JPH04238175A - Drop-out detector - Google Patents

Abstract

PURPOSE:To detect the drop-out occurring in a tape with good accuracy by using the signal obtd. by calculating the moving average value of the effective value signals of reproduced high-frequency signals as a detection reference value signal. CONSTITUTION:The drop-out detector compares the effective value signal 6 of the reproduced high-frequency signal 1 from a head and the detection reference value signal 7 and detects the drop-out. This detection reference value signal 7 is made into the signal obtd. by multiplying the signal obtd. by calculating the moving average value of the effective value signals 6 of the reproduced high-frequency signals 1 by a constant smaller than 1, for example, 0.5. The level of the detection reference value signal 7 is fluctuated as well by using such signal according to the fluctuation in the level of the effective value signals 6 even when the level of these signals fluctuates in a short period of time in such a case the contact of a head and the tape is not uniform. The drop-out occurring in the tape is thus detected with the good accuracy.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dropout detection device suitable for use in measuring the characteristics of a magnetic tape used, for example, in a rotary head type VTR.

0002

2. Description of the Related Art In order to measure the characteristics of a magnetic tape, dropouts caused by the magnetic tape are generally measured. Conventionally, a dropout detection device as shown in FIG. 5 has been used to detect this dropout.

In FIG. 5, reference numeral 1 denotes a reproduced high-frequency signal input terminal to which a reproduced high-frequency signal obtained by reproducing a predetermined signal recorded on a magnetic tape whose characteristics are to be measured by a rotating head type magnetic head is supplied. , an operational amplifier circuit that supplies the reproduced high-frequency signal supplied to the reproduced high-frequency signal input terminal 1 to an envelope detection circuit 2 to obtain an effective value signal 6, and configures a comparison circuit using this effective value signal 6 as a detected signal. 3 to the non-inverting input terminal + of the envelope detection circuit 2.
The effective value signal 6 obtained at the output side is supplied to a low pass filter 4 having a relatively long time constant, for example, on the order of several hundred ms, and the output from which high frequency components are removed is obtained at the output side of the low pass filter 4. The signal is supplied to a multiplier circuit 5 that multiplies this output signal by a constant smaller than "1", for example "0.5", and the signal obtained at the output side of the multiplier circuit 5 is used as a detection reference value signal to configure a comparison circuit and perform calculations. The signal is supplied to the inverting input terminal - of the amplifier circuit 3, and a dropout is detected by the signal obtained at the output terminal 3a of the comparator circuit 3. That is, when there is a dropout in the reproduced high-frequency signal from the rotating magnetic head, the level of the effective value signal of the reproduced high-frequency signal becomes lower than the level of the detection reference value signal, and this dropout can be detected.

0004

[Problem to be Solved by the Invention] However, in such a conventional dropout detection device, the constant value of the low-pass filter 4 that obtains the detection reference signal is relatively long, about several hundred ms, so it is difficult to measure it. In areas where there is uneven recording on the magnetic tape or where the magnetic tape and playback head have poor contact, the overall effective value signal level of the reproduced high-frequency signal decreases, albeit for a short period of time, and dropouts are not caused by the magnetic tape. However, there was a risk that it would be detected as a dropout. For example, as shown by the solid line in FIG. 6, when the contact between the magnetic tape and the reproducing head becomes poor and the effective value signal 6 obtained at the output side of the envelope detection circuit 2 of the reproduced high-frequency signal becomes an attenuated signal. Since the time constant of the low-pass filter 4 is relatively long, this detection reference signal 7 is not attenuated as shown by the broken line in FIG. 6, so there is an inconvenience that the attenuation section 6a, which should not be a dropout, is also detected as a dropout. .

[0005] In view of this point, it is an object of the present invention to improve the accuracy of dropout detection.

[0006]

[Means for Solving the Problems] The dropout detection device of the present invention detects a dropout by comparing an effective value signal 6 of a reproduced high frequency signal from a head with a detection reference value signal 7, as shown in FIG. In the dropout detection device, a constant smaller than 1, for example 0.5, is added to the detection reference value signal 7, which is obtained by calculating the moving average value of the effective value signal 6 of the reproduced high frequency signal from this head. The signal obtained by multiplying the

[0007]

[Operation] According to the present invention, a signal obtained by calculating the moving average value of the effective value signal 6 of the reproduced high-frequency signal is used as the detection reference value signal 7, so that the relationship between the head and the tape is Even if the level of the effective value signal 6 fluctuates in a short period of time, such as when the hits are not uniform, the level of the detection reference value signal 7 will also fluctuate accordingly, allowing more accurate detection of dropouts caused by the tape. be able to.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the dropout detection device of the present invention will be described below with reference to the drawings. In FIG. 1, parts corresponding to those in FIG. 5 are designated by the same reference numerals, and detailed explanation thereof will be omitted. In this example, a predetermined signal recorded on a magnetic tape whose characteristics are to be measured is supplied to the reproduced high-frequency signal input terminal 1, and the reproduced high-frequency signal is reproduced by a rotary head type magnetic head. is supplied to obtain an effective value signal 6, and this effective value signal 6 is supplied to a moving average circuit 8.

This moving average circuit 8 calculates a moving average of n samples belonging to an interval τ centered on Xk in order to obtain a moving average Yk of an input series Xk as shown in FIG.

Find [Equation 1]. Here, ai is a coefficient for determining the characteristics of the moving average. In this case, the interval τ is made variable and set according to the waveform of the effective value signal 6.

The moving average value signal obtained at the output side of the moving average circuit 8 is set to a constant smaller than "1", for example "0.5".
The signal obtained at the output side of the multiplication circuit 5 is supplied as the detection reference value signal 7 to the inverting input terminal of the operational amplifier circuit 3 constituting the comparison circuit.

Further, the effective value signal 6 obtained at the output side of the envelope detection circuit 2 is passed through a delay circuit 9 for matching the phases to the non-inverting input of the operational amplifier circuit 3 constituting the comparison circuit as a detected signal. Supply to terminal +. In this case, the delay time of the delay circuit 9 is set to 1/2 of the average interval τ of the moving average circuit 8, that is, τ/2. Output terminal 3a of this comparison circuit 3
Dropout is detected by the signal obtained at

Since this example is constructed as described above, the reproduced high frequency signal from the rotating magnetic head is as shown in FIG. 3A, for example, and in this case, the output side of the envelope detection circuit 2 is as shown in FIG. 3B. An effective value signal 6 of this reproduced high frequency signal is obtained, and at this time, the output side of this moving average circuit 8 is as shown in FIG.
As shown in FIG. 3C, a moving average value signal of the interval τ of this effective value signal 6 is obtained, and the level of this moving average value signal is attenuated to, for example, 1/2, as shown in FIG. 3D, on the output side of the multiplier circuit 5. A detection reference value signal 7 is obtained, and in the comparison circuit 3, this detection reference value signal 7 and a signal obtained by shifting the phase of this effective value signal 6 are compared as shown in FIG. 3E, and this effective value signal When the level of signal 6 is lower than the level of detection reference value signal 7, dropout is detected as shown in FIG. 3F.

Since this example is as described above, for example, FIG. 4A
As shown by the solid line (same as the solid line in Figure 6), the contact between the magnetic tape for measurement and the rotating magnetic head for reproduction becomes poor.
When the effective value signal 6 obtained at the output side of the envelope detection circuit 2 of this reproduced high-frequency signal becomes an attenuated signal, this detection reference value signal 7 also becomes an attenuated signal as shown by the broken line in FIG. 4A, and there is no dropout. The attenuation section 6a has the advantage that dropout does not occur and accurate dropout detection can be performed. This is the same as correcting the effective value signal 6 using the conventional configuration for obtaining the detection reference value signal 7 as shown in FIG. 4B. It goes without saying that the present invention is not limited to the above-described embodiments, and that various other configurations can be adopted without departing from the gist of the present invention.

[0014]

According to the present invention, a signal obtained by calculating the moving average value of the effective value signal 6 of the reproduced high-frequency signal is used as the detection reference value signal 7, so that the difference between the head and the tape can be improved. Even if the level of the effective value signal 6 fluctuates in a short period of time, such as when the hit is uneven, the level of the detection reference value signal 7 will also fluctuate accordingly, allowing more accurate detection of dropouts caused by the tape. There are profits that can be made.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of a dropout detection device of the present invention.

FIG. 2 is a diagram for explaining the present invention.

FIG. 3 is a waveform diagram for explaining the present invention.

FIG. 4 is a waveform diagram for explaining the present invention.

FIG. 5 is a configuration diagram showing an example of a conventional dropout detection device.

FIG. 6 is a waveform diagram for explaining FIG. 5;

[Explanation of symbols]

1 Reproduction high frequency signal 2 Envelope detection circuit 3 Comparison circuit 5 Multiplication circuit 8 Moving average circuit 9 Delay circuit

Claims (1)

[Claims] 1. A dropout detection device that detects a dropout by comparing an effective value signal of a reproduced high frequency signal from a head with a detection reference value signal, wherein the detection reference value signal is detected from the head. A dropout detection device characterized in that the signal is obtained by multiplying a signal obtained by calculating a moving average value of an effective value signal of a reproduced high frequency signal by a predetermined number smaller than 1.