JP2695172B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a helical scan type magnetic recording / reproducing apparatus capable of recording and reproducing an audio signal by a rotating head and a fixed head.

[Conventional technology]

Conventional. When recording a television signal on a magnetic tape, the audio signal is recorded in the deep layer of the magnetic tape by the rotary head, and the video signal is recorded on the shallow layer of the magnetic tape by the rotary head. Helical scan magnetic recording / reproducing device (hereinafter referred to as VTR)
It has been known. This is because the relative speed between the tape and the head is increased to record and reproduce the audio signal, which results in high S / S.
It is usually called a HiFiVTR because it can obtain N reproduced voices. Furthermore, as disclosed in, for example, Japanese Patent Laid-Open No. 59-124008, an audio signal is transmitted in the longitudinal direction of the magnetic tape by a fixed head. A VTR has been proposed that enables the recording of audio, and replays only the audio after recording, and the playback of magnetic tapes with audio signals recorded only in the longitudinal direction, such as commercially available soft tapes. There is.

In such a conventional VTR, the same phonetic symbol is FM-modulated on the one hand and deeply recorded in a diagonal direction with respect to the longitudinal direction of the magnetic tape by the rotating head, and on the other hand, written in the longitudinal direction of this magnetic tape by the fixed head. To be done. At the time of reproduction, the audio signal is reproduced by the rotary head and the fixed head respectively, and the detection circuit detects the presence or absence of the reproduced audio signal by the rotary head. Based on the detection result, the reproduced audio signal from the normal rotary head is detected. Is selected as the VTR playback output, but when the playback audio signal signal from the rotating head is not detected, the playback audio signal from the fixed head is selected as the playback output.

During post-recording, the VTR is set to a video signal reproduction mode and a fixed head audio signal recording mode, which enables recording of the fixed head audio signal while monitoring the image. Also, when playing back the dubbed magnetic tape, this is usually displayed when the dubbing portion of this magnetic tape is played, and by performing a predetermined operation,
Even if there is a reproduced voice signal from the rotating head, the reproduced voice signal from the fixed head can be selected as the reproduction output. If you do not record the audio signal during recording and then post-record,
During reproduction, the audio signal automatically post-recorded by the detection circuit is selected as the reproduction output.

[Problems to be solved by the invention]

By the way, in the above-mentioned conventional VTR, when the level of the reproduced audio signal by the rotating head drops due to dropout or tracking deviation, the detection circuit detects it and selects the reproduced audio signal by the fixed head as the reproduction output. To do. This makes it possible to prevent interruption of the audio signal.

However, in the case where dropout or tracking deviation occurs frequently in the reproduction scanning of the audio track due to the rotary head, the switch for switching between the reproduced audio signal by the rotary head and the reproduced audio signal by the fixed head is detected by the detection result of the detection circuit. Will be switched frequently. On the other hand, since there is a slight difference in the DC level and phase between the audio signal reproduced by the rotating head and the audio signal reproduced by the fixed head, and the reproduction output becomes discontinuous at the time of switching the switch, the switch is frequently switched. Then, abnormal sound is mixed in the reproduced sound, and the sound quality may be uncomfortable to hear.

An object of the present invention is to solve the above-mentioned problems, prevent frequent switching of the reproduced audio signal by the rotating head and the reproduced audio signal by the fixed head, and improve the reproduced sound quality. To provide.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a time constant circuit for delaying a trailing edge of an output signal of a detection circuit indicating that the level of a reproduced audio signal due to a rotary head is lowered, for a predetermined period. The output signal is used as the switch control signal.

[Action]

When the level of the reproduced audio signal decreases again within the above-mentioned predetermined period after the end of the level reduction period of the reproduced audio signal due to the rotating head, the time constant circuit continues to output the signal, and the switch outputs the reproduced audio signal from the fixed head. Control to select. As a result, when the level of the reproduced voice signal from the rotary head is frequently lowered, the switch operates as if the level of the reproduced voice signal from the rotary head is continuously lowered for a period including the level reduction period. Therefore, during the period in which the level of the reproduced voice signal by the rotating head is frequently lowered, the reproduced voice signal by the fixed head is continuously selected, and the switch is not switched during that period.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention, in which 1,1 'is an audio signal input terminal, 2,2' is an audio signal output terminal, and 3 is an audio processing circuit. ,
4,4 'is a voice recording circuit, 5,5' is a voice reproducing circuit, 6,7 is a signal switching circuit, 8,8 'is an FM modulating circuit, 9 is a mixing circuit, 10 is an amplifying circuit, and 11 is a signal switching circuit. , 12 is an input terminal for a head switching signal, 13 is a preamplifier, 14 and 14 'are BPFs (band pass filters), 15 and 15' are FM demodulation circuits, 16 is a detection circuit, 17 is a time constant circuit, and 18 and 18 '. Is a signal switching circuit, 19 is a video signal input terminal, 20 is a video signal output terminal, 21 is a video processing circuit,
22 is a rotary transformer, 23 and 24 are rotating video heads, 25 and 26
Is a rotary voice head, and 27 and 28 are fixed voice heads.

In the figure, during recording, an audio signal is input from each of the input terminals 1 and 1 ′ and a video signal is input from each of the input terminals 19. Here, recording and playback of stereo signals and audio multiplex signals are also possible, and in the case of stereo signals, the input terminal
The right channel signal is input to one of 1, 1 ', and the left channel signal is input to the other, and in the case of a voice multiplexed signal, the main signal is input to one of the input terminals 1, 1'and the sub signal is input to the other. However, here, the input signals at the input terminals 1 and 1'are both referred to as audio signals.

The audio signals input from the input terminals 1, 1'are processed by the audio recording circuits 4, 4'of the audio processing circuit 3, respectively, and then supplied to the fixed audio heads 27, 28 via the signal switching circuits 6, 7. Is
It is recorded in the length direction of a magnetic tape (not shown).

Also, the audio signals input from the input terminals 1 and 1'are different carrier frequencies f ₁ and f _{2 in the} FM demodulation circuits 8 and 8 ', respectively.
The signals are FM-modulated, mixed in the mixing circuit 9, amplified by the amplifier circuit 10, and then supplied to the rotary audio heads 25 and 26 via the signal switching circuit 11 and the rotary transformer 22.

Further, the video signal input from the input terminal 19 is supplied to the video processing circuit 21. In this video signal processing circuit 21,
The video signal is separated into a luminance signal and a carrier color signal, the luminance signal is FM-modulated, and the carrier color signal is low-frequency converted and mixed. The video signal thus processed is supplied to the rotary video heads 23 and 24 via the rotary transformer 22.

Here, rotating video heads 23 and 24, rotating audio heads 25 and 26
Are provided in the same head cylinder, the magnetic tape runs diagonally over the outer circumference of the head cylinder at approximately 180 °, and the head cylinder rotates in one frame cycle of the video signal, so that the rotation video signal 23, 24 and the rotary audio heads 25 and 26 alternately scan the magnetic tape in an oblique direction with respect to its longitudinal direction. In addition, the rotating video head 23 scans the magnetic tape following the rotating audio head 25,
The rotating video head 24 scans the magnetic tape following the rotating audio head 26. The FM-modulated audio signal is a rotary audio head.
The video signals are recorded in the deep layer portion of the magnetic tape by 25 and 26, and the video signals are recorded in the shallow layer portion of the magnetic tape by the rotating video heads 23 and 24. Further, the signal switching circuit 11 is supplied from the input terminal 12 with a head switching signal representing the magnetic tape scanning period of the rotary audio heads 25 and 26 at a cycle equal to the rotational cycle of the head cylinder, and the output signal of the amplifier 10 is a signal. The switching circuit 11 supplies the rotating audio heads 25 and 26 to the person scanning the magnetic tape.

As described above, the audio signal is simultaneously recorded on the diagonal audio track and the longitudinal audio track of the magnetic tape.

 Next, the reproducing operation of this embodiment will be described.

The video signals alternately reproduced from the shallow layer portion of the magnetic tape by the rotary video heads 23 and 24 are supplied to the video processing circuit 21 via the rotary transformer 22 and are combined into a continuous signal to obtain the luminance. The signal is FM demodulated and the carrier color signal is frequency converted to the original frequency band. The luminance signal and the carrier color signal are combined to form the original video signal, which is output from the output terminal 20.

On the other hand, the audio signal alternately reproduced from the deep layer of the magnetic tape by the rotary audio heads 25 and 26 is passed through the rotary transformer 22 and the signal switching circuit 11 controlled by the head switching signal from the input terminal 12 is supplied. To be a continuous audio signal. Thereafter audio signal is amplified by the preamplifier 13, is separated into different audio signals are supplied to BPF14,14 'with the carrier frequency f _1, f _2. These audio signals are FM-demodulated by the FM demodulation circuits 15 and 15 'and then supplied to the signal switching circuits 18 and 18'. The audio signals reproduced from the longitudinal audio tracks of the magnetic tape by the fixed audio heads 27 and 28 are processed by the audio reproduction circuits 5 and 5'of the audio processing circuit 3 via the signal switching circuits 6 and 7, respectively. It is supplied to the signal switching circuits 18, 18 '.

The FM-modulated voice signal output from BPF14, 14 'is
It is also supplied to the detection circuit 16. The detection circuit 16 synthesizes these audio signals, determines the level of the synthesized signal, and detects a period having a level lower than a preset threshold value.

Therefore, if there is a period in which the output signal of the preamplifier 13 is at a level lower than the threshold due to dropout or the like as shown in FIG.
As shown in FIG. 2 (b), outputs a detection signal that is low level during the level period above the threshold of the output signal and high level during the period below the threshold level. This detection signal is supplied to the time constant circuit 17, and as shown in FIG. 2 (c), the rising edge of the detection signal (FIG. 2 (b)) rises for a predetermined time T.
Only be delayed. That is, the time constant circuit 17 outputs a high level signal which rises at the rising edge of the detection signal shown in FIG. 2B and falls after a predetermined time T from the rising edge of this detection signal. Then, when a high level detection signal is again supplied to the time constant circuit 17 within a predetermined time T from the falling edge of the detection signal (FIG. 2 (b)), the output signal of the time constant circuit 17 remains at the high level. To maintain. Therefore, as shown in FIG. 2, the output signal of the preamplifier 13 is lowered in level and becomes high again, and if the level is lowered frequently such that the level is lowered again within a predetermined time T from now on, this frequency is increased. While the level is decreasing, the output signal of the time constant circuit 17 is continuously at the high level.

The output signal of the time constant circuit 17 is supplied to the signal switching circuits 18 and 18 'as a switching control signal. These signal switching circuits 18,
In 18 ', when the output signal of the time constant circuit 17 is at a low level, the rotary audio head 2 output from the FM demodulation circuits 15, 15'
A fixed audio head 27 is output from the audio reproduction circuit 5, 5'when the reproduced audio signal by 5,26 is selected and output from the output terminals 2, 2 ', but when the output signal of the time constant circuit 17 is at a high level. , 28 playback audio signal is selected and output terminal 2,
It is output from 2 '.

As described above, when the reproduced audio signals from the rotary audio heads 25 and 26 are frequently lowered in level due to dropout, the signal switching circuits 18 and 18 'continuously output the reproduced audio signals from the fixed audio heads 27 and 28. Selected and not switched frequently. Therefore, the rotary voice head 25,2
Even if there is a frequent drop in the level of the playback audio signal due to 6,
No abnormal sound is mixed in the reproduced sound to deteriorate the audible sound quality.

At the time of after-recording, the video processing circuit 21 is set to the reproduction mode, the audio recording circuits 4 and 4'in the audio processing circuit 3 are in the operating state, and the signal switching circuits 6 and 7 are connected to the audio recording circuits 4 and 4 '. It operates to provide an output signal to the fixed audio heads 27, 28. In addition, the voice signal input to the input terminals 1, 1'by the signal switching circuit 11 or the like is transmitted to the rotary voice head 25,
Supply to 26 is prohibited. As a result, it is possible to newly record an audio signal on the audio track in the longitudinal direction of the magnetic tape by the fixed audio heads 27 and 28 while monitoring the image.

Although not shown, the signal switching circuits 18 and 18 'are controllable by manual operation in order to enable reproduction of the post-recording portion. With dubbing, there are cases where part of the audio signal already recorded on the magnetic tape is re-recorded with a new audio signal, and there is a case where it is recorded in the part where the audio signal is not recorded at the time of recording. When the post-recording portion is reproduced by the fixed audio heads 27, 28 by a suitable display means, the post-recording is performed by manually switching the signal switching circuits 18, 18 '. It becomes possible to listen to the sound. Further, in the latter case, since the voice signal is not recorded by the rotary voice heads 25 and 26 in the post-recorded portion of the magnetic tape, the detection circuit 16 detects this and automatically switches the signal switching circuit.
18, 18 'selects the reproduced voice signal after-recorded by the fixed voice heads 27, 28.

FIG. 3 is a block diagram showing a specific example of the time constant circuit 17 in FIG. 1, in which 29 is an input terminal, 30 is an edge detection circuit, 31 is a transistor, 32 is a resistor, 33 is a capacitor, and 34 is a capacitor.
Is a level comparator, 35 is a voltage source, 36 is an OR circuit, and 37 is an output terminal.

In the figure, from the input terminal 29 to the detection circuit 16 (Fig. 1)
Detection signal is input, the edge detection circuit 30 and the OR circuit 36
And supplied to. When this detection signal is at a low level (that is, when the level of the reproduced audio signal of the audio rotary heads 25, 26 (FIG. 1) is above the threshold value), no signal is output from the edge detection circuit 30 and the transistor 31 is turned on. Since it is held in the off state, the capacitor 33 is fully charged with the power supply voltage V _cc . Charging voltage of capacitor 33
E _c is compared by the level comparator 34 with the reference voltage E _s of the voltage source 35, but when the capacitor 33 is fully charged, E _c
> E _s, which is why the output signal of the level comparator 34 is low. This output signal is supplied to the detection signal input to the input terminal 29 and the OR circuit 36. Therefore, the signal switching circuit 18, 1 obtained from the OFF circuit 36 to the output terminal 37.
The switching control signal 8 '(FIG. 1) is at a low level.

