JPH03119502A - Audio signal dubbing system - Google Patents

Abstract

PURPOSE:To prevent the occurrence of switching noise to keep the tone quality good by providing a transmission line from the master side to the slave side with respect to each channel of a rotary head for FM audio signal and transmitting the FM audio signal as a modulated signal as it is. CONSTITUTION:A rotary head 52 of the channel 1 on the master side and a rotary head 66 of the channel 1 on the slave side are synchronously operated so that the latter performs signal recording during signal reading of the former. That is, the FM audio signal outputted from the rotary head 52 on the master side passes a band-pass filter 56, and a carrier frequency component corresponding to the FM audio signal is outputted to an amplifier 58 and has the level adjusted and is sent to the slave side. On the slave side, the input FM modulated signal is subjected to the same filtering by a band-pass filter 62, and the FM audio signal is recorded on a tape by a rotary head 66. During this period, processings such as signal modulation and demodulation and noise reduction are not performed and the signal is dubbed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a dubbing method for FM audio signals in a video tape recorder.

[Prior art] For example, VH3 (registered trademark) high-fidelity (HiFi)
) In video, the audio signal is FM modulated in the same way as the luminance signal, and is recorded in a deeper part of the tape magnetic film than the video signal using a two-channel rotating head that has a different azimuth angle than the video signal head. For dubbing in the baseband, for example, a device as shown in FIG. 8 is used. Note that the circuit on the video signal side is omitted. Further, in the following description, the symbols R and L of each element indicate that the element of each part corresponds to the left and right channels of stereo.

First, I will explain from the master side. In the same figure, a rotary head 1.
The intermittent FM audio signals read by 2a and 12b are amplified by preamplifiers 14a and 14b, respectively, and are input to an AGC (automatic gain control) circuit 18 via a switch 16 that is switched by a head switching signal.

Next, the modulated audio signal output from the AGC circuit 18 is
Each band pass filter 20R12OL is manually inputted. Bandpass filter 2OR passes 1.3MHz carrier, bandpass filter 2OL passes 1.7M)
Each characteristic is set so that the carrier of Iz passes through. Therefore, the modulated audio signal of the right channel is inputted to the demodulator 22H from the bandpass filter 2OR, and the modulated audio signal of the left channel is inputted to the demodulator 22H through the bandpass filter 2OR.
'The demodulator 22L is manually powered from the OL.

Next, the left and right audio signals demodulated by demodulators 22R and 22L are processed by sample-hold circuits 24R and 24L for head switching or dropout compensation, variable resistors 25R and 25L for playback level adjustment, de-emphasis circuit 26R and 126L, Noise reduction circuit 28R12
Each signal is subjected to predetermined signal processing by 8L. Thereafter, the left and right audio signals are manually amplified by the amplifiers 30R130L, and outputted from the terminals 32R13 and 21L to the slave side.

Next, the slave side will be explained. Terminal 34R, 34
The left and right audio signals input to L are sent to the amplifier 36R,
After being amplified by 36L, the noise reduction circuit 3
8R, 38L and pre-emphasis circuits 40R, 40L, respectively. After that, the left and right audio signals are respectively FM modulated by FM modulators 42R and 42L.
In addition to being modulated, a variable resistor 44R for adjusting the recording level
, 44L, the recording amplifier 46
Each is manually powered. The modulated audio signal amplified by the recording amplifier 46 is recorded on the tape 12 by rotating heads 48a and 48b, respectively.

As shown in Figure 2 below, the audio signal recorded on the tape 10 is demodulated on the master side as shown by the arrow FA, sent to the slave side as shown by the arrow FB, and then further demodulated on the slave side as shown by the arrow FC. The signal is modulated and recorded on the tape 50.

[Problems to be Solved by the Invention] However, with the above-mentioned conventional technology, each time dubbing is repeated, periodic noise generated by sample-holding when switching heads, or so-called switching noise, increases, and the sound quality deteriorates. There is an inconvenience that it continues to decline. In addition, the noise reduction circuits 28R, 28L, 38 . By undergoing signal processing by R, 38L, demodulators 22R, 22L, modulators 42R, 42L, etc., faithful reproduction of the original signal waveform is hindered, and this also causes deterioration in sound quality.

