JPH0787568B2 - Time-lapse magnetic recording device - Google Patents

Description

The present invention relates to a time-lapse system magnetic recording apparatus for performing frame-free recording on a magnetic tape.

[Conventional technology]

A time-lapse magnetic recording device is disclosed in Japanese Patent Laid-Open No. Sho 58-
As described in No. 62985, the field video signal of one frame is extracted from the input video signal at a fixed number of frames (for example, 240 frames) and recorded on the magnetic tape. When the ratio is 240, it is 4 seconds), and by intermittently sending one track at a time, the video signal with frame skipped is recorded on the magnetic tape,
It is possible to record for a long time. For example, in the case of a frame skip ratio of 240, it is possible to record for 480 hours using a 2-hour tape.

The frame skipping ratio can be switched in several stages, and the modes are distinguished by the recording time in each case. For example, a frame removal ratio of 240 (frame removal period of 4 seconds) is called a 480-hour mode, and a frame removal ratio of 120 (frame removal period of 2 seconds) is called a 240-hour mode.

As described above, the conventional apparatus has been capable of recording for a long time by the time-lapse recording, and the time-lapse ratio can be switched in several stages. However, no consideration was given to recording audio signals.

[Problems to be solved by the invention]

Since the time-lapse system magnetic recording device runs the tape intermittently, it cannot record audio on a linear audio track. Therefore, the voice has not been recorded in the past.

An object of the present invention is to enable voice recording in all modes of a time-lapse system magnetic recording device, and to be able to cope with mode switching with a simple circuit configuration.

[Means for solving problems]

The features of the present invention include a time compression means for time-compressing an input audio signal, a recording means for recording the time-compressed audio signal between video signal tracks on a magnetic tape, and a mode switching according to the mode switching. That is, the compression ratio switching means for switching the compression ratio of the time compression is provided.

[Action]

The input audio signal is time-compressed by the time compression means and is intermittently recorded on the magnetic tape by the recording means at the same cycle as the cycle of the frame skipping of the video signal. The compression ratio of the time compression is switched by the compression ratio switching means to a value equal to or larger than the frame removal ratio of the video signal in that mode. Therefore, in all modes, the audio signal for the frame skipping period is time-compressed within one frame. Since this time-compressed voice is recorded on the magnetic tape one frame at a time in the same period as the frame skipping period, all information of the input voice signal is recorded on the magnetic tape in all modes.

〔Example〕

FIG. 1 is a block diagram of a characteristic part of an embodiment of the present invention, and FIG. 2 is a schematic block diagram of its entire configuration.

The audio signal input from the audio input terminal 10 is supplied to the audio rotary head 4 through the time compression circuit 1 and the audio signal recording circuit 3. The video signal input from the video input terminal 11 is supplied to the video circuit heads 6 and 6'through the video signal recording circuit 5. The rotary heads 4, 6 and 6'are slid on the magnetic tape 12 at a high speed, and the voice rotary head 4 has a step in the rotation axis direction with respect to the video rotary heads 6 and 6 '. The magnetic tape 12 is run by a capstan motor 9, and the capstan motor 9 is driven by a motor drive circuit 8. The system control circuit 7 includes a compression ratio switching circuit 2, an audio signal recording circuit 3,
A control signal is supplied to the video signal recording circuit 5 and the motor drive circuit 8. The compression ratio switching circuit 2 supplies a signal to the time compression circuit 1.

The input audio signal is time compressed by the time compression circuit 1,
It is recorded on the magnetic tape 12 by the voice circuit head 4. On the other hand, the input video signal is recorded on the magnetic tape 12 by the rotary heads 6 and 6'for video. A video recording gate signal g'is supplied from the system control circuit 7 to the video signal recording circuit 5, whereby a field video signal of one frame is extracted and recorded at a constant number of frames. Also,
An audio recording gate signal g is supplied to the audio signal recording circuit 3, whereby the time-compressed audio signal is intermittently recorded frame by frame at the same period as the frame removal period of the video signal. further,
The motor drive control signal d is supplied to the motor drive circuit 8, whereby the magnetic tape 12 is intermittently run at the same cycle as the frame skipping cycle of the video signal. Video and time-compressed audio are recorded while the magnetic tape 12 is stopped. The audio rotary head 4 is stepped so as to form a track between the video signal track and the next video signal track. Therefore, by the above operation, the frame-extracted field video signal and the time-compressed audio signal are alternately recorded on the magnetic tape 12.
On the other hand, the system control circuit 7 supplies the compression ratio switching circuit 2 with a mode switching signal m corresponding to the frame removal ratio, and the compression ratio switching circuit 2 receiving this supplies the compression ratio of the time compression circuit 1 to the frame removal ratio. Switch to an equal or greater value. For example, in the 480-hour mode, the compression ratio is 240 and thus the compression ratio is 240 or more. Therefore, the input audio signal for the frame removal period is for one frame (1 field time)
Since it is time-compressed within a time period, and the time-compressed audio signal for one frame is recorded at a cycle equal to the frame-free cycle,
In all modes, all information of the input audio signal is recorded on the magnetic tape 12.

In the time compression circuit 1, the input audio signal is output through the low pass filter 104, the A / D converter 102, the memory 101, the D / A converter 103, and the low pass filter 105. In response to this, the audio signal recording circuit 3 receives the pre-emphasis circuit 301,
It is supplied to the voice rotary head 4 through the FM modulation circuit 302, the gate circuit 303, and the recording amplifier 304. Compression ratio switching circuit 2
In, the output of the oscillator 201 is supplied to the frequency divider 202. Then, the high-speed clock _H that is the output of the oscillator 201
And the low-speed clock _L output from the frequency divider 202 is stored in the memory 1
Supply to 01. The mode switching signal m from the system control circuit 7 is supplied to the frequency divider 202, and the audio recording gate signal g is supplied to the gate circuit 303.

The input audio signal is band-limited by the low-pass filter 104, converted into digital data by the A / D converter 102, and written in the memory 101 at a low-speed clock _L.
Then, it is time-compressed by being read by the high-speed clock _H , is restored to an analog signal by the D / A converter 103, and only the required band is taken out by the low-pass filter 105. The time-compressed audio signal thus generated has a high frequency emphasized by the pre-emphasis circuit 301, is FM-modulated by the FM modulation circuit 302, and is recorded by the audio rotary head 4. At this time, by the gate operation of the gate circuit 303, intermittent recording is performed for each frame at the same cycle as the core removal cycle.

The low-speed clock _L is a high-speed clock generated by the frequency divider 202.
It is generated by dividing _H. The compression ratio of the time compression is the frequency ratio of the high speed clock _H and the low speed clock _L , and is therefore equal to the frequency division ratio in the frequency divider 202. In divider 202,
By switching this frequency division ratio by the mode switching signal m, the compression ratio is switched to a value equal to or larger than the frame removal ratio in that mode.

FIG. 3 shows spectrum diagrams of the input audio signal side and the time-compressed audio signal side in this embodiment. The horizontal axis represents frequency and the vertical axis represents signal level. In this embodiment, the maximum recording time is 48
0 hours a) and b) are the input audio signal side spectrum diagram and the time compression audio side spectrum diagram in the 480 time mode, and c) and d) are the input audio side spectrum diagram and the time compression audio side spectrum diagram in the 240 hour mode. Is. _H1 is the frequency of the high speed clock _{H in} the 480 time mode, and _L1 is the frequency of the low speed clock _L in the 480 time mode. The frequency axis of the spectrum diagram on the input voice side is normalized to _L1 , and the frequency axis of the spectrum diagram on the time compression voice side is normalized to _H1 . This also applies to the subsequent spectrum diagrams.

1000 is the spectrum of the input audio signal band-limited by the low-pass filter 104, 1001 is the spectrum of the time-compressed audio signal in the 480 time mode, 1002 is the spectrum of the time-compressed audio signal in the 240-hour mode, and 1040 is the frequency characteristic of the low-pass filter 104. , 1050 is a low pass filter 1
It is the frequency characteristic of 05. Divider 202 in 240 hour mode
The frequency division ratio of is set to half of the 480 hour mode. Then,
The frequency of the low-speed clock _L is as shown in FIG.
_L2 is twice as large as _L1 , and the band of the time compression audio signal is 1002
Halves like. The frequency of the high-speed clock _H is _H1
The frequency characteristic of the low-pass filter for suppressing the aliasing noise due to sampling and extracting only the necessary component may be 1050. This is the same as the compression ratio is lowered regardless of the compression ratio.

According to this embodiment, the audio signal can be recorded in all modes of the time-lapse magnetic recording device. Further, even if the compression ratio is switched, it is not necessary to switch the low pass filter. Further, when the compression ratio is lowered, the band of the time-compressed voice is narrowed, so that the influence of noise of the tape head system is reduced. Further, since the ratio of the signal band to the frequency of the high speed clock or the low speed clock becomes small, the influence of quantization noise becomes small. Therefore, there is an effect that the S / N ratio is improved in the mode in which the frame removal ratio is small.

In the above-described embodiment, as shown in FIG. 4, a low-pass filter system 106 is provided instead of the low-pass filter 104, and the low-pass filter switching circuits 107 and 107 'are used to change the pass band from the low-pass filter 104 in the 240-hour mode. You may make it switch to the wide low pass filter 104 '. 5th spectrum diagram in 240 hour mode
Shown in the figure. Reference numeral 1003 denotes a spectrum of the input audio signal band-limited by the low-pass filter 104 ', 1004 a spectrum of the time-compressed audio signal, and 1041 a frequency characteristic of the low-pass filter 104'. According to this embodiment, there is an effect that the band can be widened in the mode in which the frame removal ratio is small. In addition,
If there are a large number of modes, a low-pass filter may be provided for each mode, or a low-pass filter may be provided up to a certain mode to increase the bandwidth, and the same low-pass filter may be used for modes with a smaller frame reduction ratio. You may make it use a filter.

In the embodiment shown in FIG. 1, the compression ratio switching circuit 2 is
As shown in FIG. 6, the frequency division ratio of the frequency divider 202 'for generating the low speed clock _L from the output of the oscillator 201 is fixed, and the high speed clock _H is also divided by the frequency divider 203 into the output of the oscillator 201. The frequency division ratio may be switched depending on the mode in which it is generated. In this case, as shown in FIG. 7, a low-pass filter system 108 is provided instead of the low-pass filter 105, and the low-pass filter switching circuits 109 and 10 are provided.
It is necessary to switch from the low-pass filter 105 to the low-pass filter 105 'having a narrow pass band when the 240-hour mode is set by 9'. A spectrum diagram in the 240 hour mode is shown in FIG. 1005 is the spectrum of the time-compressed audio signal, and 1051 is the frequency characteristic of the low-pass filter 105 '. Also in this embodiment, when the compression ratio is reduced, the time-compressed audio band is narrowed and the noise of the tape head system is reduced.
This has the effect of improving the ratio. If there are many modes, a low pass filter may be provided for each mode.

In the case of the above-mentioned embodiment, since the required memory capacity also becomes smaller as the compression ratio becomes smaller, another signal may be used for time-compressing and recording a large amount of another signal. As a recording method, another rotary head may be provided to form an additional track, or frequency multiplexing may be performed on the time-compressed audio signal. FIG. 9 is a block diagram of the time compression circuit 1 of the embodiment for frequency multiplexing, in which the memories are two systems 110 and 111,
In addition to audio signal system, multiple signal input terminal 10 ', A / D converter 10
A multiple signal system including 2 ', D / A converter 103', band pass filter 114, and muting circuit 115 is provided, and an adder 116 performs frequency multiplexing.

In 480 hour mode, the selector 112 selects the audio signal,
The gate circuit 113 is opened and time compression of the audio signal is performed using both the memories 110 and 111. Then, the muting circuit 115 operates and only normal time-compressed sound is output. In the 240-hour mode, the selector 112 selects the multiplex signal, the gate circuit 113 is closed, and the memory 110 time-compresses the audio signal and the memory 111 the multiplex signal. Since the output of the D / A converter 103 'contains a folding component of the time compression multiplexed signal, if this is extracted by the bandpass filter 114, a signal obtained by frequency-converting the time compression multiplexed signal can be obtained. The muting circuit 115 passes the signal through, and the adder 116 frequency-multiplexes the time-compressed audio signal and the frequency-compressed time-compressed multiplexed signal and outputs the result.
Fig. 10 shows the spectrum for 240-hour mode. 1
006 is the spectrum of the multiplexed signal band-limited by the low-pass filter 104 ″, 1007 is the spectrum of the frequency-compressed time-compressed multiplexed signal, 1042 is the frequency characteristic of the low-pass filter 104 ″, and 1140 is the frequency characteristic of the band-pass filter 114. .

According to this embodiment, multi-channel recording can be performed in a mode with a small frame reduction ratio.

Next, a specific example of the compression ratio in each mode will be described.
In order to record all the information of the input audio signal, it is sufficient that the audio for the frame skipping period is compressed within one frame (one field time). Therefore, if the compression ratio is set to a value larger than the frame removal ratio of the mode in which the frame removal period is the maximum, the track utilization ratio (time-compressed audio 1 Since it only changes the ratio on the track), there seems to be no problem, and it is better to reduce the circuit scale. However, an actual trial evaluation shows that recording and reproduction of time-compressed audio always deviates due to uneven rotation of the rotary cylinder to which the rotary head is attached. A problem that the ratio of the time lag of the time compressed voice to the length of the time compressed voice corresponding to the voice (equal to the ratio of the shift amount of the joint to the cycle of the joint of the reproduced voice) becomes large, and good sound quality cannot be obtained. Occurs. It was found that this ratio should be within 2% to obtain good sound quality. The maximum time difference between recording and playback of time-compressed audio is about 100 μsec. Therefore, in order for this to be within 2%, the time-compressed audio equivalent to the audio for the frame removal period is 5 m.
It should be about sec or more, that is, the truck utilization rate should be about 1/3 or more.

Therefore, in the present invention, the compression ratio of each mode is switched so that the track utilization rate becomes 1/3 or more. A specific value may be selected so that the circuit scale becomes small within this range.

Table 1 shows specific examples of the compression ratio in each mode.

FIG. 11 shows a specific block diagram of the frequency dividers 202, 202 'and 203 in this embodiment. a) The frequency-divides the high speed clock _H counter 2020 in a block diagram of the frequency divider 202, Q ₈ output is 480 hours mode by the low speed clock selection circuit 2021 (division ratio 2 ^8), Q ₇ in 240-hour mode output (division ratio 2 ^7), select ..., and low-speed clock _L.

b) is a block diagram of the frequency divider 202 'and 203, low-speed clock _L is set to Q ₈ output, clock input itself at 480 hours mode by the high-speed clock selection circuit 2031, Q ₁ output is 240 hour mode, the ...... The high-speed clock _H is selected.

According to this embodiment, the compression ratio switching circuit 2 can be realized with a simple circuit by setting the compression ratio to a power of 2. Also, the level of the FM envelope at the track end may decrease due to variations in the tape running bus, and the S / N of the reproduced audio corresponding to this part may deteriorate. Since it is not necessary to use all parts, it is possible to obtain good sound quality without S / N deterioration.

By the way, as described above, since the track utilization rate in each mode may be 1/3 or more, it is not necessary to switch the compression ratio between the modes having close frame reduction ratios.

The example is shown in Table 2.

According to the present embodiment, the number of steps for switching the compression ratio can be reduced, so that the circuit can be further simplified.

〔The invention's effect〕

According to the present invention, means for switching the compression ratio of the time compression of the audio signal to a value equal to or higher than the frame removal ratio of the video signal in that mode is provided, so that all modes of the time-lapse magnetic recording device are provided. Audio recording can be performed at.

Also, by switching the compression ratio to a power of 2 which is larger than the frame removal ratio, the circuit configuration can be simplified and stable sound quality can be obtained without being affected by the level reduction of the FM envelope at the track end. it can.

[Brief description of drawings]

FIG. 1 is a block diagram of a characteristic part of an embodiment of the present invention, FIG. 2 is a block diagram of the entire configuration of the same, FIG. 3 is a spectrum diagram of signals of respective parts, FIG. 4, FIG. 6, and FIG. , FIG. 9 is a block diagram of a characteristic portion of another embodiment, FIG. 5, FIG.
FIG. 10 is a spectrum diagram of signals of respective parts of another embodiment, and FIG. 11 is a detailed block diagram of a compression ratio switching circuit of an embodiment of the present invention. 1 ... Time compression circuit, 2 ... Compression ratio switching circuit, 3 ... Voice signal recording circuit, 4 ... Voice rotary head, 7 ... System control circuit.

Claims (1)

[Claims] 1. Sampling means for extracting one field video signal for each predetermined number of field video signals from an input video signal, and recording for sequentially recording the sampled field video signals on diagonal tracks on a magnetic tape. Means and a mode switching means for switching the time-lapse ratio to several stages, and in a time-lapse magnetic recording device that performs time-lapse recording in several modes according to the time-lapse ratio, in each sampling cycle, Time compression means for time-compressing the input audio signal with the value of the compression ratio being a power of 2, and time-compression audio recording means for sequentially recording the time-compressed audio signal on an oblique track adjacent to the video signal recording track on the magnetic tape. And the ratio of the audio for the time of the sampling cycle above the diagonal track for audio is Min time-lapse mode magnetic recording apparatus characterized by having a compression ratio switching means for switching a compression ratio of said time compressing means in accordance with the switching of the mode to be 1 or more and 1 or less.