JPS6160631B2 - - Google Patents

Description

Detailed Description of the Invention This invention stores one field or one frame of a television signal in a memory, converts it into a still image, and then converts it into a narrowband signal to use a communication line such as a telephone line. The present invention relates to a signal recording and reproducing method for recording, on an audio stereo tape recorder, signals such as still images that have been converted into the band of a so-called communication circuit.

Traditionally, television images, including still images, have generally been recorded using video tape recorders,
Video equipment such as video desks are used. However, since the still image transmission device uses a communication line in the voice frequency band, such as a telephone line, as the transmission line, the still image signal is converted into the voice frequency band on the transmission line.

Therefore, if this audio band signal is recorded using an audio tape recorder, which is generally commercially available as an audio device, a still image recording means can be provided at a lower cost than using expensive video equipment. However, due to its structure, the still image transmission device adopts an independent synchronization method in which timing signals (clock pulses) for the transmitting section and the receiving section are generated by separately provided crystal oscillators. In order to synchronize the images of the transmitter and receiver, the precision of this crystal is increased to about 5×10 ^-6 .

When a still image signal that has been converted to the audio band with such precision is recorded on an audio tape recorder, the reproduced signal will have frequency fluctuations with respect to the original signal due to the wow and flutter of the tape recorder. , fluctuations occur, which causes distortions that are much larger than those due to crystal precision errors. When such a signal is converted into a still image in the television band by a receiving device, the synchronization signal is largely deviated, and when monitored with a picture monitor, the synchronization is lost and the screen becomes meandering.

An object of the present invention is to eliminate the above-mentioned drawbacks by using an audio stereo tape recorder, record signals from a still image transmission device on the audio tape recorder, and reproduce normal still images. The goal is to provide a method.

According to the present invention, one channel of an audio stereo tape recorder has a still image signal converted into an audio band, and the other channel has a low frequency clock pulse for reproducing the still image signal or writing it to memory. It is possible to obtain a signal recording and reproducing method for still images, etc., in which the band is limited by a filter, converted to a sine wave in the audio band, and simultaneously recorded.

Since the signals recorded in this manner are simultaneously subjected to frequency distortion such as wow and flutter of the tape recorder on both channels, the frequency relationship between the channels is maintained. Therefore, the clock pulse is shaped and reproduced from the reproduced clock signal, the still image signal being reproduced at the same time is demodulated, and the clock pulse is used to perform processing such as A-D conversion and memory writing to create a television band image. By converting, a normal still image with no time axis fluctuations can be obtained.

Next, the present invention will be described in detail with reference to the drawings of an embodiment of the present invention. The circuit of FIG. 1 shows the recording input side of an audio stereo tape recorder. First, a still image signal converted into an audio band from a modulator or demodulator of a transmitter or receiver of a still image transmission device is input to input terminal a. Input terminal b
Insert a clock pulse in the same way. Since the clock pulse generally contains many harmonic components, the low-pass filter 2 filters out only its fundamental wave.
Note that the amplifier 1 performs amplitude adjustment and impedance conversion, and sends out a signal from a terminal C. Then, a clock pulse is sent from terminal d. From this circuit, both channels are simultaneously recorded on an audio stereo tape recorder through terminals c and d to record a still image.

Due to its mechanism, audio stereo tape recorders suffer from crosstalk between channels.
There is a phenomenon. Cassette tape recorders, which have recently been commercially available and are used in large quantities, have more crosstalk than reel-to-reel type tape recorders due to the thinness of their cassette tapes. Due to the influence of this crosstalk, clock signal signals leak into still image signals. Then, the S/N ratio of the reproduced still image deteriorates, resulting in an image that is difficult to view. The relationship between the frequency bands of the still image signal and the clock signal for preventing the influence of crosstalk is shown in FIG. 2 and will be explained. Since the still image signal is transmitted through a telephone line, its band is set to 0.3KHz to 3.4KHz, such as _B1 . Next, the clock signal uses a slightly higher frequency band than the still image signal. In this example, the upper limit is 5.7KHz or higher like _B2 , and the upper limit is determined by the band of the audio tape, but considering the performance of cassette tapes, etc., the upper limit is 10KHz.
And so.

As described above, recording is performed with the frequencies of both channels separated, and during playback, the still image signal is passed through a low-pass filter with a cutoff frequency of 3.4KHz. The clock signal is also passed through a high-pass filter with a cutoff frequency of 5.7KHz. In this way, the cutoff characteristics of the filter will be as shown by the dotted line shown in B ₃ for a still image signal, and as shown in the dotted line shown in B ₄ for a clock pulse. The influence of talk disappears.

Next, reproduction will be explained with reference to FIG.
A still image signal is input to the input terminal e, the crosstalk component of the clock signal is attenuated by the low-pass filter 3, and the signal is returned to the demodulator of the still image transmission device from the output terminal g. A clock signal is input from input terminal f, and a high-pass filter 4 attenuates the crosstalk of the still image signal.The output is coupled by a capacitor, and the point where it crosses 0 is compared and amplified by a comparator 5. Convert to pulse signal. Schmidt trigger type inverter 6,7
absorbs the pulse edge chatter that occurs when the comparator 5 compares. Furthermore, as explained with reference to FIG. 3, the frequency of the clock signal is set higher than that of the still image signal, so the frequency divider 8
Divide the frequency to the required frequency. In this embodiment, the frequency is divided into 1/2, but the current frequency ratio can be changed as necessary.

The clock pulse reproduced as described above is output from the edge-triggered flip-flop 9 by aligning the edge of the clock pulse with the edge of the memory timing pulse supplied from the terminal i, and outputting the clock pulse to the output terminal h.
from the demodulator clock circuit. Since the memory timing pulse has a sufficiently higher frequency than the clock pulse, it does not absorb tape recorder jitter.

If a still image is reproduced by the receiver of the still image transmission device using the still image signal and clock pulse reproduced in this manner, a stable still image without time axis fluctuation can be recorded and reproduced. Note that this method can be applied not only to still image transmission but also to recording of data transmission, etc., which is transmitted using an audio line.

As explained above, the present invention makes it possible to record and reproduce still images without time axis fluctuations by simultaneously recording still image signals and clock signals on the left and right channels of an audio stereo tape recorder. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the recording input side of a tape recorder according to an embodiment of the present invention, FIG. FIG. 3 is a diagram showing the playback side of the tape recorder in the embodiment of the present invention. In the figure, 1... audio amplification circuit, 2, 3...
Low-pass filter, 4... High-pass filter, 5...
Comparison circuit, 6, 7... Schmitt trigger circuit,
8... Frequency divider, 9... Edge trigger type flip-flop.

Claims (1)

[Claims] 1 Record the converted signal that has been converted into the audio band from 300Hz to 3400Hz on one channel of an audio tape recorder, and set the clock signal used when reproducing the converted signal to the original signal.
A band of 5700 Hz or more is recorded on the other channel of the audio recorder, and during playback, the converted signal is passed through a low-pass filter with a cut-off frequency of 3400 Hz, and the clock signal is passed through a high-pass filter with a cut-off frequency of 5700 Hz. A signal recording and reproducing method characterized by reproducing through a filter.