When the detection signal input to the input terminal 29 becomes high level (that is, when the reproduced audio signal by the rotary audio heads 25 and 26 (FIG. 1) becomes lower level than the above threshold), the OR circuit 36 outputs to the output terminal 37. The switching control signal obtained at 1 becomes high level. Then, the edge detection circuit 30 detects the falling edge of the detection signal and generates a short pulse, and the pulse causes the transistor 31 to be turned on for a short period. Therefore, the capacitor 33 is discharged through the transistor 31, and when the transistor 31 is turned off again, charging is started with a time constant determined by the resistance value of the resistor 32 and the electrostatic capacitance of the capacitor 33. At this time, the charging voltage E _c of the capacitor 33 becomes lower than the reference voltage E _s when the transistor 31 is turned on, and then becomes higher than the reference voltage E _s as it is charged with the above time constant. Therefore, the output signal from the level comparator 34 is high level during the period from when the transistor 31 is turned on until E _c = E _s (this period is the period T shown in FIG. 2), This output signal is supplied to the OR circuit 36. OR circuit
In 36, the high level signal of the period T output from the level comparator 34 is spliced in the high level period of the detection signal input to the input terminal 29, and accordingly, the output terminal
In the high level period of the switching control signal obtained at 37, the high level period of the detection signal input from the input terminal 29 is extended by the period T.

When the level of the reproduced audio signals of the rotary audio heads 25 and 26 frequently drops, and the capacitor 33 causes the detection signal input to the input terminal 29 to reach a high level again before the charging voltage E _c reaches the reference voltage E _s , A high level signal is supplied to the OR circuit 36 from the input terminal 29 before the output signal of the level comparator 34 becomes low level, and the transistor 31 is turned on at the falling edge of this high level signal. Since the capacitor 33 is discharged, the switching control signal obtained at the output terminal 37 continues to be at a high level at least until the period T elapses after the falling edge of the high-level signal from the input terminal 29. Therefore, when the detection signal input to the input terminal 29 frequently becomes high level, the switching circuit signal obtained at the output terminal 37 is continuously held at high level during the period in which the level frequently changes.

It is needless to say that FIG. 3 shows only an example of the time constant circuit 17, and that another structure having the same function can be used. As the setting of the period T, a good result was obtained in 100 msec to 200 msec, but it should be set appropriately depending on the FM carrier frequency, the characteristics of the demodulation circuit, and the like.

〔The invention's effect〕

As described above, according to the present invention, it is possible to significantly reduce the number of switching operations of the signal switching circuit for switching between the reproduced audio signal by the rotary audio head and the reproduced audio signal by the fixed audio head, and the switching operation is performed. It is possible to obtain an excellent effect of significantly reducing the noise caused by, and preventing deterioration of the sound quality of the reproduced voice.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention, FIG. 2 is a waveform diagram showing main signals in FIG. 1, and FIG. 3 is a concrete example of a time constant circuit in FIG. It is a block diagram which shows. 1,1 '... Voice signal input terminal, 2,2' ... Voice signal output terminal, 3 ... Voice processing circuit, 8,8 '... FM modulation circuit,
9 ... Mixing circuit, 14,14 '... Band pass filter, 15,1
5 '... FM demodulation circuit, 16 ... detection circuit, 17 ... time constant circuit, 18,18' ... signal switching circuit, 25,26 ... rotation voice head, 27,28 fixed voice head.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masaaki Hirano Inventor Masaaki Hirata 1410 Inada, Katsuta City, Ibaraki Hitachi Ltd. Tokai Plant (56) Reference JP-A-58-114678 (JP, A)

Claims (1)

(57) [Claims] 1. An identical audio signal is recorded on a magnetic tape by a rotary head and a fixed head, and during reproduction, a missing period of a reproduced audio signal by the rotary head is detected by a detection means, and the output signal of the detection means is used. In the magnetic recording / reproducing apparatus configured to control the signal switching circuit so as to select the reproduction audio signal by the fixed head instead of the reproduction audio signal by the rotary head, the omission of the output signal of the detecting means. The signal period is extended for a predetermined period for each signal period indicating the period, and when the output signal of the detecting means is the signal period indicating the next missing period within the signal period extended for the predetermined period, the predetermined period A time constant circuit for continuing the signal period representing the next missing period to the signal period extended by the period time is provided, and the output signal of the time constant circuit is switched by the signal switching circuit. As a control signal, the signal switching circuit controls the signal switching circuit to select a reproduced audio signal by the fixed head, so that the fixed period is continuously fixed during a period in which the missing period frequently occurs. A magnetic recording / reproducing apparatus characterized in that a reproduced audio signal from a head can be selected.