JPH0630121B2 - Magnetic recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to magnetic recording in which an FM audio signal is mixed with a PCM audio signal and recorded in a deep layer of a magnetic tape, and a video signal is superposed on the magnetic recording. It relates to the device.

[Prior Art] As a magnetic recording device for mixing an FM audio signal and a PCM audio signal and recording them in a deep portion of a magnetic tape, for example, there is one disclosed in Japanese Patent Laid-Open No. 1-105301. Here, the outline of such a conventional technique will be described with reference to FIG. 3. The analog audio signals of the left and right channels input to the terminal 10 are input to the FM signal processing circuit 12 on one side, where noise reduction is performed. , Signal processing such as pre-emphasis, amplitude limitation, FM modulation, bandpass filtering, etc. is performed for each channel.

On the other hand, the audio signal is also input to the PCM signal processing circuit 14, where low-pass filtering, sample hold,
A / D conversion, encoding, OQDPSK (Off-set Quadratu
re Differential Phase Shift Keying) Processing such as modulation and band filtering is performed.

These FM signal processing circuit 12 and PCM signal processing circuit 1
The modulated outputs of 4 are input to the mixer 16, mixed, and further input to the bias superimposing circuit 18. In the bias superposition circuit 18, a high frequency signal of a predetermined frequency is superposed on the frequency multiplexed signal mixed for AC bias, and the superposed signal is supplied to the rotary recording head 20 for voice and recorded on the magnetic tape 22. It That is, a signal in which the high frequency bias signal is superimposed on the mixing signal of the FM audio signal and the PCM audio signal is recorded on the deep layer portion 24 of the magnetic tape 22 by the recording head 20 rotating in the direction of arrow F1.

On the other hand, the color video signal is input to the video signal processing circuit 26 and subjected to predetermined signal processing, and then the recording head 2
8 are supplied. Then, as the recording head 28 rotates in the direction of arrow F2, the surface layer portion 30 of the magnetic tape 22 is
That is, the modulated video signal is recorded by superimposing it on the modulated audio signal of the deep portion 24.

According to this prior art, as shown in FIGS. 7 (A) and 7 (B) of the publication, by superimposing a high frequency bias signal on a voice modulation signal, a noise spectrum due to intermodulation distortion, particularly low The noise spectrum in the vicinity of the gamut conversion color subcarrier frequency is significantly reduced.

[Problems to be Solved by the Invention] However, the following problems may occur in the above conventional techniques. First, the recording current density of the modulated audio signal to the magnetic tape 22 is shown in FIG.
It becomes as shown in (A). In the figure, f _B is the bias signal frequency, f _P is the carrier frequency of the OQDPSK signal,
f _AL and f _AR are FM center carrier frequencies of the left and right channels. Further, the graph G1 is a PCM audio signal component, the graph G2 is an FM audio signal component, and the graph G3 is a high frequency bias signal component.

On the other hand, the spectrum of the reproduction output of the modulated audio signal is as shown in FIG. 7B, and the intermodulation distortion G4 of the frequency f _D appears as a line spectrum. The recording current spectrum of the modulated video signal is as shown in FIG. In the figure, f _C is the low-frequency signal carrier frequency,
The graph G5 is a color signal component, and the graph G6 is a luminance signal component.

In the magnetic recording / reproducing system, although the odd-order distortion occurs, the above-mentioned intermodulation distortion G4 has no relation to the FM audio signal.
It is the fifth-order distortion caused by the signal and the bias signal. O
The QDPSK signal f _P (t) is expressed by f _P (t) = sin (ω _P t + nπ / 2) (1). Here, n is an integer. In contrast,
If the high-frequency bias signal f _B (t) is f _B (t) = sin ω _B t (2), the term of the fifth-order distortion of these two signals is {sin (ω _P t + nπ / 2)}. ⁴・ sinω _B t …… 3 appears. Expanding this, sinω _B t · {(3/8) − (1/2) cos (2ω _P t + nπ) + (1/8) cos (4ω _P t + 2π)} = (3/8) sinω _B t − (1/2) sinω _B t ・ cos (2ω _P t + nπ) + (1/8) sinω _B t ・ cos4ω _P t, and sinω _B t ・ cos4ω _P t = (1/2) ・ {sin (ω _B + 4ω _{P) t + sin (4ω P} -ω B) t} ...
… (4) appears.

Therefore, even if the QPSK signal has a bandwidth,
Distortion of | 4f P _-f B | = intermodulation distortion appearing _{f D} ......... ₍₅₎ to the frequency of the line spectrum.

