JP2809968B2 - Automatic recording level adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic recording level adjusting device for a HiFi VTR.

[0002]

2. Description of the Related Art A conventional example will be described with reference to a block diagram shown in FIG.

[0003] The recording circuit of the VTR includes a recording section 1, a head section 3, and a reproducing section 5.

[0004] The recording unit 1 is shown in FIG. 8 and includes a left channel audio signal input terminal 11 for inputting a left channel (LcH) audio signal, and a right channel for inputting a right channel (RcH) audio signal. Channel audio signal input terminal 1
2, an amplification (AMP) circuit 13 for amplifying the LcH input signal supplied from the LcH audio signal input terminal 11, and amplifying the RcH audio signal supplied from the RcH audio signal input terminal 12. For amplification (AMP)
Circuit 14 and LcH supplied from the amplifier circuit 13.
A noise reduction circuit 15 composed of a compression circuit + an emphasis circuit for performing dBX processing of a signal and performing emphasis for coping with a reduction in triangular noise after demodulation of an FM wave; A noise reduction circuit 16 composed of a √ compression circuit and an emphasis circuit for performing a dBX process on the supplied RcH audio signal and performing an emphasis for coping with a decrease in triangular noise after demodulation of the FM wave; FM for FM-modulating the LcH audio signal supplied from the circuit 15 at 1.3 MHz ± 150 KHz
The RcH audio signal supplied from the modulator 17 and the noise reduction circuit 16 is converted to 1.7 MHz ± 150 KHz.
An FM modulator 18 that performs FM modulation at, and a VIDEO from the LcH FM signal supplied from the FM modulator 17.
A low-pass filter (L.C.) for removing harmonic components of the HiFi FM wave that may affect the FM wave.
P. F. ) Circuit 19 and a low-pass filter (LPF) for removing the harmonic component of the HiFiFM wave which may affect the VIDEO FM wave from the RcH FM signal supplied from the FM modulator 18. ) Circuit 2
0 and L. P. F. An LcH level adjustment VR21 for adjusting the recording level of the LcH audio signal output from the circuit 19; P. F. Rc output from circuit 20
RcH level adjustment VR22 for adjusting the recording level of the H audio signal, and LcH / RcHM for mixing and amplifying the LcH signal and the RcH signal supplied from the LcH level adjustment VR21 and the RcH level adjustment VR22.
An IX circuit and a REC amplification circuit 23 are provided.

The rotary head unit 3 is shown in FIG. 9 and includes a rotary head A31 for recording and reproducing an audio signal on a video tape and a rotary head for recording and reproducing an audio signal on a video tape. B32.

The reproducing section 5 shown in FIG. 10 is a head AMP circuit 51 for amplifying the FM signal reproduced by the rotary head A31, and amplifies the FM signal reproduced by the rotary head B32. AMP circuit 52 for
A head switching pulse generator 54 for generating a head switching pulse; and the head AM in response to a head switching pulse supplied from the head switching pulse oscillator 54.
A switching circuit 53 for switching the HIFi FM waves supplied from the P circuits 51 and 52, and a band-pass filter (BP.) For extracting the LcH signal from the HiFi FM waves supplied from the switching circuit 53.
F. ) 55 and H supplied from the switching circuit 53
a band-pass filter (BPF) 56 for extracting an RcH signal from the iFiFM wave; P.
F. 55. A demodulator 57 for demodulating the original audio signal from the LcH HiFi playback FM wave supplied from the B.55. P. F. Demodulator 58 for demodulating the original audio signal from the RcH HiFi reproduction FM wave supplied from 56
A dropout detection circuit 69, a delay unit 59, a sample hold circuit 61 for reducing switching noise from the demodulated LcH audio signal, and a demodulated Rc
A dropout detection circuit 70, a delay unit 60, and a sample hold circuit 62 for reducing switching noise from the H audio signal; and a HiFi reproduction F from the LcH audio signal.
A low-pass filter for removing the M-wave component (L.
P. F. ) 63 and HiFi playback F from the RcH audio signal.
A low-pass filter for removing the M-wave component (L.
P. F. ) 64; P. F. A noise reduction circuit 65 comprising a de-emphasis circuit and a square-expansion circuit for performing de-emphasis and square decompression on the LcH audio signal supplied from 63, and performing de-emphasis on the LcH audio signal; . P. F. A noise reduction circuit 66 comprising a square expansion circuit and a de-emphasis circuit for performing square expansion, which is the inverse correction to that at the time of recording, and performing de-emphasis on the RcH audio signal supplied from 64; An amplification (AMP) circuit 67 for amplifying the LcH audio signal supplied from the reduction circuit 65, and the noise reduction circuit 6
And an amplifier (AMP) 68 for amplifying the RcH audio signal supplied from the AMP circuit 67 and an LcH for outputting the LcH audio signal supplied from the AMP circuit 67 to the outside.
H audio signal output terminal 71 and R for outputting the RcH audio signal supplied from the AMP circuit 68 to the outside.
and a cH audio signal output terminal 72.

