JPH08106602A - Reproducing device - Google Patents

Abstract

PURPOSE: To obtain the optimum equivalent characteristic without degrading quality of a reproduced signal by controlling an equalization characteristic of equalization means within the prescribed period before reproduction of a signal is started by a reproducing means. CONSTITUTION: A digital signal reproduced from a magnetic tape 1 by a magnetic head 2 is supplied to a reproducing equalizer 5 consisting of a LC filter of which a characteristic is fixed through an input terminal 4. The reproducing equalizer 5 compensates a differential characteristic in a low frequency band and an attenuation characteristic caused by various loss in a high frequency band, and outputs the signal to equalizers 7, 8 consisting of transversal filters of which a characteristic is variable through a switch 6. Switches 6 and 9 are switched in accordance with a head switch pulse, are alternately connected every one track, and supply signals from each head. Signals of which a high frequency band component is controlled by the equalizers 7, 8 are supplied to a data detecting circuit 10 and a dropout detecting circuit 14 through the switch 9. A signal converted to digital data by the data detecting circuit 10 are demodulated by a demodulation circuit 11, an error of a code is corrected by an ECC circuit 12, and outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing device,
In particular, it relates to reproduction equalization processing of a digital signal reproduced from a recording medium.

[0002]

2. Description of the Related Art Conventionally, when a signal is transmitted, an equalization process is performed on the receiving side to control the frequency characteristic of the signal based on the transmission system to compensate for the loss and obtain a good signal.

As a transmission device of this type, for example, a digital VTR which records and reproduces a video signal as a digital signal on a magnetic tape is known.
In the above, the equalization process is performed on the reproduced signal.

The equalization processing here is performed by a circuit called an equalizer, and a digital VTR of this type will be described.

FIG. 13 is a block diagram showing the structure of a reproducing system of a digital VTR.

In FIG. 13, the signal reproduced from the magnetic tape 1 by the head 2 is 40 to 40 by the head amplifier 6.
It is amplified by 50 dB and output to the reproduction equalizer 5.

As shown in FIG. 14, the frequency characteristic of the reproduced signal obtained by the magnetic head 2 has a differential characteristic in the low range and an attenuation characteristic due to various losses in the high range. Therefore,
The inverse characteristic as shown in FIG. 15 is created by combining the resonance characteristic of the head amplifier 3 and the equalization characteristic of the reproduction equalizer 3 to correct the frequency characteristic of the reproduction signal.

The output signal of the reproduction equalizer 5 is compared with a predetermined threshold value in the data detection circuit 10 and restored to digital data again, and then demodulated by the demodulator 11. At this time, if there is noise that exceeds the threshold value at the input of the data detection circuit 10 due to tape noise, amplifier noise of the head amplifier 3, or the like, for example, data that should be “0” is detected as “1”, and as it is, I get an error.

Therefore, an error correction decoding circuit (hereinafter referred to as EC
The C circuit 12 corrects the error in the reproduction signal by using the parity data added at the time of recording, and generates an error flag indicating that error in the uncorrectable data and outputs the error flag to the subsequent circuit.

[0010]

However, in the above-mentioned conventional example, the adjustment of the frequency control characteristic of the reproduction equalizer is performed only at the time of factory shipment, and is not performed after reaching the user's hand. Not not.

Therefore, when the optimum control point of the reproducing equalizer is different from the setting at the time of shipment from the factory due to the type of tape, the wear of the head, etc., the error at the time of data detection increases, and as a result, it becomes good. There was a problem that a reproduced image could not be obtained.

In view of the above problems, the present invention provides an apparatus capable of preventing the deterioration of the quality of a reproduced signal by realizing the optimum equalization characteristic of the reproduction equalizer in any case. The purpose is to

[0013]

SUMMARY OF THE INVENTION In order to solve the conventional problems and achieve the above object, the present invention provides an input means for inputting a signal obtained from a recording medium and a signal from the input means. Equalizing means for equalizing, reproducing means for performing a predetermined process on an output signal of the equalizing means to obtain a reproduced signal, and the equalizing means for a predetermined period before the reproducing means starts reproducing the signal. And a characteristic control means for controlling the equalization characteristic.

[0014]

Since the present invention is configured in this way, it is possible to realize optimum equalization characteristics and prevent deterioration of the quality of reproduced signals.

[0015]

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

In this embodiment, the case where the present invention is applied to a digital VTR will be described. FIG. 1 is a block diagram showing the structure of a reproducing system of such a digital VTR.

