JPS59131280A - Magnetic recording and reproducing device equipped with sound noise suppression circuit - Google Patents

Abstract

PURPOSE:To eliminate the deterioration in sound quality such as breathing phenomenon by regulating a compressing/stretching ratio of dynamic range in response to level ratio of a desired FM sound signal and a disturbing FM sound signal when recording density is changed to an optimum value. CONSTITUTION:A sound signal from an input terminal 1 passes through a preemphasis circuit 2 and is inputted to a 2/3 compression circuit 6 through a switch 3 at the SP mode and to a 1/2 compression circuit 4 at the LP mode. The gain of dynamic range compressing circuits 6. 4 is controlled by level detectors 7,5. An output signal of the compression circuits 6, 4 is FM-modulated by an FM modulator 9 through a switch 8 and fed to an adder 29 via an LPF10. The signal is added with a video signal from a terminal 30 at the adder 29 and recorded on a magnetic tape 12 in azimuth by a magnetic head 11. Thus, the deterioration in sound quality is reduced in changing the recording density.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is directed to solving crosstalk from adjacent tracks in a magnetic recording/reproducing device that records a frequency modulated (F''M modulated) audio signal and a video signal by superimposing the frequency a. The present invention relates to a magnetic recording and reproducing device equipped with an audio noise suppression circuit that reduces noise caused by noise.

[Background of the invention]

Conventionally, there has been a magnetic recording/reproducing apparatus which frequency-modulates a luminance signal (1''M modulation) and converts and records one chromaticity signal to the F side of the above-described M-modulated luminance signal (hereinafter referred to as 'F=VTR).

) is a method of recording audio signals on a magnetic tape using a rotating head (hereinafter referred to as Jinsei II
'This is called the M superimposition method. )It has been known. by the way.

There has been a remarkable improvement in recording activity in recent years, achieving a recording density record 17 times that of VTRs from about 10 years ago. With such high density and advances in recording technology, VTRs that are more compact have begun to be developed by reducing the size of each cassette and the diameter of the rotating cylinder. These small VT)L have smaller and lighter lids and lower magnetic tape running speeds, so conventional audio signal recording and reproducing systems that use fixed heads have wow and flutter characteristics.
It has become difficult to ensure sufficient performance in terms of playback 87N, playback frequency band, etc., and the above-mentioned audio)' IVI
There is an increasing need to adopt new audio recording and playback methods such as the superimposition method.The features of the audio b'M superimposition method include: (1) it is less susceptible to time axis fluctuations due to uneven tape running speed; Good flutter characteristics.

(2) The playback frequency band does not depend on the tape running speed and can be widened.

etc.

Here, the above-mentioned audio signal is transmitted using the audio FM superimposition method ['l-
Let's think about the recording frequency spectrum of a VTR.

The center frequency of the audio signal carrier must be determined so as to minimize its influence on the luminance signal and chromaticity signal. In addition, small VTRs, VTs with a small rotating cylinder diameter
In R, the relative speed between the tape and the head is low, so the recording frequency is narrow, and the center frequency of the luminance signal carrier wave cannot be set too high.Therefore, the center frequency of the audio signal carrier wave is There is no choice but to set the frequency as low as possible below .

FIGS. 1 and 2 show examples of frequency spectra when recording video signals and FM audio signals. Figure 1 shows b'
An example in which the FM modulated universal voice signal A1 is placed between the M modulated luminance signal Y and the frequency e-converted chromaticity signal C1, FIG. 2 shows an example in which the FM modulated audio signal A2 is placed below the frequency converted chromaticity signal C1. This is an example. By the way, a major problem with the audio FM superimposition method is that the video track width must be widened (in case of
Also, if a tracking deviation occurs, the signal of the adjacent video track will also be reproduced. Noise occurs due to the influence of the FM audio signal of the adjacent video track mixed into the reproduced audio signal (hereinafter referred to as adjacent interference). In particular, when trying to increase recording density, the video track width becomes narrower, so adjacent interference such as tracking deviation becomes very annoying and becomes a problem.
1 video track l111. '112 and a plan view schematically showing the positions of the video head H.

