JPH05182361A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To reduce the deterioration in the picture quality in comparison with the use of a video output signal by sending a Viterbi decoding circuit signal and dubbing the video signal based on the signal when the video signal is reproduced by the partial response system. CONSTITUTION:The partial response system is utilized to reproduce video signals Y, U, V recorded on a prescribed recording medium 44. In this case, a level of a reproduction signal S1 outputted from magnetic heads 13A, 13B is converted into a digital signal for a prescribed period by an A/D converter circuit 52 and a Viterbi decoding circuit 54 decodes the reproduction signal S1 based on the digital signal. Then an output signal EXO of the Viterbi decoding circuit 54 is sent externally and the video signals Y, U, V are dubbed based on the output signal EXO. Thus, the deterioration in the picture quality is reduced in comparison with the repetition of dubbing by using the video output signal.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Field of Industrial Application Conventional Technology Problems to be Solved by the Invention Means for Solving the Problems (FIG. 2) Action (FIG. 2) Embodiment (1) First Embodiment (FIGS. 1 and 2) (2) ) Second embodiment (Fig. 3) (3) Third embodiment (Fig. 4) (4) Other embodiments Effect of the invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus, and can be applied to, for example, a video tape recorder for converting a video signal into a digital signal for recording.

[0003]

2. Description of the Related Art Conventionally, there is a video tape recorder of this type which converts a video signal into a digital signal for recording and reproduction (hereinafter referred to as a digital video tape recorder).

In such a digital video tape recorder, by adding an error correction code and recording a digital video signal, deterioration of image quality can be effectively avoided even if dubbing is repeated.
For this reason, this type of digital video tape recorder is used for editing work at a broadcasting station or the like for business use.

[0005]

By the way, it would be convenient for a home video tape recorder to be able to record an image signal by converting it into a digital signal.

In such a home-use digital video tape recorder, the image data is band-compressed and recorded, so that the video data is recorded as compared with a commercial video tape recorder.
It is necessary to improve the recording density so that recording can be performed for a long time.

However, as the recording density is improved in this way, there is a risk of erroneous correction during error correction processing, and the image quality of the reproduced image deteriorates accordingly.

Therefore, if dubbing is repeated using a video output signal output to a monitor device as in a conventional home-use video tape recorder, the image quality of a reproduced image deteriorates each time dubbing is repeated. ..

The present invention has been made in consideration of the above points, and an object of the present invention is to propose a magnetic recording / reproducing apparatus capable of reducing deterioration of image quality as compared with the case where dubbing is repeated using a video output signal. Is.

[0010]

In order to solve such a problem, in the present invention, a video signal Y recorded on a predetermined magnetic recording medium 44 by utilizing a partial response system,
In the magnetic recording / reproducing apparatus 1 for reproducing U and V, an analog digital conversion circuit 52 for converting the signal level of the reproduction signal S1 output from the magnetic heads 13A and 13B into a digital signal at a predetermined cycle, and reproduction based on the digital signal. A Viterbi decoding circuit 54 for decoding the signal S1,
During reproduction, the output signal EX0 of the Viterbi decoding circuit 54 is sent out so that the video signals Y, U and V can be dubbed based on the output signal EX0.

[0011]

When reproducing, output signal EX0 of Viterbi decoding circuit 54
Of the video signal Y, based on the output signal EX0.
If U and V can be dubbed, the deterioration of the image quality of the reproduced image can be reduced even if dubbing is repeated.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings.

(1) First Embodiment (1-1) Overall Structure In FIG. 1, reference numeral 1 denotes a digital video tape recorder as a whole, which gives a luminance signal Y and color difference signals U and V to an effective information extraction circuit 2. ..

Here, the effective information extraction circuit 2 converts the luminance signal Y and the color difference signals U and V into digital signals, and then selectively outputs the signals at a predetermined timing to thereby output the luminance signal Y and the color difference signals U in the effective display area. , V are cut out and output. The compression circuit 3 receives the luminance signal Y output from the valid information extraction circuit 2, and limits the band of the luminance signal Y to reduce the data amount of the luminance signal Y and output it.

The sub-sampling circuit 4 sub-samples the color difference signals U and V output from the effective information extracting circuit 2 to reduce the data amount of the color difference signals U and V and output the data. Blocking circuits (BLK) 5 and 6 capture the luminance signal and the color difference signal in the order of raster scanning and then output them in a predetermined order, thereby outputting the luminance signal and the color difference signal in small block units of 8 × 8 pixels. Output.

The synthesizing circuit 7 time-division-multiplexes the output signals of the block-making circuits 5 and 6 and outputs them. Encoder (E
The NC) 8 performs discrete cosine conversion on the output signal of the synthesizing circuit 7 in small block units, and the conversion result is subjected to variable length coding processing and output.