In FIG. 1, the digital signal reproduced from the magnetic tape 1 by the magnetic head 2 shown in FIG. 13 is supplied via an input terminal 4 to a reproduction equalizer 5 composed of an LC filter having a fixed characteristic.

The digital VTR in this embodiment has two heads A and B having different azimuths, and the signals obtained from the respective heads are alternately supplied to the terminal 4.

The reproduction equalizer 5 corrects the low-frequency differential characteristic and the attenuation characteristic due to various losses in the high-frequency range, and outputs it via the switch 6 to the equalizers 7 and 8 which are variable transversal filters. The switches 6 and 9 are switched according to the head switch pulse shown in FIG. 2 and are connected to the opposite side for each track to supply a signal from each head.

The structure of the equalizers 7 and 8 is shown in FIG. In FIG. 3, 101 is a circuit matching resistor, 102 is a delay circuit that delays an input signal, 103 and 104 are high impedance buffers, 105 is a multiplier that multiplies the output signal of the buffer 103 by a coefficient K, and 106 is an operational amplifier. Is.

The buffer 104 is supplied with the signal delayed by the time t in the delay circuit 102 through the resistor 101. The buffer 103 is supplied with the input signal via the resistor 101 and the signal delayed by 2t after being reflected and returning due to the high input impedance of the buffer 104. Then, the output of the buffer 103 is multiplied by the coefficient K in the multiplier 105, and together with the output of the buffer 104, the operational amplifier 10
6.

The transfer characteristics from the input signal to the output of the operational amplifier 106 are:

[0023]

[Outside 1] However, ω = 2πf, and although there is a delay of time t, phase distortion does not occur even if the amplitude characteristic is changed. FIG. 4 is a diagram showing frequency characteristics with respect to the coefficient K of the equalizer.

The coefficient K is supplied from the CPU 17 as will be described later, and the frequency characteristic of the equalizer is changed by changing the value of this K to obtain the optimum equalization characteristic.

The signals whose high frequency components are controlled by the equalizers 7 and 8 are supplied to the data detection circuit 10 and the dropout detection circuit 14 via the switch 9.

The signal converted into digital data by the data detection circuit 10 as described above is demodulated by the demodulation circuit 11, and further corrected by a code error by the ECC circuit 12 and output. At this time, the ECC circuit 12 generates a flag indicating the uncorrectable error as described above and outputs it to the CPU 17.

When the envelope of the signal equalized by the equalizers 7 and 8 does not reach a predetermined level, the dropout detection circuit 14 uses that portion as a dropout period (hereinafter referred to as a DO signal).
S) is output to the CPU 17.

The CPU 17 changes the number K of the multipliers so that the equalizers 7 and 8 described above have optimum characteristics. Since the coefficient value output from the CPU 17 is digital data, it is converted to analog data by the D / A converters 18 and 19 and then output to the equalizers 7 and 8. The K output at this time will be described in detail later, but EC
The coefficient K is set so that the number of error flags output from the C circuit 12 is minimized.

Further, such a change of the equalization characteristic in this embodiment is carried out after a cassette (not shown) equipped with the tape 1 is loaded and the loading operation is performed, that is, the signal from the magnetic tape is actually reproduced. It is performed before output to the outside as a signal. The control timing of the equalizer in this embodiment is shown in FIG.

First, when the cassette is inserted into the VTR at t0, it is loaded at t1 and the tape is loaded. When the detection circuit (not shown) detects that the loading is completed at t2, equalization is performed using the signal obtained from the tape without outputting the reproduction signal, that is, without outputting the image or sound. The characteristics are controlled to find the optimum coefficient K. When the optimum K is detected at t3, the tape is rewound to the loading position based on the time code and the subcode recorded together with the image data and the audio data, and the control of the equalizer is finished.

Next, the control of the equalization characteristic of the equalizer by the CPU 17 will be described.

FIG. 6 is a flow chart for explaining the overall operation of controlling the equalization characteristic.

When the cassette is inserted and the tape loading is completed as described above, the variable P indicating the control point of the coefficient K, the number of tracks, and the number of errors are initialized to "0" (step S201).

In this embodiment, 10 tracks of errors are counted, and the optimum value of the coefficient K is determined based on this count value. This error counting is performed using the area signal shown in FIG. That is, the CPU 17
The error flag output from the circuit 12 is counted. This count value is reset each time 10 area signals are input to each head, and the value immediately before reset is taken as the error number of 10 tracks. To do. This area signal can be obtained by detecting the envelope of the reproduction signal. The area signal and the head switch pulse are supplied to the CPU 17 from a timing signal generating circuit (not shown).