Here, the noise U (t) caused by the adjacent interference is:
When the tracking deviates as shown in Fig. 3 - the first F'M audio signal (Fig. 3
The signal obtained from this part is hereinafter referred to as the desired F'M audio signal. ) is the level a, the level of the second FM audio signal obtained from the Re video track T2 (the signal obtained from the part B in Figure 3, hereinafter referred to as the interfering FM audio signal) is b, and the desired F If the difference frequency between the M audio signal and the interfering FM audio signal is Δω, then D ltloc! ! −Δω(COS Δ(d t )
===, -9, =, (expressed as 11, where t
represents time. That is, the adjacent interference noise D(tl is
Difference frequency between desired F'M audio signal and interfering FM audio signal -
(beat frequency), and its amplitude is considered to be proportional to the amplitude ratio b/a of the interfering FM audio signal to the desired 1i'M audio signal and the difference frequency. Therefore, as an effective method for reducing the adjacent interference in the VTR mentioned above, during recording, the dynamic range is compressed according to the amplitude of the audio signal S or a specific band component of the audio signal, and the effective frequency is reduced. The amount of deviation is increased so that the instantaneous difference frequency between the carrier waves of the interfering FM audio signal and the desired FM audio signal is almost outside the audible band, and then Ii'M modulation is carried out, and the frequency is superimposed with the video signal to produce a magnetic tape. Then, during playback, it is conceivable to perform FM modulation, expand the compressed dynamic range, and restore the original state.

In this method, due to the azimuth loss caused by azimuth recording, the interference F'M audio signal shown in equation (1) and the desired F'
The effect of reducing the level ratio b/a with the M audio signal to some extent, although it is not sufficient due to the low FM audio carrier frequency,
By effectively amplifying the amount of frequency deviation of the audio signal, the difference frequency component Δω in equation (1) is moved to the high range and outside the audible band, and the noise level is reduced by inversely transforming it during playback. Due to the synergistic effect of this effect, adjacent interference noise can be reduced to a practically sufficient level! to suppress it. Moreover, this method also has the following features: One, the video track width can be narrowed roughly by the amount of adjacent interference reduction (this allows for high-density recording, two, noise other than adjacent interference noise can also be reduced, and three, the frequency deviation of the actual audio signal can be reduced). Since the amount of shift may be small, the frequency band required for recording may be small.Fourly, the frequency band specifically used for recording the above-mentioned FM modulated audio signal may be small, so the amount of frequency shift is simply increased. Compared to the method, the recording wavelength of the luminance signal is longer, so the diameter Z of the rotating cylinder can be made smaller, and the size can be reduced.

However, the effect of suppressing the interfering FM audio signal level due to the azimuth loss used in the method for reducing adjacent interfering noise depends on the recording track width.

The width of the video head varies depending on each VTR system.For example, as shown in Table 1,
F' M audio carrier frequency f. = 1.3MHz - azimuth angle ψ = 17gi, relative velocity Vh = 4.1m/S are the same, one recording track width Tp and video head width 'l'w
For each h, system I with Tp = 18.7 μm, Tw = 28.0 μm and system ■ with Tp = 9.3 μm, Tw = 14 μm, the above-mentioned desired FM front signal and interference FM
The level ratio with the audio signal (hereinafter abbreviated as "approximate") is approximately 22 dB in system I and approximately 17 dB in system (II), which are significantly different. Here, system ■ has twice the recording density as system I, and system ■ is referred to as the so-called standard mode (hereinafter referred to as standard mode).

It is abbreviated as SP mode. ), system (1) corresponds to the so-called long-time mode (hereinafter abbreviated as "LP7-mode"). I want to m 1. Compared to the SP mode, the P mode generates more adjacent interference noise, which is very unpleasant to the ear, by an amount corresponding to the difference in the 0 column.

Table 1 Therefore + In LP mode, the dynamic range change characteristics used in the method of reducing adjacent interference noise, i.e. the compression ratio of the compressor that compresses the dynamic range of the audio signal during recording, and the expansion that expands the dynamic range during playback. The expansion ratio of the container (hereinafter collectively referred to as compression expansion ratio) is SP
I have to do it more like a dog than a mode. but,
If the compression/expansion ratio is increased unnecessarily, Sc will be improved, but the so-called "breathing" phenomenon in which the noise level changes depending on the signal level and the distortion rate will deteriorate, which is undesirable for the auditory sense. Therefore, there is a need to define optimal compression ratios and expansion ratios according to D/U from the perspective of sound quality.

[Purpose of the invention]

An object of the present invention is to provide a device capable of recording FM modulated audio signals on a magnetic tape obliquely with respect to the longitudinal direction of the tape and changing the recording density, in order to prevent adjacent interference to a practically sufficient level even when the recording density is maximum. To obtain a magnetic recording/reproducing device equipped with a speech noise suppression circuit that can reduce noise to a level that is low.

