JPH0610843B2 - Frequency multiplexing audio signal recording circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus for frequency-multiplexing an audio signal with a video signal and recording the video signal on a video track, and more particularly to a buzz interference of the video with the audio signal. While keeping below the allowable limit,
The present invention relates to a frequency-multiplexed audio signal recording circuit suitable for recording a video signal as wide as possible.

[Background of the Invention]

A conventional video tape recorder (hereinafter abbreviated as VTR) will be described with reference to FIG.

Taking the NTSC system as an example, at the time of recording, the video signal input from the input terminal 1 is made to have a constant input level by the AGC circuit 2 and is input to a low pass filter (hereinafter abbreviated as LPF) 3. The LPF 3 is, for example, an LPF having a cutoff frequency around 3 MHz, and only the luminance signal component is taken out, and the recording processing is performed by the emphasis circuit 4 for improving the S / N in the high frequency band, the clipping circuit 5 for suppressing the overmodulation, etc. The frequency modulation circuit 6 produces an FM modulated wave. The luminance FM modulation signal is composed of a carrier component having a frequency of about 4 to 6 MHz and sideband components of about 3 MHz before and after the carrier component. Then for example
High-frequency wave filter with cutoff frequency around 1.5MHz (hereinafter referred to as HPF
The component in the frequency band of the chroma signal, which will be described later, is removed in (7) and then added to the recording amplifier 8. On the other hand, the video signal from the input terminal 1 is a bandpass filter (abbreviated as BPF below) 9 chroma signal having a pass band of about 3.58MHz ± 0.5MHz, and the input level is constant at the ACC circuit 10 like the luminance signal. Are converted into a low-frequency conversion carrier color signal having a band of 0.75MHz + 0.5MHz by the frequency conversion circuit 11 and the conversion carrier generation circuit 12, and unnecessary components are removed by the LPF 13 having a cutoff frequency of about 1.4MHz. The signal is added to the brightness FM modulation signal by the recording amplifier 8 and recorded on the magnetic tape 15 via the video head 14.

At the time of reproduction, the reproduction signal of the video head 14 is amplified by the reproduction amplifier 15, and the switch amplifier 17 obtains a continuous reproduction signal.
Only the luminance FM modulation signal is extracted by the HPF 18 having a cutoff frequency of about 1.5 MHz, the AGC circuit 19 adjusts the level to a constant level, and the demodulation circuit 20 demodulates it into a video luminance signal. Thereafter, the de-emphasis circuit 21, the LPF 22, and the dynamic de-emphasis circuit 23, which restore the original emphasis during recording, perform reproduction processing, and the noise cancel circuit 24 suppresses high-frequency noise components, and then the post-addition circuit 25. Added to. On the other hand, low frequency conversion chroma signal is about 1.4M
It is taken out by the LPF 26 having a cutoff frequency in Hz, and the original carrier color signal is restored by the frequency conversion circuit 27 and the conversion carrier generation circuit 28. After that, reproduction processing is performed by the BPF 29 for spurious removal, the ACC circuit 30 for adjusting the level, and the comb filter 31 for removing adjacent crosstalk, and the addition circuit 25 adds the reproduction signal to the luminance signal, and the composite video signal is output from the output terminal 32. Is output.

The recording current spectrum of the video head 14 in FIG.
Shown in the figure. As can be seen from the figure, the luminance signal as the FM modulated wave and the low-pass converted chroma signal are frequency-multiplexed so that their sidebands do not overlap with each other, and the chroma signal is 10 Bias recording is performed at a level of -14 dB lower.

By the way, in a general VTR, the audio signal is recorded by a fixed head on a different track from the video signal on the magnetic tape. However, the following problems occur in increasing the recording time and reducing the size and weight.

1. Deterioration of wow and flutter characteristics due to reduction of flywheel effect in mechanical parts.

2. The recording / playback bandwidth decreases as the tape feed speed decreases.

3. Difficult to secure sufficient audio tracks as tape width decreases.

In consideration of such a point, there is a method in which an audio signal is frequency-modulated, frequency-multiplexed with a video signal, and the same video head records the same track. In this case, as shown in FIG. 3, the audio FM signal is considered to have a luminance FM at a carrier frequency of around 1.5 MHz (between the luminance FM signal and the low frequency conversion color signal), considering the reproduction level and the intermodulation level during recording and reproduction. For the signal
It is suitable to perform bias recording at a level as low as 25 dB.

A problem of frequency-multiplexing an audio signal on a video signal for recording is that mutual interference between the audio signal and the video signal occurs. That is, the band must be limited so that the sidebands of the audio signal and the video signal do not overlap each other. If this is incomplete, for example, if the video signal leaks into the audio signal, buzz occurs and the sound quality deteriorates significantly. On the other hand, if the audio signal leaks into the video signal, beat interference occurs in the reproduced image.

It is not preferable to simply increase the cutoff frequency of the HPF 7 to reduce the buzz sound and remove the frequency component of the luminance FM recording signal that overlaps with the audio FM signal, because the resolution is degraded. Therefore, a sharp trap characteristic is required,
In this case, there is a problem of phase characteristics, which causes a waveform distortion in the reproduced luminance signal, which is a problem.

On the other hand, the frequency characteristic of the current recording current often has a low-frequency emphasis characteristic in which the gain decreases as the frequency increases. The purpose of the low-frequency emphasis is to emphasize and record the lower sideband of the luminance FM signal to gain the S / N at the time of reproduction, and the differential characteristic of the tape head system in the band of the chroma signal (reproduction in proportion to the frequency). It was to compensate in advance). However, low-frequency emphasis recording has the following problems.

1. Since the FM audio signal is recorded with the luminance FM signal as a bias current, if the luminance FM signal has an AM component due to low-frequency emphasis, the audio signal is also affected by the AM component, and in particular, a sudden phase change occurs at the rising and falling portions. It occurs and is accompanied by image buzz.

2. This will cause a reversal phenomenon during playback.

3. In order to improve the S / N of the chroma signal, the so-called chroma emphasis circuit, which applies greater nonlinear response to the sideband of the chroma signal as the level decreases, was introduced. Emphasis needs to be accurately characterized and requires a dedicated chromolyse in front of the recording amplifier.

In order to solve the above problems, it is necessary to make the recording current frequency characteristic of the recording amplifier 59 flat (called constant current recording).
However, in constant current recording, the upper sideband of the luminance FM signal is emphasized and recorded more than in the past. Since the tape head system has a limiter action, a part of the upper sideband wave appears as a lower sideband wave at the time of reproduction, but this amount becomes larger than in the past. Depending on the phase characteristics of the trap of the HPF 7, the rebounding component of the upper sideband and the residual component of the lower sideband are emphasized with each other, and eventually a buzz sound may be generated in the reproduced voice signal. Also, in the worst case, the effect of the trap may even disappear altogether.

The size of the lower sideband as a result depends on the delay time characteristics and the like.

4 and 5 show an HP provided with an audio signal trap.
It is a specific circuit example of F7. In FIG. 4, 41 is an input terminal, 48 is an output terminal, 42, 44, 47 are capacitors, 43, 45,
46 is an inductance, and 49 and 50 are matching resistance.
HPF shown in Fig. 5 the high-frequency and wave with the capacitor _{C 1} and inductance _{L 1,} a first inductance _{L 3} and capacitor _{C 3}
And the inductance L ₂ and the capacitance C ₂ form a second trap. The matching impedance is selected to be 1KΩ. As the value of each element, for example, C ₁ = C ₂ = 120 PF, L ₁ = 56 μH, L ₂ = 390 μ
Select H, L ₃ = 120 μH, C ₃ = 91 PF, etc. FIG. 5 is also a concrete example of an HPF having the same characteristics as in FIG. In FIG. 5, 51 is an input terminal, 59 is an output terminal, 52, 53, 5
6 and 58 are capacitors, 54, 55 and 57 are inductances, and 60 and 61 are matching resistance. The amplitude characteristics of the HPFs of FIGS. 4 and 5 are shown in FIG. 6, and the delay time characteristics are shown in FIG. The characteristics shown in Fig. 6 are the attenuation of 25 dB at cutoff frequencies of 1.8 MHz and 1.5 MHz (voice FM carrier frequency) and 43 dB of 0.75 MHz (chromatic recording signal carrier frequency), and the sideband of the luminance signal. Sufficient attenuation in the audio signal band can be obtained while securing 3MHz.

FIG. 8 shows the spectrum of the reproduction luminance FM signal in the vicinity of the audio FM signal band when recording and reproducing using the above HPF (the luminance FM reproduction carrier level is 0 dB). As is apparent from the figure, the 1.5 MHz trap applied by the HPF during recording shifts to the higher side, and the reproduction level is rather high at 1.5 MHz. The playback level of the audio FM signal is shown by the dotted line in the figure, and the playback luminance FM signal leaks significantly into the audio signal, causing a buzz sound. As described above, even if the amplitude attenuation on the recording side is sufficient,
As shown in the figure, the delay time characteristics (phase characteristics) in the vicinity
This is because, if is large, sidebands appear again during reproduction. The magnetic tape head system has a limiter function,
This is because even if the lower sideband of the luminance FM signal is suppressed on the recording side, as long as there is an upper sideband, this appears again as a lower sideband during reproduction.

Generally, it is desirable that there is no difference in delay time characteristics between the lower sideband and the upper sideband. In order to match the delay time characteristic of the upper sideband with that of the lower sideband, it is conceivable to configure the HPPF as a BPF and increase the delay time of the upper sideband. However, the carrier of the luminance FM signal instantaneously changes within the band of 4.2 MHz to 5.4 MHz, for example, and even if the lower sideband is determined to be 1.5 MHz, the upper sideband has a wide band of 6.9 MHz to 9.3 MHz. Therefore, it is difficult to match the delay times of the lower sideband and the upper sideband with the BPF, and the lowest frequency of the upper sideband is 6.9 MHz, and the upper sideband is restricted from folding back to the lower sideband with the BPF. Even if it is possible, the band of the luminance FM signal is significantly deteriorated, which is a problem.

[Object of the Invention]

An object of the present invention is to provide a frequency-multiplexed audio signal recording circuit that solves the above-described generation of a buzz sound in a VTR of audio-FM multiplex recording and realizes a high-quality image and audio.

[Outline of Invention]

In the present invention, the luminance FM modulation signal is L
Deterioration of the resolution of the luminance signal by limiting the band with the C series trap, and further limiting the folding back from the upper sideband to the lower sideband by damping the high band of the recording amplifier.
This is to reduce voice buzz while keeping the deterioration of waveform distortion within the allowable limit.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. Input terminal
In order to avoid overmodulation, the video signal input from 101 is adjusted to a constant level by the AGC 102, band-limited by the LPF 103 and the luminance LC filter 133, and the high-frequency signal is emphasized by the nonlinear and linear emphasis circuit 104. The frequency is modulated by the frequency modulation circuit 106 via the clipping circuit 105. After that, the HPF 107 removes the audio signal and the chroma signal component, and adds them to the recording amplifier circuit 108 having a constant current characteristic.

On the other hand, the BPF 109 extracts the chroma signal from the video signal from the input terminal 101, the ACC circuit 110 aligns the burst level to a constant level, the chroma emphasis circuit 111 emphasizes the sideband signal, and the frequency conversion circuit 112 performs low frequency conversion. . Further, after the unnecessary component is removed by the LPF 113, the differential characteristic compensation of the tape head system is performed by the chromamy equalizer 114, and it is added to the recording amplification circuit 108. Also, the audio signal input terminal 135
The audio signal input from the AGC 136 has its signal level aligned, is passed through the emphasis circuit 137 to improve the S / N ratio, and is input to the compression circuit 138 that compresses the audio signal according to the amplitude to reduce crosstalk. F in the frequency modulation circuit 139
It becomes an M audio signal, and after the spurious component is removed by the BPF 140, it is added to the recording amplification circuit 108. The three signals added here are passed through the video head 115 to the magnetic tape 1
Constant current is recorded to 34. Of course, in addition to this, a signal for controlling the video head tracking at the time of reproduction may be multi-recorded.