When this intermodulation distortion appears in or near the frequency band of the audio signal components G1 and G2 and the color signal component G5 of the video signal depending on the setting method of the bias signal frequency f _B , these signals are disturbed, Degradation of video and FM audio signals,
There is an inconvenience that an error rate increases due to a decrease in C / N (carrier / noise) in the PCM voice signal.

The present invention has been made in view of the above points, and an object of the present invention is to provide a good magnetic recording apparatus without causing deterioration of a video signal and an audio signal.

[Means for Solving the Problems] According to the present invention, an audio signal is recorded on a deep portion of a magnetic tape magnetic layer by an audio rotary head, and the audio rotation is performed on a surface portion of the magnetic layer on which an audio signal track is formed. In a magnetic recording device for recording a video signal by a video rotary head having an azimuth angle different from that of the head, a first modulation means for generating a digital audio signal by performing polyphase differential PSK modulation or offset polyphase differential PSK modulation on the audio signal. Second modulating means for frequency-modulating the audio signal to generate an FM audio signal, and mixing means for frequency-division-multiplexing each modulated audio signal by the first and second modulating means to generate a mixed audio signal. , A bias superimposing means for superimposing a high frequency bias signal on the output audio signal of the mixing means, and an output signal of the bias superimposing means for the audio rotation. Recording means for supplying to the head and recording in the deep part of the magnetic layer, and a fifth-order intermodulation distortion frequency generated by simultaneously recording the high frequency bias signal and the output audio signal of the mixing means on a magnetic tape. However, the frequency of the high frequency bias signal is set so as to be outside the occupied frequency bands of the video signal, the digital audio signal and the FM audio signal.

[Operation] According to the present invention, regarding the frequency of the high frequency bias signal, the relationship between the fifth-order intermodulation distortion frequency generated between this and the mixed audio signal and the frequency bands of the digital and FM audio signals and the video signal is taken into consideration. Is set. Therefore, the intermodulation distortion has a frequency spectrum outside the occupied frequency bands of the digital audio signal, the FM audio signal, and the video signal.

[Examples] Examples of the magnetic recording apparatus according to the present invention will be described below.
Description will be given with reference to the accompanying drawings.

<First Embodiment> First, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. The configuration of the embodiment is shown in FIG. In the figure, first, the recorded color video signal is input to the video signal processing circuit 32 on the recording side. The output side of the video signal processing circuit 32 is connected to the input side of the switch 36 via the recording amplifier 34.

The switch 36 supplies the input modulated video signal to the video signal recording / reproducing heads 40 and 42 of the rotary drum 38, and reproduces the modulated video signal read from the magnetic tape 44 by the recording / reproducing heads 40 and 42. Amplifier 4
6 is output. The output side of the reproducing amplifier 46 is connected to the input side of the video signal processing circuit 48 on the reproducing side, and the output side of the video signal processing circuit 48 is the output side of the reproduced video signal.

Next, the recorded analog audio signal is input to the A / D conversion circuit 50 and the audio signal processing circuit 52, respectively. Of these, the output side of the A / D conversion circuit 50 is connected to the input side of the digital signal processing circuit 54, and the output side of this digital signal processing circuit 54 is connected to the adder 58 via the OQDPSK modulator 56. It is connected to one input side. On the other hand, the output side of the audio signal processing circuit 52 is connected to the adder 5 via the FM modulator 60.
8 is connected to the other input side.

Next, the output side of the adder 58 is connected to one input side of another adder 66 via the recording amplifier 62 and the bias trap circuit 64, respectively. On the other input side of the adder 66, the output side of the bias oscillator 68 is an amplifier 70,
The high-pass filters 72 are connected to each other. The output side of the adder 66 is connected to the input side of the switch 74.

This switch 74 is similar to the switch 36 described above,
The input modulated audio signal is supplied to the audio signal recording / reproducing heads 76, 78 of the rotary drum 38, respectively, and the modulated audio signal read by the recording / reproducing heads 76, 78 from the magnetic tape 44 is output to the reproducing amplifier 80. It is a thing.

Next, the output side of the reproduction amplifier 80 is connected to the input side of the waveform equalization circuit 82 on the one hand, and the output side of the waveform equalization circuit 82 is passed through the OQDPSK demodulator 84 to the reproduction side digital signal. It is connected to the input side of the processing circuit 86. The output side of the digital signal processing circuit 86 is one output side of the reproduced analog audio signal via the D / A conversion circuit 88.

On the other hand, the output side of the reproduction amplifier 80 is connected to the input side of the FM demodulator 90 on the other side.
The output side of 0 is connected to the input side of the audio signal processing circuit 92. The output side of the audio signal processing circuit 92 is the output side of the other reproduced analog audio signal.