The present invention has been made in view of the above problems, and provides an audio signal dubbing method with a good signal-to-noise ratio that can effectively prevent the occurrence of switching noise and maintain good sound quality. This is its purpose.

[Means for Solving the Problems] The present invention provides a method for dubbing an FM audio signal between a master-side video tape recorder and a slave-side videotape recorder using a synchronously driven audio rotary head of a plurality of channels. In the dubbing system, there is a master side transmission path that limits the amplitude of the FM audio signal using a limiter if necessary and outputs the modulated signal to the slave side for each of multiple channels, and the FM audio signal transmitted through this
The apparatus is characterized in that it includes a slave side transmission line that supplies the M audio signal as a modulated signal to the rotary head.

[Operations] According to the present invention, the FM audio signal taken out from the recording medium by the rotating head on the master side is transmitted as a modulated signal to the slave side and recorded on the recording medium on the slave side, and the signal is recovered in the meantime. Processing such as modulation and noise reduction is not performed. Further, amplitude limitation is performed by a limiter as necessary.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings. In addition, in the present invention, in all embodiments, channels 1 and 1 of each rotary head on the master side and the slave side
A circuit is configured for every 2, and both have the same configuration. Therefore, in all embodiments, channel 1 will be mainly explained, and for channel 2, the same number n will be used for similar components.

<First Embodiment> First, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 shows the configuration of a first embodiment. In the figure, a master-side audio rotary head 52 is connected via a preamplifier 54 to an input end of a bandpass filter 56 having a band corresponding to the carrier frequency of the modulated audio signal. The output side of this bandpass filter 56 is connected to the input end of a drive amplifier 58, and the output side of this amplifier 58 serves as a master side output and is connected to a connection line 60.

Next, the connection line 60 is connected to the input end of a bandpass filter 62 on the slave side, and the output side of this bandpass filter 62 is connected to the input end of a recording amplifier 64. The output side of this recording amplifier 64 is connected to an audio rotary head 66 on the slave side.

Furthermore, a GEN ROCK signal is input as an external reference signal to each of the above master side and slave side parts so that the operations of both parts are performed in synchronization. .

Next, the operation of the first embodiment configured as above will be explained. First, in order to perform dubbing, when the master side is set to a playback state and the slave side is set to a recording state, the master and slave sides operate in synchronization with a gen lock signal. In other words, channel 1 (
When the rotary head 52 of channel 2) is reading signals, the slave side operates as if the rotary head 66 of channel 1 (channel 2) is recording signals.

The FM audio signal output from the rotary head 52 on the master side is amplified by a preamplifier 54.

The high frequency (R
F) The signal is inputted to the band pass filter 56, and the F
The carrier frequency component corresponding to the M audio signal is transmitted to the amplifier 58.
is output to. The amplifier 58 adjusts the level of the input signal and sends it to the slave side.

On the slave side, a bandpass filter 62 performs similar filtering on the human FM modulation signal. After the signal is amplified by the recording amplifier 64, the FM audio signal is recorded on a tape (not shown) by the rotary head 66.

As described above, in this embodiment, dubbing is performed without performing processing such as signal modulation/demodulation or noise reduction. Also, as shown in Figure 2, F on the tape
The M audio signal is recorded with an overlap equivalent to three scans (3H) or more with respect to the switching point Q of the rotary head 52 according to the standard. That is, with respect to the signal envelope in the figure, there is a relationship of A≧3H. Therefore, if the rotary head arrangement on the drum is the same on the master side and the slave side, and if the phase offset of the drum servo on the master side and the slave side is within ±3H of the overlap, then each dubbing Dubbing can be performed without increasing head switching noise. Therefore, good sound quality can be maintained.

In this embodiment, when performing dubbing at two speeds, the filtering frequency f of the bandpass filter 56°62. for example from 15 MHz to 3.0 M)
Just double it with Iz.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. This second embodiment is an improvement on the first embodiment. Note that the same reference numerals are used for the same components as in the first embodiment described above (the same applies to the following embodiments).

In the figure, first, the slave side has the same configuration as the first embodiment described above. Next, on the master side, the output side of the preamplifier 54 is connected to a bandpass filter 68 .
40 input terminals, respectively. The output sides of these bandpass filters 68 and 70 are respectively connected to the addition input sides of an adder 72, and the output side of the adder 72 is
It is connected to the output side of the amplifier 58.

