JP2672207B2 - Magnetic recording and reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus, and more particularly to a magnetic recording / reproducing apparatus for recording an audio signal on a long-time VTR (video tape recorder) for monitoring which is mainly used for crime prevention.

[0002]

2. Description of the Related Art In general, a long-time VTR for monitoring uses a magnetic tape as a magnetic recording medium to intermittently run a magnetic tape in order to record video and audio for as long a time as possible. Is to record only the field of the selected video signal within the period when the magnetic tape is running. For the audio signal, the continuous analog audio signal is converted to a digital signal and time-axis compressed. Is magnetically recorded on the intermittently running magnetic tape.

FIG. 6 is a block diagram of a conventional magnetic recording / reproducing apparatus disclosed in Japanese Patent Application No. 2-216540. In FIG. 6, 1 is a video input terminal, 2 is a video signal amplifier, 3 is a video signal recording circuit for FM-modulating a video signal, and 4a is a mode change switch for switching the input / output of the video head between a recording mode and a reproduction mode, Reference numeral 5 is a video signal reproducing circuit for demodulating an FM signal detected from the magnetic tape during reproduction, 6 is a video output terminal, 7 is two rotary video heads VR and VL and two rotary audio heads A for deep recording.
A rotary drum 8 having R and AL is an intermittent drive and head switching circuit for intermittently advancing the magnetic tape and switching the head of the rotary drum 7.

On the other hand, in the audio circuit, an analog audio signal input to the audio input terminal 9 is digitized by the A / D converter 11 via the audio signal amplifier 10 and the mode changeover switch 4b. RAM1 for storing
2. D / A the digital signal stored in RAM12 again
The signals are sequentially input to the D / A converter 13 for conversion. Reference numeral 14 denotes a first reference clock generation circuit that controls a series of circuits that digitally processes the analog signal, the output of which is divided into two, and the time axis compression that compresses the time axis of the signal stored in the RAM 12 is performed. And a time axis expander 16 for expanding the time axis compression reproduction analog signal which operates at the time of reproduction. Time axis compressor 15
And two outputs provided on the time axis expander 16 are transfer mode switch 4c,
It is connected to the switching terminal of 4d. The COM terminal of the mode changeover switch 4c has an A / D converter 11 and a RAM.
12, and the COM terminal of the mode changeover switch 4d is connected to the RAM 12 and the D / A converter 13.

The output of the D / A converter 13 is connected to one switching terminal of the mode switching switch 4f via the mode switching switch 4e and the recording amplifier 18.
The other switching terminal of the mode switching switch 4f is connected to the FM demodulator 20 via the regenerative amplifier 19, and further connected to one terminal of the mode switching switch 4b. The FM demodulator 20 operates during reproduction and is reproduced by the rotary audio heads AR and AL.
It functions to demodulate the M signal and obtain a reproduced analog signal whose time axis is compressed. Mode changeover switch 4
The other terminal of e is connected to the audio output terminal 22 via the reproduced audio signal amplifier 21. The mode changeover switches 4b, 4c, 4d, 4e, and 4f are formed so as to be switched at the same timing as the mode changeover switch 4a for switching between the recording mode and the reproduction mode of the audio signal.

Next, the operation will be described. First, the audio signal amplified by the audio signal amplifier 10 passes through the mode changeover switch 4b, is converted into a digital signal by the A / D converter 11, and is written in the RAM 12. Next, the RAM is clocked with a clock having a frequency higher than the sample clock when the audio signal is converted into a digital signal by the A / D converter 11.
The digital audio signal written in 12 is read out, and D /
By returning to the analog signal again by the A converter 13, the time axis compressed analog audio signal is obtained. A clock for controlling this series of compression sequences is generated by the time axis compressor 15 based on the first reference clock generated by the first reference clock generation circuit 14 and supplied through the mode changeover switches 4c and 4d. It The time-axis-compressed audio signal is FM-modulated by the FM modulator 17, and the recording amplifier 18
Rotating audio heads AR and AL of the rotating drum 7
To be recorded on a magnetic tape.