The framing circuit (FRM) 9 sequentially takes in the output data of the encoder 8 and outputs it in a predetermined order, thereby correcting the data amount of the variable length coded data that changes for each small block to a constant amount. And output.
A parity code generation circuit (PTG) 10 adds a parity code to the output data of the framing circuit 9 and outputs it.

Audio signal coding circuit (ENC) 15
Converts the audio signal into a digital signal, encodes it, and outputs it to a parity code generation circuit (PTG) 16, where a parity code is generated for each predetermined block. On the other hand, the parity code generation circuit (PTG) 17
Receives sub-code data from a predetermined sub-data generating circuit (not shown), adds a parity code to the sub-code data, and outputs it.

The adder circuit 14 is a parity code generator circuit 1.
The output data of 0, 16, and 17 are time-division-multiplexed and output, thereby generating a predetermined sync block. The encoder circuit (END) 11 shuffles the output data of the adder circuit 14 and then executes a predetermined arithmetic process, thereby converting the input data into recording data.

The adder circuit 18 adds the preamble signal SP generated by a predetermined signal generating circuit to the output signal of the encoder circuit 11 and outputs it. As a result, in the video tape recorder 1, the output signal of the adder circuit 18 is amplified by the amplifier circuits 12A and 12B, and the magnetic head 13 is amplified.
The signals are output to A and 13B, and the luminance signal and the color difference signals can be converted into digital signals and recorded.

In the case of this embodiment, a part of the output data of the audio signal encoding circuit 15 is output to the framing circuit 9 to correct the data amount of the variable length encoded data using the audio data. It is done like this.

On the other hand, in the reproducing system, the output signals of the magnetic heads 13A and 13B are amplified by the amplifier circuits 21A and 21B.
To the decoder 22 through which the reproduced signal is demodulated and then de-scuffed. At this time, in the video tape recorder 1, the tracking control circuit (AT
F) A reproduction signal is output to 34, a tracking error signal is detected here, and tracking control is performed based on the tracking error signal.

The time axis correction circuit (TBC) 23 corrects the reproduction data output from the decoder 22 on the time axis and outputs the corrected reproduction data. Error detection and correction circuits (ECC) 24, 37,
Reference numeral 39 executes error correction processing on image data, audio data, and subcode data, respectively.

In the output data of the error detection / correction circuit 24, audio data and image data are separated by a deframerization circuit (DFRM) 25 and decoded by decoders (DEC) 26 and 35, respectively. As a result, in the video tape recorder 1, after the output data of the error detection / correction circuit 37 is decoded by the decoder (DEC) 38, the decoded data obtained as a result is combined with the output data of the decoder 35 by the combining circuit 36 to generate an analog signal. By converting the signal into a signal, it is possible to reproduce the audio signal recorded by the digital signal processing.

The distribution circuit 27 performs the reverse processing of the synthesizing circuit 7, and thereby separates the image data into a luminance signal and a color difference signal and outputs them. Deblocking circuit (DBLK) 28
And 29 sequentially fetch the image data and output it in a predetermined order, thereby outputting the image data processed in block units of 8 × 8 pixels in the order of raster scanning.

The interpolation circuit 30 reproduces the image data lost in the compression circuit 3 by executing the interpolation process, so that the video tape recorder 1 reproduces the luminance signal Y through the interpolation circuit 30. It is designed to be able to do. The distribution circuit 31 separates the color difference signals into two systems,
The color difference signals U and V are demodulated by being interpolated by the interpolation circuit 32.

(1-2) Encoder and Decoder Here, in this embodiment, the video tape recorder 1 is
By executing a predetermined calculation process by the encoder 11, it is possible to effectively use the frequency characteristic of the electromagnetic conversion system to efficiently record the record data.

That is, as shown in FIG. 2, the encoder 1
In 1, the output data of the adder circuit 14 is given to the randomizer 40, and shuffling is performed in a predetermined unit. Further, the encoder 11 gives the output data of the randomizer 40 to the precoding circuit 42, where

[Equation 1] The arithmetic processing is executed to generate recorded data such that the spectrum is concentrated in the middle range. MOD2 here
Represents the remainder of 2.

That is, when a signal is recorded on the magnetic tape, the CN ratio of the reproduced signal is deteriorated in the low range because the electromagnetic conversion system such as the magnetic head has a differential characteristic. On the other hand, on the high frequency side, the CN ratio similarly deteriorates due to the magnetization characteristics of the magnetic tape. If the frequency characteristic of this magnetic recording / reproducing system is expressed using the delay operator D, it will be class 4
It can be expressed by approximating the frequency characteristic of the partial response (1-D ² ).

Therefore, if the recording data is generated so that the spectrum is concentrated in the middle range by executing the arithmetic processing of the equation (1), the recording data can be efficiently recorded by effectively utilizing the frequency characteristic of the electromagnetic conversion system. You can

On the other hand, the transfer function of the entire reproducing system is 1-
If it is set to D ² , the transfer function of the entire recording / reproducing system will be 1
Therefore, even if the arithmetic processing of the formula (1) is executed at the time of recording, the reproduced data can be surely obtained. As a result, in the video tape recorder 1, the class 4
The digital video signal can be efficiently recorded on the magnetic tape 44 by using the partial response method.

On the other hand, in the reproducing system, the reproducing signal S1 is applied to the PLL circuit 46, and the reproducing clock signal CK0 is generated here. The decoder 22 gives the reproduction signal S1 to the equalizer circuit (EQ) 48, where the reproduction signal S1
After the frequency characteristic of is corrected, it is output to the arithmetic processing circuit 50.

The arithmetic processing circuit 50 executes the arithmetic processing of (1 + D) on the reproduced signal S1 and outputs it. That is, in the electromagnetic conversion system, since the frequency characteristic is the differential characteristic, the frequency characteristic can be expressed by (1-D) using the delay operator D. Therefore, when recording, (1)
If the arithmetic processing of the formula is executed and the arithmetic processing circuit 50 executes the (1 + D) arithmetic processing at the time of reproduction, the frequency characteristic of the entire recording / reproducing system can be held at 1, and thus the reproduced data can be demodulated. You can

By the way, when the digital signal is recorded and reproduced by using the class 4 partial response method as described above, if the arithmetic processing circuit 50 executes the arithmetic processing of (1 + D), it is reproduced from the input side of the precode circuit 42. While the entire transfer function can be set to 1 by looking at the system, if the reproducing system is viewed from the output side of the precoding circuit 42,
The transfer function can be represented by (1-D ² ).

In this case, if the output data of the arithmetic processing circuit 50 is decomposed into an even column and an odd column, the output data of the odd column and the even column respectively have a function of 1-D when viewed from the output side of the precoding circuit 42. Can be expressed as

That is, if the output data of the arithmetic processing circuit 50 is decomposed into even-numbered columns and odd-numbered columns, in the output data of even-numbered columns and odd-numbered columns, respectively, 1-
There will be a correlation of D.

Therefore, if the output signal of the arithmetic processing circuit 50 is demodulated by utilizing the correlation, the output signal of the arithmetic processing circuit 50 can be surely demodulated by effectively utilizing the intersymbol interference.

Based on this demodulation principle, the decoder 22
Converts an output signal of the arithmetic processing circuit 50 into a digital signal by an analog digital conversion circuit (A / D), thereby converting the output signal into an 8-bit 2-system digital signal. Further, the digital signal is output to a Viterbi decoding circuit (also composed of two systems in this case) 54, where the digital signal is decoded by applying the Ferguson algorithm, and the input data of the precoding circuit 42 is obtained from the decoding result. Demodulate.

Thus, as compared with the case where the output signal of the arithmetic processing circuit 50 is simply decoded with reference to a predetermined signal level, the Viterbi decoding circuit 54 demodulates using the intersymbol interference to reduce the bit error rate. It can be improved significantly. Therefore, even when the dubbing is repeated, the image quality deterioration of the reproduced image can be reduced accordingly.

By the way, even when the reproduced signal is demodulated in this way, if it is converted into an analog signal and the dubbing is repeated, the image quality of the reproduced image is deteriorated by repeating the interpolation process, the band compression process, and the analog digital conversion process. .. In addition, there is a possibility that the error correction process may make an erroneous correction. Therefore, in this embodiment, the output data EX0 of the Viterbi decoding circuit 54 is output to the time axis correction circuit 23 to demodulate the video signal, and the output data EX0 is externally transmitted through the buffer circuit 56 together with the reproduction clock signal CK0. Output to the device.

As a result, the video tape recorder 1 can perform dubbing based on the output data EX0 of the Viterbi decoding circuit 54.

That is, in the video tape recorder 1, the selection circuit 58 is inserted between the randomizer 40 and the precode circuit 42, and the output data EX1 of the Viterbi decoding circuit which is output from another video tape recorder at the time of dubbing.
Is input to the precoding circuit 42 via the selection circuit 58. As a result, in the video tape recorder 1, the output data EX1 of the Viterbi decoding circuit can be input and the video signal can be recorded, and at the time of reproduction, the output data EX0 of the Viterbi decoding circuit 54 can be transmitted to the external device. It is designed to be recordable.

(1-3) Effects of the Embodiments According to the above configuration, by directly outputting the output data of the Viterbi decoding circuit, it is possible to perform dubbing based on the output data, and even if dubbing is repeated, reproduction is performed. It is possible to reduce image quality deterioration of an image.

(2) Second Embodiment In FIG. 3 in which parts corresponding to those in FIG. 2 are assigned the same reference numerals, 60 denotes a digital video tape recorder according to the second embodiment. In the case of this embodiment, Viterbi decoding circuit 5
Instead of directly outputting the output signal of No. 4, the output signal EX2 of the time axis correction device 23 is sent.

As a result, in the digital video tape recorder 60, the output data of the Viterbi decoding circuit 54 is time-axis corrected and output, so that even if the dubbing is repeated, the time-axis fluctuation is not accumulated. ing. Therefore, even if the dubbing is repeated by that amount, it is possible to reduce the image quality deterioration of the reproduced image.

Accordingly, the digital video tape recorder 60 outputs the clock signal CK2 output from the predetermined reference signal generating circuit in place of the reproduction clock signal CK.

According to the configuration shown in FIG. 3, the output data of the Viterbi decoding 54 is corrected on the time axis and is output, whereby the deterioration of the image quality of the reproduced image can be further reduced in addition to the effect of the first embodiment. it can.

(3) Third Embodiment In FIG. 4, reference numeral 70 denotes a digital video tape recorder according to the third embodiment. In this embodiment, instead of directly outputting the output signal of the Viterbi decoding circuit 54, After the time axis correction, it outputs through the precode circuit 42.

Therefore, in the digital video tape recorder 70, the output data of the time axis correction circuit 23 is given to the precode circuit 42 through the selection circuit 72, and the output signal of the precode circuit 42 is passed through the selection circuit 74. Output.

Further, a digital video tape recorder 7
At 0, the precoding circuit 4
The preamble signal SP is added to the output signal 2 and output. Thus, on the recording side, when dubbing based on the output signal EX3 of the selection circuit 74, a clock signal can be extracted from the output signal EX3, and the connection between the video tape recorders can be simplified accordingly.

Further, in the video tape recorder on the recording side, not only the clock signal but also the switching pulse signal can be generated from the output signal EX3, whereby the whole operation can be easily synchronized on the recording and reproducing side.

Corresponding to this, the video tape recorder 70
, The external input signal EX4 is applied to the preamble detection circuit 76 of the PLL circuit configuration, where the clock signal C
K and the switching pulse signal SWP are generated, and the servo circuit 78 and the like are driven based on the clock signal CK and the switching pulse signal SWP. Further, in the video tape recorder 70, the external input signal EX4
To the amplifier circuits 12A and 12B via the selection circuit 80, and the external input signal EX4 is recorded thereby.

According to the configuration of FIG. 4, instead of directly outputting the output signal of the Viterbi decoding circuit, the signal is once output via the precoding circuit and then the preamble is added and output. Thus, the effect of the first embodiment is obtained. In addition, the connection between devices can be simplified.

(4) Other Embodiments In the above embodiments, the case where the present invention is applied to a video tape recorder has been described. However, the present invention is not limited to this, and a video signal is converted into a digital signal. It can be widely applied to a magnetic recording / reproducing apparatus for recording / reproducing.

[0055]

As described above, according to the present invention, when a video signal is reproduced by using the partial response method, the output signal of the Viterbi decoding circuit is sent to the outside and dubbing is performed based on the output signal. By doing so, it is possible to obtain a magnetic recording / reproducing apparatus capable of reducing image quality deterioration as compared with the case where dubbing is repeated using a video output signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of a digital video tape recorder according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the encoder and the decoder.

FIG. 3 is a block diagram showing a digital video tape recorder according to a second embodiment.

FIG. 4 is a block diagram showing a digital video tape recorder according to a third embodiment.

[Explanation of symbols]

1, 60, 70 ... Digital video tape recorder,
11 ... Encoder, 22 ... Decoder, 23 ... Time axis correction circuit, 42 ... Precode circuit, 54 ... Viterbi decoding circuit.

Claims (1)

[Claims] 1. A magnetic recording / reproducing apparatus for reproducing a video signal recorded on a predetermined magnetic recording medium by using a partial response method, wherein a signal level of a reproduction signal output from a magnetic head is a digital signal at a predetermined cycle. An analog digital conversion circuit for converting into a digital signal, and a Viterbi decoding circuit for decoding the reproduction signal based on the digital signal, the output signal of the Viterbi decoding circuit is transmitted during reproduction, and the video based on the output signal. A magnetic recording / reproducing apparatus characterized in that a signal can be dubbed.