In this way, the bandpass filter connected to the output side of the preamplifier 54 is divided into two. The pass frequency band of the band pass filter 68 is set to 1 and 3 MHz, which correspond to the carrier of the left channel audio signal, and the pass frequency band of the band pass filter 70 is set to 1 and 7 MHz, respectively, which correspond to the carrier of the right channel audio signal. There is.

The modulated signals of each of these bands are added after the ratio thereof is appropriately adjusted by an adder 72.

To explain the operation of this second embodiment, the FM audio signal output from the preamplifier 54 is filtered through the bandpass filter 68. '70, and the left and right channel components are extracted here. Each of these components is added at a desired ratio by an adder 72, and then level-adjusted by an amplifier 58 and sent to the slave side.

Currently, in the FM audio signal recording that is normally performed, the higher frequency carrier of the two carriers for the left and right channels (
The signal level of the right) is set approximately 10 CIB higher than the lower frequency (left). In this second embodiment,
Since the carrier level ratio of the left and right channels is adjusted by the adder 72.

It becomes possible to perform dubbing under the same conditions as such normal audio signal recording.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIGS. 4 to 6. FIG. 4 shows the configuration of the third embodiment, and an example of the configuration and characteristics of a limiter included therein are shown in FIGS. 5 and 6, respectively.

In the conventional device, a noise component (approximately 15.4 KHz), which is thought to be the effect of the video system, appears significantly, which increases the background noise level, which is undesirable. One possible cause of this is amplitude fluctuations in the high frequency signal transmitted from the mask side to the slave side, but such amplitude fluctuations cannot be suppressed in the first and second embodiments. This third embodiment is an improvement on this point.

FIG. 4 shows the configuration of the third embodiment. In the figure, a bandpass filter 68 of the second embodiment described above is shown.
．． The input ends of limiters 74 and 76 are connected to the output sides of 70, respectively, and the output sides of these limiters 74 and 76 are connected to the input ends of adder 72, respectively.

By the way, a normal limiter is one in which differential amplifiers are connected in multiple stages and have a large finite gain. but,
The limiters 74 and 76 of this embodiment include, for example, a single-stage differential amplifier 78 and a guide limiter 8 as shown in FIG.
It consists of a soft limiter connected to 0, and the gain is not very large. In the figure, the differential amplifier 78 is mainly composed of NPN type transistors 78A and 78B, and the guide limiter 80 is a diode 80A connected in antiparallel.

It is composed mainly of 80B.

The human output characteristics of such limiters 74 and 76, for example, are shown in graph LA in Figure 6, and compared to the characteristic LB of a normal limiter, the output is suppressed when the human force is small. ing.

Next, the operation of the third embodiment as described above will be explained. The high frequency signals of the left and right channels respectively output from the band pass filters 68 and 70 are input to limiters 74 and 76, respectively. Therefore, the amplitude of each high-frequency signal is limited to a constant value, and amplitude fluctuations are eliminated. The high frequency signals of each channel are added by an adder 72, then amplified by an amplifier 58 and output to the slave side. Note that the operation on the slave side is similar to that of the first embodiment described above.

In this case, since the input/output characteristics of the limiters 74 and 76 are as shown in graph LA in FIG. 6, for example, when no FM audio signal is recorded on the master tape (not shown), That is, when the input to the limiters 74 and 76 is absent or small, the output is also greatly suppressed. This prevents the inconvenience that when no FM audio signal is recorded on the master side, high-level noise is supplied to the slave side and recorded on the tape.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described with reference to FIG. This embodiment uses a hard limiter instead of the soft limiter of the third embodiment. The output side of the bandpass filter 68.70 is connected to the input side of a limiter 82, 84 constituted by a normal hard limiter. In addition, a band pass filter 7o
The non-inverting input side of the comparator 86 is connected to the output side of the comparator 86, and an appropriate reference voltage is input to this inverting input side. One of the selection terminals 5 of the switches 88 and 90 is connected to the output side of the limiters 82 and 84, and the other selection terminal is grounded.

