JPS6117591Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In a conventional magnetic recording and reproducing device (VTR), an audio signal is recorded or reproduced by a fixed head on a magnetic track separate from a video signal.

By the way, in general household VCRs, the magnetic tape speed has recently become slower and slower in order to enable long-term recording, and the current tape speed is 2cm/
Some tape speeds are sec. However, if the tape speed becomes even slower than this,
Bias recording and playback of audio signals using conventional fixed heads becomes nearly impossible.

Therefore, a device has been proposed that uses a rotating magnetic head (hereinafter referred to as a rotary head) to record a video signal to record an audio signal in a superimposed manner on a recording track of a video signal, or to reproduce it from this. Due to the high relative speed of the head for recording audio signals with respect to the magnetic tape, the above-mentioned disadvantages are avoided. An example of this will be explained with reference to FIG. 1. A video signal supplied to a terminal 1 is supplied to a reduced-pass filter 2, where a luminance signal component is extracted, and this is supplied to a frequency modulator 3.
The signal is frequency modulated into a 3.5 MHz to 4.7 MHz signal corresponding to the brightness, and sent through mixers 4 and 5 to a rotary head 6 (actually, a pair of heads record and reproduce, but in this example, one head is shown). The information is supplied and recorded on the magnetic tape 7.

On the other hand, the video signal supplied to the terminal 1 is supplied to a band pass waver 8, where a color signal component is extracted, and this is supplied to a frequency converter 9, for example.
The frequency of the signal centered around 688 KHz is converted to a so-called low frequency range, and is supplied to the rotary head 6 through the mixers 4 and 5 mentioned above.

Furthermore, the audio signal supplied to the terminal 10 is supplied to the frequency modulator 12 through the low-pass wave generator 11, where it is frequency-modulated into a signal centered at, for example, 1.5 MHz, and this is transmitted through the mixer 5 to the rotary head 6. is supplied to

Luminance signal Y and color signal C in such a device
and the spectrum of audio signal A are shown in FIG.
As is clear from this, in this device,
If the frequency of the carrier signal for FMing the audio signal A is selected low, crosstalk will occur with the chrominance signal C, and if the frequency of the carrier signal is selected high, crosstalk with the luminance signal Y will occur. It's difficult.

This invention avoids the above-mentioned drawbacks, and an example of a device according to this invention is shown in FIG. 3 and subsequent figures. In this example, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and their explanation will be omitted.

In this invention, the audio signal is sampled by a horizontal synchronization signal or a signal related to this,
Frequency modulation of the thus sampled signal
FM, and this signal is recorded on the magnetic tape 7 by the rotating head 6. In this case, during the unblanking period of the video signal, the audio signal current or carrier wave signal current is lower than the normal proper recording state. It is designed to drastically lower the power level (including blocking it).

That is, FIG. 4A obtained from the low-pass wave generator 11
_The signal S ₁ shown in FIG. , the audio signal _S1 is sampled and held using this signal _S2 . The signal _S3 shown in FIG. 4C shows the output from this sampling and holding circuit 13.

The signal S ₃ sampled and held in this way is supplied to the pulse amplitude modulator 15 that modulates the amplitude of the pulse, while the horizontal synchronization signal S ₂ is supplied to the delay circuit 1
6 to obtain a signal _S4 (see FIG. 4D) which is delayed by a predetermined time γ from the horizontal synchronizing signal _S2 and has a constant time width W, and sampling is performed within this time width W. The signal _S3 sampled by the hold circuit 13 is modulated by the pulse amplitude modulator 15 mentioned above. The signal _S5 shown in FIG. 4E is the output from the pulse amplitude modulator 15 obtained in this manner. Such signal S ₅ is transmitted to frequency modulator 12
to obtain a frequency signal corresponding to the amplitude of the signal _S5 . In this case, the frequency of the carrier signal can be selected to be about 1.5MHz.

Further, in this invention, the output from the frequency modulator 12 is supplied to the mixer 5 through a variable attenuator 17, and this variable attenuator 17 is connected to the output signal S ₄ as described above, for example.
At least during the unblanking period of the horizontal image signal, the signal from the frequency modulator 12 is attenuated by -20 dB to -30 dB compared to the normal appropriate recording current, and then sent to the rotating head 6. supply. FIG. 5 shows the state of the output signal _S6 from the variable attenuator 17, where H indicates one horizontal period. Note that the time width W in this figure is the same time width as that shown in FIG.
Within this time width W, the signal S ₅ shown in FIG.
It has been shown that a signal with a frequency corresponding to the amplitude of is obtained at a level that allows normal recording, and is significantly attenuated in other periods. Note that this period W may be within the horizontal planking period, but if necessary, it may be selected to be located at the front porch or back porch portion, and the period W may be selected to be, for example, about 2 microseconds. Therefore, this audio signal is recorded as a burst signal with respect to the video signal. Further, in this example, the recording signal is attenuated by the variable attenuator 17 during periods other than the period W.

According to such a configuration, in the video signal supplied to the terminal 1, the luminance signal component Y separated by the low-pass wave generator 2 is FM-modulated by the frequency modulator 3, while the luminance signal component Y is FM-modulated by the frequency modulator 3. The separated color signals are low frequency converted by a frequency converter 9 and supplied to a rotary head 6 through mixers 4 and 5, respectively, so that the video signal is recorded on a magnetic tape 7 as usual.

On the other hand, the audio signal supplied to the terminal 10 is sampled and held in the sampling hold circuit 13 using the horizontal synchronizing signal, and is amplitude-modulated in the pulse amplitude modulator 15 by the delay signal from the delay circuit 16, which is then applied to the frequency modulator 12. The signal is frequency modulated and supplied to the rotary head 6 through the variable attenuator 17 and the mixer 5, where it is recorded on the magnetic tape 7.

In this case, according to this invention, the audio signal is significantly attenuated by the variable attenuator 17 during the unblanking period of the video signal, as shown in FIG. 5, so crosstalk to the luminance signal is reduced compared to the conventional one. It has the characteristic that it can be almost completely avoided.

In the example shown in FIG. 3, the pulse amplitude modulator 15 is provided, but this is omitted and the output from the sample and hold circuit 13 is directly transmitted to the frequency modulator 1.
2 may be supplied.

FIG. 6 shows a circuit for reproducing audio signals from the magnetic tape 7 recorded as described above.
That is, as is generally known, the signals reproduced from the rotary head 6 are supplied to a well-known video signal reproducing circuit, ie, a monitor 18, and monitored by a picture tube 19. Reference numeral 20 indicates an internal horizontal synchronizing signal separation circuit. The horizontal synchronizing signal (corresponding to signal _S2 shown in FIG. 4B) separated by this separation circuit 20 is supplied to a signal delay circuit 21, thereby obtaining a delayed signal. The delay time in this case is selected to be the same or almost the same as the time γ shown in FIG. 4 mentioned above.

On the other hand, the signal reproduced by the rotary head 6 is supplied to the band pass waver 22, where the audio signal A shown in FIG.
3 to the demodulator 24 for demodulation.
The signal demodulated in this way is supplied to a sample and hold circuit 25, where it is sampled and held using the delayed signal from the delay circuit 21 described above. This sampling point is the point in time when the audio signal has just been recorded in relation to the horizontal synchronization signal _S2 , so it is clear that the sampled and held audio signal is extracted from the output side. be. This signal is passed through the low-pass wave generator 26 to the output terminal 2.
7, an audio signal is obtained.

In the embodiment shown in FIG. 3, the audio signal is sampled once per horizontal period H. As will be explained with reference to the drawings, in this example as well, parts corresponding to those in FIG. 3 are designated by the same reference numerals. However, since the sample and hold circuits 13 and the pulse amplitude modulators 15 are provided in pairs (first and second), suffixes a and b are attached to each pair, and two delay circuits 16 are provided to connect them to each other. Since they are connected in series, they are also shown with suffixes a and b.

In this example, the horizontal synchronizing signal Sb (see FIG. 8B) separated by the horizontal synchronizing signal separation circuit 14 is supplied to the delay circuit 28 which delays it by 1/2H, and from this, the signal Sc shown in FIG. 8C is supplied. The horizontal synchronizing signal Sb causes the first sampling and holding circuit 13a, and the signal Sc causes the second sampling and holding circuit 13.
b so as to drive the first delay circuit 1.
The second pulse amplitude modulator 15b is controlled by the delayed signal Sf (same F) from the second delay circuit 16a, and the first pulse amplitude modulator 15a is controlled by the delayed signal Sg (same G) from the second delay circuit 16b. It's like driving.
The delayed signals Sf and Sg have respective times γ _a and γ _b with respect to the horizontal synchronizing signal Sb, and are selected so as to be temporally located within the blanking period of the video signal.

These first and second pulse amplitude modulators 15a
The outputs of 15b and 15b are respectively supplied to the same frequency modulator 12 as described above through a mixer 29.

According to this configuration, the eighth
The audio signal Sa shown in FIG.
Sb and Sc are sampled and held, so that the signals Sd and Se shown in FIG. 8D and E, respectively, can be obtained at the output sides of the respective circuits 13a and 13b. These signals Sd and Se are further amplitude-modulated by signals Sf and Sg in first and second pulse amplitude modulators 15a and 15b, respectively, and then supplied to a mixer 29. Therefore, the signal Sh shown in FIG. This recording period is within the blanking period of the video signal. Therefore, in this example, two types of signals are recorded.

FIG. 9 shows an apparatus for reproducing signals from the magnetic tape 7 on which such signals are recorded, and parts corresponding to those in FIG. 6 are given the same reference numerals and their explanation will be omitted. In this example, the signal from the demodulator 24 is transferred to first and second sample and hold circuits 25a and 25b.
Also, the horizontal synchronizing signal S ₁₁ (see FIG. 10A) from the horizontal synchronizing signal separation circuit 20 is supplied to the second delay circuit 21b through the first delay circuit 21a. 1st from 21b
_The delay signals S _{12 and} S ₁₃ shown in FIGS. They are designed to drive each. Furthermore, each of these delayed signals
The delay times of S ₁₂ and S ₁₃ are chosen to be the same as the delay times γ _a and γ _b shown in FIGS. 8F and 8G.

Since the demodulator 24 obtains a signal (temporarily assumed to be Si) similar to the signal Sh explained in FIG. The signals S ₁₄ and S ₁₅ shown in FIGS. 10D and E are obtained. These signals S ₁₄ and S ₁₅ have the same waveform as the signals Sd and Se shown in FIGS. 8D and E, which were explained at the time of recording. However, the times at the time of recording and the time of playback do not match in terms of time. In order to facilitate understanding, V ₁ and V ₂ are attached to the corresponding positions of corresponding signals in FIGS. 8 and 10, respectively.

Furthermore, the output from the first delay circuit 21a is supplied to a switching circuit 28, and the outputs from the sampling and hold circuits 25a and 25b are switched and supplied to a low-pass wave generator 26. In this case, a monostable circuit, for example, may be used as the switching circuit, and it may be triggered by the output from the first delay circuit 21a, and the duty at this time may be selected to be approximately 50%. The signal _S16 shown in FIG. 10F shows the switching waveform at this time.

Since the signals _S14 and _S15 from the first and second sample and hold circuits 25a and 25b are switched by the switching circuit 28 described above, the output signal _S17 has a waveform as shown in FIG. 10G. That is, in this embodiment, since the audio signal is sampled twice in the 1H period, the high frequency band can be extended compared to the previous example. Although the above description has been made of the case where the audio signal is sampled twice in the 1H period, it is of course possible to sample, record, and reproduce the audio signal three or more times. Furthermore, in each of the embodiments described above, the audio signal is sampled using the horizontal synchronization signal during recording, but if necessary, a signal related to the horizontal synchronization signal, for example, a signal delayed by a certain period of time, may be sampled. It will be obvious that sampling may also be carried out. Furthermore, when recording an audio signal, the variable attenuation circuit 17 attenuates the signal from the modulator 12 during the unblanking period of the video signal, but it may also be completely cut off. In addition to controlling the signal, only the carrier wave current may be controlled as described above.

Furthermore, in order to prevent mutual interference with the video signal, the frequency of the carrier wave signal is selected to be (n+1/2) _H during recording. Note that n is an integer and _H is the repetition frequency of the horizontal synchronization signal. FIG. 11 is a block diagram showing an example thereof. A pulse amplitude modulator 15 is connected to the terminal 29.
, which is supplied to the frequency modulator 12.
The signal is frequency modulated at the output terminal 30, that is, the variable attenuator 17 in the above example, and is also supplied to the phase comparator 32 through the gate circuit 31, where the phase is compared with the oscillation signal from the oscillator 33. ing. The frequency of this oscillator 33 is selected as (n+1/2) _H mentioned above.

On the other hand, a signal S ₂₂ (FIG. 12B) in an unblanking period (as is clear from the above, the frequency is not modulated by the audio signal) is extracted from the video signal S ₂₁ (see FIG. 12A). (This extraction circuit is not shown), connect this to the terminal 34
It is supplied to the gate circuit 31, the sampling hold circuit 35, and the phase comparator 32.
The output from this sampling hold circuit 35
The signal is supplied to the frequency modulator 12 through the signal. The sampling and holding circuit 35 samples the comparison output (an error output, for example, a DC voltage) from the phase comparator 32 at the end of unblanking, that is, at the rising edge of the signal _S22 .
And it shall be held at that value. Therefore, the comparison output _S23 shown in FIG. 12C is obtained from the sampling and hold circuit 35.

In this way, the frequency modulator 12 is sampled every 1H and is locked by the output whose phase is compared with the signal from the oscillator 33 during the unblanking period in which no frequency modulation is performed. Therefore, the carrier frequency is The carrier signal is locked to (n+1/2) _H as described above, and therefore, during playback, this carrier signal is interleaved with the playback video signal, and is thus visually reduced.

According to this invention explained above, the rotary head 6
Of course, it is possible to record an audio signal on the recording track of a video signal, but in this case,
It has the characteristic that it can almost completely avoid the drawbacks that occur when recording using the conventionally considered apparatus shown in Fig. 1, that is, the crosstalk between audio and video signals, and it can also be frequency-modulated and recorded on magnetic tape. Even during the unblanking period of the video signal, the audio signal is recorded continuously, although the level is low, as shown in Figure 5. Therefore, when playing back this and performing so-called FM demodulation, this demodulation is It is easy to carry out and has the characteristics of being able to perform reproduction with reduced noise.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional audio signal recording device using a rotating magnetic head, FIG. 2 is a spectrum diagram thereof, FIG. 3 is a block diagram showing an example of a recording device according to this invention, and FIGS. 6 is a block diagram showing an example of a playback device, FIG. 7 is a block diagram showing another embodiment of this invention, and FIG. 8 is a waveform diagram for explaining the same. Fig. 9 is a block diagram showing another example of the reproducing device, Fig. 10 is a waveform diagram for explaining the same, Fig. 11 is a block diagram for frequency control of a frequency modulator that can be used in this invention, and Fig. 12 is a block diagram showing another example of the reproducing device. The figure is an explanatory diagram of the operation. 1 is a video signal input terminal, 6 is a rotating magnetic head, 10 is a low frequency signal input terminal, 13 is a sampling hold circuit, 14 is a horizontal synchronization signal separation circuit, 15 is a pulse amplitude modulator, 16 is a delay circuit, 12 is a frequency modulator, and 17 is a variable attenuator.

Claims (1)

[Claims for Utility Model Registration] The luminance signal in the video signal is FM-modulated as an FM modulated wave, and the color signal is converted to a frequency lower than the band of the FM modulated wave as a low-frequency converted color signal, which is transmitted to a magnetic medium by a rotating magnetic head. In the method of recording
a sampling and holding circuit that samples an audio signal using a horizontal synchronizing signal in the video signal or a signal related thereto; a frequency modulator that frequency modulates a carrier signal using the audio signal sampled by the sampling and holding circuit; a variable attenuator that attenuates and supplies a signal frequency-modulated by the carrier signal to the rotating magnetic head during the unblanking period of the video signal _; (where n is an integer and _H is the repetition frequency of the horizontal synchronizing signal) and is selected between the band of the FM modulation wave and the band of the low-frequency conversion color signal.