JPH0690768B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention reduces noise due to crosstalk from adjacent recording tracks in a magnetic recording / reproducing apparatus that records a frequency-modulated (FM-modulated) audio signal with a rotary head. The present invention relates to a magnetic recording / reproducing apparatus for an audio signal that reduces other noises such as noises generated when switching heads.

[Background of the Invention]

Conventionally, a magnetic recording / reproducing apparatus (hereinafter referred to as a VTR) that frequency-modulates (FM-modulates) a luminance signal and frequency-converts a chromaticity signal to the lower side of the FM-modulated luminance signal to record. As one of the recording methods of the audio signal in the above, there is known a method of recording the FM-modulated audio signal and the above-mentioned video signal on the same magnetic tape in a superimposition manner (hereinafter referred to as an audio FM superposition method). . By the way, there has been a remarkable improvement in recording density in recent years, and the recording density has reached 17 times as high as that of the VTR about 10 years ago. Along with such advances in high-density recording technology, compact VTRs have begun to be developed by miniaturizing cassettes and rotating cylinder diameters. In these compact VTRs, in order to reduce the size and weight and reduce the magnetic tape running speed, conventional audio signal recording methods that use fixed heads have wow and flutter characteristics, playback S / N, playback frequency band, etc. In this respect, it is becoming difficult to obtain sufficient performance, and it is increasingly necessary to adopt a new audio recording / reproducing system such as the audio FM superimposing system described above. The characteristics of the audio FM superimposing method are: (1) Straw-flutter characteristics are good because they are not easily affected by fluctuations in the time axis due to uneven tape running speed.

(2) The reproduction frequency band does not depend on the high speed of the tape layer, and the band can be widened.

And so on.

Now, let us consider the recording frequency spectrum of a VTR that records and reproduces the above-mentioned audio signal by the audio FM superposition method.

The center frequency of the audio signal carrier should be determined so as to minimize the influence on the luminance signal and the chromaticity signal. Further, in a small VTR, especially in a VTR having a small rotating cylinder diameter, the relative speed between the tape and the head is low, so that the recording frequency band is narrow and the center frequency of the luminance signal carrier cannot be set too high. Therefore, the center frequency of the audio signal carrier must be as low as possible below the FM modulation luminance signal.

FIG. 1 and FIG. 2 show examples of frequency spectrums during recording of video signals and FM audio signals. FIG. 1 shows an example in which the FM modulation audio signal A1 is arranged between the FM modulation luminance signal Y1 and the frequency conversion chromaticity signal C1, and FIG. 2 shows the FM modulation audio signal A2 below the frequency conversion chromaticity signal C1. This is an example of arrangement.

Generally, in VTR, to obtain a margin of tracking,
In order to perform so-called variable speed reproduction in which the tape speed is different from the tape speed at the time of recording, a wide head having a head width wider than the video track width is used. Therefore, in the audio FM superposition method, when the signal of the adjacent video track is also reproduced due to the above-mentioned wide head and tracking deviation, etc., the influence of the FM audio signal of the adjacent video track (hereinafter,
Neighboring disturbance. ), There is a problem in that a very annoying noise is generated in the reproduced audio signal.

In particular, when the recording density is increased, the width of the video track is narrowed, so that adjacent interference due to tracking deviation or the like is a serious problem.

FIG. 3 shows a video track T ₁ formed on the magnetic tape 21,
And T _2, is a plan view showing a schematic view of the position of the video head H.