First, the recording system 1 will be described.

Each of the LcH and RcH audio signals input from the LcH and RcH audio input terminals 11 and 12 is an AM signal.
It is supplied to P circuits 13 and 14.

The AMP circuits 13 and 14 amplify each input audio signal and output it to the next stage.

The amplified LcH and RcH audio signals are
The signals are input to the noise reduction circuits 15 and 16 and are subjected to √ compression processing and emphasis for coping with the reduction of the triangular noise after the demodulation of the FM wave, and then supplied to the FM modulators 17 and 18.

The FM modulator 17 FM-modulates the input LcH audio signal at 1.3 MHz ± 150 KHz.
The FM modulator 18 converts the RcH audio signal into 1.7
FM modulation is performed at MHz ± 150 KHz.

Each of the FM-modulated LcH and RcH audio signals is based on L.H. P. F. VIDEO FM in circuits 19 and 20
The harmonic components of the FM wave that may affect the wave are removed.

The LcH and RcH audio signals from which the harmonic components have been removed are input to the LcH level adjustment VR21 and the RcH level adjustment VR22.

The adjustment of the LcH / RcH REC FM wave level (LcH × RcHMIX ratio determination) by the LcH level adjustment VR21 and the RcH level adjustment VR22 is 1.3.
The operation is performed so that the difference component (beat component) between the MHz carrier and the 1.7 MHz carrier, that is, the 400 KHz component, is minimized, and after being fixed in that state, LcH / RcH MIX
Circuit and the REC AMP circuit 23.

[0015] Each audio signal is LcH / RcH.
After the LcH signal and the RcH signal are mixed in the MIX circuit and the REC AMP circuit 23, they are amplified and output to the head unit 2.

The head section 2 receives the mixed audio signal output from the recording system 1 and inputs the mixed audio signals to the rotating heads CH A31, CH A31.
32 is recorded.

The rotary heads CH A31, B32
Reproduces the audio from the video tape and outputs it to the reproduction system 5.

On the other hand, in the reproducing system 5, the reproduced FM wave taken out from the head section 3 is amplified by the head AMP sections 51 and 52 and then supplied to the switching SW 53.

The playback F switched by the switching SW 53
The M wave is P. F. After the VIDEO FM waves are removed at 55 and 56, they are supplied to demodulators 57 and 58.

The head switching pulse generator 54 generates a head switching pulse, and the sample and hold circuits 61 and 6
2 and the head AMP units 51 and 52 to B.2. P. F. 5
Switch SW53 for switching output to 5, 56
Supplied to

In the demodulators 57 and 58, the input Lc
The original audio signal is demodulated from the H and RcH FM signals.

