JPH0120485B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic bias adjustment method in a magnetic recording/reproducing device such as a tape recorder.

Generally, in a magnetic recording/reproducing device employing a high frequency bias recording method such as a tape recorder, adjustment is made to set the bias amount to an appropriate value depending on the type of magnetic tape used.
There is a magnetic recording and reproducing apparatus that automates this adjustment by having a digital control unit using a microcomputer, and can automatically handle different types of magnetic tapes.

For example, a bias oscillation circuit that oscillates a sine wave with a frequency of about 1KHz and whose output, that is, the amount of bias, can be varied in steps, and a mid-range frequency signal (1KHz) and a high-range frequency signal (10KHz) that serve as reference signals to be recorded. A sine wave oscillation circuit that oscillates, a recording and reproducing circuit that superimposes the bias signal on the medium and high frequency signal outputs of the sine wave oscillator circuit to record and reproduce the signals, and a reproduction output level from the recording and reproducing circuit. an A/D converter that converts the
It has a built-in automatic bias adjustment device equipped with a control unit that digitally controls each of the circuits according to the output of this A/D converter, and repeats the recording/reproduction test by sequentially varying the bias amount by the bias oscillation circuit. By doing so, the appropriate value of the bias amount was automatically detected.

Conventionally, the following two methods have been used to adjust the bias using such an automatic bias amount adjustment device.

(1) As shown in Figure 1, the bias amount is changed sequentially in a certain step range (1 to n) and recorded.
A method of detecting the bias amount (indicated by P in the figure) at which the reproduced output reaches its peak level and determining the appropriate bias amount from that value.

(2) As shown in Figure 2, mid-range frequencies (e.g.
1KHz) and high frequency (for example, 10KHz) signals are recorded and played back one after another while varying the amount of bias, and the playback output level of both frequency ranges becomes almost equal (the frequency characteristics become flat). A method of detecting this using the amount of bias (4 in the illustrated example).

However, in all of these conventional methods, when the number of steps for varying the bias amount is increased in an attempt to increase the resolution in order to improve detection accuracy,
The disadvantage is that the amount of testing increases by the number of steps, and the time required for bias adjustment becomes long.

The present invention has been made in view of the above points, and an object of the present invention is to significantly shorten the enormous amount of time consumed for bias adjustment.

Therefore, in the automatic bias amount adjustment method for a magnetic recording/reproducing device according to the present invention, when measuring the bias amount with a resolution of n steps, first
In other words, record and reproduce the mid-range frequency signal and the high-range frequency signal respectively with the bias amount of (1+n)/2nd bias, compare the playback output levels, and if the playback output levels of the mid-range and high-range are equal, Determine that the amount of bias is an appropriate value, and if it is not equal, determine whether the appropriate value is smaller or larger than the number of steps during the test depending on which is larger, and then make that judgment. Depending on the results, record and play back signals in both frequency ranges again using a bias amount approximately at the center of one of the ranges, compare the playback output levels, and make the same judgment repeatedly. By doing so, the appropriate bias amount can be set and adjusted in a short time.

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

FIG. 3 is a diagram showing the relationship between the bias amount and the recording/playback level for explaining the principle of the automatic bias adjustment method according to the present invention, and the solid line in the diagram is
The broken line for the 1KHz signal indicates the recording/playback level for the 10KHz signal.

Similar to method (2) above (Figure 2), the equalizer EQ amount of the recording system is determined by the frequency to be measured (here 1K).
Hz and 10KHz).

When measuring the bias amount with the number of steps n corresponding to the required resolution, first superimpose the bias signal of the bias amount of the central _m1 step, that is, the (1+n)/2nd step, and then
A 10KHz signal is recorded, and it is determined whether the reproduction output levels shown in Fig. 3A are equal.

Here, if the two are equal, the bias amount of the _m1th step can be obtained as an appropriate value. However, if the playback output level at 1KHz is higher than 10KHz, the amount of bias is too large, so it is determined that the appropriate value is between 1 and _m1 steps, and then the center of this step range is determined. m ₂ = (1+
m ₁ )/again at the 2nd step bias data value
Compare the recording and playback levels between 1KHz and 10KHz.

By the way, the recording and reproducing levels of the mid-range frequency signal and the high-range frequency signal with respect to the bias amount show change characteristics as shown by curve A (1KHz) and curve B (10KHz) in FIG. 4, respectively, and the appropriate bias amount C is At the border, the size relationship is reversed. The above-mentioned determination can be made using this characteristic.

Also, by comparing the playback output levels of 1KHz and 10KHz when the bias data value is _m1 step, 1K
If the Hz output level is lower, as is clear from Figure 4, the bias amount is too small, so it is determined that the appropriate value is between m ₁ and n steps, and then (m ₁ + n) / Compare the recording and playback levels of 1KHz and 10KHz again using the bias data value of the second step. As shown by B in Figure 3, 1KHz at this time
If the recording and playback levels of 10KHz and 10KHz are the same, the bias data value at this test is the appropriate value.

In this way, the bias data value at the center of n steps (m ₁ step) is first recorded and reproduced, and if it is determined that this bias amount is too large, the bias data value is changed from 1 to m ₁
Take the test halfway through. On the other hand, if it is determined that the amount of bias is small, the test is performed at half of m ₁ to n. By repeating this test in the same manner, the bias data value is given to a successive approximation formula, and an appropriate bias value can be obtained by comparing and determining the reproduction output levels of 1KHz and 10KHz.

In this case, if the number of steps calculated for the bias amount during each test is not an integer, a larger number of steps close to the integer may be selected.

FIG. 5 shows a flowchart for implementing the automatic bias adjustment method according to the invention with a resolution of n=16, ie, 4 bits and 16 steps.

After starting, first test (1+n)/
This is done with a two-step bias amount, but in this case n
= 16, so (1 + 16)/2 = 8.5, 8.5
There is no step, so the closest and larger 9
Record and play back 1KHz and 10KHz reference signals using the step data (referred to as data 9) as the bias amount, and check whether the playback output levels are equal (this is indicated as "10K = 1K" in the figure). to judge.

If they are equal, Y, data 9 at this test is set as the appropriate value. If they are not equal, determine whether N and 10KHz are larger (10K>1K), and if they are larger, there is an appropriate value in the step range that is larger than the Y9 step, so (9+16)/2=12.5, so 13 If the step data (data 13) is not larger, the appropriate value is in the step range smaller than the N9 step, so (1+9)/2=5, the 5th step data (data 5) is A second test is carried out for the quantity.

If the playback output levels of 10KHz and 1KHz are equal, data 13 or data 5 is the appropriate value, and if they are not equal, the 3rd step, 7th step, 11th step, or 15th step, respectively, depending on whether 10K>1K. A third test is conducted using the eye data as the bias amount.

In this way, in the case of 16 steps, up to 3
Since it is possible to determine the appropriate value of the bias amount by performing the test twice, the number of tests required in the conventional method, which was 16 times, can be significantly reduced, and the adjustment time can be significantly shortened.

As described above, according to the present invention, the recording and reproducing levels of the mid-range frequency signal and the high-range frequency signal are compared based on the bias amount at the center of the range in which the bias amount is varied in a stepwise manner. Based on the results, the test was repeated to determine whether the bias amount was an appropriate value, and if it was not, whether the appropriate value existed in a range larger or smaller than the current step, and the test step range was successively halved. Therefore, the number of tests required to set the appropriate value of the bias amount can be drastically reduced, and thereby the level adjustment time can be significantly shortened.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing the relationship between the bias amount and the recording/reproducing level, respectively, for explaining different examples of conventional bias adjustment methods. Figure 3 shows
FIG. 3 is a diagram showing the relationship between the bias amount and the recording/reproducing level for explaining the bias adjustment method according to the present invention. FIG. 4 is a characteristic curve diagram showing changes in the recording and reproducing levels of the mid-range frequency signal A and the high-range frequency signal B with respect to the amount of bias. FIG. 5 is a flowchart showing an embodiment of the invention.

Claims (1)

[Claims] 1. A bias oscillation circuit that can vary the amount of bias in steps, a sine wave oscillation circuit that oscillates a medium frequency signal and a high frequency signal that serve as reference signals to be recorded, and the sine wave oscillation circuit. A recording and reproducing circuit that records and reproduces the output of each frequency range and the output of the bias oscillation circuit by superimposing the same, an A/D converter that converts the reproduction output level from the recording and reproducing circuit into a digital signal, and An automatic bias adjustment method for automatically adjusting the bias amount of a magnetic recording and reproducing device using an automatic bias adjustment device including a control unit that digitally controls each of the circuits according to the output of the /D converter, First, a medium frequency signal and a high frequency signal are respectively recorded and reproduced with a bias amount at approximately the center of the bias amount variable step number of the bias oscillation circuit, and the reproduction output levels are compared, and the output of both frequency regions is calculated. If the levels are equal, the bias amount at that test is set as the appropriate value; if not, depending on which is larger, it is determined whether the appropriate value is smaller or larger than the number of steps at that test. Repeat the same test with the bias amount at approximately the center of the determined step range, and by repeating this, you can determine the appropriate bias amount when the playback output levels of the mid-range frequency signal and the high-frequency signal become equal. 1. An automatic bias adjustment method for a magnetic recording/reproducing device, characterized in that the bias is adjusted to a value of 0.