JPH0762887B2 - Video tape recorder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a video tape recorder for recording an FM-modulated audio signal in a deep layer of a magnetic tape.

(Prior Art) In order to satisfy the demand for recording a high-quality audio signal, a video tape recorder of the type that records an FM-modulated audio signal in a deep layer of a magnetic tape is generally provided, and FIG. 1 shows an electrical configuration of a conventional technique.

At the time of recording the audio signal, the audio signal 91a is modulated by using the FM modulation circuit 91, and then an unnecessary signal is removed by the bandpass filter 92. Then, after setting the optimum level using the variable resistor 93, recording is performed on a magnetic tape (not shown) by the magnetic head 95 via the amplifier 94.

On the other hand, the FM audio signal detected by the magnetic head 81 and amplified by the amplifier 99 is an AGC circuit 8 for adjusting the level.
After being guided to the equalizer 83 via 4 and being subjected to the characteristic correction, the FM demodulation circuit 82 extracts the audio signal 82a.

Further, the low-pass conversion color signal taken out at the same time as the FM audio signal by the magnetic head 81 is guided to the low-pass filter 98 via the amplifier 99 and then sent to the ACC circuit 97 for adjusting the level of the low-pass conversion color signal. To be done. Then, the frequency of the original color signal is converted by the conversion circuit 96. Then, the converted signal is sent to the subsequent processing circuit as the color signal 96a.

(Problems to be Solved by the Invention) In the video tape recorder having the above-described configuration, the optimum level of recording is performed at the time of manufacture,
The variable resistor 93 adjusts the recording level of the FM audio signal. After that, the recording of the set level is performed. However, since different types of magnetic tape have different magnetic characteristics, the recording level set above is not always the optimum recording level, and the recording level of the FM audio signal is smaller than the optimum recording level. Then, there arises a problem that the dynamic range of the audio signal is insufficient.

The present invention has been conceived in order to solve the above problems, and an object thereof is to provide a video tape recorder capable of always adjusting the recording level of an FM audio signal to an optimum level.

(Means for Solving the Problems) In order to solve the above problems, a video tape recorder of the present invention is applied to a video tape recorder for recording an FM audio signal, which is an FM-modulated audio signal, in a deep layer of a magnetic tape, and
Before starting to record the audio signal, FM for a predetermined period
A recording control unit for recording a low-frequency conversion color signal on the magnetic tape together with an audio signal, a magnetic head for detecting the low-frequency conversion color signal recorded on the magnetic tape by the recording control unit, and an output from the magnetic head. The configuration includes a level detection circuit that detects the level of the low-frequency converted color signal and a recording level setting unit that sets the recording level of the FM audio signal corresponding to the output of the level detection circuit.

(Function) Since the maximum value of the recording level of the FM audio signal is limited by the recording level of the low frequency conversion color signal, if the recording level is set to the maximum level that the recording level of the low frequency conversion color signal allows. good. Therefore, before the recording of the FM audio signal is started, the recording level of the low frequency conversion color signal recorded on the magnetic tape is detected by the level detection circuit, and the recording level of the FM audio signal is based on the detection result. The recording level of the FM audio signal is set by the recording level setting unit so that the recording level of the low-frequency conversion color signal becomes the maximum level allowed.

(Embodiment) FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the present invention.

In the figure, the output of the magnetic head 11 for detecting the signal recorded on the magnetic tape is passed through an amplifier 12, and an AGC circuit 13 for controlling the level to be kept constant, and a low-pass for passing only the low-frequency conversion color signal. It is led to the filter 16. The output of the AGC circuit 13 is sent to the equalizer 14, the output of the equalizer 14 is guided to the FM demodulation circuit 15, and the output is sent to the outside as the audio signal 15a.

The output of the low-pass filter 16 is the low-frequency conversion color signal 16a.
Are sent to the ACC circuit 17 for adjusting the level and the level detection circuit 19, the output of the ACC circuit 17 is guided to the frequency conversion circuit 18, and the output of the frequency conversion circuit 18 is the color signal 18
It is output to the outside as a.

From the control unit 21 to which the output of the level detection circuit 19 is guided, the output for control is sent to the trigger signal generation circuit 20 and the voltage control variable resistor 22, and the cassette storing the magnetic tape is The output 21a of the cassette detection switch 29 for detecting that the video tape recorder is inserted in the main body (not shown) and the output 21a of the REC switch (not shown) for instructing the start of recording are led to the controller 21. ing.

The output of the FM modulation circuit 28 to which the audio signal 28a is guided is guided to one terminal of the variable resistor 24 via the bandpass filter 27, and the other terminal of the variable resistor 24 is One terminal is connected to the voltage controlled variable resistor 22 grounded and the other terminal of the switch 23, respectively. The sliding terminal of the variable resistor 24 is led to the magnetic head 26 as an FM audio signal 25a via the amplifier 25. The output of the trigger signal generation circuit 20 is given to the level detection circuit 19 and the switch 23.

The recording level setting unit is configured by software, stores the output value of the level detection circuit 19, and outputs the stored value to the control unit 21 and the voltage control variable resistor to which the output of the control unit 21 is guided. It is composed of a container 22.

The operation of one embodiment of the present invention having the above configuration will be described below.