The demodulated LcH and RcH audio signals are
Dropout detection circuits 69 and 70, delay units 59 and 6
0, after the switching noise is reduced by the sample and hold circuits 61 and 62, P. F. 63,
64.

L. P. F. In 63 and 64, after removing the HiFi reproduction FM wave from each input audio signal, the signal is supplied to the noise reduction circuits 65 and 66.

In the noise reduction circuits 65 and 66,
Square expansion and de-emphasis, which are corrections opposite to those at the time of recording, are performed.

Thereafter, each of the LcH and RcH audio signals is A
After being amplified by the MP circuits 67 and 68, they are output to the LcH and RcH audio signal output terminals 71 and 72.

[0026]

In the prior art, HiF
1.3 MHz which is the carrier frequency of LFM of iFM wave
And a 400 KHz component which is a difference component between the RcH carrier frequency of 1.7 MHz and the chroma signal (6
29KHz ± 500KHz) and recorded as HiFi beats, and appear as chroma noise and chroma beats on the screen during reproduction.

This phenomenon occurs between 1.3 MHz and 1.7 MHz.
In the case of only the carrier frequency, that is, a screen with no sound, a single color chroma and a large area is more conspicuous.

As a measure to reduce this, conventionally, an adjustment was made so that the 400 KHz component was minimized, and in that state, the REC signal levels of LcH and RcH were fixed respectively.

However, in the above setting method, since the magnetization levels at 1.3 MHz and 1.7 MHz are not constant due to the variation between tape types, the 400 KHz component is dependent on the combination of the tape and the head. , Was not always the smallest.

In view of the above, the present invention provides an automatic recording level adjusting apparatus which absorbs variations between tape types and minimizes the 400 kHz component to suppress chroma noise and chroma beat on the screen. Is what you do.

[0031]

SUMMARY OF THE INVENTION An automatic recording level adjusting apparatus according to the present invention is capable of transmitting 1.3 MHz from a HiFi reproduction FM wave.
A first band-pass unit for extracting only the carrier component of the HiF, a second band-pass unit for extracting only the 1.7 MHz carrier component from the HiFi reproduction FM wave,
a third band-pass means for extracting only a 400 KHz component which is a difference component between 1.3 MHz and 1.7 MHz from the reproduced FM wave, and a carrier component supplied from the first and second band-pass means The envelope detection means for outputting the first control signal only when both of the envelope detection waveforms are flat, and the comparison between the value of the 400 KHz component supplied from the third band-pass means and a preset reference value And a first comparing means for outputting a second control signal only when it is larger than a reference value, and only when both the first control signal and the second control signal are output, the first 1.3MHz HiFiFM wave supplied from the band-pass unit and the second band-pass unit, and 1.7MH
a second comparing means for comparing the level with the HiFiFM wave of z and outputting a third control signal in response to the difference voltage, and receiving the third control signal to reduce the 400 KHz component to a minimum. And adjusting means for adjusting the recording levels of LcH and RcH.

[0032]

The first band-pass means extracts only the 1.3 MHz carrier component from the HiFi reproduced FM wave, and the second band-pass means extracts the 1.7 MHz carrier component from the HiFi reproduced FM wave.
Only the carrier component is taken out and supplied to the envelope detecting means and the second comparing means, respectively. In the third band-pass unit, 1.3 MHz and 1.7 M from the HiFi reproduction FM wave are used.
Only the 400 KHz component, which is the difference component from Hz, is taken out and supplied to the first comparing means.

The envelope detection means outputs the first control signal only when the envelope detection waveforms of the carrier components supplied from the first and second band pass means are both flat. The first comparing means compares the value of the 400 KHz component supplied from the third band-pass means with a preset reference value, and generates a second control signal only when the value is larger than the reference value. Supply to the second comparison means. In the second comparison means, only when both the first control signal and the second control signal are output, 1 is supplied from the first band-pass means and the second band-pass means. .3 MHz carrier component level and 1.7 MHz
A comparison is made with the level of the carrier component of z, and a third control signal responsive to the level difference voltage is supplied to the adjusting means. The adjusting means receives the third control signal and
The recording levels of LcH and RcH are adjusted so that the KHz component is minimized.

