JPS6386137A - Digital signal recording and reproducing device - Google Patents

Abstract

PURPOSE:To simplify circuit constitution by measuring a period of a specified frequency signal in a recording signal, detecting a feeding speed of a magnetic tape, and detecting a relative speed of a rotary head and the tape. CONSTITUTION:A counter 7 counts a block from a oscillator 11 only in an input period of a reproducing signal from a comparator 6 and a gate signal from a generator 10, and a reproducing signal in a period in which this counting value is within a prescribed range is held in a register 13 by a pilot signal selecting circuit 12. A system control part 14 designates a necessary speed, and refers to a counting value per one period of a reproducing pilot signal by using a speed correspondence table 19. As for this value, a duty value is prepared, based on the contents of the register 13, and supplied to a generator 21. The output of the generator 21 controls a speed of a reel motor 18 through a driving circuit 17.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital signal recording and reproducing apparatus, and more particularly to a digital signal recording and reproducing apparatus having means for recording and reproducing digital signals on a magnetic tape using a rotary head.

2. Description of the Related Art Digital signal recording and reproducing apparatuses have been known that record digitally modulated information signals (for example, pulse code modulated digital audio signals) on a magnetic tape using a rotating head and reproduce the recorded information. During playback, the playback signal is waveform-equalized and then phase-locked.
A pit clock is generated by a loop (PLL), and the original digital signal is demodulated from the reproduced signal using this pit clock. For this reason, the frequency characteristics of the waveform equalization circuit and the lock range and capture range of the PLL are related to the bit rate of the reproduced signal, so the relative linear velocity (hereinafter referred to as relative velocity) between the rotating head and the running speed of the magnetic tape
It is necessary to detect the relative speed and control the relative speed to be constant based on the detection result, or to variably control the relative speed so that the bit rate of the reproduced signal is constant. Also,
In order to search for recorded signals in a short time, even during high-speed playback when playing back recorded edge digital signals from a magnetic tape whose running speed is faster than that during recording, the direction is the same as that during recording (
Since the tape is run in either the forward direction or the reverse direction, it is necessary to detect and control the above-mentioned relative speed.

For this reason, the tape speed has traditionally been detected by generating pulses corresponding to the number of rotations of a rotary encoder that is in contact with the magnetic tape while the tape is running, and measuring this pulse. ■Parts accuracy control is required; ■Encoder tends to slip during high-speed feeding, causing errors in speed detection. ■ Errors occur in speed detection due to aging of bearings due to wear. ■Since an encoder is added to the driving system, there are drawbacks such as affecting driving performance. It is also possible to form a linear track other than the track recorded by the rotating head and record and reproduce speed detection signals there, but this requires a fixed head and a recording/reproducing circuit dedicated to the linear track, which reduces the number of parts. This will increase the cost. Moreover, all of the above methods detect the running speed of the magnetic tape, and do not detect the relative speed.

For this reason, a method of detecting the relative velocity from the reproduction signal of the rotary head was proposed, for example, in Japanese Patent Laid-Open No. 60-231952. This method calculates the tape speed based on the number of tracks that the rotary head traverses during one rotation during high-speed feeding, and controls the speed of the single motor accordingly to keep the relative speed constant.

According to this method, when recording and reproducing using two rotary heads with different azimuth angles, the recording track is reproduced from the track (main track) recorded by the rotary head having the same azimuth angle as the rotary head during reproduction. Rebirth of time R
The F signal level and the reproduced RF signal level when a track recorded by a rotary head with a different azimuth angle (reverse track) is significantly different depending on the presence or absence of the azimuth loss effect. , the number of tracks traversed is counted by utilizing changes in the envelope of the reproduced RF signal, and the relative speed is detected based on the number of tracks crossed.

Problems to be Solved by the Invention However, in the above-mentioned conventional device, during high-speed feed, the reproduction R
The envelope of the F signal itself tends to have undulations, and the output level fluctuates due to variations in tape speed. Therefore, in order to count the number of tracks crossed, changes in the envelope of the reproduced RF signal are detected and waveform shaped. The set value of the threshold value becomes extremely delicate, which poses a practical problem.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a digital signal recording/reproducing apparatus capable of detecting relative speed.

Means for Solving the Problems As shown in FIG. 1, the low-pass filter 5 is a means for frequency selecting a specific signal in a specific frequency range from the reproduced signal during high-speed reproduction, and the counter and pilot signal selection circuit 12 are The register 13 is a means for holding the measured value, the speed correspondence table 19, the duty selection circuit 21, and the variable duty signal generator 21 compare the target value and the held value and obtain the comparison result. The reel motor drive circuit 17, which is a means for obtaining a control signal of a corresponding duty, is an embodiment of a means for controlling a reel motor using a control signal.

The specific signal recorded on the magnetic tape together with the digitally modulated information signal is reproduced by the rotary head, frequency selected by the frequency selection means, and supplied to the measurement means, where its period is measured and measured. The value is retained. The reel motor control means compares the target value and the held value, and the reel motor is controlled by a duty control signal according to the comparison result.

Embodiment FIG. 1 shows a block system diagram of a first embodiment of a digital signal recording/reproducing apparatus according to the present invention. This device uses a part of the same circuit as that of Japanese Patent Application No. 61-30119 (title of the invention ``Digital Signal Recording/Reproducing Apparatus'') previously proposed by the present applicant in order to solve the conventional problems.

In the figure, a magnetic tape 2 pulled out from a cassette 1 is wound around a head drum 3 having a diameter of, for example, 30 ItR over a predetermined angle (for example, 90 degrees) during recording and reproduction. This magnetic tape 2 has two tapes with different azimuth angles.
Digital audio signals are recorded by alternately forming tracks that are inclined with respect to the longitudinal direction of the tape by the rotating heads. If one block is, for example, 288 bits, a total of 196 blocks of signals are recorded per track on this inclined track.
Hz, quantization bit count: 16 bits) is recorded in the center of each 128-block track along with parity, synchronization bits, etc., and is recorded in the remaining 68-block area at the front of the digital audio signal recording area of each track. are each margin.

Subcodes, auto-tracking codes, etc. are recorded.

Here, the transmission frequency fch is, for example, 9.408 MHz
The signals recorded on each track are (1/2) f ch, (1/2) except for the auto tracking code.
6)・fch etc., whereas the first and second Domei signals recorded as auto tracking codes are fc
h/18 and fch/12. Erase signal is f ch
/6, and the frequency of the pilot signal is selected to be f ch/72. In other words, in the area where the auto-tracking code is recorded (the so-called ATF area), low-frequency signals with little azimuth loss effect are recorded, and among these, the pilot signal has a particularly low frequency and is significantly different in frequency from other signals. , so that it can be played on either rotating head.

On the other hand, looking at the bit rate during high-speed tape feed, for example, if the head drum rotation is kept at the same number of rotations as during recording, but the tape running speed during playback is made different from that during recording, then the tape running speed during recording The speed is the linear speed of the rotating head! (
If the rate of change in the bit rate r8 is assumed to be sufficiently small relative to the circumferential speed (circumferential speed) and the azimuth loss effect is ignored, the bit rate change rate r8 can be expressed by the following equation.

(However, N: Tape speed ratio, VNρ: Tape running speed a during normal playback, VH: Circumferential speed of rotating head, θ Ni-tracking angle) In equation (1), tape speed ratio N is tape running speed. The value is negative when the direction is forward, and positive when the direction is backward.

Now, the tape running speed is set to 200 times the speed (that is, N=±
200) and VN p = 8.15 mlI/
S.

VH-3,133m/S, θ-6"22'59"
Then, the bit rate change rate r days is 1 from equation (1).
It will be about ±0.52. As mentioned above, the pilot signal is the recording signal with the lowest frequency, and the pilot signal is the recording signal with the next lowest frequency.
Since the frequency is 1/4 times that of the synchronization signal, it is possible to identify the pilot signal by observing the playback signal as long as the tape running speed is about 200 times or less.

Returning to FIG. 1 again, in this embodiment, the number of revolutions of the head drum 3 is set to the same number of revolutions as that during recording (for example, 20
This is an example in which high-speed reproduction is performed by maintaining the speed at 0Orpm>.

The reproduction signal reproduced from the magnetic tape 2 by two rotating heads mounted 180 degrees opposite to the rotating surface of the head drum 3 is supplied to a low-pass filter 5 through a head amplifier 4, where only low frequency signals are extracted. After that, the signal is converted into a rectangular wave by the comparator 6 and supplied to the counter 7. On the other hand, a drum pulse generator 9 extracts a drum pulse having a period corresponding to the rotational speed of the head drum 3 and supplies it to an ATF gate signal generator 10 . ATF
Since the area is reproduced at a constant timing when the rotational speed of the head drum 3 is constant, a gate signal indicating that the area is approximately in the ATF area is extracted from the ATF gate signal generator 10 and supplied to the counter 7. Thereby, the counter 7 measures the reproduced signal only during the input period of this gate signal (within the ATF region), and can detect the pilot signal with high reliability.

The counter 7 is supplied with a pulse train of frequency fch (in this case, 9.408 MH2) extracted from the crystal oscillator 11 as a clock, and the input period of the reproduced signal from the comparator 6 and the gate signal from the ATF gate signal generator 10 Only this clock counts. During normal reproduction, this count value Np per cycle of the reproduced pilot signal is "72" when counted using the above clock, but during high-speed reproduction, the count value Ns per cycle of the reproduced pilot signal is approximately 200 times faster. If the change rate r8' of the bit rate is considered as 1-0.6≦r days≦1 when running in the forward direction and 1≦r9≦1+0.6 when running in the reverse direction (3), then when running in the forward direction is approximately 72≦Ns≦180 (-7210,4) (A)
When traveling in the opposite direction, approximately 45 (=72/1.6)≦Ns≦720.

The bit signal selection circuit 12 assumes that the reproduced signal whose period is within the range of Ns in which the count value of the counter 7 is expressed by formula (4) or formula 0 is a pilot signal, and selects the count value. register 13, which in turn supplies counter 7.
retains its value until the argument is passed. in this case,
Based on the signal from the system controller 14, the count value of the counter 7 is within the range of the value Ns shown by equation (4) during high-speed regeneration when traveling in the forward direction, and is expressed as 0 during high-speed regeneration when traveling in the reverse direction. By limiting the value to be within the range of the value Ns, the reliability of pilot signal detection is increased.

Also, since this pilot signal contains 10 clocks in one ATF area, if one with approximately the same period is detected several times (for example, 4 times), it is treated as a pilot signal to increase the reliability of detection. can be increased.

On the other hand, the speed correspondence table 19 contains counts per period of the reproduced pilot signal corresponding to each double speed. For example, when running at 150x speed in the forward direction, the bit rate change rate re (150) is re (150) = 0.612 from the above formula (1), and therefore, the number of words per - cycle is , Nc=5
It becomes 2. Further, when traveling in the reverse direction at 150 times the speed, the count value per cycle is Nc=118. The speed correspondence table 19 is constituted by a ROM, or by a simple theoretical circuit if the number of required double speeds is small.

High-speed playback is necessary for search functions such as finding the beginning of a song.
For example, if the current position of the magnetic tape 2 is far from the target position, it is played back at a relatively fast speed and sent quickly forward and backward to the target position, and when the target position is close, it is played back at a relatively slow speed. This is used when the target position is found and stopped.

In this case, in order to increase the precision of stopping, it is desirable to switch the speed during high-speed playback into several stages.

To do this, specify the required speed (for example, 150th speed in the forward direction) in the system controller 14, and
The count value per cycle of the reproduced pilot signal at the required speed is extracted from the speed compatible tape 19, and this count value is supplied to the duty selection circuit 20. On the other hand, the duty selection circuit 20 is supplied with the value held in the register 13.

In the duty selection circuit 20, speed correspondence table 1
The target count value from register 9 and the hold count value from register 13 are supplied, a duty value is created based on the relationship between these two values, and is supplied to variable duty signal generator 21.

The variable duty signal generator 21 generates a signal whose duty is changed according to the duty value created in the duty selection circuit 20, and the reel motor drive circuit 1
7. Note that the duty selection circuit 20 is composed of a subtraction circuit and a simple logic circuit or a ROM, and the variable duty signal generator 21 is composed of a simple logic circuit that operates based on the clock and duty value supplied from the crystal oscillator 11. be done.

The reel motor drive circuit 17 controls the reel motor 18 using the signal whose duty is changed. In the variable duty signal generator, the signals are set to appropriate synchronization (to facilitate later signal processing), and when the target value Nc of the speed correspondence table 19 mentioned above and the value Ns held in the register 13 are equal. , or if they are very close, the duty is 50%; on the other hand, if the difference between the target value Nc and the held value Ns is large, the duty is changed in relation to the value of the difference and the feeding direction.

The reel motor drive circuit 17 switches the rotation direction depending on the running method, passes the output signal through a filter (a simple one with one capacitor and one resistor), and converts the output into the drive voltage of the reel motor 18. In addition to the error voltage, whether the vehicle is running in the forward or reverse direction, if the error voltage is positive, it will cause acceleration, and if it is negative, it will cause deceleration. That is, in such a method, if the duty of the signal increases, acceleration occurs, and if the duty decreases, deceleration occurs.

In this case, the duty can be changed in seven stages, for example, as shown in FIG. For example, in the case of forward running at 150 times speed playback and the target straight line Nc = 52, the value held in the register 13, the difference (N s = N c ),
A correspondence table for selecting the duty shown in FIG. 2 is shown below.

Here, in forward travel, the smaller the holding value Ns is, the faster the feeding speed is, and the larger the holding value Ns is, the slower the feeding speed is.

For this reason, if the held value Ns is smaller than the target value Nc, select the one with the smaller duty (the smaller number in Figure 2) so that it will decelerate, and conversely, if the held value Ns is larger, choose the one with the larger duty so that it will accelerate. (the one with the larger number in FIG. 2) is selected and controlled so that the duty is approximately 50%. Similarly, set the forward direction 25x, if the target values are far apart, it will rotate at 150x, and if the target values are close, it will rotate at 25x.
Rotate at 5x. Note that when traveling in the opposite direction, the above will be reversed.

For example, when playing in the reverse direction at 150x speed (target value Nc = 1
18), the correspondence table is shown below.

In order to make the ratio of the change rate of the reel motor control sensitivity, that is, the duty, in the forward direction 150 times and the reverse direction 150 times the same, and the ratio of the actual speed (relative speed detected by the pilot signal) to the target speed, the system controller 14 The duty selection circuit 20 holds 1m by the signal from
The vj sum of the difference between Ns and the target value Nc is made variable.

The types of duty (for example, seven types) and the rate of change in duty (equal intervals in FIG. 2) may be set to values that are easy to control.

Hold value Ns and target value Nc counted from the above-mentioned reproduced signal
By using a value corresponding to several cycles of the pilot signal (for example, 4 cycles) and by setting many types of duty, it is possible to improve the accuracy of control of the reel motor 18. Furthermore, by using the average value of a plurality of count values as a holding value instead of the count value of only - times, smooth control with less influence of jitter can be performed.

The waveform equalization circuit 15 is a circuit that equalizes the waveform of the reproduced digital signal taken out from the head amplifier 4, and uses a delay line (the amount of delay is switched between 25 times and 150 times by the system controller 14). Often configured. The output signal of the waveform equalization circuit 15 is supplied to a level comparator in the PLL, where it is converted into a digital signal, and then supplied to a data latch and latched. The output signal of this data latch is output to the digital system as reproduced digital data.

Effects of the Invention According to the present invention, a signal of a specific frequency that is different in frequency from other signals in a recording signal such as a pilot signal is reproduced and its period is measured, thereby detecting the feeding speed of the magnetic tape. Compared to conventional devices that detect level changes in the envelope of the reproduced RF signal, this method has problems such as difficulty in setting thresholds (it can detect the feed speed and record a signal dedicated to speed detection). Since there is no need for a linear track or a head, the linear track recording area can be secured in the information signal recording area, and the speed of the reel motor can be controlled in several stages, so the time required to complete the search can be shortened. , and can improve the accuracy of stopping at the target value, and
Reel motor control signal is variable duty signal (PWM)
Since only one signal generator is required and the signal generator can be constructed from a logic circuit, it is suitable for IC implementation, and the subsequent control section can also be constructed from simple circuits.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram showing an embodiment of the present invention, and FIG.
The figure is a signal waveform diagram illustrating the duty of the block diagram shown in FIG. 1. 2...Magnetic tape, 3...Head drum, 4...
Head amplifier, 5...Low pass filter, 6...Comparator, 7...Counter, 10...ATF gate signal generator, 11...Crystal oscillator, 12...Pilot signal selection circuit, 13 ...Register, 14...System controller, 17...Reel motor drive circuit,
18... Reel motor, 19... Speed correspondence table, 20... Duty selection circuit, 21... Variable duty signal generator. Patent applicant: Japan Victor Co., Ltd. Fig. 2 ■ November 17, 1986 of procedure Nefti positive Commissioner of the Patent Office Black 1) Akio Kuhe 1, case display address Moriya-cho, Kanayō-ku, Yokohama-shi, Kanagawa Prefecture 221 3-12 Name (432) Victor Japan Co., Ltd. Representative Director and President Kunio Kakiki 4, Agent address 5-7 Kojimachi, Chiyoda-ku, Tokyo 102 Voluntary amendment 6 Details of the invention in the memorandum subject to amendment An explanation column. 7. Contents of amendment (1) In the specification, “taperu” written in line 4 on page 14 has been changed to “
``table''. ■ "Target value is far away...Target value is near" written in line 8 on page 17 of the same page is corrected to "If the target position is far away, rotate at 150 times and the target position is near." ■ Correct N31J written in line 8 on page 18 to rl 29J. (4) "13" written in line 8 on page 18 is corrected to "11". 6) Correct r132J written in page 18, line 9, to r130J. (6) "14" written on page 18, line 9 of the same is corrected to "12".

Claims (1)

[Claims] In a device that records a digitally modulated information signal and a specific signal in a different frequency range from the information signal on a magnetic tape using a rotating head, and then reproduces this, the frequency of the specific signal is selected from among the reproduced signals during high-speed reproduction. a measuring means for measuring the period of the specific signal whose frequency has been selected; a holding means for holding the measured value; a target value calculated in advance and a held value held by the holding means; 1. A digital signal recording and reproducing apparatus, comprising: a control means for comparing the values and obtaining a duty control signal according to the comparison result; and a means for controlling a reel motor using the control signal from the control means.