When the output 21a of the REC switch for instructing the start of recording instructs the start of recording, the control unit 21 gives an instruction to start the operation to the trigger signal generating circuit 20 and a recording circuit for the low-frequency conversion color signal (not shown). Is operated to record the low frequency conversion color signal and the FM audio signal on the magnetic tape for several seconds.

On the other hand, the trigger signal generation circuit 20 closes the switch 23 and grounds the terminal of the variable resistor 24 when an operation start instruction is given.
The level of the FM audio signal sent from 28 and guided to the variable resistor 24 via the bandpass filter 27 is set to the minimum level. That is, the recording level of the FM audio signal 25a recorded on the magnetic tape is set to the minimum level (the recording level of the low frequency conversion color signal is the same as the normal level).

Then, in the above operation, the magnetic tape is rewound by an amount corresponding to the length of travel.

Next, the control unit 21 causes the magnetic tape to run at the reproduction speed. Therefore, the signal detected by the magnetic head 11 from the magnetic tape, which is a mixture of the low-frequency converted color signal and the luminance signal, is guided to the low-pass filter 16. Then, the low-pass filter 16 converts the mixed signal into the low-frequency converted color signal 16a.
Only the signal is taken out and sent to the level detection circuit 19.

The level detection circuit 19 detects the level of the guided low-frequency conversion color signal 16a in accordance with the operation start instruction from the trigger signal generation circuit 20, and sends the detection result to the control unit 21. The control unit 21 controls the resistance value of the voltage control variable resistor 22 in accordance with the detection result from the level detection circuit 19,
When the level of the detection result is high, the recording level of the FM audio signal may be set high, and the resistance value of the voltage control variable resistor 22 is changed to a large resistance value, so that the amplifier 25 is guided. Increase the level of the FM audio signal that is received. When the detection result is at a low level,
As it is necessary to set the FM audio signal level low,
Change the resistance value of the voltage controlled variable resistor 22 to a small value,
The level of the FM voice signal guided to the amplifier 25 is reduced (the recording level of the FM voice signal is lowered).

When the setting of the voltage controlled variable resistor 22 is completed, the resistance value of the voltage controlled variable resistor 22 is maintained at a constant value without changing in the subsequent operations. In addition, the trigger signal generation circuit 20 uses the level detection circuit to give an instruction to stop the operation.
It is given to 19 and the switch 23 is opened. With the above operation, the setting of the recording level of the FM audio signal 25a corresponding to the magnetic tape is completed.

In this state, the audio signal 28a is guided to the FM modulation circuit 28 to become an FM audio signal, and by the bandpass filter 27, the variable resistor 24, and the amplifier 25, becomes an FM audio signal 25a of a level corresponding to the magnetic tape. The data is recorded on the magnetic tape by the magnetic head 26. The low frequency conversion color signal is recorded on the magnetic tape by a recording circuit (not shown).

Then, at the time of reproduction, among the mixed signals detected by the magnetic head 11, the FM audio signal is guided to the AGC circuit 13 and amplified so that the level becomes constant, and then the characteristics are corrected by the equalizer 14. It is demodulated by the FM modulation circuit 15. Then, it is sent to the outside as an audio signal by the output 15a.

In addition, the low-pass conversion color signal is converted into AC through the low-pass filter 16.
After being guided to the C circuit 17, the level fluctuation is removed, it is converted into a color signal by the frequency conversion circuit 18, and is output to the outside by the output 18a.

When the magnetic tape is taken out from the video tape recorder main body, a signal to that effect is given to the control unit 21 from the cassette detection switch 29, so that the control unit 21 determines that the operation relating to the corresponding magnetic tape has ended and the voltage control variable Cancel the setting of resistor 22. When a new magnetic tape cassette is inserted, the same operation as described above is repeated to set the voltage control variable resistor 22.

The present invention is not limited to the above embodiment, and the magnetic head 26 for recording the FM audio signal and the magnetic head 11 for reproducing can be configured as the same magnetic head.

(Effect of the Invention) The video tape recorder according to the present invention uses the level detection circuit before recording on the magnetic tape.
The level of the low-frequency conversion color signal detected by the magnetic head is detected, and the level of the FM audio signal to be recorded on the magnetic tape is newly set by the recording level setting unit according to the detection result. Even if the magnetic tape is changed, it is possible to always set the recording level of the FM audio signal to the optimum level.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the present invention, and FIG. 2 is a block diagram showing an electrical configuration of a conventional technique. 11 …… Magnetic head 16a …… Low frequency conversion color signal 19 …… Level detection circuit 21 …… Control section 22 …… Voltage control variable resistor 25a …… FM voice signal

Claims (1)

[Claims] 1. A video tape recorder for recording an FM audio signal, which is an FM-modulated audio signal, in a deep layer of a magnetic tape, before starting the recording of the FM audio signal, for a predetermined period of time.
A recording control unit that records a low-frequency conversion color signal together with an FM audio signal on the magnetic tape, a magnetic head that detects the low-frequency conversion color signal recorded on the magnetic tape by the recording control unit, and a magnetic head A level detection circuit that detects the level of the low-frequency conversion color signal that is output, and a recording level setting unit that sets the recording level of the FM audio signal corresponding to the output of this level detection circuit are provided. Characteristic video tape recorder.