JP2555151B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary head type digital audio tape recorder (hereinafter referred to as DAT), and more particularly to a control device of a cylinder rotational speed in a high-speed sati such as music selection. .

[Conventional technology]

In DAT of the rotary head system, in order to perform high-speed random music selection (cueing of music) at a speed of several tens to several hundred times the normal playback speed, a signal indicating the start of the music recorded in the track, It is necessary to accurately read the control signal recorded at the same recording density as the music PCM signal such as a signal for displaying the time and the music number information signal when the tape is running at high speed.

By the way, when the tape is run at a speed different from that during normal recording / reproduction, the scanning locus of the head crosses a plurality of signal tracks recorded on the tape, and assuming that the cylinder rotation speed is constant, the relative speed of the head and the tape. Will change.

On the other hand, in the DAT, a data punching (data strobe) circuit is used as a circuit for reproducing a digital signal from a signal reproduced from the head. Normally, the input transmission rate of this circuit has a margin for the speed deviation and jitter of the tape running system ±. It is around 10%, the relative speed with the head changes due to the high speed running of the tape, and the transmission rate of the input signal is ± 10
If it deviates from the range of around%, data reproduction is impossible, that is, random access cannot be performed.

Therefore, in DAT, the cylinder rotation speed cannot be made the same as that during normal recording / reproduction when the tape is running at high speed, and the relative speed between the head and the tape is always constant, or the tape is within the allowable jitter of the data strobe circuit. It is essential to perform follow-up control according to the traveling speed of the vehicle. An apparatus for controlling the relative speed between the tape and the head by changing the rotational speed of the cylinder in accordance with the running speed of the tape is disclosed, for example, in Japanese Patent Laid-Open No. 61-110359. This device controls the cylinder rotation speed so that the reproduction clock frequency obtained as a frequency synchronized with the reproduction signal in the data strobe circuit becomes a predetermined fixed frequency.

[Problems to be Solved by the Invention] However, in the above-described prior art, the re-pull-in control in the case where the cylinder servo is unlocked during the cylinder rotation speed follow-up control with a constant relative speed with respect to the tape running is not taken into consideration. However, if the cylinder servo is once unlocked due to, for example, a scratch on the tape or a dropout of a signal, there is a problem that re-drawing cannot be performed.

An object of the present invention is to make it possible to reliably re-engage the cylinder rotation speed following servo even if it is once disengaged, and determine that it is abnormal if the servo lock is disengaged for a long time. Then, the cylinder speed is controlled to a fixed value.

[Means for solving the problem]

The above object is achieved by first sweeping the cylinder rotational speed upward and downward about the cylinder rotational speed that matches a predetermined tape speed when the servo lock is released. In other words, if the cylinder rotation speed is kept on standby by sweep control, when the signal returns to a state where it can be read correctly, the point where the relative speeds of the tape and head match is inevitably passed. The number can be re-pulled into constant relative velocity servo control.

Further, the determination that the tracking servo deviation of the cylinder rotation speed continues for a long time can be realized by, for example, measuring the number of times of the above-mentioned cylinder rotation speed sweep control, and the control signal controls the cylinder rotation speed to a predetermined fixed value. to do so,
For example, it is achieved by driving the cylinder in an independent FG servo state of another system.

[Action]

The state determination means determines the state of the relative speed of the tape and the head, and outputs a predetermined control signal when the relative speed exceeds the allowable value. The first cylinder rotation speed control means is driven by the control signal of the state determination means to accelerate and decelerate the cylinder motor so that the cylinder sweeps up and down by a predetermined range around the rotation speed that matches a predetermined tape speed. Output voltage. The detecting means also monitors the number of sweeps of the cylinder rotation speed, and outputs a control signal for driving the second cylinder rotation speed control means when the number of sweeps exceeds a predetermined number.

The second cylinder rotation speed control means constitutes a servo loop including an FG (frequency generator) mounted integrally with the cylinder motor, and operates so as to control the cylinder rotation speed to a predetermined constant value. . The switching means selects and supplies a drive signal to the cylinder motor to the cylinder rotation speed follow-up control means and the first and second cylinder rotation speed control means, the operation of which is controlled by the control means. The control means discriminates the control signals of the state discriminating means and the detecting means, and when receiving the control signal from the state discriminating means that the lock of the cylinder rotational speed following servo is released, the switching means is connected from the cylinder rotational speed following control means to the above. After switching to the first cylinder rotation speed control means side and further receiving a control signal from the detection means, a control signal for switching the connection of the switching means to the first to second cylinder rotation speed control means side is output.

With this configuration, even if the cylinder servo is unlocked due to a scratch on the tape or a signal dropout during the servo that follows the cylinder rotation speed for high-speed tape running, the cylinder rotation speed will be higher than the original value corresponding to the tape speed. ， In order to sweep down, when the signal returns to the state where it can be read correctly, it always passes the point where the relative speed of the tape and the head match, and at this point, the cylinder rotation speed following servo can be re-engaged. it can. In addition, in the case of an abnormal situation where the sweep control of the cylinder speed continues for a long time, this is detected and the cylinder speed is switched from the sweep control to the fixed control, preventing cylinder noise caused by repeating the sweep control more than necessary. it can.

〔Example〕

Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. In the figure, 1 is a cylinder, 2a and 2b are magnetic heads, 3 is a magnetic tape, 4 and 5 are tape winding, respectively.
A reel base for sending out, 6 is a reel motor, 7 is a gear connected to the reel motor and drives the reel bases 4 and 5 according to the rotation of the reel motor, 8 is a high speed tape running means,
Reference numeral 9 is a cylinder rotation speed control means for controlling the cylinder rotation speed so that the relative speed with the head becomes constant according to the tape running speed, 10 is a state judgment means for judging the state of the relative speed of the tape and the head, and 11 is First cylinder speed control means for sweeping the cylinder speed up and down, 12 is detection means for detecting the sweep time of the cylinder speed by the first cylinder speed control means 11, and 13 is a predetermined cylinder speed. Second cylinder speed control means for controlling to a fixed value of
Reference numeral 14 is a switching means, 15 is a control means for controlling the switching means 14, 16 is a cylinder motor, and 17 is an FG (frequency generator) of the cylinder motor.

In the embodiment shown in FIG. 1, when the lock of the cylinder rotation speed following servo is released due to a scratch or dropout of the tape during high speed tape running, this is discriminated by the state discrimination means 10, and The first cylinder rotation speed control means 11 is operated by the control signal, and at the same time, the switching means 14 is switched to switch the cylinder rotation speed control from the cylinder rotation speed control means 9 to the first cylinder rotation speed control means 11. The number is swept up and down by a predetermined range centered on the value that matches the predetermined tape speed. When the signal returns to a state where it can be read correctly, the cylinder rotation speed is swept so that the point where the relative speeds of the tape and the head match is inevitably passed. Is used to re-engage the rotation speed following servo by switching the cylinder rotation speed to the control by the cylinder rotation speed control means 9 again. In addition, when the tape is damaged or the dropout continues for a long time, The detection means 12 detects this, and the control signal further switches the switching means 14 to change the cylinder speed from the first cylinder speed control means 11 to the second cylinder speed control means 13.
To control the rotation speed to a predetermined fixed value.

The tape high-speed running means 8 is composed of, for example, a servo loop in which the sum of the cycles of the FG signal synchronized with the number of rotations of the well-known reel stands 4 and 5 is constant. In the forward search, the gear 7 moves to the A side to move the tape at a high speed in the A'direction, and in the reverse search, the gear 7 moves in the B direction to move the tape at a high speed in the B'direction. Although they are configured, they are well known, and since they are not the essence of the present invention, their details are omitted.

The operation of the control of the cylinder rotational speed, which is the gist of the present invention, will be described below, while showing concrete configuration examples of each part.

FIG. 2 shows the configuration of the cylinder rotation speed control means 9. In the figure, 18 and 19 are reproduction amplifiers for reproducing the magnetic head outputs of 2a and 2b, respectively, 20 is a switching circuit for switching the reproduction amplifier outputs of 18 and 19, 21 is a head switching signal generation circuit, and 22 is a waveform equivalent of the reproduction signal. An equalizer circuit for performing the operation, 23 a comparator for binarizing the output of the equalizer circuit, 24 a PLL circuit for reproducing a data synchronous clock from reproduced data, and 25 a -V (frequency-voltage) converter having a reproduced clock frequency as an input , 26 is an error amplifier, and 27 is a reference voltage source. 18 to 24 are indispensable parts for reproducing the data synchronous clock from the reproduced data in the DAT, and their specific circuits and control operations are known in, for example, JP-A-61-110359. Although details are omitted, the clock frequency reproduced by the PLL circuit 24 is proportional to the relative speed of the tape and the head. That is, when the relative speed of the head is faster than the original speed with respect to the running speed of the tape, the reproduction clock frequency becomes higher than the frequency corresponding to the transmission rate, and conversely, when the relative speed of the head is slow, it becomes low. By the way, DA
Transmission rate of T, that is, reproduction clock frequency is 9.408MH
z.

The −V converter 25 converts the reproduction clock frequency of the PLL 24 into a voltage, and outputs a control signal according to the deviation of the reproduction clock frequency from the transmission rate. That is, when the reproduction clock frequency matches the transmission rate, a predetermined reference voltage is output, and when the reproduction clock frequency becomes higher, the reproduction clock frequency decreases, and when the reproduction clock frequency decreases, it increases. Error amplifier
26 also serves as a cylinder motor drive, and the reference voltage 27
And the output signal of the −V converter 25 are compared, and the comparison error e ₁
Is applied to the cylinder motor 16 via the switching means 14.

If the value of the reference voltage 27 is set to be equal to the operation center of the -V converter 25, that is, the output voltage when the reproduction clock frequency coincides with the transmission rate, for example, the head voltage relative to the tape speed can be set by the pendant configuration. When the relative speed is faster than the original speed, the output e _{1 of the} error amplifier is decreased to lower the cylinder speed, and conversely, when the head relative speed is slow, the cylinder speed is increased. Control is performed so that servo control of cylinder speed is performed so that the reproduction clock frequency is always constant, that is, the relative speed between the tape and the head is constant.

FIG. 3 shows the configuration and operation of the state determination means 10. In the figure, 28 is a reproduced clock frequency discriminator, and the other parts designated by the same reference numerals as those in FIGS. 1 and 2 are the same. The following accuracy of the cylinder rotation speed with respect to the tape speed has a certain allowable range with respect to the theoretical value with a constant relative speed due to the allowable jitter of the PLL circuit described above. The reproduction clock frequency discriminator 28 monitors the reproduction clock frequency of the PLL circuit 24, and as shown in FIG.
A control signal e ₂ is output to the tape to notify that the relative speed of the head has exceeded the permissible range when the reproduction clock is output in which the cylinder rotational speed deviates from the following permissible range for the constant relative speed. work. The specific circuit of the reproduction clock frequency discriminator 28 can be simply configured by counting the cycle of the reproduction clock frequency and the like, and the details thereof will be omitted.

FIG. 4 shows the configuration and operation waveform of the first cylinder rotation speed control means 11. In the figure, 29 is the cylinder motor.
Comparator that binarizes FG signal, 30 is binarized FG
Signal period measurement circuit, 31 and 32 are switches, 33 and
Reference numerals 34 and 35 denote positive and negative DC voltage sources, respectively, and a driving amplifier, and other parts denoted by the same symbols as in FIGS. 1 to 3 are the same. First, when the control signal e ₂ is input from the above state determining means 10, the switch 32 is closed, and at the same time, the FG signal cycle measuring circuit 30 operates so that the contact of the switch 31 is closed to the side a. As a result, a positive DC voltage source 33 voltage is generated at the output of the drive amplifier 35. As will be described later, when the control signal is output from the state determination means 10, the switching means 14 is operated by the control means 15 shown in FIG.
Since a drive signal from the first cylinder rotation speed control means 11 is applied to the cylinder rotation speed, the cylinder rotation speed is accelerated by the positive DC voltage source 33 and rises. The FG signal cycle measuring circuit 30 monitors the cycle of the FG signal, that is, the rotation speed of the cylinder. When the cylinder rotation speed reaches a predetermined value due to acceleration by the positive DC voltage source 33, the contact of the switch 31 is turned to the b side. A control signal for switching to is output. Next, when the contact of the switch 31 is switched to the b side, the negative direct-current voltage source 34 is output to the output of the drive amplifier 35, so that the cylinder motor moves so that braking is performed by this voltage and the rotation speed decreases. When the cylinder speed drops to a predetermined value, the FG signal cycle measuring circuit 30 detects this and outputs a control signal for switching the contact of the switch 31 to the a side again.
The operation waveform is shown in FIG. The cycle measuring circuit 30 for the FG signal detects the upper and lower limits of the cylinder speed, and the control signal applies a DC voltage e ₃ of (c) to brake and accelerate the cylinder to the cylinder motor to determine the cylinder speed ( It is possible to sweep up and down within the set range as in d).

It should be noted that the sweep width of the cylinder rotation speed needs to be appropriately selected above and below the rotation speed at a constant relative speed with respect to a predetermined tape speed. That is, the relative speed constant cylinder rotational speed to the tape speed in the example of (b) of Figure (d) is N _O
If so, it is necessary to sweep up and down around this. This is because the relative speed of the tape and head must be within the sweep range in order to ensure that the cylinder rotation tracking servo will be re-engaged when the signal can be read correctly due to scratches or dropouts on the tape. This is because they have to pass through the coincident points. As a result, for example, in the operation of (d), when the cylinder rotation speed following servo is unlocked due to a scratch or dropout of the tape at time t ₀ , the sweep control is started, but the signal can be correctly read before time t _1. If it has returned, at the time when the relative speed of t ₁ matches, t ₁
From when the signal is restored between t ₂ can be performed retraction re cylinder rotational speed tracking servo each at time t _2.

FIG. 5 shows the operation of the detecting means 12. The detection means 12 operates to monitor the elapsed time from time t ₀ when the cylinder rotation speed sweep control starts in the operation waveform of FIG. 4 (b) and output a control signal after a predetermined time has elapsed. is there. Although it can be simply configured by a time-limit circuit or the like synchronized with the control signal of the state determination means 10, in the present embodiment, an example in which the number of sweeps of the cylinder rotation speed by the first cylinder rotation speed control means 11 is monitored Was used. Specifically, it is composed of a counter or the like, and counts the number of repetitions of the switching signal of the switch 31 or the output e ₃ shown in FIG. 4B as shown in FIG. 4A, and the total count value is a predetermined value. When it reaches n, the control signal e ₄ of "H" shown in (b) is output. The counter is also controlled by the control signal e ₂ , and the output is reset at the falling edge thereof.

FIG. 6 shows the configuration of the second cylinder rotation speed control means 13. In the figure, 36 is a -V converter, 37
Is a switch, 38 and 39 are reference voltages, 40 is error amplification, and other parts denoted by the same reference numerals as those in FIGS. 1 to 5 are the same. The -V converter 36 is for converting the FG signal of the cylinder motor into a voltage, the reference voltages 38 and 39 are for changing the control value of the cylinder rotational speed according to the search direction, and the switch 37 is for an error amplifier. The reference voltage of 40 is switched, and its control is performed by a switching signal such as a microprocessor for controlling the system, which is not shown in FIG. 1, but controls the system, for example.

This configuration is a well-known FG servo device, and the cylinder rotation speed is fixedly controlled according to the values determined by the reference voltages 38 and 39 by the same operation as the cylinder rotation speed follow-up control means 9 described above.

Now, let us explain the intention of changing the control value of the cylinder rotation speed according to the direction of the search.

In order to keep the relative speed with the head during high tape feeding the same as during normal recording / playback, the cylinder speed must be changed according to the tape speed. Forward search and reverse search are different. That is, for example, if the tape running speed for search is set to 200 times that for normal recording / playback, the cylinder rotation speed must be controlled to 3000 rpm for forward search, whereas it must be controlled to 3000 rpm for forward search. It is 1000 rpm. On the other hand, the control by the second cylinder rotation speed control means 13 detects the cylinder rotation speed when the sweep control of the cylinder rotation speed which is performed when there is a scratch or dropout on the tape continues for a long time, and the cylinder rotation speed is detected. It is something that is fixed. Therefore, considering the case where the second cylinder rotation speed control means operates to control the cylinder rotation speed to a fixed value and the signal of the tape can be read correctly, the cylinder rotation speed following servo is activated at that time. To enable quick re-engagement, depending on the search direction, for example, if the search speed is 200 times, control the cylinder speed to 3000 rpm during forward search and 1000 rpm during reverse search. It is preferable to do so.

FIG. 7 shows the configuration and operation of the control means 15. In the figure, 41 is a NOR gate, 42 is an inverter, and 43.
Reference numerals 44 and 44 denote AND gates, and the other portions denoted by the same symbols as in FIGS. 1 to 6 are the same. (B) The control signal e ₂ of the state determination means 10 and the detection means as shown in the operation waveform of FIG.
When 12 control signals e ₄ are input at the timings (a) and (b), the logic circuits 41 to 44 output the control signals S _{1 to} S ₃ shown in (c) to (e). The control signal S ₁ is “H” only when the control signal e ₂ of the state determination means 10 is “L”, and S ₂ is “H” when e ₂ is “H”.
A control signal e ₄ of it by detecting means 12 only for the period of "L""H", S 3 only period e ₂ and e ₄ are both "H""H" becomes, S ₁ to S ₃ each It is connected to the switches ac of the switching means 14, and the switches ac are configured to close only when the control signal is "H".

The configuration and operation of each unit have been described above. The overall operation in the case where the tape has scratches and dropouts in such a configuration will be described below.

FIG. 8 shows the operation. (A) is a tape, and the shaded portion represents an area where signal reproduction is impossible due to scratches or dropouts. Before the time t ₀ , the cylinder rotation number follow-up control means 9 performs cylinder follow-up servo control so that the relative speed of the head becomes constant with respect to the tape running speed. At time t ₀ , when a tape scratches or drops out,
Since the PLL circuit is unlocked, the state determining means 10 outputs the control signal e ₂ shown in (b). And control means
Control signal for switching the switch of the switching means 14 from a to b by judging the state of e ₂ from the control signal e ₄ of the detecting means 12 from 15
S ₂ is output, and at the same time, the control signal e ₂ causes the first cylinder rotation speed detecting means 11 to start operating, and the cylinder rotation speed is swept upward and downward around the tape speed N _O as shown in (c). Start. If specifically set the search speed to 200 times N _O is almost 3000rpm with a forward search (reverse search 1000 rpm), the upper limit of the rotational speed sweeps,
If the lower limit is 500 rpm for N _O , the upper limit N _U is 3500
rpm (1500 rpm for reverse search), 2500 rpm for lower limit N _D
(Reverse search is 500 rpm).

Here, if the number of sweeps n of the number of cylinder revolutions by the detection means 12 is set to, for example, n = 5, the scratch or dropout of the tape is relatively short (n <5) and the signal returns at time t _1. In this case, when the relative speeds of the tape and the head match with each other due to the sweep of the cylinder rotation speed after t ₁ , e ₂ disappears, and at the same time, the control signal from the control means 15 switches the switch of the switching means 14 from b to a again.
Since S ₁ is output, the cylinder speed is re-pulled into the normal follow-up servo control by the cylinder speed control means 9.

Next, in the case where the tape scratches or drops out at time t ₂ and this time is long, the cylinder rotation speed is swept by the first cylinder rotation speed control means 11 in the same manner, but the detection means 12 causes At the time t ₃ when n = 5 is counted, the detection means 12 outputs the control signal e ₄ . As a result, the control means 15 outputs the control signal S ₃ for switching the switch of the switching means 14 from b to c this time, so that after t _3, the cylinder rotation speed is set to a fixed value by the second cylinder rotation speed control means 13. Constant speed control to N _C. Of course, this N _O is set to match N _O as described above. Then, at time t ₄ exiting the wounds, or dropouts of the tape, firstly, t ₄ relative velocity of the tape and the head from the previous cylinder rotational speed N _C is set to match the N _O is substantially equal to Therefore, the control signal e ₂ of the state determination means 10 disappears. At the same time, since the control signal e ₄ of the detecting means 12 disappears due to the falling edge of e _2, the control means 15 outputs the control signal S ₁ for switching the switch of the switching means 14 from c to a, and after the time t _4, the cylinder The rotation speed is re-pulled into the normal follow-up servo control by the cylinder rotation speed control means 9.

The embodiments of the present invention have been described above. The state discriminating means 10 in FIG. 1 is composed of a reproduction clock frequency discriminator as shown in FIG. 3, but this is not particularly limited, and for example, a signal processing LS for reproducing a signal from reproduced data.
It is also possible to detect the error state of I or the deviation of the VCO (voltage controlled oscillator) control voltage of the PLL circuit. Further, the sweep control of the cylinder rotational speed by the first cylinder rotational speed control means 11 is also performed by switching the positive and negative DC voltage sources as shown in FIG. In the case of a structure having a rotatable cylinder motor and a drive circuit, the rotational drive direction may be switched by a control signal of the cycle measuring circuit of the FG signal. Further, in FIG. 1, the switching means 14 and the control means 15 are provided independently, but this is not particularly limited, and the same control is of course possible even if they are integrated by, for example, a well-known logic circuit. It is easy to make various modifications within the scope of the invention.

〔The invention's effect〕

As described above, according to the present invention, when the cylinder servo becomes inoperable due to a scratch or dropout of the tape during the cylinder revolution tracking servo during high-speed tape traveling, this is detected and the cylinder revolution speed is determined by the tape. Since the value that matches the speed is swept up and down, the point where the relative speed of the tape and head matches when the tape returns from scratches or dropouts and the signal can be read correctly. It is possible to pass through without fail, and at this time, the cylinder rotation speed can be surely re-pulled into the follow-up servo control with a constant relative speed. In addition, if the tape is damaged or the dropout continues abnormally for a long time, the cylinder speed is switched from the sweep control to the fixed control by detecting this, and the sweep control is repeated more than necessary. It is possible to prevent the generation of noise.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention, FIG. 2 is a block diagram of a cylinder rotation speed follow-up control means, and FIGS. 3 (a) and 3 (b) are a configuration of state determination means. A block diagram and a waveform diagram showing the operation, FIG. 4 is a block diagram showing the configuration of the first cylinder rotation speed control means, FIG. 5 is a waveform diagram showing the operation of the detection means, and FIG. 6 is the second cylinder rotation. 7 is a block diagram of the number control means, FIGS. 7A and 7B are block diagrams and waveform diagrams of the control means, and FIG. 8 is a waveform diagram of each part of the magnetic recording / reproducing apparatus of the present invention. 10 ... State determination means, 11 ... First cylinder speed control means, 12 ... Detection means, 13 ... Second cylinder speed control means, 14 ... Switching means, 15 ... Control means, 1 …… Cylinder, 3 …… Tape.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keiji Noguchi Keiji Noguchi, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture Home Appliance Research Laboratory, Hitachi, Ltd. (72) Shozaburo Sakaguchi 25 Nishimachi, Kawagoe-shi, Saitama Prefecture 1 Pioneer Kawagoe Factory Co., Ltd. (72) Inventor Kenichiro Kawasaki 25-1 Nishimachi, Yamada, Kawagoe City, Saitama Pioneer Kawagoe Factory

Claims (4)

(57) [Claims] 1. A magnetic recording / reproducing apparatus for scanning a magnetic tape by a head mounted on a rotary cylinder to record a signal and reproducing the recorded signal, wherein a reel shaft is driven to perform normal recording / reproduction. Magnetic recording comprising high speed running control means for running the magnetic tape at a speed higher than the speed, and cylinder speed control means for controlling the cylinder speed so that the frequency of the clock signal reproduced from the reproduction signal becomes constant. In the reproducing device, a state discriminating means for discriminating a reproduction state of a signal, and a first cylinder rotational speed control means for sweeping the rotational speed of the rotary cylinder up and down within a predetermined range by a control signal of the state discriminating means. Detecting means for detecting the sweep time of the rotational speed of the rotary cylinder controlled by the first cylinder rotational speed control means, and a control signal of the detecting means. Second cylinder rotation speed control means for controlling the rotation speed of the cylinder to a predetermined fixed value, cylinder rotation speed control means for controlling the cylinder rotation speed so that the frequency of the reproduced clock signal becomes constant, and Switching means for switching the output signals of the first and second cylinder speed control means, and control means for controlling the switching means in response to these states by inputting the control signals from the state determination means and the detection means. When the cylinder rotation speed control servo by the cylinder rotation speed control means is disengaged by the state determination means, the cylinder rotation speed is swept up and down by the first cylinder rotation speed control means to change the cylinder rotation speed. When the sweep time reaches a predetermined value, the cylinder rotation speed is set to the second value by the control signal of the detecting means.
2. A magnetic recording / reproducing apparatus characterized in that the cylinder rotation speed control means is controlled to a predetermined fixed value. 2. The magnetic recording / reproducing apparatus according to claim 1, wherein said detecting means detects the number of times of sweeping of the cylinder rotation speed by said first cylinder rotation speed control means. 3. The magnetic element according to claim 1, wherein the state discriminating means discriminates by discriminating the frequency of the clock signal reproduced from the reproduced signal or the error state of the reproduced signal. Recording / playback device. 4. The cylinder rotation speed by the second cylinder rotation speed control means is different from each other according to the tape running direction.
The magnetic recording / reproducing apparatus described.