Among the above units, the A / D conversion circuit 50, the digital signal processing circuit 54, and the OQDPSK modulator 56 are the modulation processing units of the PCM audio signal, and the audio signal processing circuit 5
2. The FM modulator 60 is a modulation processing part of the FM audio signal. Further, the bias oscillator 68, the amplifier 70, and the high-pass filter 72 are parts that generate a high frequency bias signal.

Further, the waveform equalizing circuit 82, the OQDPSK demodulator 84, the digital signal processing circuit 86, and the D / A conversion circuit 88 are PCs.
The FM demodulator 90 and the audio signal processing circuit 92 are the demodulation processing part of the M audio signal.

Next, the operation of the circuit configured as described above will be described. Also in this embodiment, as shown in FIG. 2, the modulated audio signal is recorded in the deep layer portion of the magnetic tape 44, and the modulated video signal is recorded in the surface layer portion thereof. That is, the FM modulation signal output from the FM modulator 60 and the OQDPSK modulation signal on the PCM side output from the OQDPSK modulator 56 are added by the adder 58. This addition output is input to the other adder 66 after being subjected to signal processing by the bias trap circuit 64.

Then, the high frequency bias signal output from the bias oscillator 68 is further added here, and the added modulated sound signal is recorded in the deep layer portion of the magnetic tape 44 by the action of the switch 74 and the recording / reproducing heads 76 and 78. Become.
On the other hand, the video signal is processed by the video signal processing circuit 32, and then the switch 36 and the recording / reproducing heads 40, 42.
Is recorded on the surface layer of the magnetic tape 44.

By the way, in the present embodiment, the frequency f _B of the high frequency bias signal is set as follows. In addition, O
The bandwidth of the QDPSK modulation signal is f _P ± 1 MHz, and the frequency shift of the FM modulation signal is f _AL ± 150 KHz, f _AR ± 150 KHz.

For example, the carrier frequency of the OQDPSK signal f _P = 3MH
z, FM center carrier frequency of left and right channels f _AL =
1.3 MHz, f _AR = 1.7 MHz, color signal carrier frequency f _C =
Assuming 629KHz, f _B = 11MHz ± 150KHz …… (6) f _B = 10.5MHz ± 50KHz …… (7) f _B = 13MHz ± 150KHz …… (8) f _B = 13.5MHz ± 50KHz …… (9) In any of the above, the oscillation frequency of the bias oscillator 68, that is, the bias signal frequency f _B is set.

Of the signals recorded on the magnetic tape 44 under these conditions, the video signal is read by the recording / reproducing heads 40 and 42 and input to the video signal processing circuit 48, where the video signal is reproduced. .

On the other hand, the audio signal is read from the magnetic tape 44 by the recording / reproducing heads 76 and 78. Then, the waveform equalization circuit 8
2, the OQDPSK demodulator 84 and the digital signal processing circuit 86 perform reproduction processing on the PCM side, and the reproduced analog audio signal is output from the D / A conversion circuit 88. On the other hand, F
The reproduction processing on the M side is performed by the FM demodulator 90 and the audio signal processing circuit 92, and the reproduced analog audio signal is similarly output.

By the way, the intermodulation distortion frequency f _D of the reproduced audio signal in each of the above equations (6) to (9) is calculated from the above equation (5) as follows: f _D = 1 MHz ± 150 KHz (10) f _D = 1.5MHz ± 50KHz …… (11) f _D = 1MHz ± 150KHz …… (12) f _D = 1.5MHz ± 50KHz …… (13)

Considering these cases in order, first, in the cases of the equations (6) and (10), the intermodulation distortion frequency f _D is the graph G10 in FIG.
, And is not included in the signal band of either audio or video. Next, in the case of the equations (7) and (11), the intermodulation distortion frequency f _D comes to be located in the graph G11 in the same figure, and similarly it is not included in the signal band of either audio or video.
Further, in the case of the formulas (8) and (12), it is the same as the case of the above formulas (6) and (10), and in the case of the formulas (9) and (13), the above (7) and (11) It is similar to the case of the formula. Therefore, in both cases, the adverse effect of the intermodulation distortion on the audio signal and the video signal can be effectively prevented.

If f _B > 16 MHz is set, f _D > 4
MHz, and interference with the signal is removed as in the case described above.

Second Embodiment Next, a second embodiment of the present invention will be described. In this embodiment, among the bias signal frequency settings in the first embodiment, the setting condition that f _B > 16 MHz, f _D > 4 MHz and the intermodulation distortion is a frequency higher than the frequency band of the color signal component and the audio signal component is set. Is excluded. And f _B ≦ 13.55MHz
Is selected, and the frequency is set so that the intermodulation distortion frequency f _D is generated only between the color signal and the FM audio signal and between the FM audio signals as shown in FIG.