At the time of reproduction, a signal reproduced from the magnetic tape 134 via the video head 115 is amplified by the reproduction amplifier circuit 116, and a continuous reproduction signal is obtained by the switch amplifier 117. The HPM 118 extracts only the luminance FM signal, the AGC 119 adjusts the level to a constant level, and the demodulation circuit 120 demodulates it. afterwards,
The de-emphasis circuit 121, the LPF 122, and the dynamic de-emphasis circuit 123, which restore the original emphasis during recording, perform reproduction processing, and the noise cancel circuit 124 suppresses high-frequency noise components, and then the addition circuit 125. Added to. On the other hand, the low-frequency conversion chroma signal is taken out by the LPF 126, and the frequency carrier conversion circuit 127 restores the original carrier color signal. After that, the BPF 128 for removing spurious, the ACC circuit 129 for adjusting the level, the comb filter 130 for removing adjacent chromatographs, and the chroma de-emphasis circuit 131 having the inverse characteristic of the pre-emphasis circuit 111 perform reproduction processing, and the addition circuit 125. , The luminance signal of the previous time is added, and the composite video signal is output from the output terminal 132.

As for the audio signal, of the reproduced signals output from the reproduction amplifier circuit 116, only the audio FM signal is extracted by the BPF 141.
The demodulation circuit 142 demodulates. Further, the audio signal from which the spurious component has been removed by the LPF 143 is restored to the original compression by the expansion circuit 144 at the time of recording, and the de-emphasis circuit 145 also returns the emphasis performed at the time of recording, and is output from the audio signal output terminal 146. It

The features of FIG. 9 are: In addition to the LPF 103, a luminance comb filter 133 is also provided, and by removing the chroma signal component without damaging the luminance signal component, it is possible to reduce the buzz sound and secure the luminance signal band.

2. The HPF 107 is configured to have a small phase shift while maintaining the attenuation of the voice FM signal trap.

3. In order to improve the chroma S / N, a nonlinear (or linear) emphasis circuit 111, which responds to the sideband of the chroma signal smaller as the level is smaller, is provided on the recording side, and the de-emphasis circuit with the opposite characteristic is provided on the reproducing side. 131 is provided.

4. A tape / head differential compensation circuit (SD mycorise) 114 is provided.

5. The frequency characteristic of the recording / amplifying circuit 108 is not a low-frequency emphasis but a substantially flat characteristic.

6. A voice trap is provided in the LPF 113.

7. The HPF118 has a voice trap.

That is.

Here, the carrier frequency of the luminance FM signal is 4.2 MHz to 5.
4MHz (center about 5MHz), about 3M before and after the sideband
Hz, 1.5MHz ± 0.1MHz as carrier frequency of voice FM signal,
Another general case is shown where the frequency of the chroma signal is about 0.75MHz ± 0.5MHz.

The HPF 107 used in the present invention will be described. Ideally, the amplitude characteristic of the HPF for limiting the band of the luminance FM signal during recording is 1.6 MHz (the upper limit of the audio FM signal band).
Of course, it is desirable to completely cut off the following and completely pass 1.6MHz or more. However, as described above, the wave device used in the present invention can be used for magnetic tapes if the delay time in the vicinity is large even if the amplitude attenuation is sufficient.
Due to the limiter action of the head system, sidebands appear again during reproduction, which is a problem. Therefore, the delay time characteristics of the wave device are flattened in the band so that there is no difference between the upper and lower sidebands.
Furthermore, it has been confirmed by experiments that the performance of a voice signal can be secured if the amplitude attenuation of the voice FM signal band is about 10 dB.

From the above, the tenth characteristic of the wave device of the present invention is
It suffices if the characteristics shown in Fig. 11 and Fig. 11 are satisfied. FIG. 10 shows the amplitude characteristic of the wave device of the present invention, and an attenuation of about 10 dB is obtained at 1.5 MHz. FIG. 11 shows the delay time characteristics of the wave device of the present invention, in which the phase shift is sufficiently suppressed.