[0034]

FIG. 1 is a block diagram showing one embodiment of the present invention.
Shown in

The automatic recording level adjusting device according to the present invention comprises:
It comprises a recording system 1, a head unit 3, a reproducing system 5, and an adjusting unit 9.

The recording system 1 is shown in FIG. 4 and has a left channel audio signal input terminal 11 for inputting a left channel (LcH) audio signal and a right channel for inputting a right channel (RcH) audio signal. Channel audio signal input terminal 1
2 and L supplied from the LcH audio signal input terminal 1.
an amplification (AMP) circuit 13 for amplifying a cH input signal; an amplification (AMP) circuit 14 for amplifying an RcH audio signal supplied from the RcH audio signal input terminal 12; , A noise reduction circuit 15 for performing the dBX processing of the LcH signal supplied from the AMP circuit, and performing an emphasis to cope with the triangular noise reduction after the demodulation of the FM wave, and the dBX of the RcH audio signal supplied from the AMP circuit 14. A noise reduction circuit 16 for performing processing and performing emphasis to cope with a decrease in triangular noise after demodulation of the FM wave;
LcH supplied from the noise reduction circuit 15
An FM modulator 17 for FM-modulating an audio signal at 1.3 MHz ± 150 KHz, and an RcH audio signal supplied from the noise reduction circuit 16 at 1.7 MHz
FM modulator 1 for performing FM modulation at ± 150 KHz
8 and the LcH FM supplied from the FM modulator 17
A low-pass filter (LPF) circuit 19 for removing a harmonic component of a HiFiFM wave that may affect a VIDEO FM wave from a signal, and an RcH FM signal supplied from the FM modulator 18 To VIDE
A low-pass filter (LPF) circuit 20 for removing a harmonic component of the HiFiFM wave that may affect the OFM wave, and an adjustment unit 9 described below.
LcH / RcH for adjusting the recording level of LcH and RcH so that the 400 KHz component is minimized in response to the control signal from the 3 MHz & 1.7 MHz level comparator 96.
REC level variable circuit 24 and LcH / RcHR
The LcH signal supplied from the EC level variable circuit 24 and R
LcH / RcHMIX for mixing and amplifying with cH signal
And a REC AMP circuit 23.

The head section 3 is shown in FIG. 8 similarly to the conventional example, and includes a rotary head A31 for recording and reproducing an audio signal on a video tape, and recording and reproducing an audio signal on a video tape. And a rotary head B32.

The reproducing system 5 shown in FIG. 2 is a head AMP circuit 51 for amplifying the FM signal reproduced by the rotary head A31, and amplifies the FM signal reproduced by the rotary head B32. AMP circuit 52 for
A head switching pulse oscillator 54 for generating a head switching pulse, and the head switching pulse oscillator 54
A switching circuit 53 for switching the HIFiFM waves supplied from the head AMP circuits 51 and 52 in response to a head switching pulse supplied from
B. for extracting a signal P. F. 55 for extracting the RcH signal from the HiFiFM wave supplied from the switching circuit 53; P. F. 56; P.
F. 55. A demodulator 57 for demodulating the original audio signal from the LcH HiFi playback FM wave supplied from the B.55. P. F. Demodulator 58 for demodulating the original audio signal from the RcH HiFi reproduction FM wave supplied from 56
And a dropout detection circuit 69, a delay unit 59, a sample hold circuit 61 for reducing switching noise from the demodulated LcH audio signal supplied from the demodulator 57, and a demodulated signal supplied from the demodulator 58. RcH
A dropout detection circuit 70, a delay unit 60, a sample hold circuit 62 for reducing switching noise from an audio signal, and a HiFi reproduction FM from an LcH audio signal.
L. for removing wave components P. F. 63 and L.H. 63 for removing the HiFi reproduction FM wave component from the RcH audio signal. P. F. 64; P. F. A noise reduction circuit 65 composed of a de-emphasis circuit and a de-emphasis circuit for performing a de-emphasis and a square decompression circuit for performing de-emphasis and square decompression on the LcH audio signal supplied from the L.H. P. F. A noise reduction circuit 66 composed of a square expansion circuit and a de-emphasis circuit for performing square expansion, which is the inverse correction to the recording, and performing de-emphasis on the RcH audio signal supplied from the RcH audio signal; Amplification (A) for amplifying the LcH audio signal supplied from the circuit 65
MP) circuit 67, an amplification (AMP) circuit 68 for amplifying the RcH audio signal supplied from the noise reduction circuit 66, and outputting the LcH audio signal supplied from the AMP circuit 67 to the outside. LcH for
An audio signal output terminal 71 and an RcH for outputting the RcH audio signal supplied from the AMP circuit 68 to the outside.
An audio signal output terminal 72 is provided.