On the other hand, the video signal is input from the video input terminal 1, FM-modulated by the video signal amplifier 2 and the video signal recording circuit 3, and recorded on the magnetic tape by the rotary video heads VR and VL through the mode changeover switch 4a. It The relationship between the video signal and the audio signal recorded on the magnetic tape is as follows.

As shown in FIG. 7 (a), the video signal from the television camera is sent out in order of V0, V1 ,. On the other hand, the audio signal from the microphone or the like is sequentially sent out as A0, A1, ... As shown in FIG. 7 (b). Originally, these audio signals have no reference signal and are transmitted as continuous analog signals. However, for convenience of explanation, it is easier to understand that the audio signal is also time-separated, so in FIG.
, ... are named and shown. In a general VTR for continuous recording, a magnetic tape runs at a constant speed, and a video signal is diagonally V0 and V1 by a rotary video head.
, Etc., and the audio signal is recorded by a fixed linear audio head with A0, A on the tape width of 1 mm.
It is recorded continuously, such as 1. However, in the intermittent VTR, the traveling speed of the magnetic tape is stepped as shown in FIG. 8A, and only the field (or frame) of the selected video signal is recorded during the traveling period of the magnetic tape. To be done. So, first,
As the audio signal, a continuous analog audio signal of A11 to A40 for 0.333 seconds is converted into a digital signal as described above, time-axis-compressed, and as shown in FIG.
Stored in 12. Thus, the audio signal is temporally all information (A11A12-A39A40) (A41A42-A69A).
70) is compressed and stored. On the other hand, the video signal is
V11 of 0.333 seconds from V11 to V40 continuously,
Only the V12 field and only the V41 and V42 fields in 0.333 seconds from V41 to V70 are selected and recorded.

Next, the operation during reproduction will be described. An FM signal obtained by further FM-modulating the audio signal compressed on the time axis by the above-mentioned recording system is deeply recorded on the magnetic tape, and the video F
The magnetic tape on which the M-modulated signal is recorded on the surface layer is attached to the rotary drum 7.
The rotary heads VR, VL, AR and AL are used for reproduction. First, the video FM modulated signal is the mode changeover switch 4a.
The video signal is reproduced by the video signal reproduction circuit 5 and output to the video output terminal 6. Next, the deeply recorded audio FM signal is demodulated by the FM demodulator 20 to obtain a time-axis-compressed audio signal. The time-base compressed audio signal is input to the time-base decompressor 16 with the first reference clock generated by the first reference clock signal generation circuit 14 which is the same as during recording, and the A / D converter is supplied. 11, RAM12, D
/ A converter 13 to extend the time axis,
It passes through the mode changeover switch 4e, is amplified by the reproduced audio signal amplifier 21, and is output to the audio output terminal 22.

FIG. 8 shows a state of a video signal and an audio signal at the time of reproduction, and as shown in FIG. 8 (a), the running speed of the magnetic tape at the time of reproduction also becomes stepwise as at the time of recording. When the magnetic tape runs and the playback track moves,
For example, fields V41 and V42 are reproduced by the rotating video heads VR and VL of the rotating drum 7, the magnetic tape is stopped, and the video signal continues to reproduce V42 until the next magnetic tape running. Rotating audio head AR of the rotating drum 7,
AL reproduces the deep recording portion, is time-axis expanded by the above-mentioned procedure, and continuously reproduces until the next magnetic tape runs, thereby obtaining a continuous voice.

[0011]

FIG. 9A shows a recording state of an audio signal. The audio signal during the time T of the input audio signal shown in (a) is time-axis compressed by the compression rate 1 / α. , Is compressed at time T / α and recorded deeply. now,
Assuming that there is no fluctuation in the time axis of the magnetic recording / reproducing system, FIG. 9B
As shown in (d), a reproduced FM signal of the same time T / α as that at the time of recording is obtained, and after demodulating this, the time axis extension is performed by α times, so that continuous audio can be obtained as shown in (d). . However, when a magnetic recording medium (magnetic tape) is intermittently sent and an audio signal is recorded by a rotary head and simultaneously recorded with a video signal, the writing time at the time of recording and the time at the time of reproducing are inevitable. Will be different. Considering the case where β is the ratio of the fluctuation and β> 1, as shown in FIG. 9C, the reproduced FM signal is reproduced for the length of time Tβ / α, and if this is expanded on the time axis at the expansion rate α, It becomes Tβ, which is longer than the intermittent cycle T. Therefore, as shown in (f), for example, the reproduced sound A10 is switched to the reproduced sound A11 in the middle thereof, and an abnormal sound is generated.

Considering the case of β <1, as shown in FIG. 9D, the reproduced FM signal is reproduced for the length of time Tβ / α, and when this is expanded in the time axis at the expansion rate α, it becomes Tβ. It becomes shorter than the intermittent cycle T. As a result, as shown in (h), for example, after the reproduction sound A10 ends, the reproduction sound A11 becomes silent, and then the reproduction sound A11 is heard, resulting in an unnatural sound output signal.

As described above, the conventional long time VTR for monitoring
Since a magnetic recording / reproducing apparatus for recording an audio signal on a recording medium is configured so that the compression rate at the time of recording the audio signal and the expansion rate at the time of reproduction are always the same, for example, the time axis fluctuation is caused in the magnetic recording / reproducing process. If there is, there is a problem that the time-axis-extended audio signal does not continue during playback and an abnormal noise is generated. Further, in a long-time VTR in which a magnetic tape is intermittently run and a video signal is recorded and reproduced by a rotary head, so-called STILL reproduction, which is a reproduction of the magnetic tape in a stopped state during reproduction, is usually the main component. In this case, since the trajectory of the rotary head tracing the recording track and the angle of the recording track are different, the video signal is reproduced by setting the rotational speed of the rotary head during reproduction to a rotational speed different from that during recording. Therefore, there is a problem that there is always a reproduction time difference of one track between recording and reproduction, and the audio signal is not continuous. Therefore, there is a problem that the above problem must be solved.

The present invention has been made to solve the above-mentioned problems, and when a voice signal is time-axis compressed and magnetically recorded and expanded to be reproduced, a time-axis fluctuation occurs in a recording / reproducing system. It is an object of the present invention to provide a magnetic recording and reproducing device that can output a continuous reproduced audio signal without any sound or interruption.

[0015]

In order to achieve the above object, a magnetic recording apparatus according to claim 1 has an A / D converter for converting an analog signal into a digital signal and a RAM for temporarily storing the digital signal. A D / A converter for converting the digital signal output of the RAM into an analog signal, and a first reference clock generation circuit for generating a reference clock of an arbitrary frequency which is a reference for a series of signal processing operations. There is.

Further, the reference clock generated by the first reference clock generating circuit is frequency-divided, and this frequency-divided output is divided into the above A.
/ D converter, RAM, and D / A converter and time-axis compressor for time-axis compression of analog signal, FM modulator for FM-modulating the time-axis-compressed analog signal, and FM modulation And an FM signal which is the output of the container and a reference clock of an arbitrary frequency generated by the first reference clock generation circuit, which is time-sequentially switched and recorded on the magnetic recording medium.

Furthermore, magnetic playback apparatus according to the second aspect,
A signal reproducing means for reproducing a signal recorded in time series on the magnetic recording medium, a reproduction signal output from the signal reproducing means is time-axis-compressed and FM-modulated analog signal, and the first reference. responsibility, which is output from the clock generation circuit
A switch for separating a reproduction first reference clock, which is a reproduction signal of a reference clock having a desired frequency, and a second circuit configured to oscillate a PLL circuit using the reproduction first reference clock as an input.
Of the reference clock generating circuit, an FM demodulator for demodulating a time-axis-compressed and FM-modulated analog signal, a signal demodulated by the FM demodulator, and a reference clock obtained from the second reference clock generating circuit. The signal obtained by frequency division is digitized, and a signal obtained by dividing the reference clock of an arbitrary frequency output from the first reference clock generation circuit is supplied to the RAM and the D / A converter, And a variable time axis expander for axial expansion.

[0018]

In the magnetic recording / reproducing apparatus according to the present invention, at the time of recording, the reference clock for determining the compression ratio at the time of recording is recorded together with the audio signal, and the reference clock is reproduced at the time of reproduction, so that the time axis fluctuation in the recording / reproduction is suppressed. Get the recovered reference clock. Then, the reproduced audio signal is expanded on the time axis by the reference clock generated by the second reference clock generation circuit which constitutes the PLL based on the reproduction reference clock including the time axis fluctuation. Therefore, since the time base fluctuation in the recording / reproducing system is included in the reproduction reference clock, by expanding the time axis of the audio signal based on the reproduction reference clock during reproduction, the time base fluctuation in the recording / reproducing system is not affected. , It is possible to reproduce a continuous audio signal without interruption.

[0019]

EXAMPLES The following first embodiment, will be described with reference to associated drawings an embodiment of the present invention. FIG.
FIG. 1 is a configuration diagram of an embodiment of a magnetic recording and reproducing apparatus according to the present invention. In the figure, a video input terminal 1, a video signal amplifier 2, a video signal recording circuit 3 for FM-modulating a video signal, a mode selector switch 4a for switching the input / output of a video head between a recording mode and a reproducing mode, and a magnetic tape detected during reproduction. Video signal reproducing circuit 5 for demodulating the generated FM signal, video output terminal 6, two rotary video heads V
R, VL and two rotary audio heads AR for deep recording
, AL, an intermittent drive and head switching circuit 8 for switching the head of the rotating drum 7 while advancing the magnetic tape intermittently, an audio input terminal 9, an audio signal amplifier 10, a mode switching switch 4b, A / D converter 11, RAM 12 for storing digital audio signals, RA
D / for D / A converting the digital signal stored in M12
A converter 13, first reference clock generation circuit 14, time axis compressor 15, mode changeover switches 4c and 4d, mode changeover switch 4e, FM modulator 17, recording amplifier 18, mode changeover switch 4f, reproduction amplifier 1
9, the FM demodulator 20, the reproduced audio signal amplifier 21, and the audio output terminal 22 are formed in the same manner as the conventional example already described with reference to FIG.

Reference numeral 30 denotes a switch which switches at the time of recording according to the timing generated from the intermittent drive and the head switching signal from the head switching circuit 8, and the output of the FM modulator 17 which is a time-compressed and FM-modulated audio signal. , And the first reference clock from the first reference clock signal generation circuit 14 for generating the reference clock to be supplied to the time axis compressor 15. Reference numeral 31 denotes a switch that switches at the same timing as the switch 30 at the time of reproduction, and functions to separate the reproduction FM signal and the reproduced first reference clock from the reproduction signal of the deep recording portion.
Further, 32 is a second reference clock generation circuit that takes in the above-mentioned reproduced first reference clock and constitutes a PLL (phase locked loop) to oscillate, and 33 is a variable time axis expander, and 2 reference clock generation circuit 32
By dividing the second reference clock output by
A clock to be supplied to the mode changeover switch 4d is supplied by creating a reference clock to be supplied to the mode changeover switch 4c and dividing the first reference clock output from the first reference clock generation circuit 14. is there.

Next, the operation of the apparatus shown in FIG. 1 will be described with reference to FIG. FIG. 3 shows the relationship between the video signal at the time of recording the intermittent cycle T, the FM modulation signal of the time-axis compressed audio, and the reference signal.

First, the operation of the recording system will be described.
The audio signal input to the audio input terminal 9 is amplified by the audio signal amplifier 10, passes through the mode changeover switch 4b, and is input to the A / D converter 11. Next, the first reference clock of the cycle t generated by the first reference clock generation circuit 14 is supplied to the time-base compressor 15 and frequency-divided, and the cycle is set to at, passing through the mode changeover switch 4c. The audio signal is sampled by being supplied to the / D converter 11 and the RAM 12, and is converted into a digital signal for RA.
It is stored in M12. Next, the first reference clock is frequency-divided by the time axis compressor 15, and the cycle is set to bt and R
It is supplied to the AM 12 and the D / A converter 13, and R is supplied as described above.
Read the digital signal stored in AM12, and D / A
The converter 13 restores the analog signal again. as a result,
This analog signal is a time-axis compressed audio signal whose time axis is compressed to bt / at = b / a. The compression rate can be arbitrarily set by the frequency division ratios a and b of the time axis compressor 15. This time-axis compressed audio signal is FM-modulated by the FM modulator 17 through the mode changeover switch 4e.

The FM-modulated time-base compressed audio signal and the first reference clock output from the first reference clock generation circuit 14 are switched by the switch 30.
Passing through the recording amplifier 18 and the mode selector switch 4f,
Deep recording is performed by the rotary audio heads AR and AL of the rotary drum 7. An example of the switching timing of the switch 30 is shown in FIG. On the other hand, the video signal is the same as in the conventional example shown in FIG. 6, and the rotary video heads VR and VL of the rotary drum 7 are used.
Is recorded on the surface.

Next, the operation during reproduction will be described with reference to FIG. FIG. 4 shows the relationship between the time axis compression during recording and the variable time axis expansion during reproduction. First, the video signal is output to the video output terminal 6 by the same method as the conventional technique. Next, regarding the reproduction of the deep recording portion, if there is a time-axis fluctuation β between the time of magnetic recording and the time of reproduction, the duration of the FM signal of the time-axis-compressed audio becomes bTβ / a. , And the period of the first reference clock reproduced from the portion where the first reference clock is recorded is βt.
become. These reproduction signals are output from the rotary audio heads AR and AL of the rotary drum 7 and then reproduced.
The audio FM signal is demodulated by the FM demodulator 20 through the switch 31 at the same timing as that at the time of recording through the switch 31, and becomes a time-axis compressed audio signal, which passes through the mode changeover switch 4b and the A / D converter. 11 is input.

On the other hand, the reproduced first reference clock is
The second reference clock generation circuit 32 passes through the switch 31.
And is oscillated stably by the PLL in the cycle βt. The second reference clock that oscillates at this cycle βt and the reference clock that has a cycle t oscillated from the first reference clock generation circuit 14 are input to the variable time axis expander 33, and the second reference clock is divided. Then, the clock of the cycle bβt is supplied to the A / D converter 11 and the RAM 12 via the mode changeover switch 4c, and the time axis-compressed audio signal is digitized and stored. Next, a clock having a cycle at obtained by dividing the first reference clock is supplied to the RAM 12 and the D / A converter 13 via the mode changeover switch 4d, and the time-axis-compressed audio signal is at / ( bβ
t) = Time axis extension at a ratio of a / b / β. Eventually, the signal time bTβ / a becomes bTβ / a × a / b / β = T, the length is the same as that at the time of recording, and a continuous audio signal can be obtained. This audio signal is a mode switch 4e.
Is output from the audio output terminal 22 via the reproduced audio signal amplifier 21. Voice FM recording carrier 1.5MH
z, if the frequency of the first reference clock is selected to be around 1.5 MHz, both can be magnetically recorded and reproduced equally.

Second Embodiment In the first embodiment , the reproduced voice signal of time T is obtained with respect to the intermittent cycle T, but the compression and expansion rate of the voice signal is increased so that the reproduced voices overlap each other. By outputting the sound in the better condition, it is possible to deal with the dropout of the FM signal.

Third Embodiment In the above embodiment, the first reference clock is arranged in the first half of the deep recording and the voice FM signal is arranged in the latter half, but they may be arranged alternately. By doing so, During playback,
The accuracy of the PLL of the second reference clock generation circuit 32 is improved, and more accurate time axis expansion can be expected.

Fourth Embodiment In the above embodiment, the carrier of the audio FM signal and the first reference clock have a close frequency. However, for example, the carrier of the audio FM signal is 1.6 MHz and the first reference clock is 1.
As shown in FIG.
B. to detect the first reference clock, as shown in FIG. P.
If an F (band-pass filter) is provided and the switching timing of the switch 31 is set, the accuracy of cueing the audio FM signal can be further improved.

Fifth Embodiment In the present invention, the compression rate at the time of recording is determined together with the audio signal.
The first reference clock that is
To recover the recovered reference clock by recovering the first reference clock of
Therefore, use an arbitrary frequency as the first reference clock.
Can be Therefore, in the fourth embodiment, the frequency of the first reference clock may be changed according to the intermittent cycle T. By doing so, it is possible to automatically determine the intermittent cycle during reproduction.

[0030]

As described above, the magnetic recording and reproducing apparatus according to the present invention records and reproduces a reference clock that serves as a reference for audio compression during recording and uses it as a reference signal during reproduction and expansion. This has an excellent effect that a continuous audio signal without interruption can be obtained without being affected by the time axis fluctuation.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of a magnetic recording and reproducing apparatus according to the present invention.

FIG. 2 is a timing chart of the switch 30 according to the first embodiment of the present invention.

FIG. 3 is a timing chart showing the relationship between a video signal, an audio signal, and a reference clock during recording in the first embodiment of the present invention.

FIG. 4 is a diagram illustrating time axis compression and expansion according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram of Embodiment 4 of the present invention.

FIG. 6 is a block diagram of an example of a conventional magnetic recording and reproducing apparatus.

FIG. 7 is a recording timing chart of a conventional magnetic recording and reproducing apparatus.

FIG. 8 is a reproduction timing chart of a conventional magnetic recording and reproducing device.

FIG. 9 is a diagram showing a problem of the conventional magnetic recording and reproducing apparatus.

[Explanation of symbols]

 1 video input terminal 2 video signal amplifier 3 video signal recording circuit 4a-4f mode selector switch 5 video signal reproducing circuit 6 video output terminal 7 rotating drum 8 intermittent drive and head switching circuit 9 audio input terminal 10 audio signal amplifier 11 A / D Converter 12 RAM 13 D / A converter 14 First reference clock generating circuit 15 Time axis compressor 16 Time axis expander 17 FM modulator 18 Recording amplifier 19 Reproducing amplifier 20 FM demodulator 21 Reproducing audio signal amplifier 22 Audio output Terminal 30 Switch 31 Switch 32 Second Reference Clock Generating Circuit 33 Variable Time Extender

Claims (2)

(57) [Claims] 1. An A / D converter for converting an analog signal into a digital signal, a RAM for temporarily storing the digital signal, and a D / A converter for converting a digital signal output of the RAM into an analog signal. And a first reference clock generating circuit for generating a reference clock of an arbitrary frequency which is a reference for the signal processing operation of 1., and dividing the reference clock generated by the first reference clock generating circuit, A / D converter, RA
A time axis compressor for supplying an analog signal to the M and D / A converters for time axis compression; and an FM for FM modulating the time axis compressed analog signals
A modulator, and means for recording in the magnetic recording medium by time-sequentially switching the FM signal output from the FM modulator and the reference clock of an arbitrary frequency generated by the first reference clock generation circuit. A magnetic recording device having: 2. A signal reproducing means for reproducing signals recorded in time series on the magnetic recording medium by the magnetic recording apparatus according to claim 1, and a reproduction signal output from the signal reproducing means for time axis compression. And an FM-modulated analog signal and a reproduction first reference clock which is a reproduction signal of a reference clock of an arbitrary frequency output from the first reference clock generation circuit, and the reproduction first reference clock A second reference clock generation circuit that forms a PLL circuit with the input as an input and oscillates; an FM demodulator that demodulates an analog signal that is time-axis compressed and FM modulated; and a signal demodulated by the FM demodulator The reference clock obtained from the second reference clock generation circuit is digitized by a signal obtained by dividing the reference clock, and the first reference clock generation circuit is provided. Any frequency to be a force
The signal obtained by dividing the reference clock of
A magnetic reproducing apparatus comprising: a variable time axis expander that supplies the A converter and expands the time axis.