Switches 88 and 90 are operated by the outputs of comparator 86, and their outputs are each connected to the inputs of adder 72. The comparator 86 detects that the bandpass filter 70 is also not outputting an FM audio signal, and the detection output at this time causes the switches 88 and 90 to be switched from the limiter side to the ground side.

Next, the operation of the fourth embodiment as described above will be explained. First, when the FM audio signal is output from the bandpass filter 68.70, the detection operation by the comparator 86 is not performed, and the switches 88 and 90 are connected to the limiter side. For this reason, the bandpass filter 6
The FM audio signal output from the 8°70 is sent to the limiter 82.
．． After amplitude limitation by 84, switch 88.90
are input to the adder 72 via each of them. And each FM
The audio signals are added by an adder 72, further amplified by an amplifier 58, and sent to the slave side.

On the other hand, when the FM audio signal is not output from the bandpass filter 70, that is, when the FM audio signal is not recorded on the tape on the master side, this is detected by the comparator 86, and the switch 88.
is switched to the ground side. In other words, no signal is transferred from the master side to the slave side. This avoids the inconvenience of amplified noise being recorded on the tape on the slave side when no audio signal is recorded on the tape played back on the master side.

This third. According to the fourth embodiment, compared to the conventional dubbing method, the noise level around 15.4 KHz is reduced, the background noise level is also reduced, and the SN ratio can be improved. Furthermore, the fourth embodiment is advantageous in terms of mass production, since it is easier to determine the gain of the limiter than in the third embodiment.

In addition, in the above-mentioned second to fourth embodiments, when dubbing is performed at a speed of 1:1 similar to that during recording, the band frequency f of the bandpass filter 68, for example. 1. ．． 3MHz
, the band frequency f of the bandpass filter 70. 1.7M
Hz, the band frequency f of the band pass filter 62. is set to 15 MHz. However, when double-speed dubbing is performed, the band frequency f0 of the bandpass filter 68 is set to 2.
6 MHz, and the band frequency of the band pass filter 70 is f.

is 3.4 MHz, and the band frequency f of the band pass filter 62 is 3.4 MHz. 3. Let it be OMHz.

<Other Examples> Note that the present invention is not limited to the above embodiments. For example, in the embodiment described above, a gen lock signal was used to synchronize the master side and slave side.
In addition, for example, the reproduced video signal output on the master side may be used as a servo reference on the slave side. Furthermore, the circuit configuration can be modified in various ways to achieve the same effect, and these are also included in the present invention.

[Effects of the Invention] As explained above, according to the present invention, a transmission path is provided from the master side to the slave side for each channel of the rotary head for FM audio signals, and the FM audio signals are transmitted as modulated signals. As a result, it is possible to effectively prevent the occurrence of switching noise, and it is also possible to dub an audio signal with a good SN ratio while maintaining good sound quality.

[Brief explanation of drawings]

1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is an explanatory diagram showing the operation of the first embodiment, FIG. 3 is a block diagram showing a second embodiment of the present invention, and FIG. 5 is a circuit diagram showing an example of the structure of the limiter of the third embodiment, FIG. 6 is a graph showing an example of the characteristics of the limiter of the third embodiment, and FIG. FIG. 7 is a block diagram showing a fourth embodiment of the present invention, and FIG. 8 is a block diagram showing an example of a conventional dubbing device. 52... Rotating head for audio, 54... Preamplifier,
56.62.68.70...Band pass filter, 5
8... Amplifier, 60... Connection line, 64... Recording amplifier, 66... Audio rotary head, 72... Adder, 74.76.82.84... Limiter, 78...・・・
Differential amplifier, 80...Diode limiter, 86...
・Comparator, 88.90...switch. 0 20- JP-A-3 119502 (10)

Claims (1)

[Scope of Claim] An audio signal dubbing method in which dubbing of an FM audio signal between video tape recorders on a master side and a slave side is performed using rotary heads for audio of a plurality of channels that are synchronously driven, comprising: A master side transmission line that limits the amplitude of the signal using a limiter if necessary and outputs it to the slave side as a modulated signal for each multiple channels, and rotates the FM audio signal transmitted by this line as a modulated signal. An audio signal dubbing method characterized by comprising a slave-side transmission line that supplies a signal to a head.