The adjusting section 9 is a narrow band 1.3 MHz band pass filter circuit (B.B.) for separating the carrier frequency component of the LcH audio signal from the HiFiFM wave supplied from the switching circuit 53 shown in FIG. P.
F. ) 92 and H supplied from the switching circuit 53.
A narrow band 1.7 MHz band-pass filter circuit (BPF) 93 for separating the RcH audio signal carrier frequency from the iFiFM wave, and LcH and RcH from the HiFiFM wave supplied from the switching circuit 53. Narrow band 400K for separation of 400KHz which is the difference
Hz band pass filter circuit (BPF) 91
And B. P. F. 400KHz supplied from 91
A comparator 94 which compares the value of the beat component with a preset limit level and outputs an (H) voltage only when the level is equal to or higher than the limit level; P. F. LcH separated at 92
B. the carrier frequency component of the audio signal and P. F. 93
An envelope detector 95 that detects a silent part during broadcasting from the carrier frequency component of the RcH audio signal separated by the above and outputs a (H) voltage only when there is no audio, and the comparator 9
4 and the envelope detector 95 only output the (H) voltage. P. F. 52 and the 1.3 MHz carrier frequency component output from B.52. P.
F. 1.3 MHz & 1.7 MH for performing level comparison with the 1.7 MHz carrier frequency component output from 93 and generating a control signal according to the result and outputting the control signal to the recording system.
and a z-level comparator 96.

Hereinafter, the operation of the above-described automatic recording level adjusting apparatus will be described in detail.

In the recording system 1, the LcH audio signal input terminal 1
1 and LcH input to the RcH audio signal input terminal 12,
The RcH audio signal is supplied to AMP circuits 13 and 14,
Each is amplified.

The amplified LcH and RcH audio signals are
The signals are input to the noise reduction circuits 15 and 16, and are subjected to Δ compression processing and emphasis for coping with the reduction of the triangular noise after demodulation of the FM wave, and then supplied to the FM modulators 17 and 18.

The FM modulator 17 converts the input LcH audio signal to 1.3 MHz ± 150 KHz, and the FM modulator 18 converts the input RcH audio signal to 1.7 MHz ± 150 kHz.
After FM modulation at 150 KHz respectively, it is output to the next stage.

The FM-modulated LcH and RcH audio signals are transmitted according to L.H. P. F. After removing the harmonic component of the FM wave which may affect the VIDEO FM wave in the circuits 19 and 20, the LcH / RcH REC level variable circuit 24
Is input to

LcH / RcH REC level variable circuit 2
In L.4, LcH and RcH are controlled according to a control signal output from a 1.3 MHz & 1.7 MHz level comparator 96 described later.
After the recording level of the cH audio signal is changed, LcH /
It is supplied to the RcHMIX circuit and the REC amplifier circuit 23.

LcH / RcH MIX circuit and REC
The amplifier circuit 23 mixes the LcH and RcH audio signals, amplifies them, and supplies them to the head unit 3 as REC FM waves.

The head unit 2 receives the mixed audio signal output from the recording system, and inputs the mixed signals to the rotary heads CH A31 and B3.
2 is recorded.

The rotary heads CH A31, B32
Reproduces the audio from the video tape and outputs it to the reproduction system 5.

Next, the reproduction system 5 will be described below.

The reproduced FM wave taken out from the HiFi rotary head is amplified by the head AMP circuits 51 and 52 and then supplied to the switching circuit 53.

The head switching pulse switching circuit 54 generates a head switching pulse and outputs a sample / hold circuit 61,
62, an envelope detector 95, and a switching circuit 53
To supply.

In the switching circuit 53, the input audio signal is switched by the head switching pulse supplied from the head switching pulse switching circuit 54, and B.I. P. F. 5
5,56, and B.I. P. F. 91, 92, and 93.

B. P. F. In 55 and 56, LcH and R
After separating cH and removing VIDEOFM waves, the signals are supplied to demodulators 57 and 58.

The demodulators 57 and 58 demodulate the original LcH and RcH audio signals from the FM signals and output the demodulated signals to the next stage.

The demodulated audio signal is subjected to switching noise reduction by dropout detection circuits 69 and 70, delay units 59 and 60, and sample and hold circuits 61 and 62. P. F. 63, 64, HiFi
The reproduction FM wave is removed, and the noise reduction circuit 6
5,66.

In the noise reduction circuits 65 and 66,
The signal is output after performing the square expansion, which is the inverse correction to the recording, and performing the de-emphasis.

The output LcH and RcH audio signals are A
After being amplified by the MP circuits 67 and 68, they are output to an LcH audio signal output terminal 71 and an RcH audio signal output terminal 72, respectively.

In the adjusting section 9, a narrow band 1.3 MHz B.W.
P. F. Reference numeral 52 denotes Hi supplied from the switching circuit 53.
A 1.3 MHz frequency component, which is a carrier signal of the LcHFM audio signal, is extracted from the Fi-reproduced FM wave, and supplied to the envelope detector 95. In addition, narrow band 1.7MHz
B. P. F. At 93, a 1.7 MHz frequency component, which is a carrier signal of the RcHFM audio signal, is extracted from the HiFi reproduction FM wave supplied from the switching circuit 53 and supplied to the envelope detector 95. Envelope detector 9
5 indicates that the (H) voltage is equal to the following 1.3M only when the detection waveform is flat.
The frequency is output to a Hz & 1.7 MHz level comparator 96. In other words, the envelope detector 95 has a function of detecting a silent part being broadcast.

Note that a narrow band of 1.3 MHz P. F. 9
2 and narrow band 1.7 MHz P. F. Hi after 93
The FiFM wave is input to the envelope detector 95 and at the same time, the 1.3 MHz & 1.7 MHz level comparator 96
Also supplied to

Here, the operation of the envelope detector 95 will be described with reference to FIG. As shown in FIG. 5 (a), in the broadcast non-audio section, from CH A to CH B,
Although the envelope detection waveform becomes flat, except for the non-sound part, the deviation is ± 150K as shown in FIG.
Hz, so the envelope has a narrow band of 1.3 MHz. P. F. 92 and narrow band 1.7MHz
B. P. F. Since some components cannot pass through 93, the envelope is uneven, and the envelope detection waveform from CH A to CH B is not flat.

On the other hand, 400 kHz narrow band B. P. F. 9
In 1, the 400 kHz component, which is the beat component of the LcH audio signal and the RcH audio signal, is extracted from the input HiFiFM wave, and is sent to the comparator 94.