When the above-described initialization is performed in step S201, it is determined in step S202 whether the reproduction signal is the signal obtained by the head A based on the head switch pulse. If the reproduced signal is from the head A, the number of errors in the reproduced signal for 10 tracks is counted in step S203, and the characteristic of the equalizer 7 that equalizes the reproduced signal of the head A is controlled to obtain an optimum value. It is set (step S204). If the reproduction signal is not that of the head A, that is, if it is the reproduction signal from the head B, the head B is similarly read at step S205.
The number of errors in the reproduction signal for 10 tracks from is counted, the characteristic of the equalizer 8 is controlled, and the optimum value is set (step S206).

Next, the error number counting process in FIG. 6 will be described. FIG. 7 is a flowchart for explaining the operation of the error number counting process. In the present embodiment, 32 control points of the coefficient K are set, and the number of errors in the reproduction signal for 10 tracks is counted for each point.

When the error number counting process is started,
In step S301, it is determined whether the control point P of the coefficient K is 32, and if P indicates 32, that is, the coefficient K is changed for all 32 points, the process ends.

If P is less than 32, it is determined in step S302 whether the number of reproduced tracks tr has reached 10. Here, when tr is 10, the counted error number is read into the internal memory (not shown), the error count number and the track number tr are reset, and at the same time, P is changed by 1 point, and the process proceeds to step S304. If tr is less than 10 in step S302, the process directly proceeds to step S304.

In step S304, it is determined whether or not there is a dropout in the signal of the currently reproduced track.
It is determined based on S, and if there is a dropout, the reproduction signal of this track is not used for error counting, and the process returns to step S301. If DOS is not supplied and there is no dropout, an error in the reproduction signal is detected in step S305, the number of errors is counted in step S306, and 1 is added to the track number tr in step S307. In addition, the process returns to step S301.

In this way, the number of errors in the reproduced signal is counted, and when the control point P of the coefficient K reaches 32, the counting of the number of errors is terminated and the optimum value setting process is started.

Next, the operation of the optimum value setting process will be described. In this optimum value setting operation, a point having the smallest number of counted errors is searched out of the 32 control points and is set as the set value of the coefficient K.

FIG. 8 is a flow chart for explaining the operation of the optimum value setting process.

In FIG. 8, when the optimum value setting process starts, the point P and the minimum value Emin of the number of errors are initialized in step S401. Specifically, 1 is substituted into P, and the count value of the number of errors at point 1 is substituted into Emin which shows the minimum value of the number of errors.

In step S402, 1 is added to P, and the number of errors counted at the next point is read from the memory. Then, in step S403, it is determined whether or not the number of errors E just read out is smaller than Emin. If E is larger, step S4 is performed as it is.
Go to 05. Also, if E is smaller, Emin becomes E
Value is substituted, and the process proceeds to step S405.

In step S405, the control point P is 3
It is determined whether or not the value becomes 2, and if P does not become 32 yet, the process returns to step S402. Also, P is 32
When it becomes, it progresses to step S406, and E at this time
Set the control point corresponding to min as the optimum value.

The state at this time is shown in FIG. FIG. 9 is a diagram showing each control point and the number of errors counted at the control point.

As is apparent from the figure, in this example, the coefficient K corresponding to the point 19 is set as the optimum value.

Then, the CPU 17 outputs the optimum value K set in this way to the equalizers 7 and 8 to control the equalization characteristic. Since the above processes are independently performed by the heads A and B, the equalization characteristics can be controlled according to the characteristics of each head.

As described above, in the present embodiment, the optimum set value of the equalizer is searched based on the number of errors in the reproduced signal, so that it is affected by what kind of head wear and tape type. It is possible to always obtain the optimum equalization characteristic.

Further, as can be seen from FIG. 9, if the control characteristics of the equalizer are greatly changed, the number of errors may be very large. If such an equalizer control is carried out while the reproduced image or sound is output, the reproduction is performed. It leads to deterioration of image quality and sound quality, and it becomes very unsightly. According to this embodiment, after the cassette is inserted, the optimum setting value is searched by changing the characteristics of the equalizer before outputting the reproduced image or sound. There is no effect on the playback image quality.

Furthermore, since loading is always performed when the cassette is exchanged, even if the type of magnetic tape is changed, the reproduction signal can be equalized with a frequency characteristic that is optimum for each tape. Therefore, the number of errors in the reproduced signal is reduced and a good reproduced signal can be obtained.

Next, a second embodiment of the present invention will be described.