[Summary of the invention]

According to the present invention, when changing the record K, depending on the level ratio (D/U) of the desired FM audio signal and the interfering FM audio signal,
By setting the compression/expansion ratio of the dynamic range of the audio signal to be recorded to an optimal value, deterioration of sound quality such as the so-called breath phenomenon, in which the noise level changes depending on the signal level, occurs even when the recording density is maximum. This is to prevent adjacent interference from occurring and to reduce adjacent interference to a practically sufficient level.

[Embodiments of the invention]

As mentioned above, in SP mode and LP mode, the desired FM
Level ratio (D/U) between audio signal and interfering F'M audio signal
Accordingly, the compression ratio and expansion ratio of the dynamic range of the audio signal must be changed in order to reduce adjacent interference noise. here.

The higher the compression ratio/expansion ratio is, the more noise such as adjacent interference noise is suppressed and the S/N ratio is improved. This will cause the above discomfort. Therefore, it is necessary to specify an optimal compression ratio and expansion ratio according to the D/UK, which does not cause deterioration of sound quality such as breath-breathing phenomenon and reduces adjacent interference noise to a practically sufficient level.

Figure 4 shows how the compression ratio and expansion ratio change depending on each D/CJ value?
This is an experimental example showing how much the improvement effect due to compression/expansion 1/n corresponds to the apparent value of D/lJ when X is increased. Here, a range of about 2 or less is used as the compression ratio/expansion ratio. Here, for example, when a compressor compresses an audio signal to a size equal to the dynamic range of the audio signal, and an expander expands this compressed signal to twice that, the compression/expansion ratio is referred to as 2. When compressing the dynamic range to 7 and expanding it by a factor of 6, the compression/expansion ratio is called 3. If the compression ratio and expansion ratio are much higher than 2 (for example, 3), the noise level expanded during playback, that is, the noise reduction effect, will vary greatly depending on the input audio signal level, and this noise level fluctuation will affect the auditory sense. This is because it causes serious deterioration in sound quality. for example,
Assuming that the dynamic range of recorded audio 1g is 120 bB, the S/N of the transmission path is 40 dB, and the compression/expansion operation is performed ideally, the dynamic range of the audio signal will depend on the compression ratio and expansion due to the compression effect during recording. 60dB at ratio 2, compression ratio and expansion ratio 60:40
dB. However, during reproduction, one transmission line S is 40 dB, and the expansion action operates according to the input signal level. 3
Both are 40 dB, and the reproduction S when the modulation factor is 0 is @ 80 dB when the compression ratio and expansion ratio are 2, and 120 dB when the compression ratio and expansion ratio are 3. Therefore.

The noise level width that fluctuates from 0% to 100 degrees of modulation is 40 dB at compression ratio and expansion ratio 2, and 80 dB at compression ratio 3. It becomes remarkable when the ratio is 3.

FIG. 4 will be explained. Applying compression and expansion ratios of 2 to a system with D/U 17 d B results in D/U 26 d B.
The adjacent interference noise level VC is equivalent to that of a comparable system,
Applying a compression ratio and an expansion ratio of 15 l)/[J 21
This shows that the interference noise level is equivalent to that of a system equivalent to dB. Additionally, experiments have shown that if the level is about 22 dB or more, the level of adjacent interference noise is at the audibly permissible limit. Note that when high-quality audio such as stereo audio is required, D/U 2'6 dB or more is desirable.

Therefore, once the lulu value required for sound quality is determined, the optimum compression ratio and expansion ratio can be found from FIG. First, find the value corresponding to the D/U of the system on the horizontal axis of Figure 4, then search the value equivalent to the D/U required for sound quality on the vertical axis of Figure 4, and then The value of the compression/expansion ratio straight line near the intersection of is approximately the optimum compression/expansion ratio to be sought. For example, if the D/U of the system requires 17 dL, and D/U 26 d B , there is a 1:2 compression/expansion ratio straight line near these intersections from Figure 4, so this 1:2 is the optimal compression/expansion ratio. Note that in this example, a ratio of 1:2 was adopted, but ' : 1.6 + 1 :
A nearby value such as 2.4 may be used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The audio noise suppression circuit of the magnetic recorder according to the present invention will be described below with reference to the embodiments shown in the drawings. Figure 5 shows a rotary head type VT that can change the recording density or recording time in two ways.
1 is a circuit configuration diagram showing an embodiment in which the present invention is applied to an audio recording circuit that records an audio signal using an audio FM superimposition method in R. FIG. 6 is a circuit diagram showing an embodiment of the audio reproduction circuit of the VTR to which the present invention is applied. Here, the specifications of the VTR whose recording density can be changed to two are the same as those described in Section 1 above. Also - D/ required for sound quality
Assume that U is 26 dB. therefore.

Recording density (S) equivalent to system ■ with D/U approximately 22dB
P mode), set the compression ratio and expansion ratio to 1.5 from Figure 4.
, recording density (L) equivalent to System H of approximately 17 dB
P mode), the compression ratio and expansion ratio may be set to 2 from FIG. In FIG. 5, the audio signal input from input terminal 1 passes through pre-emphasis circuit 2 and then goes to SP
In mode, it passes through switch 3 and goes to /3 compression circuit 6.

When in LP mode, /2 compression circuit 4 is passed through switch 3.
is input to. Here, the switch 3 is controlled by an SP mode/LP mode switching signal inputted from the input terminal 28. In the SP mode, the dynamic range of the pre-emphasized audio signal is compressed to 73 in the compression circuit 6, and in the LP mode, the dynamic range of the pre-emphasized audio signal is compressed to 73. In the LP mode, the dynamic range of the preemphasized audio signal is compressed to 73.
The gain is controlled by -1j by the output signal of the detector 5.7, each of which receives a pre-emphasized audio signal as an input. The output signal of the /compression circuit 6 or the Z2 compression circuit 4 is inputted to the FM modulator 9 through the switch 8 and subjected to F'M modulation. Here, the switch 8 is controlled by an SP mode/LP mode switching signal inputted from the input terminal 28. The output of the FM modulator is passed through a low-pass filter (hereinafter referred to as LPF) 10 to remove unnecessary band components, and then passed through an adder 29 to input terminal 3.
0, the magnetic head 1
Azimuth recording is performed on the magnetic tape 12 at step 1.

Next, in the audio reproduction circuit shown in FIG. 6, the signal traces reproduced by the magnetic head 11 from the magnetic tape 12 are input to a band pass filter (hereinafter referred to as BPF) 13. B p p
13 extracts only the F''M audio signal from the reproduced signal.

Further, the signal reproduced by the magnetic head 11 is also output from the output terminal 25 to a video signal reproduction circuit (not shown). The extracted FM audio signal is demodulated into an audio signal by the FM demodulator 14. The demodulated audio signal is LPP,1
After FM carrier wave leakage and the like are removed in step s, the hold circuit 16 processes noise caused by head switching by holding the previous value. Here, the hold circuit 16 receives a control signal synchronized with the head switching signal input from the input terminal 26.
The previous value is held for a certain period of time.

The output of the hold circuit 16 (signal is input through the switch 17 to the 72-fold expansion circuit 18 in the SP mode and the 2-fold expansion circuit 20 in the P mode. Here, the switch 17 is input to the SP input from the input terminal 27. It is controlled by the mode-LP mode switching signal.

The hold circuit output signal is restored to its original dynamic range by the /22 expansion circuit 18 in the SP mode and by the 2X expansion circuit 20 in the LP mode. Here, the gain of the double expansion circuit 18 and the double expansion circuit 20 is controlled by the output signal of the detection circuit 1z31 which uses the hold circuit output signal as a human power,
The dynamic range of the demodulated audio signal is extended to the original range. The expanded signal passes through switch 22,
After being de-emphasized by the de-emphasis circuit 2, it is output from the output terminal 24. here.

The switch 22 is connected to the switch 17. The reproduced audio signal expanded by the expansion circuit 1'8-20 undergoes the same expansion operation with respect to its noise level, and has a low noise level, so that it is output as an audio signal with suppressed adjacent interference noise.

Needless to say, this output audio signal is compressed and expanded at the optimal compression and expansion ratios, so there is little deterioration in sound quality such as the so-called breathing phenomenon in which the noise level changes depending on the signal level, and distortion rate deterioration. Furthermore, W5
The embodiment shown in FIGS. 6 and 6 uses a switch circuit to change the compression ratio and expansion ratio for each of two recording densities, but the structure is a little complicated. Therefore.

It is also possible to simplify the two compression/expansion ratios of the SP mode and the LP mode in the embodiment to only one of the two for the LP mode. In this case, the reproduced audio signal in the SP mode is more improved in terms of S/N K, but the above-mentioned breathing phenomenon and distortion rate are somewhat degraded. However, these deterioration caps are within a sufficiently tolerable range compared to the effect of reducing noise such as adjacent interference noise.

FIGS. 7 and 8 show examples of the circuit configuration of the audio recording and reproducing circuit in the case where the compression/expansion ratio is simplified to only 2 in the LP mode in the above-mentioned VTR.

Here, circuits in FIGS. 7 and 8 that are the same as those in FIGS. 5 and 6 are given the same numbers. The operation in Figure 7 is in SP mode and LP mode.
In either mode, the audio signal input from input terminal 1 passes through pre-emphasis circuit 2, and then
A compression circuit 4 compresses the pre-emphasized audio signal to a dynamic range t/. Here, the gain of the /2 compression circuit is controlled by the output signal of the detector 5 which inputs the pre-emphasized audio signal.
''compression·/? The output signal of the compression circuit 4 is subjected to FM modulation by an F'M modulator 9. FM modulator output is LPFlo
After removing unnecessary band components in the adder 29, the circuit in FIG. The signal reproduced by the S air head 11 is input to B P Fls, and only the FM audio signal is extracted. Further, the signal reproduced by the magnetic head 11 is also outputted from the output terminal 25 to a video signal reproduction circuit (not shown). The extracted FM audio signal is sent to FM demodulator 1
4, the signal is demodulated into an audio signal. The demodulated audio signal is L
After the leakage of the FM carrier wave is removed by the PF 15, the noise caused by head switching is processed by the hold circuit 16 by holding the previous value. The hold circuit 16 operates based on a control signal input from an input terminal 26.

The output signal of the hold circuit 16 has its dynamic range doubled by a doubling expansion circuit 20, and is returned to its original range. Here, the gain of the double expansion circuit 20 is controlled by the output signal of the detector 31.

The output signal of the double expansion circuit 20 is sent to the de-emphasis circuit 2.
6 and then output from the output terminal 24. Also,
In the recording circuit of the embodiment, consideration is given to compressing the dynamic range of the pre-emphasized audio signal so that overmodulation is less likely to occur. Furthermore, although compression and expansion are performed according to the amplitude of the entire band of the audio signal, the amplitude of a specific band component of the audio signal may be used.

〔Effect of the invention〕

As explained above, if the present invention is used, the following will be achieved.
J: Sea urchin.

1. With a simple circuit configuration, the noise level changes depending on the signal level even during high-density recording, minimizing quality deterioration due to the so-called breathing phenomenon and distortion rate deterioration, and effectively suppressing adjacent interference noise. can be reduced.

2. Noises other than adjacent interference noise can be reduced at the same time. 6. Since the required frequency bandwidth is small, the diameter of the rotating cylinder can be reduced, allowing for a smaller size.

It has many features such as miniaturization of VTR and.

The effect of this method on the reduction of adjacent interference noise in the audio FM superimposition method is significant.

[Brief explanation of the drawing]

Figures 1 and 2 are frequency spectrum diagrams showing examples of signal frequency spectra in the audio I''M superimposition method.
Figure 4 is a plan view of a magnetic tape for explaining adjacent interference.
The figure is a characteristic diagram showing the relationship between D/lJ of the system and the apparent D/U of the system improved by the compression/expansion effect.
FIGS. 5, 6, 7, and 8 are circuit diagrams showing an embodiment of an audio recording/reproducing path using the present invention. 4.6... Compression circuit 18.20... Expansion circuit 5.7119.31... Detector 3.8, 17.22... Switch representative patent attorney Akio Takahashi No. 1 Violent liquid My 2nd Soukumaki Kaya 3 Figure

Claims (1)

[Claims] Magnetic recording in which a frequency-modulated audio signal is sequentially recorded on a magnetic tape as a recording locus inclined at a predetermined angle with respect to the longitudinal direction of the tape using a plurality of rotating heads, and the recording density is varied by changing the running speed of the magnetic tape. In the reproducing device, the dynamic range of the audio signal is compressed and the carrier wave signal is frequency modulated according to the amplitude length of the entire frequency band or the amplitude of a specific frequency band of the audio signal to be recorded during recording, and the magnetic tape is reproduced. The frequency modulated audio signal is demodulated during playback, the dynamic range of the demodulated audio signal is expanded and restored to the original dynamic range, and the compression ratio and expansion ratio of the dynamic range are set to Ai? 1. A magnetic recording and reproducing device equipped with an audio noise suppression circuit, characterized in that the maximum recording density is approximately 2 or less to eliminate interference with frequency modulated audio signals recorded on adjacent recording trajectories.