Here, the noise D (t) caused by the adjacent interference is the first FM audio signal (first noise) obtained from the video track T ₁ to be traced by the video head H when the tracking is deviated as shown in FIG. A signal obtained from the portion of FIG. 3A, hereinafter referred to as a desired FM audio signal) is a, and a second FM audio signal obtained from the adjacent video track T ₂ (a signal obtained from the portion of FIG. 3B) And below, jamming FM
It is called an audio signal. ), And the difference frequency between the desired FM voice signal and the interfering FM voice signal is Δω, Is represented. Here, t represents time. That is, the adjacent jamming noise D (t) is output as a sine wave having a difference frequency Δω (beat frequency) between the desired FM sound signal and the disturbing FM sound signal, and its amplitude is between the disturbing FM sound signal and the desired FM sound signal. It is considered to be proportional to the amplitude ratio b / a and the difference frequency Δω. Therefore, in order to reduce the adjacent interference in the above-mentioned VTR, several methods have been considered. One method is to form a non-recorded portion (guard band) between the video track and its adjacent video track. is there. However, in the method of forming a card band,
The utilization efficiency of magnetic tape is extremely low, and it is impossible to measure high density recording. As another method, a video signal is recorded by a rotating head having a different head gap inclination (azimuth angle) for each scanning of one video track, and azimuth loss is used to eliminate the guard band and adjacent interference noise. (Azimuth recording method) is available. Here, assuming that the azimuth loss La is the video track width W on the tape, the azimuth angle, and the recording wavelength λ, Can be expressed as Here, π represents the pi. Therefore, in this azimuth recording system, the shorter the recording wavelength, the narrower the width of the video head tracing the adjacent tracks, and the larger the azimuth angle, the larger the azimuth loss La and the smaller the adjacent interference. . Here, FIG. 4 shows a characteristic example of the characteristics of azimuth angle and frequency versus azimuth loss, which shows that adjacent interference is reduced by the azimuth recording method. This is the track width TW
Is 58 μm, the relative velocity v is 5.8 m / S, and the recording signal frequency is 629 KHz and 3.4 MHz. By the way, voice FM
Since the center frequency of the audio carrier wave in the superposition method cannot be set to a very high frequency as described above, and the width of the adjacent video track traced by the video head cannot be narrowed so much in order to achieve high recording density. In order to reduce the adjacent interference to a level where there is no practical problem, the azimuth angle must be increased as described above.If the FM voice carrier frequency is 1.3 MHz in the above VTR, the azimuth angle must be 20 degrees or more. Is. However, if the azimuth angle is too large, the relative output between the magnetic tape and the head becomes cos times, and the reproduction capability decreases, the head production problem such as the yield, and the tracking deviation cause the head. A time-axis discontinuity of the reproduced signal at the time of switching, or so-called skew occurs.

Here, if the skew amount t is the tracking shift amount x, the azimuth angle, and the head-tape relative speed Vh, And changes greatly depending on the azimuth angle. Also,
In particular, during so-called search reproduction in which reproduction is performed at a high tape speed, many skews occur on the screen, which causes a serious problem of image quality deterioration. Therefore, the azimuth recording method has a limit to reduce the adjacent interference in the audio FM superposition method, and it cannot be said that the level is practically sufficient.

Further, as another method, there is a method of reproducing with a reproducing head having the same head width as the video track width. The problem with this method is that the tracking accuracy must be greatly increased in order to reduce adjacent interference to a practically sufficient level as the video track width becomes smaller due to high-density recording, and the magnetic tape running during recording. The so-called variable speed reproduction in which reproduction is performed at a traveling speed different from the speed is difficult.

As a means for solving the above two problems, it is possible to introduce an auto-tracking method in which a video head automatically and accurately traces a video track. This auto-tracking method requires a detection head to detect where on the video track is being traced, and an electro-mechanical conversion element, such as a bimorph, for correcting the video head position when a tracking deviation occurs. There is a big problem that not only the machine and the circuit become extremely complicated but also the reliability is lowered.

The three methods described above try to reduce the adjacent interference noise D (t) by reducing the amplitude ratio between the disturbing FM voice signal and the desired FM voice signal, but as another method, the voice signal is FM-modulated. It is possible to increase the reproduced audio signal level by suppressing the adjacent interference noise by increasing the frequency shift amount at the time. In this method, even if the frequency shift amount is increased, the adjacent interference noise is proportional to the difference frequency between the desired wave and the interference wave as shown in the equation (1). Since it is out of the audible frequency band because it exists, the component in the audible band hardly increases. That is, the frequency shift amount of the audio signal is set to 2
If it is doubled, the reproduced voice output signal signal level will be doubled, but since the adjacent interference noise in the audible band is almost constant,
Adjacent jamming is effectively reduced by 6 dB.

However, in order to increase the frequency shift amount of the audio signal as described above, the frequency band necessary for recording the audio signal must be widened by the amount of the frequency shift amount increase.
The occupied band of the FM-modulated luminance signal Y ₁ or the frequency conversion chromaticity signal C ₁ shown in FIG. 2 must be reduced or set to a frequency higher than the center frequency of the luminance signal carrier.

Reducing the occupied band of the FM-modulated luminance signal or frequency-converted chromaticity signal leads to deterioration of image sharpness and transient characteristic deterioration, and deterioration of image quality such as color bleeding.
Further, raising the center frequency of the luminance signal carrier causes a shortening of the recording wavelength, and in order to avoid it, the diameter of the rotating cylinder must be increased, which is a big problem in downsizing. there is a possibility.

Further, when the audio signal occupied band is widened, it is likely to be interfered with from the video signal such as sidebands of the FM-modulated luminance signal and the frequency-converted chromaticity signal, and the so-called buzz sound is likely to occur to cause deterioration in sound quality.

As mentioned above, each method has drawbacks,
It is difficult for a single method to reduce adjacent interference to a practically sufficient level in the above sound quality FM superimposing method, and to achieve high functionality such as high recording density and variable speed reproduction, and mechanical downsizing of the circuit. Is.

Therefore, as a method of compensating for the drawbacks of the above-described various methods, the effect of superimposing the FM-modulated audio signal and the video signal on the azimuth recording and the effect of effectively increasing the frequency deviation of the audio signal, As a means to keep the frequency outside the audible band, a noise removal circuit that suppresses noise by changing the amplitude and amplitude frequency characteristics according to the amplitude of the audio signal during recording and restoring the changed characteristics during playback. Adjacent interference noise is reduced to a practically sufficient level by the synergistic effect with the effect of adding, and at the same time, high density recording and multifunctionalization such as variable speed reproduction and downsizing of mechanical system and circuit system are performed at the same time. Possible methods are possible. This method has the effect of reducing adjacent interference due to azimuth loss by the azimuth recording method, and when the frequency shift amount of the audio signal is increased, one difference frequency is out of the audible band, and the component within the audible band is Adjacent interference noise is reduced by the synergistic effect of suppressing the adjacent interference noise by taking advantage of the property that the adjacent interference noise does not increase and the component of the adjacent interference noise moving to a high frequency range and reducing the discomfort in hearing. In addition, since the azimuth recording method is adopted, high density recording is of course possible.

Furthermore, this method also has the following features.

One is that the video track width can be further narrowed by the amount of adjacent interference reduction, so that high-density recording can be performed, two that noise other than adjacent interference noise can be reduced, and three that the frequency shift amount of the actual audio signal is small. Since the frequency band required for recording may be small, the frequency band used for recording the FM-modulated audio signal may be small in four, so compared with the method of simply increasing the frequency shift amount, Since the recording wavelength of the luminance signal can be lengthened, the diameter of the rotating cylinder can be made smaller and the size can be reduced. Five uses a complicated mechanism / circuit such as auto-tracking using a bimorph element (electromechanical conversion element). There are many advantages such as variable speed reproduction that can be performed without the need. However, the voice
The FM superimposing recording / reproducing system is provided with a pre-emphasis circuit and a de-emphasis circuit in order to convert what is called triangular noise, in which the noise level peculiar to FM modulation is proportional to the noise frequency, to white noise with a constant noise level. Therefore, if the means for effectively increasing the frequency shift amount is simply added to the audio signal input end, the means for effectively increasing the frequency shift amount changes the amplitude or amplitude frequency characteristic of the audio signal. After that, since the high-frequency part is further emphasized by the action of the pre-emphasis circuit, the input to the FM modulator becomes too large and overmodulation is likely to occur, and as a result, sound quality deterioration due to overmodulation occurs. . To prevent this, it is conceivable to reduce the level of the input audio signal, but this will reduce the average amount of frequency deviation, and the effect of reducing the adjacent interference noise will diminish. It's a problem.

It is also necessary to reduce other noise such as noise generated when switching heads.

[Object of the Invention]

An object of the present invention is to provide a magnetic recording / reproducing apparatus capable of reducing noise due to adjacent interference of an audio FM signal and reducing noise generated at the time of switching heads in a system for recording / reproducing an audio signal in a rotating head. It is provided.

[Outline of Invention]

The present invention pre-emphasizes an audio signal during recording, effectively increases the frequency shift amount of the pre-emphasized audio signal, and changes the amplitude and amplitude frequency characteristics of the audio signal according to the amplitude of the audio signal. After that, the data is FM-modulated and recorded, and at the time of reproduction, the characteristics changed after the FM-modulation are returned to the original, and then de-emphasis is performed, so that the sound quality deterioration due to overmodulation is less likely to occur.

As described above, as a method of reducing adjacent interference noise in the audio FM superposition method, the amplitude and amplitude frequency characteristics are changed according to the amplitude of the audio signal during recording to increase the effective frequency deviation amount and perform FM modulation recording. However, at the time of reproduction, the method of suppressing noise by restoring the changed characteristics after FM demodulation and the method of using the azimuth recording method together are very effective,
Overmodulation is likely to occur simply because of the pre-emphasis characteristic added to the input terminal of the audio FM superposition method. Therefore, in the present invention, at the time of recording, the audio signal is first pre-emphasized, and then the amplitude and the amplitude frequency characteristic of the audio signal are changed to effectively increase the frequency shift amount and FM-modulate and then superimpose it on the video signal. Then, azimuth recording is performed, and during reproduction, FM demodulation is performed, the changed characteristics are restored, and then de-emphasis is used to prevent overmodulation.

Example of Invention

 The present invention will be described below with reference to the embodiments shown in the drawings.

FIG. 5 is a circuit diagram showing an embodiment of an audio signal recording circuit of a rotary head type VTR for recording an audio signal by the magnetic recording / reproducing apparatus of the present invention. FIG. 6 is a circuit diagram showing an embodiment of a VTR audio signal reproducing circuit for reproducing a magnetic tape recorded by the recording method of the present invention.
In FIG. 5, the audio signal input from the input terminal 1 passes through the pre-emphasis circuit 2 and then the 1/2 compression circuit 3 follows the compression-expansion characteristic shown in FIG. The level is changed so that the larger amplitude part becomes smaller and the smaller amplitude part becomes larger than the noise level. Here, the 1/2 compression circuit 3 has its gain controlled by the output signal of the detection circuit 4 that receives the pre-emphasized audio signal as an input, and compresses the dynamic range of the pre-emphasized audio signal to 1/2. The output signal of the 1/2 compression circuit is FM-modulated by the FM modulator 5. The output of the FM modulator 5 has an unnecessary band component removed by a low pass filter (LPF) 6 and then added with a video signal input from an input terminal 8 by an adder 7 and a magnetic tape by a magnetic head 9. Azimuth is recorded on 10.

As mentioned above, in this recording system, the dynamic range of the pre-emphasized audio signal is compressed to 1/2,
Since the / 2 compressed signal is input to the FM modulator, overmodulation is less likely to occur compared to the method of simply adding the means for effectively increasing the amount of frequency deviation described above to the input end, and A large amount of average frequency shift can also be recorded.

Next, in the audio signal reproducing circuit of FIG.
The signal reproduced by the magnetic head 9 is input to the band pass filter (BPF) 11. BPF11 is more FM than playback signal
Extract audio signals. Here, the level ratio between the desired FM audio signal and the interfering FM audio signal in the extracted FM audio signal is, for example, azimuth angle ± 17 degrees, audio carrier frequency 1.3 MHz, track width 18.5 μm, video head width 25 μm. Then about 22 dB
Is. The signal reproduced by the magnetic head 9 is also output from the output terminal 19 to a video signal reproducing circuit (not shown). The extracted FM voice signal is demodulated by the FM demodulator 12 into a voice signal. The demodulated voice signal is subjected to removal of FM carrier leaks and the like by the LPF 13, and then the hold circuit 14 processes the noise due to head switching by holding the previous value. Here, the hold circuit 14 performs the previous value holding operation for a certain period of time with the control signal synchronized with the head switching signal input from the input terminal 20.

The output signal of the hold circuit 14 is 1/2 the dynamic range.
Since it is still compressed, the double expansion circuit 15 expands it to the original dynamic range. Here, double engraving circuit 15
Is a detection circuit 16 that receives the output signal of the hold circuit 14 as an input.
Gain control is performed by the output signal of the above, and the dynamic range of the demodulated audio signal is doubled. The decompressed signal is
It is output from the output terminal 18 through the de-emphasis circuit 17. The reproduced audio signal expanded by the double expansion circuit 15 is
Since the noise level also undergoes the same expansion operation and becomes a low noise level, it is output as an audio signal in which adjacent interference noise is suppressed.

That is, for example, FM modulation 5 operates so that a frequency deviation of ± 100 KHz occurs when the audio input signal is 0 dB, and if the pre-emphasized audio input signal is -20 dB, this -20 dB audio input signal Is modulated by the FM modulator 5 without being compressed by the compression circuit 3, A frequency shift of When this FM modulated signal is recorded as the adjacent video tracks T1 and T2 and reproduced simultaneously by the video head H, the difference frequency between the instantaneous frequencies of the two reproduced signals read from the video tracks T1 and T2 is 0.
It is in the range of 20KHz, and all adjacent interference is within the audible frequency band below 20KHz. However, the -20dB voice input signal is compressed to -10dB signal by the 1/2 compression circuit 3 and F
When M-modulated, the frequency deviation becomes ± 31.5KHz, and the frequency of adjacent interference noise (the difference frequency between the instantaneous frequencies of two reproduced signals) is distributed in the range of 0 to 63KHz, and most of them are The adjacent interference noise of can be set to a frequency outside the audible frequency band of 20 KHz or more. In other words, 0
From 20 to 20 KHz, the adjacent noise is spread in frequency from 0 to 63 KHz.
The noise energy in the audible frequency band is reduced so that adjacent jamming noise is barely perceptible. If the difference frequency changes sinusoidally in the case of individual pieces, about 80% of the entire period is above the audible frequency. Generally speaking, the input signal is
For FM modulator 5 with a frequency deviation of ± θKHz at 0 dB, all frequency deviations are within ± 10KHz (difference frequency is 20KHz
Below is the upper limit input level On the other hand, the upper limit input level is reduced by the 1/2 compression circuit 3. When input to the FM modulator 5 after being compressed into Within (ie at difference frequency Below). Therefore, when not compressed, all the difference frequencies are in the audible frequency band. When the input signal level such as is also input to the FM modulator 5 after being compressed, the difference frequency between the instantaneous frequencies of the two signals simultaneously reproduced from the adjacent video tracks T1 and T2 becomes an audible frequency of 20 KHz or more. A frequency shift will occur in the FM modulated signal, reducing adjacent interference.

Here, one characteristic example of the noise frequency spectrum of adjacent interference noise when an FM voice signal is reproduced by the above VTR,
FIG. 8 shows the case of using the noise removing circuit composed of the compression circuit 3 and the double expansion circuit 15 and the case of not using the noise removing circuit. In FIG. 8, I shows the case where there is no noise elimination circuit, and II shows the case where the noise elimination circuit is used. As is clear from FIG. 8, it is understood that the adjacent interference noise can be improved by about 20 dB when the noise removing circuit is used.

The present invention is less likely to cause sound quality deterioration due to overmodulation, and
It can be a low source of adjacent interference to a level that is practically sufficient.
The numerous advantages mentioned above also result. The noise elimination circuit described in the present embodiment does not change the amplitude frequency characteristic but merely compresses and expands the dynamic range, but other methods, for example, the amplitude frequency characteristic is also changed to remove noise. It may be something that operates. Further, a device that performs noise removal operation by changing the amplitude and amplitude frequency characteristics in accordance with the signal level of a specific band of the audio signal during recording can be used in the present invention. Further, when changing both the amplitude and the amplitude frequency characteristic of a voice signal during recording as a noise elimination circuit, it is best to change the amplitude frequency characteristic first and then the amplitude to prevent overmodulation. . At the time of reproduction, the changed characteristics may be restored.

〔The invention's effect〕

As described above, according to the present invention, as shown below, 1. With a simple circuit configuration, sound quality deterioration due to overmodulation is unlikely to occur, and noise due to adjacent interference is reduced to a practically sufficient level. it can.

2. High-density recording is possible because the video track width can be further reduced.

3. Head switching noise other than adjacent interference noise can be effectively reduced.

Since this is a method of increasing the frequency shift amount of the apparent audio signal, the frequency bandwidth required for recording may be small.

4. The rotating cylinder diameter can be reduced because the required frequency bandwidth is small.

5. Variable speed reproduction with good sound quality can be performed without using a complicated mechanism or circuit.

It has many special features, and its effect is great for miniaturizing VTRs.