Generally, in a digital VTR, an error rate (error rate) in a signal after error correction decoding is often on the order of 10 ^-5 or less. Therefore, the S / N for counting the number of errors and setting the optimum value tends to be insufficient.

Therefore, if the equalizer is adjusted while counting the number of errors in the signal reproduced in the off-track mode in which the head is intentionally off-tracked to reproduce the signal, the error in the reproduced signal increases. N is improved and it becomes easier to detect the optimum point. In the following embodiment, a case where the equalizer is adjusted by using such an off-track mode will be described.

In a digital VTR, there has been proposed a method of multiplexing a tracking pilot signal by subjecting recorded data to 24/25 conversion, and a specific method thereof is described in JP-A-4-255969. ing.

In this type of method, the magnetic tape shown in FIG.
The digital signal is recorded while forming tracks for recording three types of signals having the frequency spectrums shown in FIG.

FIG. 10A is a recording signal of a track in which pilot signal components are not multiplexed, FIG. 10B is a recording signal of a track in which frequency components of frequency f1 are multiplexed as pilot signals, and FIG. 10C is a frequency as pilot signals. f2
It is the frequency spectrum of the recording signal of the track in which the frequency components of

These recording tracks are formed as shown in FIG. In FIG. 11, track F0 is a track on which a signal without a pilot signal component is recorded, F1 is a track on which a signal with a frequency f1 component is recorded, and F2 is a track with a frequency f2 component. It is a track on which a multiplexed signal is recorded.

In the tracking control method during reproduction by such a recording method, when the head is scanning the F0 track, the magnitude of the pilot signal leaking from the adjacent track is detected, and the magnitude of each pilot signal is detected. Tracking control is carried out by controlling the running of the tape so that the values become the same.

In the off-track mode in the present embodiment, when the F0 track is scanned, the balance of the magnitudes of the pilot signals leaking from the adjacent tracks is
For example, the tape running is controlled so that the magnitude of the pilot signal leaking from the F1 track is smaller than the magnitude of the pilot signal leaking from the F2 track.

As a result, the head tracing traces the F0 track by leaning toward the F2 track side. Thus, the off-track amount can be made constant by changing the balance of the leaking pilot signal and controlling the tape running.

In this embodiment, the number of errors in the reproduced signal is increased by setting the optimum value by counting the number of errors using this off-track mode during the error number counting process shown in FIG. The S / N of the required number of errors can be improved.

Therefore, the difference in the number of error counts between control points becomes large, and the optimum point can be detected quickly.

Incidentally, such an off-track mode is
In many cases, it is already provided for adjustment at the time of factory shipment, and in many cases, it is sufficient to use the existing system without providing such an off-track mode.

In the above-described embodiment, the equalizer is adjusted between the time when the cassette is inserted and the time when the image is actually reproduced, but the equalizer may be adjusted during reproduction. However, if it is performed during reproduction, as described above, the number of errors increases if the characteristics of the equalizer are greatly changed. Therefore, it is necessary to perform the adjustment within a very narrow range that does not significantly affect the reproduced image quality and sound quality.

In this case, as described above, if the optimum value of the equalizer is adjusted before actually reproducing and outputting the image / sound, the characteristic can be changed in a narrow range with that point as a reference. It is possible to control the equalization characteristic without significantly affecting the reproduction signal.

Specifically, in response to an instruction to reproduce a signal, the number of errors at the control points of about 8 points before and after the optimum value is counted, the point at which the number of errors is minimized is obtained, and this is optimized. As a value, the coefficient K of the equalizer is set. The state of the operation at this time is shown in FIG.

Thus, by adjusting the characteristics of the equalizer within a narrow range every time reproduction is started other than after loading, a slight deviation of the optimum point due to heat or temperature change by the digital VTR itself can be corrected. .

In this embodiment, the equalizer is adjusted each time the reproduction is started, but it may be performed after the reproduction is stopped.

In the above-described embodiment, the case where the frequency characteristic of the reproduction signal is controlled by adjusting the characteristic of the equalizer has been described, but the present invention is not limited to this, and the resonance characteristic of the head amplifier shown in FIG. 13 is controlled. May be configured to compensate the frequency characteristic of the reproduction signal, and the present invention can be applied to this case as well, and has the same effect.

Further, although the case where the present invention is applied to the digital VTR has been described in the above-mentioned embodiment, the present invention is not limited to this, and the present invention can be applied to any one that controls the frequency characteristic of a signal reproduced from another recording medium or the like. The invention can be applied and has the same effect.

[0072]

As is apparent from the above description, in the present invention, the equalizing characteristic of the equalizing means is controlled in a predetermined period before the reproduction means starts reproduction of the signal. It is possible to eliminate the influence on the reproduced signal due to the change of the characteristic, and it is possible to obtain the optimum equivalent characteristic without deteriorating the quality of the reproduced signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a digital VTR as an embodiment of the present invention.

FIG. 2 is a timing chart for explaining error number counting processing according to the embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of an equalizer in FIG.

FIG. 4 is a diagram showing frequency control characteristics of the circuit of FIG.

FIG. 5 is a timing chart for explaining an equalization characteristic control operation in the first exemplary embodiment of the present invention.

FIG. 6 is a flowchart for explaining the overall operation of the first exemplary embodiment of the present invention.

FIG. 7 is a flowchart for explaining error number counting processing according to the embodiment of the present invention.

FIG. 8 is a flow chart for explaining an optimum value setting process in the embodiment of the present invention.

FIG. 9 is a diagram showing a relationship between control points of equalization characteristics and the number of errors.

FIG. 10 is a diagram showing a frequency spectrum of a reproduction signal in the example of the present invention.

FIG. 11 is a diagram showing a recording format in an embodiment of the present invention.

FIG. 12 is a timing chart for explaining the operation of another embodiment of the present invention.

FIG. 13 is a block diagram showing a configuration of a conventional digital VTR.

FIG. 14 is a diagram showing a frequency characteristic of a reproduction signal in the example of the present invention.

FIG. 15 is a diagram showing frequency control characteristics by a reproduction equalizer and a head amplifier in an example of the present invention.

[Explanation of symbols]

 3 head amplifier 7 equalizer 8 equalizer 12 error correction decoding circuit 17 CPU

Claims (13)

[Claims] 1. An input unit for inputting a signal obtained from a recording medium, an equalizing unit for equalizing a signal from the input unit, and a reproduction signal obtained by subjecting an output signal of the equalizing unit to a predetermined process. And a characteristic control means for controlling the equalization characteristic of the equalizing means for a predetermined period before the reproducing means starts reproducing the signal. 2. An error detection means for detecting an error in an output signal of the equalization means, wherein the characteristic control means controls the equalization characteristic of the equalization means according to the output of the error detection means. The reproducing apparatus according to claim 1, wherein: 3. The reproducing apparatus according to claim 2, wherein the characteristic control means sets the equalization characteristic so that an error rate of an output signal of the equalization means becomes the lowest. 4. The reproducing apparatus according to claim 2, wherein the characteristic control means controls the equalization characteristic according to a cumulative result obtained by accumulating outputs of the error detecting means. 5. A dropout detection means for detecting a dropout of a signal from the input means, wherein the characteristic control means outputs the error detection means during a period in which no dropout is detected by the dropout detection means. 5. The reproducing device according to claim 4, wherein 6. The reproducing apparatus according to claim 1, wherein the characteristic control unit changes the equalization characteristic within a predetermined range. 7. The reproduction according to claim 6, wherein the characteristic control means further changes the equalization characteristic within a range narrower than the predetermined range for a predetermined period from the start of reproduction of the reproduction signal. apparatus. 8. The input means has a plurality of heads for tracing the track formed on the recording medium to obtain the signal, and the equalizing means has a plurality of equalizers corresponding to the respective heads. The reproducing apparatus according to claim 1, wherein 9. The reproducing apparatus according to claim 8, wherein the characteristic control unit independently controls equalization characteristics of the plurality of equalizers. 10. The recording medium is a tape-shaped recording medium, the input means further comprises loading means for loading the tape-shaped recording medium, and the characteristic control means completes loading of the tape-shaped recording medium. 9. The reproducing apparatus according to claim 8, wherein the equalizing characteristic of the equalizing means is controlled for a predetermined period before being set. 11. The characteristic control means controls the equalization characteristic using a signal obtained by off-tracking the head before the tape recording medium completes loading. 8. The playback device according to item 8. 12. The reproducing apparatus according to claim 1, wherein the equalizing means performs equalization processing on the amplitude and the phase of the input signal. 13. An input unit for inputting a signal obtained from a recording medium, a control unit for controlling a frequency characteristic of a signal from the input unit, and a reproduction signal obtained by subjecting an output signal of the control unit to a predetermined process. A reproducing apparatus comprising: a reproducing unit that obtains the above; and a unit that changes a control characteristic of the control unit to a greater extent than in another period in a predetermined period before the reproducing unit starts reproducing the signal.