Then, since the bias signal frequency is low, it is not necessary to use a high frequency bias current amplifier as a bias signal amplifier. Therefore, the load is reduced, the circuit scale is reduced, and the configuration is simplified.

Third Example Next, a third example of the present invention will be described. The configuration of this embodiment is similar to that of the first embodiment described above. But,
The numerical value of each frequency is different. In this second embodiment, the OQD
PSK signal carrier frequency f _P = 3.1 MHz, left and right channel FM center carrier frequencies f _AL = 1.4 MHz, f _AR = 1.
It is assumed that 8 MHz and the color signal carrier frequency f _C = 629 MHz. The oscillation frequency of the bias oscillator 68, that is, the bias signal frequency f _B is f _B = 11.3 MHz ± 150 KHz …… (14) f _B = 10.8 MHz ± 50 KHz …… (15) f _B = 13.6 MHz ± 150 KHz …… (16 ) f _B = 14MHz ± 50KHz …… Set to either (17).

Then, the intermodulation distortion frequency f _D of the reproduced audio signal in each of these cases can be calculated from the equation (5) as follows: f _D = 1.1 MHz ± 150 KHz …… (18) f _D = 1.6 MHz ± 50 KHz …… (19 ) f _D = 1.1MHz ± 150KHz …… (20) f _D = 1.6MHz ± 50KHz …… (21) Therefore, as in the case of the first embodiment described above, the intermodulation distortion frequency f _D does not appear in the signal band of either audio or video, and the adverse effect of intermodulation distortion can be effectively prevented.

If f _B > 16.5 MHz is set, f _D
> 4.1 MHz, the interference with the signal is removed as in the case described above.

It should be noted that the present invention is not limited to the above-mentioned embodiment at all, and for example, even when QPSK modulation is performed instead of OQDPSK modulation, the modulation signal is the same as that of the above formula (1), and therefore, the above description is made. The numerical values of the embodiment can be applied as they are.

Further, the numerical values are not limited to those indicated in each embodiment, and may be appropriately set as necessary so as to achieve the same operation. The same applies to the circuit configuration.

As described above, according to the present invention, the fifth-order intermodulation distortion frequency generated between the high frequency bias signal and the mixed audio signal is the occupied frequencies of the digital audio signal, the FM audio signal and the video signal. Since the frequency of the high frequency bias signal is set so as to be out of the band, it is possible to effectively prevent the interference due to the intermodulation distortion with respect to each signal, and to perform signal reproduction with good quality without deterioration. There is.

According to one of the main aspects, the circuit configuration is simplified by setting the high frequency bias signal frequency lower than a predetermined value.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a magnetic recording apparatus according to the present invention, FIG. 2 is a graph showing the operation of the first embodiment, FIG. 3 is a configuration diagram showing a conventional example, and FIG. Is a graph showing the operation of the conventional example. 32, 48 ... Video signal processing circuit, 52, 92 ... Audio signal processing circuit, 54, 86 ... Digital signal processing circuit, 56 ... OQDPSK modulator, 58, 66 ... Adder,
68 ...... bias oscillator, 84 ... digital signal processing circuit, f B _... bias signal frequency, f _AL, f _AR ... FM center carrier frequency, f C _... color signal carrier frequency, _{f P} ...
Carrier frequency of the OQDPSK signal.

Claims (1)

[Claims] 1. An audio signal having a azimuth angle different from that of the audio rotary head is recorded on a surface portion of the magnetic layer where an audio signal track is formed, while a modulated audio signal is recorded in a deep portion of a magnetic tape magnetic layer by an audio rotary head. In a magnetic recording device for recording a video signal by a rotary head for use, first modulation means for generating a digital audio signal by polyphase differential PSK modulation or offset polyphase differential PSK modulation of an audio signal, and frequency modulating the audio signal. Second to generate an FM audio signal
Modulating means, mixing means for frequency-division-multiplexing the modulated audio signals by the first and second modulating means to generate a mixed audio signal, and a bias for superimposing a high frequency bias signal on the output audio signal of the mixing means. The superimposing means and the recording means for supplying the output signal of the bias superimposing means to the rotary head for voice to record in the deep portion of the magnetic layer, the high frequency bias signal and the output voice signal of the mixing means are simultaneously provided. The frequency of the high-frequency bias signal is set so that the fifth-order intermodulation distortion frequency generated by recording on the magnetic tape is outside the occupied frequency bands of the video signal, digital audio signal and FM audio signal. A magnetic recording device characterized by: