JPS60260279A - Sound fm signal recording device - Google Patents

Abstract

PURPOSE:To suppress the deterioration in resolution of a reproduced picture image to a minimum value by suppressing the execution of a trap processing attenuating the signal component of the frequency band of the sound FM signal from the luminance FM signal in a VTR to a minimum value. CONSTITUTION:When the detection level of a frequency band signal component SN of the sound FM signal from the luminance FM signal exceeds the Schmitt level, a Schmitt trigger circuit 411 outputs a high level signal and gives it to a base of a transistor (TR)Q11. Thus, the TRQ11 is turned on, a TRQ12 constitutes an AND circuit with the TRQ11, and since an output signal of an AFM carrier signal detecting circuit 42 is given to the base of the TRQ12, the TRs Q11, Q12 are turned on only when the mode is the sound FM signal recording mode and the signal component Sn exceeds the Schmitt level or over. As a result, the deterioration in reproduced sound by buzz noise is avoided.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is applicable to, for example, a video recorder (hereinafter referred to as VT).
The present invention relates to a device for frequency-multiplexing and recording a frequency-modulated (hereinafter referred to as FM) audio signal with a video signal on a video signal track, as seen in the audio signal recording of FM R.

[Technical background of the invention]

In recent years, in VTRs, in order to obtain high quality sound, audio signals are recorded on video signal tracks by rotating magnetic heads. In this case, the audio signal is converted to FM. This FM audio signal (hereinafter referred to as audio FM signal) is frequency-multiplexed with the video signal and recorded.

FIG. 6 shows the recording system in the VTR.

In the figure, a luminance signal Y separated from a standard color video signal is input to a frequency modulation circuit 12 from a terminal 11, and
Becomes M. This FM luminance signal (hereinafter referred to as luminance F
The YFM (referred to as the M signal) is supplied to an adder circuit 13, where it is added to the color signal CFC input from a terminal 14.

This color signal CFC is a signal that is separated from the standard color video signal and frequency-converted to a lower frequency band.

The output signal of the adder circuit 13 is input to the adder circuit 16 through the buffer circuit 15. Then, in this adder circuit 16, it is added to the audio FM signal AFM input from the terminal 17. This addition output is amplified by a recording amplifier (not shown) connected to the terminal 18, and then recorded on a magnetic chip (not shown) by a rotating magnetic head (not shown).

FIG. 7 shows the frequency bands of the three signals YFM, CFC, and AFM recorded on the video signal track. As shown in the figure, the frequency band of the audio FM signal AFM is the frequency band of the luminance FM signal YFM and the frequency band of the audio FM signal AF.
M frequency bands. The carrier frequency of the audio FM signal AFM is set to approximately 1.5 MHz, and the frequency deviation is set to approximately 100 kHz. Further, the carrier frequency of the luminance FM signal YFM is set to approximately 4.8 MHz.

By the way, the brightness signal Y with a wide band is input and becomes upper, and its lower sideband extends below 1.8 MHz, and the audio FM
It overlaps with the signal AFM. In this way, the brightness FM
When the signal YFM and the audio FM signal AFM overlap, a buzz sound is generated in the reproduced sound, and fine noise is generated in the contour part of the reproduced image.

Therefore, in the VTR, as shown in FIG. 6, a trap circuit 1 that attenuates the signal component SN included in the luminance FM signal YFM and having the frequency band of the audio FM signal AFM
9 is provided.

Reference numeral 20 is provided on the transmission path of the audio FM signal M, and a mode for recording the audio FM signal AFM by detecting the carrier signal of the audio FM signal AFM flowing therethrough (hereinafter referred to as audio FM signal recording mode) is provided. ) is an AFM carrier signal detection circuit that determines whether or not. When the carrier signal of the audio FM signal AFM is detected on the AFM carrier signal path 20, the drag control circuit 21 turns on the trap circuit 19. This attenuates the signal component SN.

In some cases, there may be a configuration in which the AFM carrier signal detection circuit 20 is not provided and the trap control circuit 2 is driven in accordance with an operational output that specifies the mode in which the audio FM signal-AFM is recorded.

[Problems with background technology]

In the case of the above configuration, the drag circuit 19 outputs the luminance FM signal Y
FM audio FM signal AFM frequency band signal component SN
It works even when the signal component 8N is not included or the level of the signal component 8N is low. In other words, the audio drag circuit 19 operates even when the mutual interference between the luminance FM signal YFM and the audio FM signal AFM does not affect the reproduced image or the reproduced sound.

Here, in order to suppress the influence of mutual interference between the two signals YFM and AFM as much as possible, the attenuation band of the drag circuit 19 is set wider than the frequency band of the audio FM signal AFM, as shown by diagonal lines in FIG. . Therefore, in the audio FM signal recording mode, compared to the normal mode in which the audio FM signal AF'M is not recorded, the band of the luminance FM signal YFM is significantly narrowed, a phase plane of 9 is generated, and the resolution of the reproduced image is deteriorated. This is also the above-mentioned signal YFM,
In cases where the influence of mutual interference between AFMs becomes a problem, this must be tolerated. However, in the conventional configuration, the trap circuit 19 operates even when the influence of mutual interference between the two signals YFM and AFM does not pose a problem, so in the audio FM signal recording mode, it is necessary to allow unnecessarily poor resolution. There was a problem that it had to be done.

[Purpose of the invention]

The present invention has been made in order to deal with the above-mentioned circumstances, and by minimizing the execution of trap processing that attenuates signal components having the frequency band from the luminance FM signal to the audio FM signal, the resolution of the reproduced image is degraded. An object of the present invention is to provide an audio FM signal recording device that can minimize the noise.

[Summary of the invention]

This invention detects the level of the signal component SN of the luminance FM signal YFM having the frequency band of the audio FM signal AFM, and controls the trap processing of the signal component 8N according to the detection result, so as not to affect the reproduced sound. This is to prevent the resolution of the reproduced image from deteriorating due to the signal component SN attenuating to such a level.

[Embodiments of the invention]

Hereinafter, one embodiment of this invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention.

In FIG. 1, a luminance signal Y input to a terminal 31 is converted into an FM signal by a frequency modulation circuit 32.

This luminance signal YFM is applied to an adder circuit 34 through a buffer circuit 33. Then, in this adder circuit 34,
It is added to the color signal CFC input to the terminal 36. This addition output is given to an addition circuit 37 via a buffer circuit 36. Then, in this adder circuit 37, it is added to the audio FM signal AFM input to the terminal 38. This addition output is applied from the terminal 39 to a rotary magnetic head (not shown) through a recording head (not shown), and is recorded on a magnetic tape (not shown).

The drag circuit 4 is connected to the output terminal of the 21277 circuit 33 above.
0 is connected. This trap circuit 40 is turned on by a trap control circuit 41.

Off is controlled. This trap control circuit 41 is an AFM
The trap circuit 40 is turned on and off according to the output signals of the carrier signal detection circuit 42 and the level detection circuit 43. Similar to the AFM carrier signal detection circuit 20, the AFM carrier signal detection circuit 42 detects whether the mode is the audio FM signal recording mode or the normal mode by detecting the carrier signal of the audio FM signal AFM. Note that, as described above, this determination may be made in accordance with the operational output that designates the audio FM signal recording dirt.

The ``detection circuit 4'' extracts a signal component SN having the frequency band of the audio FM signal AFM from the luminance FM signal YFM output from the frequency modulation circuit 32), and detects its level. Only when a detection result indicating that the audio FM signal recording mode is in the audio FM signal recording mode is obtained from the AFM carrier signal detection circuit 42 and the level of the signal component 8N detected by the level detection circuit 43 is higher than a predetermined level, a trap is detected. The circuit 40 is turned on and the signal component 8
Attenuate N. In other words, even in the audio FM signal recording mode, the trap circuit 40 is not turned on when the level of the signal component is lower than the predetermined level.

5- Figure 2 shows the recording level of signal component SN and audio FM signal AF.
The ratio of recording levels of M is shown according to the amount of attenuation of the trap circuit 40. However, Fig. 2 shows a case where the level of the signal component SN before being attenuated is the same as the level of the audio FM signal AFM. Note that the ratio of the above image recording levels is the ratio of the level of the audio FM signal AFM, which is the main signal, and the level of the signal component SN mixed into it as a noise signal in terms of the playback output of the audio FM signal AFM. , this is called the C/N ratio.

When the above C/N ratio is OdB, Tsuma Shitratsuno circuit 40
When the amount of attenuation is OdB, the reproduced sound of the audio FM signal AFM is buried in the pass sound and cannot be heard at all. When the C/N ratio is -5 dB, the reproduced sound can be heard, but there is a large amount of path sound included, which causes hearing problems. C
When the /N ratio is -19 dB, the pass sound included in the reproduced sound is not very magnetic. When the C/N ratio is -15 dB, the pass sound is almost inaudible. C/N ratio is 120d
In case B, the pass sound cannot be heard at all. therefore,
If the attenuation amount is set to be smaller than about -8 dB, the C/N ratio will be about -10 dB or less, so generation of pass sound can be suppressed and good reproduced sound can be obtained.

The trap control circuit 41 shown in FIG. 1 has a C/N ratio of 11.
The drag circuit 40 is operated for a signal component SN that is larger than 0 dB, but the trap circuit 40 is not operated for a signal component SN that is smaller than this. Therefore, even though the signal components S and N are at a level that does not adversely affect the reproduced sound, it is possible to prevent the occurrence of a phenomenon in which the signal components S and N are attenuated and the resolution of the reproduced image deteriorates.

FIG. 3 shows an example of a specific configuration of the level detection circuit 43. In the figure, a brightness FM signal YFM is input to a terminal 431. The bandpass filter 432 extracts the signal component SN in the frequency band of the audio FM signal AFM from the luminance FM signal YFM. Extracted signal component SN
is connected to the diode detection circuit 43 through the buffer circuit 433.
4 and level detected. This detection output is given to the trap control circuit 41 from a terminal 435.

FIG. 4 is a circuit diagram showing an example of a specific configuration of the trap circuit 40 and the trap control circuit 41. In the figure,
411 is a Schmitt trigger circuit to which the detection output of the diode detection circuit 434 is input. The Schmitt level of this Schmitt trigger circuit 411 is set so that it has a level ratio of about -10 dB to the level of the audio FM signal AFM. When the detection level exceeds the Schmitt level, a high level signal is output and applied to the pace of the transistor Qll. Therefore, the transistor Qll is turned on when the level of the signal component SN is equal to or higher than the Schmitt level. However, this transistor Q1□ is connected to a transistor Q1° so as to form an AND circuit. The output signal of the AFM carrier signal detection circuit 42 is applied to the base of this transistor Q.

This signal is set to be at a high level in the audio FM signal recording mode. Therefore, the transistor QlllQl□ is turned on only when the mode is the audio FM signal recording mode and the signal component SN is equal to or higher than the seamit level. With this, υ, trap circuit 4
0 is connected to ground, and this trap circuit 40 is turned on. As a result, the signal component SN is attenuated to a level of -10 dB or less in C/N ratio, and deterioration of reproduced sound due to path sound can be avoided.

Although the case where the amount of attenuation of the trap circuit 40 is constant has been described above, FIG. 5 shows a case where the amount of attenuation can be changed according to the level of the signal component SN.

That is, a junction FET Qsa is provided whose drain is connected to the trap circuit 40, whose source is supplied with a predetermined positive voltage higher than the power supply VcC, and whose dart is supplied with the detection output of the level detection circuit 43. In the audio FM signal recording mode, the transistor Q1 is turned on by the output signal of the AFM carrier signal detection circuit 42.
4, in this mode, by grounding the gate of FET QIS, it is negatively biased.

In this way, the impedance between the drain and source of the FET Q13 changes as the gate potential of the FET Q1m changes in accordance with the level detection output of the signal component SN. Since this impedance becomes a resistance component of the trap circuit 40, the amount of attenuation of the trap circuit 40 can be controlled according to the level of the signal component SN. As a result, the recording level of the signal component SN is always -10 dB in C/N ratio, regardless of the level before attenuation.
The following predetermined values can be used.

By making the amount of attenuation variable in this way, the signal component S
The N is left at a level that does not affect the reproduced sound and is completely removed (if the amount of attenuation is fixed, the level before attenuation is only slightly larger than -10 dB in C/N ratio). Since the signal component SN is completely removed by trap processing, further improvement in resolution can be expected than in the previous embodiment.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an audio FM signal recording device that can minimize the deterioration in resolution of a reproduced image caused by drag processing.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the configuration of one embodiment of Fi Jin's invention, Fig. 2 is a characteristic diagram for explaining the operation of the m1 diagram, and Fig. 3 is a circuit diagram showing the configuration of an embodiment of Fi Jin's invention.
A circuit diagram showing an example of a specific configuration of the level detection circuit shown in the figure,
FIG. 4 is a circuit diagram showing an example of a specific configuration of the trap control circuit and trap control circuit shown in FIG. Conventional audio F
FIG. 7 is a circuit diagram showing the M signal recording device, and is a diagram showing the frequency band of a recording signal in a VTR. 40... Trap circuit, 41... Trap control circuit, 43... Level detection circuit. ° Applicant's agent Patent attorney Takehiko Suzue 2'shi1
Figure dobut t7'+2 soru 1σ〕me group, B)? 56 figure T: 'S7 figure

Claims (1)

[Scope of Claims] An audio FM signal recording device that records a frequency-modulated audio signal on a video signal track whose luminance signal is a frequency-modulated signal by frequency-multiplexing the video signal, wherein the frequency-modulated luminance signal is frequency-modulated. a trap means for attenuating a signal component included in the signal and having the same frequency band as the frequency modulated audio signal; and a level for extracting the signal component from the frequency modulated luminance signal and detecting its level. detection means; and drag control means for setting the recording level ratio of the frequency-modulated luminance signal and the audio signal within a predetermined ratio by driving the trap means according to the detection output of the level detection means. An audio FM signal recording device comprising: