JPH0425606B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for adjusting frequency characteristics, and particularly to a method for adjusting the frequency characteristics of a reproduction equalizer of a magnetic tape reproducing device using a single variable element for adjustment. .

[Technical background of the invention and its problems]

When a flat amplifier is connected to the playback head of a magnetic tape playback device, the frequency characteristics of the playback output change depending on the input impedance of the amplifier, and the output voltage of the head has a characteristic of 6 dB/octave as shown by a in Figure 7. The input voltage of the reproduction input circuit is attenuated in the low range. The purpose of equalizer adjustment is to flatten this characteristic as shown by b in FIG. 7, and this compensation is performed by giving the equalizer a characteristic as shown in FIG. 8.

Figure 9 shows a reproduction equalizer circuit, in which a flat amplifier A that amplifies the output signal of the reproduction head H is provided with a negative feedback circuit NFB, the constant of which is determined by the compensation characteristic standard. A flat frequency characteristic is obtained by using the semi-fixed resistor VR in the negative feedback circuit NFB.

Conventionally, this adjustment was performed by hand on the factory adjustment line as follows.

By the way, the semi-fixed resistor for adjusting the playback equalizer
Type B VR is used in which the resistance changes linearly with the rotation angle, but when adjusting it, adjust the millivolt so that the 315Hz playback level and the 6.3KHz playback level are the standard value. The resistance VR is varied while being measured with a meter. As shown in FIG. 10, the output level characteristics at 315 Hz and 6.3 KHz with respect to the rotation angle of the resistor VR are almost flat at 315 Hz, but vary greatly at 6.3 KHz.
Therefore, first vary the resistance VR until the 6.3KHz level reaches a certain level, then measure the level difference from 315Hz, and if the deviation is greater than the negative standard value, turn it clockwise (increasing resistance). If the value exceeds the positive standard value, repeat the adjustment by rotating each resistor VR counterclockwise (resistance decreasing direction).

The magnetic tape playback output level varies greatly depending on factors such as loss in the tape and playback head, but 315
The adjustment of the playback equalizer, which measures the level deviation between Hz and 6.3KHz, is greatly affected by this.
In addition, since the rotation angle of the resistor VR is determined based on the intuition of the measurer based on the measured level deviation, there is a drawback that this adjustment takes a very long time for those who are not used to it.

[Purpose of the invention]

The present invention has been made in order to eliminate the drawbacks of the conventional methods described above.The present invention measures reproduced signals at at least two frequencies for a variable amount of a variable element, and uses the data obtained from this measurement to determine the optimum To provide a frequency characteristic adjustment method capable of accurately and automatically adjusting the frequency characteristics of a reproduction equalizer in a magnetic tape reproducing device in a short time by determining an adjustment point and adjusting a variable element to this adjustment point. The purpose is to

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

As an embodiment of the present invention, reproduction equalizer adjustment of a magnetic tape reproduction device will be described. When adjusting the playback equalizer, the deviation of the 6.3KHz level from the level at 315Hz is the standard value, for example -
The adjustment semi-fixed resistor is adjusted so that the output voltage is 0.5 dB, and the adjustment method will be explained in detail with reference to the flowchart of FIG. 1 showing the procedure.

By the way, when the deviation of the adjustment semi-fixed resistor VR with respect to the rotation angle is calculated as a dB value, it becomes as shown in Figure 2. In general, the level deviation D on the frequency characteristic is
is expressed by the following formula, where A is the level (volt) at the measurement frequency (for example, 6.3 KHz), and B is the level (volt) at the reference frequency (for example, 315 Hz).

D (dB) = 20logA - 20logB = 20logA/B From this, the above two frequencies of 315Hz and
The level deviation can be found by reading the level at 6.3KHz as a voltage value and taking the ratio, and the rotation angle vs. level deviation characteristic found in this way is:
As shown in FIG. 3, it is approximately linear. Therefore, by determining the slope of this straight line, the optimum adjustment point can be determined.

Returning to FIG. 1 again, in step S1, the rotation angle at any two points of the adjustment semi-fixed resistor VR is adjusted.
Level deviations D ₁ and D ₂ at P ₁ and P ₂ are measured.
After that, in step S2, the rotation angles P ₁ , P ₂
From the deviations D ₁ and D ₂ , the slope K of the straight line in FIG. 4, which shows the relationship between the deviation and the rotation angle, is determined from the following formula.

K=(D ₂ - D ₁ )/(P ₁ - _{P 2} ) In the following step S3, the semi-fixed resistance for adjustment VR
is set to the initial state (base point of rotation angle), and then in step S4, the resistor VR is rotated by the rotation angle _P1 . Since the level deviation D ₁ at this rotation angle has already been determined in step S1, it is determined in the next step S5 whether or not this level deviation D ₁ is within the standard. If this determination is YES, the adjustment ends.

If the determination in step S5 above is NO,
Proceeding to step S6, the rotation angle from this inclination K to the next adjustment point _P3 (FIG. 5) at which the level deviation becomes 1 is determined by the following equation.

(1-D ₁ )/K=P ₃ -P ₁ In the above equation, P ₃ - _{P 1} is the rotation angle of the adjustment semi-fixed resistor VR up to the adjustment point, but depending on the direction of rotation by this rotation angle, There may be play between the semi-fixed resistor VR and the bit that rotates it, so if there is play, it is necessary to correct it. Therefore, in the next step S7, it is determined whether or not correction is necessary. If the determination is YES, the rotation angle is corrected in the subsequent step S8. If the determination is NO, the process immediately proceeds to step S9, where the rotation angle is corrected. The semi-fixed resistor VR is rotated by a predetermined angle and the level deviation at that point is measured. Then, in the next step S10, it is determined whether or not the level deviation obtained in step S9 is within the standard.
If YES, the adjustment is finished here, and if the determination is NO, the process returns to step S6, and steps S6~
Repeat S10.

By the way, the level deviation measured by rotating the semi-fixed resistor VR in step S7 by the rotation angle determined in step S6 above is as shown in FIG.
If D ₃ is not within the standard, calculate the rotation angle from the following formula (1-D ₃ )/K = P ₃ '-P ₃ to the next adjustment point, and calculate the level deviation when rotated by this rotation angle. If D ₃ ′ is within the standard, the adjustment ends here. Note that when determining the rotation angle up to the next adjustment point P ₃ ' using the above equation, the slope K of the straight line β in FIG. 5 is used, and the slope of the straight line α is not used.

FIG. 6 is a block diagram showing an automatic adjustment device that implements the method of the present invention. In the figure, 10 is a product signal detection unit that detects a playback signal of a programming tape attached to a product, and 12 is a product signal detection unit that detects a reproduction signal of a programming tape attached to a product. It is a measurement unit that measures the signal of the frequency measuring device 12.
a and a level measuring device 12b. Reference numeral 14 denotes a control section, which includes a signal control means 14a that takes in a signal from the measurement section 12 and detects an adjustment signal, a calculation means 14b that performs the above-mentioned calculation based on the signal from the measurement section, and the calculation means. a memory means 14c for storing the calculation result of the calculation means 14c, a comparison means 14d for comparing the calculation result of the calculation means 14b and the contents stored in the memory means 14c, and control for rotating the adjustment semi-fixed resistor VR based on the comparison result of the comparison means. It has an adjustment semi-fixed resistance VR rotation control means 14e and a running control means 14f. The running control means 14f controls switching of the tape drive by a stop/play operation of the operating section 16. The adjustment semi-fixed resistance VR rotation control means 14e controls the drive device 18 to rotate the adjustment semi-fixed resistance VR by a predetermined amount.

When performing automatic adjustment using a device with the above configuration, a programming tape is installed in the playback system, and in order to extract the playback equalizer adjustment signal from the tape, the signal obtained with the tape in the playback state is measured. The measurement result is input to the signal control means 14a, and the adjustment is started upon detection of the adjustment signal. This adjustment is performed while the tape continues to be played back, and the travel control means 14f controls the stop of tape drive and the start of playback based on commands from the operating section 16. In the measuring section 12, frequency measurement is performed before level measurement, and the result of the calculation performed by the calculation means 14b based on the measured level is temporarily recorded in the memory 14c for later comparison. The comparison result by the comparison means 14d indicates that the adjustment semi-fixed resistor
In addition to the VR rotation control 14e, the drive device 18
It is used to adjust the rotation of the adjustable semi-fixed resistor VR.

In addition, in the above embodiment, the slope is determined using two points, but it is possible to obtain a more accurate slope by using four points, for example, and using the average slope of the two straight lines. can.

Furthermore, when rotating the semi-fixed resistor to the adjustment point, 1
Returning to the origin and then rotating allows for more appropriate adjustment than correcting play.

〔Effect of the invention〕

As explained above, according to the present invention, the first level deviation is obtained by taking the ratio of the reproduced signal levels at at least two frequencies when the variable element is varied by the first variable amount, and the first level deviation is obtained by A second level deviation is obtained by calculating the ratio of the reproduced signal levels at the two frequencies when the variable amount is varied, and the first and second level deviations thus obtained are combined with the first and second variable levels. The slope of the level deviation with respect to the variable amount of the variable element is determined based on the amount, and the variable amount of the variable element at which the level deviation becomes a predetermined value is determined based on the slope of this determined level deviation, and the variable amount is varied by this determined variable amount. Repeat varying the variable element by varying the element, finding a variable amount of the variable element at which the level deviation becomes a predetermined value based on the above-mentioned slope until the level deviation after performing this variation is close to a predetermined value. Accordingly, even if the level changes of the reproduced signals of at least two frequencies due to variable elements in the reproduction equalizer of the magnetic tape reproducing device are different, the relationship between the two frequencies of the reproduced signals is maintained as desired. frequency characteristics can be obtained by automatic adjustment of the variable element, and compared to the conventional method that relied on intuition, adjustment work can be standardized and labor savings can be achieved through automation.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing an embodiment of the method of the present invention, FIGS. 2 and 3 are graphs showing rotation angle-level deviation characteristics of a semi-fixed resistor, and FIGS. 4 and 5 are graphs showing an embodiment of the method of the present invention. A graph for explaining the method, FIG. 6 is a block diagram showing an apparatus for carrying out the method of the present invention, FIGS. 7 and 8 are graphs showing contents of reproduction equalizer adjustment, and FIG. 9 is a reproduction equalizer. 10 is a circuit diagram showing a general configuration of the reproducing equalizer, and FIG. 10 is a graph showing semi-fixed resistance rotation angle-reproducing output characteristics of the reproducing equalizer with respect to two frequency characteristics. VR...Semi-fixed resistance (variable element).

Claims (1)

[Scope of Claims] 1. A method for adjusting the reproduction equalizer frequency characteristics of a magnetic tape reproduction device using one variable adjustment element, comprising: reproduction at at least two frequencies when the variable element is varied by a first variable amount; determining a first level deviation by determining a ratio of signal levels; determining a second level deviation by determining a ratio of reproduced signal levels at the two frequencies when the variable element is varied by a second variable amount; The obtained first and second level deviations and the first
and a second variable amount, determine the slope of the level deviation with respect to the variable amount of the variable element, and determine the variable amount of the variable element with respect to a predetermined level deviation based on the slope of the determined level deviation, The variable element is varied by a variable amount determined by the variable amount, and the variable amount of the variable element for a predetermined level deviation is determined based on the slope until the level deviation after performing the variation becomes close to a predetermined level deviation, and the variable element is A frequency characteristic adjustment method characterized by repeatedly varying the frequency characteristics.