately equal to an integer multiple of 4.43 MHz based on the horizontal synchronization signal.
Further, the modulator 4 is not limited to the NRZ system.

EFFECTS OF THE INVENTION As is clear from the above description, by applying the present invention, both the 525/60 format video signal and the 625/50 format video signal can be efficiently recorded and reproduced, and both are approximately the same. The error rate and the recording / reproducing time of about the same level can be achieved, and many mechanical parts and electric circuit parts can be shared.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a timing diagram for explaining FIG. 1, FIG. 3 is a block diagram showing a conventional example, FIG. 4 is FIG. FIG. 1 is a tape pattern diagram, and FIG. 5 is a timing diagram for explaining FIG. 2 ... A / D converter, 3 ... recording side processor, 4 ... modulator, 7 ... rotating cylinder, 18 ... demodulator, 19 ... reproducing side processor, 20 ... D / A conversion vessel.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area H04N 9/808

Claims (1)

[Claims] 1. A recording data rate in the 525/60 system R _5, 625
The recording data rate in the / 50 system is R ₆ , the color subcarrier frequency in the NTSC signal is _scn , the color subcarrier frequency in the PAL signal is _scp , and the rotation speed of the rotating cylinder in the _525/60 system is
K _5, 625/50 K ₆ the rotational speed of the rotary cylinder in a manner, 525/60
The frame frequency of the system is ₅ , 625/50 The frame frequency of the system is ₆ , and a and b are respectively troubles, and R ₅ = a ・_scn R ₆ ＝ a ・_scp K ₅ ＝ b ・₅ K ₆ ＝ 1.5 ・ b・ A digital magnetic recording / reproducing method for video signals, characterized in that it satisfies item ₆ .