An example of the structure of a wave device that can realize the characteristics shown in Figs.
Shown in Figure 12. In FIG. 12, 151 is an input terminal, 161 is an output terminal, and the output terminal is derived from the middle of the variable resistor 159. The variable resistor 159 is also used as a recording current adjusting resistor. Reference numerals 152, 153, 156 and 159 are resistors, 154, 157 and 160 are capacitors, and 155 and 158 are inductances. In FIG. 12, the inductance L ₁₁ and the capacitance C
₁₁ and ₁₁ form a first trap circuit, and the inductance L ₁₂ and the capacitance C ₁₂ form a second trap circuit. Fig. 10 shows the attenuation characteristics and delay time characteristics.
As a value for making it as shown in FIG. ₁₁ , R ₁₁ = 820Ω,
R ₁₂ = 390Ω, R ₁₃ = 560Ω, R ₁₄ = 4.7KΩ, L ₁₁ = 220
μH, L ₁₂ = 180 μH, C ₁₁ = 51 PF, C ₁₂ = 150 PF,
C ₁₃ = 0.022 μF, or R ₁ = 390Ω, R ₁₂ = 180
Ω, R ₁₃ = 270Ω, R ₁₄ = 2.2KΩ, L ₁₁ = 120μH, L
₁₂ = 180 μH, C ₁₁ = 94 PF, C ₁₂ = 150 PF, C ₁₃ = 0.
Choose 022μF. Especially inductance L ₁₁ and capacitance C
_It is desirable to finely adjust the value of the first trap frequency according to ₁₁ to 1.5 MHz. Also, the value of R ₁₂ connected in series with the first trap circuit is important. That is, 1.5M
Although there are many combinations of R ₁₂ , L ₁₁ , and C ₁₁ for trapping Hz, for example, L ₁₁ and C ₁₁ are R as they are.
_When the combination of ₁₂ is reduced, the attenuation of the trap is increased, but the delay time is also increased and the sideband of the luminance signal during reproduction is rather increased. Further, when the combination of R ₁₂ is increased, the degree of trap attenuation is lowered. For this reason, the lower sideband suppression of the luminance signal on the recording side becomes insufficient, and the buzz sound increases.

By the way, as described above, the magnetic tape head system has a limiter action, and even if the lower sideband of the luminance FM signal is suppressed on the recording side, as long as the upper sideband is present, this appears as a lower sideband during reproduction. It may hinder the buzz. As a result, the size of the lower sideband is greatly influenced by the delay time characteristics of the upper sideband. Generally, it is desirable that there is no difference in delay time characteristics between the lower sideband and the upper sideband. First
This will be described with reference to FIGS. 13 and 14.

FIG. 13 shows a specific example of the recording amplifier circuit of the present invention. In FIG. 13, 181 is an input terminal, 182 is a recording current supply transistor, 183 is an inductance, 184 and 185 are resistors, 186 is a capacitance, 187 is a rotary transformer, and 188 is a magnetic head. A signal voltage of 3-4V _PP is required for the collector of Q ₁ (from the recording amplifier to the rotary transformer 20).
(When the inductance seen at 7 is about 9 μH), it is desirable to maximize the dynamic range by selecting V _CC low and setting the load to the inductance 183 in order to minimize power consumption in forming the class A amplifier. The resistor 184 is used as a damping resistor. FIG. 14 shows the recording current frequency characteristics of FIG. As shown in the figure, the frequency characteristics are almost flat. As described above, how to select the high frequency characteristic of the recording amplifier is important from the viewpoint of suppressing buzz interference.
As shown by the solid line in Fig. 14, if the high-frequency characteristics are not completely flat and are dropped from 7 to 8MHz gently, the folding of the upper sideband to the lower sideband will be suppressed and buzz interference will occur. It is possible to reproduce high quality sound without sound. The values for making the recording current frequency characteristics as shown by the solid line in FIG. 14 may be selected as L ₂₁ = 56 μH and R ₂₁ = 390 Ω in the circuit of FIG. When R ₂₁ is increased to have the characteristic shown by the dotted line in FIG. 14, the delay time characteristic difference with the lower sideband also increases, and the lower sideband of the luminance signal during reproduction becomes large, resulting in buzz interference.
On the other hand, when R ₂₁ is made small to have the characteristic as shown by the alternate long and short dash line in FIG. 14, the suppression of the upper sideband becomes large, causing special deterioration and inversion phenomenon.

