Patent Publication Number: US-2004042106-A1

Title: Magnetic reproducing apparatus and magnetic reproducing method

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to a magnetic reproducing apparatus and a magnetic reproducing method, in which a magnetoresistive element which has been conventionally used for reproducing a hard disk and the like, may be applied, for example, to reproducing a magnetic tape, and more particularly, relates to a magnetic reproducing apparatus and a magnetic reproducing method suitable for use in reproduction of a magnetic tape employing the magnetoresistive element.  
       BACKGROUND ART  
       [0002]FIG. 11 shows a block diagram of a data magnetic recording and reproducing apparatus as one example of a magnetic reproducing apparatus. In FIG. 11, video data, audio data, additional data, data in files of a computer and the like are input to a data input  80 . A signal input from the data input  80  is processed by a recording signal processing circuit  81  into a signal suitable for magnetic recording, that is, undergoes processing of error correction and packetization, and after modulation the signal is recorded by a recording head  83  on a recording medium  84  such as a magnetic tape through a recording amplifier  82 .  
       [0003] Here, with respect to recording on the above-described recording medium  84 , in order to increase relative speed and recording density, the recording is performed according to what is called helical scanning method. That is, the recording according to the helical scanning method is performed, for example, such that a rotating drum  91  and tape guides  92  and  93  at the front and rear of the drum  91  are arranged as shown in FIG. 12 and the magnetic tape recording medium  84  is diagonally transported thereon. Then, the recording head  83  provided on the rotating drum  91  performs recording such that diagonal recording tracks Tr are sequentially formed in a parallel manner as shown in FIG. 13, for example.  
       [0004] Further, the recording tracks Tr formed as described above are read by a reproducing head  85  provided on the same rotating drum  91 . That is, since the recording medium  84  is also diagonally transported when the signal is reproduced, signals recorded on the above recording tracks Tr are read by the reproducing head  85 . Then, as shown in FIG. 11, the read signal is supplied to an A/D converter  87  through a reproduction equalizer amplifier  86  and further sent to a reproduction signal processing circuit  89  through a signal detection circuit  88 . Subsequently, the signal is output to a data output  90  after demodulation, restoration to the original form from the packetized state, error correction and the like are executed.  
       [0005] In the above magnetic recording, in order to further improve the recording density, the track pitch and the minimum width of a recording bit at the magnetic recording have been intended to reduce. However, in the recording according to the above-described helical scanning method, there is a limit in the linearity of the recording track pattern when the track pitch is made narrower. Accordingly, for example, when the recorded patterns which have been formed by the recording head  83  as shown by solid lines in FIG. 13 are reproduced by the reproducing head  85  at another opportunity, reproduction traces become as shown by dashed lines to make correct reproduction impossible.  
       [0006] Therefore, in the data magnetic recording and reproducing apparatus, reproducing has been performed according to a non-tracking method as shown in FIG. 14. Specifically, the reproduction according to the non-tracking method is performed, for example, by scanning one recording track Tr two times. In this manner, for example, as shown in FIG. 15 pieces of packetized data  1  to  14  are reproduced by a reproduction trace Tp 1  of the first scanning, and pieces of packetized data  15  to  19  are reproduced by a reproduction trace Tp 2  of the second scanning. Then, these pieces of data are synthesized in memory to reproduce the whole of the recording track Tr.  
       [0007] Accordingly, by using the above-described non-tracking method, even in the case of recording tracks in which, for example, the track pitch has been made narrower in the linearity beyond the limit, data reproduction may be performed. However, as shown in FIG. 16, in the reproduction according to the above non-tracking method, the amount of a reproduction trace which laps over adjacent recording tracks becomes larger than that of reproduction according to conventional tracking methods. Specifically, for example, when a recording track Tr 1  shown by a solid line is reproduced, a reproduction trace Tp shown by dashed lines largely laps over an adjacent recording track Tr 2 .  
       [0008] In the above-described non-tracking method, especially when the reproducing head  85  and the recording head  83  are separately provided, in order to obtain reproduction signals reliably the width of the reproducing head  85  is made larger, thereby the amount of a reproduction trace Tp lapped over adjacent tracks further increasing. Moreover, when the track pitch is made narrower beyond the limit of linearity as described above, since the recording track Tr is not corresponding to the reproduction trace Tp, a state in which the reproduction trace Tp laps over the adjacent recording track Tr 2  unavoidably occurs.  
       [0009] On the other hand, in the magnetic recording and reproducing apparatus of a helical scanning type, by inclining the gap of the recording and reproducing heads within a range of about 5 to 30 degrees, the amount of a crosstalk signal read from the adjacent track has been reduced. However, as shown in frequency characteristics of FIG. 17, the amount of reduction, that is, azimuth loss can not be anticipated especially in the low-frequency area. Accordingly, though a method in which low-frequency components are suppressed by modulating recording signals or other methods has been conventionally adopted, the data amount tends to increase such that ten bits are assigned to an eight-bit code.  
       [0010] The present application has been made in light of the above-described circumstances, and problems to be solved are described as follows. Although reproduction according to the non-tracking method is efficient when the width of a recording track is intended to be made narrower in order to improve the recording density, in conventional apparatuses the amount of reduction in crosstalk signals caused by the fact that the reproduction trace laps over the adjacent recording tracks virtually can not be anticipated especially in the low-frequency area, and therefore there is a possibility that the quality of the reproduction signal is extremely damaged and that the data amount tends to increase and thus reduce the recording capacity when modulation by which low-frequency components are suppressed is used.  
       DISCLOSURE OF INVENTION  
       [0011] Claim 1 of the present invention is a magnetic reproducing apparatus in which reproduction is performed according to a non-tracking method, wherein a detecting method in which low-frequency components of a reproduction signal are not used is employed as reproduction means.  
       [0012] Accordingly, effects of a crosstalk signal caused by the fact that a reproduction trace laps over adjacent recording tracks may be eliminated, whereby reproduction according to the non-tracking method can be adopted to enable the width of a recording track to be made narrower, and to improve the recording density of a magnetic tape.  
       [0013] Further, according to claim 2 of the present invention, since a Partial Response Class 4 is employed as a detecting method, a detecting method in which low-frequency components of a reproduction signal are not used is obtained to eliminate effects of a crosstalk signal caused by the fact that a reproduction trace laps over adjacent recording tracks.  
       [0014] Further, according to claim 3 of the present invention, since an E-Partial Response Class 4 is employed as a detecting method, a detecting method in which low-frequency components of a reproduction signal are not used is obtained to eliminate effects of a crosstalk signal caused by the fact that a reproduction trace laps over adjacent recording tracks.  
       [0015] Further, according to claim 4 of the present invention, since an EE-Partial Response Class 4 is employed as a detecting method, a detecting method in which low-frequency components of a reproduction signal are not used is obtained to eliminate effects of a crosstalk signal caused by the fact that a reproduction trace laps over adjacent recording tracks.  
       [0016] Further, according to claim 5 of the present invention, a problem of what is called Thermal Asperity Noise (TA noise) which occurs when a reproduction signal is reproduced using a magnetoresistive element may be solved.  
       [0017] Further, according to claim 6 of the present invention, since a reproduction signal is reproduced using a magnetoresistive element and electric current is supplied to the magnetoresistive element with a low-frequency signal, effects of alternating-current components of a power signal which sends to an upper drum a power source supplied to a reproducing head for electric current for detection may be favorably eliminated.  
       [0018] Furthermore, the claim 7 of the present invention is a magnetic reproducing method in which reproduction is performed according to a non-tracking method, wherein a detecting method in which low-frequency components of a reproduction signal are not used is employed as reproduction means.  
       [0019] Accordingly, effects of a crosstalk signal caused by the fact that a reproduction trace laps over adjacent recording tracks may be eliminated, whereby reproduction according to the non-tracking method can be adopted to enable the width of a recording track to be made narrower, and to improve the recording density of a magnetic tape.  
       [0020] Further, according to claim 8 of the present invention, since a Partial Response Class 4 is employed as a detecting method, a detecting method in which low-frequency components of a reproduction signal are not used is obtained to eliminate effects of a crosstalk signal caused by the fact that a reproduction trace laps over adjacent recording tracks.  
       [0021] Further, according to claim 9 of the present invention, since an E-Partial Response Class 4 is employed as a detecting method, a detecting method in which low-frequency components of a reproduction signal are not used is obtained to eliminate effects of a crosstalk signal caused by the fact that a reproduction trace laps over adjacent recording tracks.  
       [0022] Further, according to claim 10 of the present invention, since an EE-Partial Response Class 4 is employed as a detecting method, a detecting method in which low-frequency components of a reproduction signal are not used is obtained to eliminate effects of a crosstalk signal caused by the fact that a reproduction trace laps over adjacent recording tracks.  
       [0023] Further, according to claim 11 of the present invention, a problem of what is called Thermal Asperity Noise (TA noise) which occurs when a reproduction signal is reproduced using a magnetoresistive element may be solved.  
       [0024] Further, according to claim 12 of the present invention, since a reproduction signal is reproduced using a magnetoresistive element and electric current is supplied to the magnetoresistive element with a low-frequency signal, effects of alternating-current components of a power signal which sends to an upper drum a power source supplied to a reproducing head for electric current for detection may be favorably eliminated. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0025]FIG. 1 is a block diagram showing an embodiment of a magnetic reproducing apparatus to which the present invention is applied;  
     [0026]FIG. 2 is a diagram showing an embodiment of a principal part of the magnetic reproducing apparatus in FIG. 1;  
     [0027]FIG. 3 is a characteristic curve to explain the embodiment in FIG. 2;  
     [0028]FIG. 4 is a diagram to explain a magnetic head using a magnetoresistive element;  
     [0029]FIG. 5 is a diagram to explain a Thermal Asperity Noise;  
     [0030]FIG. 6 is a block diagram showing a circuit configuration when signal transmission is performed using a rotary transformer;  
     [0031]FIG. 7 is a block diagram showing another embodiment of the magnetic reproducing apparatus to which the present invention is applied;  
     [0032]FIG. 8 is a diagram showing an embodiment of a principal part of the magnetic reproducing apparatus in FIG. 7;  
     [0033]FIG. 9 is a block diagram showing further another embodiment of the magnetic reproducing apparatus to which the present invention is applied;  
     [0034]FIG. 10 is a diagram showing an embodiment of a principal part of the magnetic reproducing apparatus in FIG. 9;  
     [0035]FIG. 11 is a block diagram to explain a conventional magnetic reproducing apparatus;  
     [0036]FIG. 12 is a constitutional diagram to explain a rotating drum;  
     [0037]FIG. 13 is a diagram to explain recording according to a helical scanning method;  
     [0038]FIG. 14 is a diagram to explain reproduction according to a non-tracking method;  
     [0039]FIG. 15 is a diagram to explain reproduction according to a non-tracking method;  
     [0040]FIG. 16 is a diagram to explain a state in which a reproduction trace laps over adjacent recording tracks; and  
     [0041]FIG. 17 is a characteristic curve to explain azimuth loss. 
    
    
     BEST MODE FOR CARRYING OUT INVENTION  
     [0042] In the present invention, a detecting method in which low-frequency components of a reproduction signal are not used is employed as reproduction means for reproduction according to a non-tracking method, and thus effects of a crosstalk signal caused by the fact that a reproduction trace laps over adjacent recording tracks may be eliminated, whereby a reproduction according to the non-tracking method can be adopted to enable the width of a recording track to be made narrower, and to improve the recording density of a magnetic tape.  
     [0043] Referring to drawings, hereinafter the present invention will be explained, and FIG. 1 is a block diagram showing an embodiment of a data magnetic recording and reproducing apparatus to which a magnetic reproducing apparatus according to the present invention is applied.  
     [0044] In FIG. 1, video data, audio data, additional data, data in files of a computer and the like are input to a data input  1 . A signal input from the data input  1  is processed by a recording signal processing circuit  2  into the signal suitable for magnetic recording, namely, undergoes processing of error correction and packetization, and is supplied to a predetermined precoder  3 . Then, in the precoder  3  preceding, for example, shown in the following numerical expression (1) is executed.  
             1     (     1   ⊕     D   2       )             (   1   )                       
 
     [0045] where, ⊕ indicates mod2 operation.  
     [0046] Subsequently, the signal from the precoder  3  is recorded by a recording head  5  on a recording medium  6  such as a magnetic tape through a recording amplifier  4 . Here, recording on the recording medium  6  is executed according to a helical scanning method using the above-described rotating drum (refer to FIG. 12). Further, the recording medium  6  on which recording has been executed as described above is read by a reproducing head  7  provided on the same rotating drum. In other words, reproduction according to the helical scanning method is also executed when the signal is reproduced, and the signal recorded on the recording medium  6  is read by the reproducing head  7 .  
     [0047] The signal read by the reproducing head  7  is supplied to a reproduction equalizer amplifier  8  for amplification and equalization. Here, a signal reproduced by a magnetic head has a wave form as if the signal were subjected to time differentiation. Therefore, by executing integration and equalization in the reproduction equalizer amplifier  8  a wave form approximately equal to that of a recorded electric-current wave form is obtained. The equalized signal is supplied to an A/D converter  9 , and the signal digitized in the converter is supplied to a circuit  10  having a channel characteristic of a Partial Response Class 4 (hereinafter called PR4), for example.  
     [0048] Specifically, the circuit  10  having the PR4 channel characteristic is configured as shown in FIG. 2. In FIG. 2, delay elements (D)  14  and  15  are provided in one sample period, and an input signal is supplied to the delay element (D)  14  to subtract the original input signal from the output signal of the element  14  in an arithmetic circuit  16 . Further, the subtracted signal is supplied to the delay element (D)  15 , and the original subtracted signal is added to the output signal of the element  15  in an arithmetic circuit  17 . Thus, equalization is executed such that the operation expressed as follows is carried out.  
     (1 −D )*(1 +D )=(1 −D   2 )   (2)  
     [0049] Accordingly, when the above equalization is executed, as shown in FIG. 3, there are obtained frequency characteristics in which low and high frequencies are cut off. That is, as described above, the amount of reduction in crosstalk signals read from adjacent tracks, which is caused by the azimuth loss can not be anticipated especially in the low frequency area as shown in FIG. 17. However, since the circuit  10  has the PR4 channel characteristics in which low frequencies are cut off, effects of crosstalk signals from the above-described adjacent tracks may be favorably eliminated.  
     [0050] Then, an output signal from the circuit  10  having the PR4 channel characteristics is supplied to a PR4 decoder circuit  11  to detect the signal according to the PR4. Further, a signal from the decoder circuit  11  is sent to a reproduction signal processing circuit  12 . Subsequently, the signal is output to a data output  13  after demodulation, restoration to the original form from the packetized state, error correction and the like are executed. Consequently, in this apparatus, since the detecting method (PR4) in which low-frequency components of the reproduction signal are not used is employed as reproduction means, there may be performed reproduction in which the effects of crosstalk signals from adjacent tracks are eliminated.  
     [0051] Accordingly, in this embodiment, the detecting method without using low-frequency components of a reproduction signal is employed as reproduction means for reproduction according to the non-tracking method, whereby effects of crosstalk signals caused by the fact that a reproduction trace laps over adjacent recording tracks may be eliminated and reproduction according to the non-tracking method can be adopted to enable the width of a recording track to be made narrower, and to improve the recording density of a magnetic tape.  
     [0052] Consequently, though reproduction according to the non-tracking method is useful when the width of a recording track is made narrower to improve the recording density, there have been problems in conventional apparatuses that the amount of reduction in crosstalk signals caused by the fact that a reproduction trace laps over the adjacent recording tracks virtually can not be anticipated especially in a low frequency area, thereby causing a possibility that the quality of the reproduction signal is extremely damaged, and that the data amount becomes larger and the recording capacity is reduced when modulation by which low-frequency components are suppressed is used. However, according to the present invention, the above problems may be easily solved.  
     [0053] Then, in the case where the width of a recording track is made narrower as described above to improve the recording density of the magnetic tape, in a conventional induction-type magnetic head since the output of the head is not sufficient and the S/N ratio of a reproduction signal becomes small, data of sufficient quality may not be reproduced. Accordingly, it has been considered that the problems on the S/N ratio and the like are solved by using a magneto-resistive head (hereinafter called MR head) which has an output several times larger than that of the conventional induction-type magnetic head.  
     [0054] Specifically, the above-described MR head has a configuration shown in FIG. 4, for example. As shown in FIG. 4, a magnetoresistive element MR is provided in such a manner that the magnetoresistive element MR crosses a recording track Tr. Thus, the direction of magnetization of the magnetoresistive element MR is changed in response to change in the external magnetic field caused by the recording track Tr, and the electric resistance value of the element MR is changed. Then, predetermined electric current I is allowed to flow into the magnetoresistive element MR from electrodes D at both ends, and changes in the resistance value of the element MR are detected by a voltage drop, thereby obtaining an output voltage V corresponding to a signal recorded on the recording track Tr.  
     [0055] Accordingly, when the above MR head is used, since reproduction of extremely high output may be obtained compared with reproduction by a conventional induction-type magnetic head, data of sufficient quality may be reproduced by making the S/N ratio of the reproduction signal larger even in the case of the recording track Tr, for example, the width of which is made narrower. Further, compared with an induction-type magnetic head, a signal may be reproduced by the head of simple construction, whereby a small-size magnetic head is provided to enable the whole size of the apparatus to be smaller. In addition, using a magnetic head of a simple structure may reduce a possibility of breakdown or the like and may improve the stability, reliability, and the like of the apparatus.  
     [0056] Here, it has been known that a problem of what is called Thermal Asperity Noise (hereinafter called TA noise) occurs, when data recorded on, for example, a magnetic tape are reproduced using the above MR head having such a magnetoresistive element. That is, the MR head detects the change in resistance value of the magnetoresistive element, which is caused by rotation of magnetization angles in the element caused by the external magnetic field. In this case, the external magnetic field indicates a magnetic field caused by a magnetization pattern recorded on such a medium as a tape and a disk.  
     [0057] However, when such MR head collides with a projecting material such as dust generated on media, there occurs a phenomenon in which the temperature of the MR head is rapidly (in one μsec. or less) changed by frictional heat generated by the collision and then the temperature slowly (in several μsec.) returns to the original state due to the thermal diffusion. Thus, the resistance value of the magneto resistive element is also changed by such heat, and in this case the thermal fluctuation in the resistance value is larger than that caused by the above external magnetic field. Accordingly, when the above thermal fluctuation in the resistance value is generated by such heat, there occurs the fluctuation in the output signal voltage of the MR head in which the above change in the resistance value is obtained as change in voltage.  
     [0058] Specifically, as shown in FIG. 5, for example, there occurs such a phenomenon in which a reproduction signal originally held at a constant amplitude by an AGC amplifier or the like suddenly changes immediately after the collision and slowly returns to the original state. Such phenomenon is called Thermal Asperity (TA), and noise caused by TA is referred to TA noise. However, with respect to the above TA noise, experiments have confirmed that length of the influence of the TA noise is made shorter by, for example, cutting off low-frequency components of an input signal (refer to the Japan patent application 2001-115590).  
     [0059] Then, in the above-described apparatus, the detecting method without using low-frequency components of a reproduction signal is employed, whereby the influence of such TA noise is also favorably eliminated. That is, in the above apparatus, low-frequency components of the input signal are cut off in the circuit  10  having the PR4 channel characteristic, whereby the influence of fluctuations caused by the above TA noise may be removed and favorable reproduction signals may be obtained.  
     [0060] On the other hand, when recording is executed according to the above-mentioned helical scanning method, recording and reproducing are executed by mounting the recording head and the reproducing head on the rotating drum. In this case, since the rotating drum is rotated at high speed, it is impossible to be electrically connected by wire. Accordingly, signal transmission is conventionally performed using a transformer called a rotary transformer. Then, an electric configuration is shown in FIG. 6 when signal transmission is performed using the above rotary transformers.  
     [0061] In FIG. 6, a part enclosed by a chain double-dashed line shows the inside of the rotating drum, and the right side separated by a chain line within the part shows, for example, circuits of a rotating upper drum. Then, a signal is applied, for example, from a recording amplifier  18  to a recording head  20  through a rotary transformer  19  provided for recording signals, and is converted into a magnetic signal to be recorded on a magnetic tape  21 . On the other hand, the signal recorded on the magnetic tape  21  is picked up by a reproducing head  22  to be amplified by a reproduction amplifier  23 . Subsequently, the reproduction signal is sent to a reproduction signal processing circuit  25  through a rotary transformer  24  provided for reproduction signals, and the signal is restored to the original state.  
     [0062] Further, when the MR head is used as the reproducing head  22  in the above configuration, since the electric current for detection is required to be supplied to the head, a power source is then required to be sent to the upper drum. Accordingly, an alternating-current power signal is generated by a power drive amplifier  26 , and the power signal is supplied to a rectifying constant voltage circuit  28  through a power rotary transformer  27 , and after obtaining direct current in the rectifying constant voltage circuit  28 , the signal is supplied to the reproduction amplifier  23 .  
     [0063] However, in this case, there is a possibility that alternating-current components of the power signal generated in the above power drive amplifier  26  are mixed into the reproduction signal to deteriorate the reproduction signal. Then, in the above-described apparatus, by utilizing the condition under which the low-frequency components of the input signal are cut off in the circuit  10  having the PR4 channel characteristic, frequencies lower than the cut off low-frequency component in the circuit  10  having the PR4 channel characteristic are, for example, used as frequencies for alternating-current components of the power signal generated in the power drive amplifier  26 .  
     [0064] According to the above configuration, the power signal generated by the power drive amplifier  26  is supplied to the rectifying constant voltage circuit  28  through the power rotary transformer  27 , and after obtaining direct current in the rectifying constant voltage circuit  28 , the signal supplied to the reproduction amplifier  23 , and therefore even when the alternating-current components of the power signal are mixed into the reproduction signal, the alternating-current components are cut off in the circuit  10  having the PR4 channel characteristic, thereby the influence of fluctuation caused by the alternating-current components of the power signal being removed. Accordingly, a favorable reproduction signal may be obtained.  
     [0065] Thus, according to the magnetic reproducing apparatus of the present invention, the apparatus in which reproduction is performed according to the non-tracking method is provided, and effects of a crosstalk signal caused by the fact that a reproduction trace laps over adjacent recording tracks may be eliminated by using the detecting method without using low-frequency components of a reproduction signal as reproduction means, whereby reproduction according to the non-tracking method can be adopted to enable the width of a recording track to be made narrower, and to improve the recording density of a magnetic tape.  
     [0066] Furthermore, although in the above description the circuit  10  having the PR4 channel characteristic has been employed as the detecting method without using the low-frequency components of the reproduction signal, other detecting methods may be applied to the present invention.  
     [0067] Thus, in FIG. 7 there is shown another embodiment in which a circuit having an E-Partial Response Class 4 (hereinafter called EPR 4) channel characteristic is employed as the detecting method without using the low-frequency components of the reproduction signal. In FIG. 7, video data, audio data, additional data, data in files of a computer and the like are input to a data input  31 . A signal input from the data input  31  is processed by a recording signal processing circuit  32  into a signal suitable for magnetic recording, that is, undergoes processing of error correction and packetization, and is supplied to a predetermined precoder  33 .  
     [0068] In the precoder  33 , similar preceding to that of the above numerical expression (1) is executed. Then, the signal from the precoder  33  is recorded by a recording head  35  on a recording medium  36  such as a magnetic tape through a recording amplifier  34 . Here, recording on the recording medium  36  is executed according to the helical scanning method. Further, with respect to the recording medium  36  on which recording has been executed as described above, reproduction is also executed according to the helical scanning method when a signal is reproduced, and a signal recorded on the recording medium  36  is read by a reproducing head  37 .  
     [0069] Furthermore, the signal read by the reproducing head  37  is supplied to a reproduction equalizer amplifier  38  to be amplified and equalized by means of integration and equalization, in which an electric current wave form similar to that of the recorded electric current wave form is obtained. The equalized signal is supplied to an A/D converter  39 , and the signal digitized in the converter is supplied to a circuit  40  having EPR4 channel characteristic, for example. Specifically, the circuit  40  having the EPR4 channel characteristic is configured as shown in FIG. 8.  
     [0070] In FIG. 8, delay elements (D)  44 ,  45 , and  46  are provided in one sample period and an input signal is supplied to the delay element (D)  44 , and then in an arithmetic circuit  47  the original input signal is subtracted from the output signal of the element  44 . The subtracted signal is supplied to the delay element (D)  45 , and in an arithmetic circuit  48  the original subtracted signal is added to the output signal from the element  45 . Further, the added signal is supplied to the delay element (D)  46 , and in an arithmetic circuit  49  the original added signal is added to the output signal from the element  46 . Accordingly, in the circuit  40  equalization is executed such that the operation expressed as follows is carried out.  
     (1−D 2 )*(1+D)   (3)  
     [0071] Accordingly, the above equalization is also executed in the circuit having the frequency characteristics, in which low and high frequencies are cut off in a similar manner to that of the circuit in FIG. 2, that is, as described above, though the amount of reduction in crosstalk signals read from adjacent tracks caused by the azimuth loss virtually can not be anticipated especially in the low frequency area, the circuit  40  has the EPR4 channel characteristic in which low frequencies are cut off, whereby effects of the above-described crosstalk signals from adjacent tracks may be favorably eliminated.  
     [0072] Then, the output signal from the circuit  40  having the EPR4 channel characteristics is supplied to an EPR4 decoder circuit  41  to detect the signal. Further, the signal from the decoder circuit  41  is sent to a reproduction signal processing circuit  42 , and the signal is output to a data output  43  after demodulation, restoration to the original form from the packetized state of the signal, error correction and the like are executed. Accordingly, also in this embodiment, by using the detecting method according to the E-Partial Response Class 4 there may be executed reproduction in which effects of crosstalk signals from adjacent tracks, the TA noise, the alternating-current components of the power signal, and the like are eliminated.  
     [0073] In FIG. 9, there is shown further another embodiment in which a circuit having an EE-Partial Response Class 4 (hereinafter called EEPR 4) channel characteristic is employed as the detecting method without using the low-frequency components of the reproduction signal. In FIG. 9, video data, audio data, additional data, data in files of a computer and the like are input to a data input  51 . A signal input from the data input  51  is processed by a recording signal processing circuit  52  into a signal suitable for magnetic recording, that is, undergoes processing of error correction and packetization, and is supplied to a predetermined precoder  53 .  
     [0074] In the precoder  53 , similar preceding to that of the above-described numerical expression (1) is executed. Then, the signal from the precoder  53  is recorded by a recording head  55  on a recording medium  56  such as a magnetic tape through a recording amplifier  54 . Recording on the recording medium  56  is executed according to the helical scanning method. Further, with respect to the recording medium  56  on which recording has been executed as described above, reproduction is also executed according to the helical scanning method when the signal is reproduced, and a signal recorded on the recording medium  56  is read by a reproducing head  57 .  
     [0075] Furthermore, the signal read by the reproducing head  57  is supplied to a reproduction equalizer amplifier  58  to be amplified and equalized by means of integration and equalization, in which an electric current wave form similar to that of the recorded electric current wave form is obtained. The equalized signal is supplied to an A/D converter  59 , and the signal digitized in the converter is supplied to a circuit  60  having EEPR4 channel characteristic, for example. Specifically, the circuit  60  having the EEPR4 channel characteristic is configured as shown in FIG. 10.  
     [0076] In FIG. 10, delay elements (D)  64 ,  65 ,  66 , and  67  are provided in one sample period and an input signal is supplied to the delay element (D)  64 , and then in an arithmetic circuit  68  the original input signal is subtracted from the output signal of the element  64 . The subtracted signal is supplied to the delay element (D)  65 , and in an arithmetic circuit  69  the original subtracted signal is added to the output signal from the element  65 . The added signal is supplied to the delay element (D)  66 , and in an arithmetic circuit  70  the original added signal is added to the output signal from the element  66 . Further, the added signal is supplied to the delay element (D)  67 , and in an arithmetic circuit  71  the original added signal is added to the output signal from the element  67 . Accordingly, in the circuit  60  equalization is executed in such a manner that the operation expressed as follows is carried out.  
     (1−D 2 )*(1+D) 2    (4)  
     [0077] Accordingly, the above equalization is also executed in the circuit having the frequency characteristics, in which low and high frequencies are cut off in a similar manner to that of the circuit in FIG. 2, that is, as described above, though the amount of reduction in crosstalk signals read from adjacent tracks caused by the azimuth loss can not be anticipated especially in the low frequency area, the circuit  60  has the EEPR4 channel characteristic in which low frequencies are cut off, whereby the above-described effects of crosstalk signals from adjacent tracks may be favorably eliminated.  
     [0078] Then, the output signal from the circuit  60  having the EEPR4 channel characteristics is supplied to an EEPR4 decoder circuit  61  to detect the signal. Further, the signal from the decoder circuit  61  is sent to a reproduction signal processing circuit  62 , and the signal is output to a data output  63  after demodulation, restoration to the original form from the packetized state of the signal, error correction and the like are executed. Accordingly, further in this embodiment, by using the detecting method according to the EE-Partial Response Class 4 there may be executed reproduction in which effects of crosstalk signals from adjacent tracks, the TA noise, the alternating-current components of the power signal, and the like are eliminated.  
     [0079] Moreover, each of the above-described embodiments may use what is called Viterbi decoder as the decoder circuit  11  according to PR4, the decoder circuit  41  according to EPR4, and the decoder circuit  61  according to EEPR4. Furthermore, in the above decoders it is possible to employ a trellis modulation method at the same time.  
     [0080] The present invention is not limited to the embodiments described above, and can take various modifications without departing from the gist of the present invention.  
     DESCRIPTION OF REFERENCE NUMERALS  
     [0081] Reference Numerals Particulars  
     [0082] 1 —DATA INPUT  
     [0083] 2 —RECORDING SIGNAL PROCESSING CIRCUIT  
     [0084] 4 —RECORDING AMPLIFIER  
     [0085] 5 —RECORDING HEAD  
     [0086] 6 —RECORDING MEDIUM SUCH AS MAGNETIC TAPE  
     [0087] 7 —REPRODUCING HEAD  
     [0088] 8 —REPRODUCTION EQUALIZER AMPLIFIER  
     [0089] 9 —A/D CONVERTER  
     [0090] 10 —CIRCUIT WITH CHANNEL CHARACTERISTIC OF PARTIAL RESPONSE CLASS 4  
     [0091] 11 —DECODER CIRCUIT OF PARTIAL RESPONSE CLASS 4  
     [0092] 12 —REPRODUCTION SIGNAL PROCESSING CIRCUIT  
     [0093] 13 —DATA OUTPUT