In the comparator 94, B.P. P. F. The 400 KHz beat component supplied from 91 is compared with a preset limit level that affects the image, and only when the limit level is exceeded, the (H) voltage is output from the comparator 94, and 1.3 MHz and 1.7 MHz are output. The signal is input to the level comparator 96. That is, the comparator 94 determines whether the signal 4
It plays the role of determining whether or not the 00 KHz beat component has occurred.

The 1.3 MHz & 1.7 MHz level comparator 96 compares the levels of the input 1.3 MHz carrier frequency component and the 1.7 MHz carrier frequency component, and generates a control signal corresponding to the voltage of the level difference. Only when the (H) voltage is input from both the comparator 94 and the envelope detector 95 to the 1.3 MHz & 1.7 MHz level comparator 96, the control signal is LcH /
RcH is applied to the REC level variable circuit 24.

That is, only when the 400 KHz beat in the audio non-signal portion exceeds the set level, LcH / Rc
The H REC level is changed, and the LcH carrier REC level and the RcH carrier REC level are adjusted so that the 400 KHz component is minimized. (Because ADJ is repeated in a silent section) The operation of the above adjustment is described below with reference to FIG. 6 showing the LcH / RcH REC level variable circuit 24.

LcH / RcH REC level variable circuit 2
4 are coupling capacitors C1 and C shown in FIG. 6A for adjusting the recording level of the LcH audio signal.
2, C3, Tr1 for performing amplification, and bias resistor R
FIG. 1 is a diagram for adjusting the recording level of a RcH audio signal, and a voltage variable resistor VR1 that changes a resistance value according to a control signal from a 1.3 MHz & 1.7 MHz level comparator 96, and R2, R3, and R4. 6 (b) and coupling capacitors C4, C5, C6 and Tr2 for performing amplification.
And bias resistors R5, R6, R7, R8 and 1.3 MH
and a voltage variable resistor VR2 that changes a resistance value according to a control signal from the z & 1.7 MHz level comparator 96.

LcH / RcH REC level variable circuit 2
4 includes voltage variable resistors VR1 and VR2 in parallel with the emitter resistors R4 and R8 of the LcH-side Tr1 and RcH-side Tr2. Here, the voltage variable resistors VR1, VR2
Shall increase in proportion to the voltage to which the resistance value is applied.

Therefore, the gain of each Tr amplifier is
Changes according to the voltage level applied to the voltage variable resistor, so that the REC FM wave level is controlled by the voltage applied to the voltage variable resistor.

For example, compared to the LcH carrier level, R
When the cH carrier level is smaller, LcH × R
The voltage variable resistor VR1 in parallel with the emitter resistance of the LcH side Tr1 of the cH REC level varying circuit 24
Has a level difference voltage of the carrier between LcH and RcH,
The voltage is superimposed on the currently applied voltage.

Therefore, the resistance value of the voltage variable resistor VR1 increases, and the combined resistance value of the emitter of the LcH side Tr1 increases.

As a result, the gain of Tr1 decreases, and L
The level of the recording FM wave on the cH side decreases, and the level is adjusted to the REC FM wave level on the RcH side with the lower level, and
× RMIX and REC AMP circuit 23

On the other hand, the emitter resistance R8 of the RcH side Tr2
, The current applied voltage is held as it is, and the recording FM wave level on the RcH side is kept at the same level as L × RMIX and REC.
It is supplied to the AMP circuit 23.

Here, the reason why the REC level is adjusted to a smaller one is to reduce the influence (interference) on the REC chroma signal (629 KHz ± 500 KHz) by reducing the level as much as possible. In this embodiment, after the tape is attached to the VTR, recording is performed, and when the recorded portion is reproduced, the non-voice portion of the broadcast audio recording portion being reproduced is detected by the envelope detector. 1.3
1.3MHz Hi with MHz & 1.7MHz level comparator
By comparing the Fi carrier component with the 1.7 MHz HiFi carrier component, a control signal is generated based on the difference voltage, and the control signal reduces the recording level of the 1.3 MHz side and the 1.7 MHz side of the REC system to a minimum of 400 KHz. The HiFi beat is reduced by controlling so that the same tape is reproduced again after the reproduction of the tape.
When you record while attached to the effect is to come out.

If the user wants to reduce the HiFi beat immediately after the first recording by attaching a tape other than the above, a control signal is output from the system control microcomputer at the time of attaching the tape, whereby a predetermined time is determined. Perform a pre-recording, then immediately play that part,
After that, in the same procedure as above, control the 1.3MHz side recording level and 1.7MHz side recording level on the recording system side, then rewind the tape to the start point of pre-recording, stop there, and stop the next recording (It is the first recording for the user.) A method of setting the standby state is also conceivable.

[0074]

In the prior art, as a HiFi beat reduction measure, the LcH and RcH REC FM wave signal levels are set so that the 400 KHz component of the difference component of the HiFiFM wave carrier frequency (1.3 MHz and 1.7 MHz) is minimized. It is adjusted and fixed in that state. However, in this case, depending on the combination of the tape and the head, 1.3 MHz and 1.7 MHz are used.
Since the magnetization level in MHz is not always constant, 4
The 00 KHz component is not always minimum.

In the present invention, the 1.3 MHz recording FM wave level and 1.7 are used so that the 400 KHz component is always minimized at the non-speech part by using the non-speech part of the broadcast to be recorded.
Align with the FM recording FM wave level.

Therefore, for example, when the tape is replaced,
Automatic control is always performed so that the LcH / RcHMIX ratio is optimal for the replacement tape, which is very effective in preventing the occurrence of HiFi beats.

[Brief description of the drawings]

FIG. 1 shows a block diagram of one embodiment according to the present invention.

FIG. 2 shows a configuration diagram of a reproduction system according to an embodiment of the present invention.

FIG. 3 shows a configuration diagram of a reproduction system according to an embodiment of the present invention.

FIG. 4 is a configuration diagram of a recording system according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating the operation of an envelope detector used in one embodiment of the present invention.

FIG. 6 shows LcH / RcH used in one embodiment of the present invention.
The figure used for the operation explanation of a RECLEVEL variable device is shown.

FIG. 7 shows a block diagram of a conventional example.

FIG. 8 shows a configuration diagram of a conventional recording system.

FIG. 9 shows a configuration diagram of a conventional head unit.

FIG. 10 shows a configuration diagram of a conventional reproduction system.

[Explanation of symbols]

 91 Narrow band 400 KHz band pass filter 92 Narrow band 1.3 MHz band pass filter 93 Narrow band 1.7 MHz band pass filter 94 Comparator 95 Envelope detector 96 1.3 MHz & 1.7 MHz level comparator

Claims (1)

(57) [Claims] A first band-pass means for extracting only a 1.3 MHz carrier frequency component from a HiFi reproduced FM wave, and a 1.7 MHz carrier frequency component from a HiFi reproduced FM wave in an automatic recording level adjusting device for a HiFi VTR. A second bandpass means for extracting only
An envelope detection means for outputting a first control signal only when both envelope detection waveforms of the carrier frequency components supplied from the first and second band-pass means are flat; and 1.3 MHz from the HiFi reproduction FM wave. 1.7MH
a third band-pass unit for taking out only a 400 KHz component which is a difference component with z, and comparing a value of the 400 KHz component supplied from the third band-pass unit with a preset reference value. The first comparing means for outputting the second control signal only when the value is larger than the reference value, and only when both the output of the first control signal and the output of the second control signal are present, 1.3 MHz HiFi supplied from the first band-pass means and the second band-pass means
A second comparing means for comparing the level of the FM wave with the level of the HiFiFM wave of 1.7 MHz and outputting a third control signal in response to the difference voltage; Lch and R so that the 400 KHz component is minimized
An automatic recording level adjusting device comprising an adjusting means for adjusting a recording level of a channel.