Next, in order to remove the sideband component of the luminance signal which interferes with the sound at the time of recording, not only the above HPF 107 but also the LPF 103 shown in FIG. 4 is required. Originally, if the high frequency component of the image brightness is attenuated here, the upper and lower sideband components that interfere with the audio signal do not occur. However, if the high frequency components are simply attenuated, the image quality deteriorates. In addition, the chroma component that has not been completely removed remains in the high-frequency component of the luminance signal of the video signal that is extracted by the LPF, and is emphasized by the emphasis circuit or the like, so that the lower sideband of the luminance FM signal is eventually detected. It contains a chroma component, which is one of the causes of buzz. Therefore, the optimum design of the LPF 103 is important.

FIG. 15 shows a specific characteristic example of the LPF 103. Since the cutoff frequency of this filter is 3 MHz, the resolution of the reproduced image can be secured at about 240 lines, and the attenuation of frequencies higher than this is sufficient. However, in case of NTSC system, the chroma signal is 3.58MH
It is frequency-multiplexed with the luminance signal in the z ± 0.5MHz band.
Therefore, with the band limitation shown in FIG. 15, buzz interference becomes a problem as described above.

Therefore, a recording luminance comb filter 133 using a 1H delay line is added before or after the LPF to remove the chroma signal component without damaging the luminance signal component. This comb filter is well known and will not be described. FIG. 16 shows the frequency characteristic when the comb filter 133 is added to the LPF 103. As shown in the figure, in the band in which the chroma signal component is present, a comb-shaped characteristic is obtained to remove this.
As a result, the component originally unnecessary for the luminance recording system is F
It becomes an M-modulated signal and does not give buzz interference to the voice.

The interference from the luminance signal to the audio signal has been described above, but it is of course necessary to consider the interference from the chroma signal to the audio signal. Specifically, the audio signal band is attenuated by the chroma signal recording LPF 113. However, the buzz interference from the chroma signal cannot be suppressed only by securing the same 1.5 MHz attenuation as the luminance signal recording HPF107 described above, and only the voice band from the voice carrier is taken into consideration at 1.5 MHz-0.
It is necessary to insert a trap of 1MHz = 1.4MHz. FIG. 17 shows a concrete example, and FIG. 18 shows a characteristic example. In FIG. 17, 201 is an input terminal, 209 is an output terminal, 202, 204, 206 and 208 are capacitors, 203, 205 and 207 are inductances, and 220 and 221 are matching resistors. Inductance L ₂₁ and capacitance C ₂₁
It constitutes a trap of 1.4MHz, for example L ₂₁ = 470μ
H, C ₂₁ = 27PF, etc. are selected.

Furthermore, in order to suppress the interference of the reproduced audio FM signal with the video signal, a 1.5 MHz trap may be provided in the reproduced luminance HPF 118. FIG. 19 shows a specific example. In FIG. 19, 211 is an input terminal, 212 and 215 are resistors, 213 and 216 are inductances, 214 and 217 are capacitors, and 218 is an output terminal. The resistor 212, the inductance 213, the capacitance 214, and the resistor 215 are reproduction F
The M peaking circuit is configured to improve that the output of the reproducing head decreases as the frequency becomes higher, by raising the vicinity of the FM white carrier. Then the inductance L
Re-voiced FM with 1.5MHz trap composed of ₂₂ and capacity C ₂₂
Suppressing the signal. As a numerical value, for example, L ₂₂ = 180
μH, C ₂₂ = 56PF, etc. are selected.

As described above, in the audio signal frequency multiplexing magnetic recording / reproducing apparatus, the luminance signal recording HPF has the configuration of FIG. 12 of the present invention, and the recording / amplifying circuit has the configuration of FIG. 13, the reproduction luminance FM near the audio FM signal band. The signal spectrum is shown in Fig. 20. Compared to the conventional spectrum shown in FIG. 8, a 1.5 MHz trap characteristic can be realized during reproduction, and sufficient C / N can be secured for the reproduction level of the audio FM signal shown by the dotted line.

That is, the characteristics of the HPF 107 and the recording / amplifying circuit 108, which greatly influence the buzz interference, may be set so that the trap characteristic of 1.5 MHz can be realized in the spectrum of the reproduction luminance FM signal as shown in FIG. For example, the HPF107 has the first characteristic.
As shown in Fig. 0 and Fig. 11, when the characteristic has a trap near 1.5MHz (audio FM signal band) and the delay time characteristic is flat, the characteristic of the recording amplifier circuit 108 is set as shown by the solid line in Fig. 14. do it. Moreover, the trap characteristics of HPF are steep,
If the delay time is also large, the HPF trap is set to the voice FM.
By setting the frequency lower than the signal band, the trap at the time of reproduction can be realized in the audio signal band.

Next, FIG. 21 shows the configuration of the HPF when the audio signal carrier is provided not only at 1.5 MHz but also at 1.7 MHz to perform stereo conversion. In FIG. 21, 162 is a resistance, 163 is a capacitance, 164 is an inductance, 165 is a transistor, and 166 is a stereo control signal input terminal, which are the same as those in other FIG. First
In FIG. 21, L ₁₃ and C ₁₄ form a third trap. The transistor 165 is turned on by a signal from the control signal input terminal during stereo, and turned off the third trap except during stereo. R ₁₅ = 390 Ω, C ₁₄ = 47 PF, L ₁₃ = 220 μH, etc. are selected as values for suppressing leakage of the audio signal of the reproduction luminance FM signal and eliminating buzz interference. The characteristics at this time are shown by the solid lines in Figs. 24th
The solid line in the figure shows the spectrum of the reproduced luminance FM signal when the above circuit is used. By the way, when the above values are combined with the values that satisfy the voice carrier frequency of 1.7 MHz provided along with the stereoization, C ₁₄ = 39 PF and L ₁₃ = 220 μH, and the characteristics at this time are the dotted lines in FIGS. 22 and 23. become that way. As can be seen from the figure, the delay time characteristics change when a trap is installed at 1.7MHz, and as a result, as shown by the dotted line in Fig. 17, 1.5M
The reproduction luminance signal sideband near Hz has increased to 1.7 MHz.
The trap also shifts to the higher side. Therefore, the HPF 107 is set so that the characteristics shown by the above solid line can be obtained even in stereo processing.

Also, in stereo processing, it is necessary to consider the interference from the chroma signal to the audio signal.

Specifically, a trap is added to the sub audio carrier frequency of 1.7 MHz by the chroma signal LPF113. FIG. 25 shows a specific circuit example. In FIG. 25, 222 is an inductance, 223
Is a capacitor, 224 is a transistor, and 225 is a control signal input terminal in stereo. Inductance L _{22 and} capacitance C ₂₂
A 1.7 MHz trap is configured, and for example, L ₂₂ = 330 μ
H, C ₂₂ = 27 PF, etc. are selected. The characteristics of the circuit of FIG. 25 are shown in FIG. Control signal input terminal 225 when stereo
The transistor 224 is turned on by the control signal from, and a trap of 1.7 MHz is added by L ₂₂ and C ₂₂ as shown in FIG.

Here, the reason why the trap frequency is not set to a frequency lower than the voice carrier by the voice band as in FIGS. 17 and 18 is that the chroma signal component is considerably low near 1.7 MHz, and When 1.7MHz is used as the sub-voice, the band is required to be ± 0.05MHz. Therefore, by installing a wide band trap at 1.7MHz, the buzz in stereo can be suppressed. Of course, the performance can be ensured by providing a trap at 1.6MHz.

By the way, the second trap composed of L ₁₂ and C ₁₂ for trapping the chroma band in the HPF structure of the present invention shown in FIGS. 12 and 21 is not necessarily restricted to the above-mentioned structure and numerical values, and should be removed. Is also possible.

The points for carrying out the present invention are summarized below.

1. When multiple recording of audio FM signal of 1.5MHz ± 0.1MHz.

(i) ₀ (trap frequency) for luminance FM signal
A trap with a resonance Q of 3 to 4 is provided at 1.5 MHz or less.

(ii) The characteristics of the upper sideband of the luminance FM signal are set by the recording / amplifying circuit shown in FIG. 13, and L ₂₁ and R ₂₁ are selected so that 1.5 MHz of the reproduced luminance FM signal is minimized.

(iii) ₀ = 1.5MHz, Q for low frequency conversion chroma signal
= 40-60, and ₀ = 1.4MHz, Q = 40
Provide a trap for ~ 60.

2. Two audio FM of 1.5MHz ± 0.1MHz and 1.7MHz ± 0.1MHz
When recording multiple signals.

(i) To a luminance FM _{signal, 0} = 1.5 MHz or less, trap and ₀ = 1.5 as a Q = 3 to 4
Provide a trap with 1.6MHz and Q = 3-4.

(ii) ₀ = 1.4MHz, Q =
40-60 to become _{trapped, 0} = 1.5 MHz, Q = 40-60 to become trapped, and ₀ = 1.7 MHz, providing a trap comprising a Q = 30 to 50.

Of course, the upper sideband of the luminance FM signal is the same as in the above 1.

3. When switching the multiplexed audio FM signal between one and two.

(i) With respect to the luminance FM signal, the above configuration 2 is adopted and ₀ = 1.5
ON at ~ 1.6MHz, Q = 3 ~ 4 trap for 2 carriers
Then, it turns off at the time of one carrier.

(ii) For the low-frequency conversion chroma signal, the above-mentioned configuration 2 is adopted.
₀ = 1.7MHz, Q = 30 to 50 traps turned on during 2 carriers
Then, it turns off at the time of one carrier.

Of course, the upper sideband of the luminance FM signal is the same as in the above 1.

〔The invention's effect〕

According to the present invention, in a magnetic recording / reproducing apparatus which frequency-modulates an audio signal and frequency-multiplexes it with a video signal for recording, while keeping the band of the luminance signal practically no problem or bell,
It is possible to suppress the buzz interference to the voice.

[Brief description of drawings]

FIG. 1 is a block diagram of a video signal circuit of a conventional magnetic recording / reproducing apparatus, and FIGS. 2 and 3 are spectrum diagrams of recording signals.
4 and 5 are circuit diagrams of conventional HPF circuits, FIG. 6 and FIG.
FIG. 7 is a characteristic diagram of the HPF of FIG. 4, and FIG. 8 is H of FIG.
FIG. 9 is a block diagram of the recording / reproducing circuit of the present invention, FIG. 10 and FIG. 11 are characteristic diagrams of the HPF of the present invention, and FIG. 12 is the HPF of the present invention. FIG. 13, FIG. 13 is a circuit diagram of the recording amplifier circuit of the present invention, FIG. 14 is a characteristic diagram of FIG. 13, and FIG. 15 is a characteristic diagram of the LPF of the present invention.
FIG. 16 is a characteristic diagram of the comb filter of the present invention, FIG. 17 is a circuit diagram of the chroma signal recording LPF of the present invention, FIG. 18 is a characteristic diagram of the LPF of FIG. 17, and FIG. 19 is a luminance signal reproducing HPF. FIG. 20 is a spectrum diagram of a reproduced signal of the present invention, FIG.
FIG. 22 is a circuit diagram of another HPF of the present invention, FIGS. 22 and 23 are characteristic diagrams of the HPF of the present invention, and FIG. 24 is a spectrum diagram of a reproduced signal when another HPF of the present invention is used. FIG. 25 is another circuit diagram of the chroma signal recording LPF of the present invention, and FIG. 26 is a characteristic diagram of FIG. Reference numeral 107 …… Luminance signal recording HPF, 113 …… Chroma signal recording LPF, 108 …… Recording amplification circuit, 118 …… Luminance signal reproducing HPF, 133 …… Recording luminance comb filter, 154 …… Capacity, 155… … Inductance, 183 …… Inductance, 184 …… Damping resistance.

Claims (1)

[Claims] 1. A signal obtained by converting an image luminance signal into an FM-modulated wave having a carrier frequency near 5 MHz and a signal obtained by subjecting an image chromaticity signal to low-frequency conversion so that a carrier has a frequency lower than the FM modulation band. In a magnetic recording / reproducing apparatus for frequency-multiplex-recording an audio signal, which is arranged in a frequency band between the two and becomes an FM modulated wave, on a video track of a recording medium through a constant current recording amplifier having a substantially flat frequency characteristic, recording brightness A frequency characterized in that a high-pass filter for band-limiting the FM signal is composed of an LC series trap, and the high-pass characteristic of the recording amplifier is suppressed to compensate the phases of the upper and lower sidebands of the recorded luminance FM signal. Multiplex audio signal recording circuit.