[Brief description of drawings]

1 and 2 are frequency spectrum diagrams showing an example of a signal frequency spectrum in a voice FM multiplexing system, FIG. 3 is a plan view of a magnetic tape for explaining adjacent interference, and FIG. 4 is an azimuth angle and recording. FIGS. 5 and 6 are circuit configuration diagrams showing an embodiment of an audio signal recording / reproducing circuit using the present invention, and FIG. 7 is a 1/2 compression circuit and 2 FIG. 8 is an input / output characteristic diagram of the double expansion circuit, and FIG. 8 is a frequency characteristic diagram of adjacent interference noise amplitude showing an effect of reducing adjacent interference noise. 1 …… Pre-emphasis circuit, 3 …… 1/2 compression circuit, 4,16 …… Detection circuit, 15 …… Double expansion circuit, 17 …… De-emphasis circuit.

Claims (4)

[Claims] 1. A compression circuit for compressing an audio signal, a frequency modulation circuit for frequency-modulating the compressed audio signal, and a frequency-modulated audio signal output from the frequency modulation circuit on a magnetic tape in the longitudinal direction thereof. A guard bandless recording means as a voice recording track inclined by a predetermined angle, a magnetic head device for reproducing the recorded frequency modulated sound signal, and a demodulation circuit for frequency demodulating the frequency modulated sound signal reproduced by the magnetic head device. , A noise removal circuit for removing noise from the frequency-demodulated audio signal by a signal corresponding to the head switching signal, and an expansion circuit for expanding the output signal of the noise removal circuit. The compression ratio of the compression circuit and the expansion circuit of the expansion circuit A magnetic recording / reproducing apparatus having an expansion rate of 2. 2. A compression circuit for compressing an audio signal, a frequency modulation circuit for frequency-modulating the compressed audio signal, and a frequency modulation audio signal output from the frequency modulation circuit on a magnetic tape in the longitudinal direction thereof. A guard bandless recording means as a voice recording track inclined by a predetermined angle, a magnetic head device for reproducing the recorded frequency modulated sound signal, and a demodulation circuit for frequency demodulating the frequency modulated sound signal reproduced by the magnetic head device. A hold circuit for holding the previous value of the frequency-demodulated audio signal by a signal corresponding to the head switching signal, and an expansion circuit for expanding the output signal of the hold circuit. The compression ratio of the compression circuit and the expansion of the expansion circuit A magnetic recording / reproducing apparatus having a rate of 2. 3. A recording audio signal processing circuit for pre-emphasising and compressing an audio signal, a frequency modulation circuit for frequency modulating an output signal of the recording audio signal processing circuit, and a frequency modulation audio signal output from the frequency modulation circuit. A means for performing guard bandless recording on a magnetic tape as an audio recording locus inclined by a predetermined angle with respect to the longitudinal direction, a magnetic head device for reproducing the recorded frequency-modulated audio signal, and a frequency reproduced by the magnetic head device. Demodulation circuit that frequency demodulates the modulated audio signal, noise removal circuit that removes noise from the frequency demodulated audio signal by a signal that corresponds to the head switching signal, and playback audio signal that expands and de-emphasizes the output signal of the noise removal circuit A processing circuit, and the compression ratio of the compression action by the recording audio signal processing circuit and the reproduction. The expansion rate of the expansion effect by the audio signal processing circuit is 2
A magnetic recording / reproducing apparatus characterized in that 4. A recording audio signal processing circuit for pre-emphasising and compressing an audio signal, a frequency modulation circuit for frequency modulating an output signal of the recording audio signal processing circuit, and a frequency modulation audio signal output from the frequency modulation circuit. A means for performing guard bandless recording on a magnetic tape as an audio recording locus inclined by a predetermined angle with respect to the longitudinal direction, a magnetic head device for reproducing the recorded frequency-modulated audio signal, and a frequency reproduced by the magnetic head device. Demodulation circuit that frequency-modulates the modulated audio signal, hold circuit that holds the frequency-demodulated audio signal in the previous value by a signal according to the head switching signal, and reproduction audio signal processing that expands and de-emphasis the output signal of the hold circuit Circuit, and the compression ratio of the compression action by the recording audio signal processing circuit and the reproduction described above. The expansion rate of the expansion effect by the audio signal processing circuit is 2
A magnetic recording / reproducing apparatus characterized in that