JPS63188868A - Dropout correcting circuit - Google Patents

Abstract

PURPOSE:To attain correction so as not to give unnatural sense of listening to a user even when a dropout takes place by selecting a data interpolation means in response to the length of dropout period thereby correcting the data. CONSTITUTION:An audio signal inputted to an input terminal 47 is inputted to an interpolation data loading circuit 49 via an A/D conversion circuit 48. The circuit 49 receives a dropout detection signal, replaces a digital data inputted during H level period of the signal into a prescribed interpolation data and sends the result to a memory 52 via a switch 51 for storage. The data is read via a switch 53 and fed to a detection circuit 54, the interpolation data is detected and the result is outputted to a dropout length detection circuit 55 and a switch 56. The circuit 55 detects the length of the dropout and sends the interpolation data to circuits 57-60 selectively via the switch 56 and the circuits 57, 58 apply correction by the least square approximation and mean value approximation respectively. When the length becomes longer further, the data is corrected by the least square approximation by the circuit 61 via the circuits 59, 60.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a signal reproducing device such as a video tape recorder, and particularly relates to an improvement of a dropout correction circuit for correcting a dropout portion thereof. .

(Prior Art) Recently, video tape recorders (hereinafter referred to as VTRs), which use 1/2-inch wide tape and employ a high-fidelity audio deep recording system, have become popular. In this type of VTR, what is especially important is how to correct the data in that part to maintain high sound quality when a dropout occurs in the audio playback signal due to dust or scratches on the tape. That is to say.

FIG. 5 shows an audio reproduction system of a high-fidelity VTR that includes a conventional audio dropout correction means. That is, in the figure, reference numeral 11 denotes a rotating drum, and a plurality of (two in the illustrated case) video heads 12, 13 and audio heads 14, 15 are arranged along the circumference of the drum.

In this case, the video heads 12.13 and the audio heads 14.15 are arranged at positions facing each other across the center of the rotating drum 11, and a straight line connecting the video heads 12.13 and Audio head 14
．． The straight lines connecting the 15 comrades are arranged so as to be perpendicular to each other, that is, at positions shifted by 90 degrees.

During tape reproduction, the rotary drum 11 is rotated in the direction of arrow A in the figure, and the magnetic tape 1G is brought into contact with the circumferential side of the rotary drum 11 and run in the direction of arrow B in the figure. Therefore, the video heads 12 and 13 and the audio heads 14 and 15 alternately trace the magnetic tape 16 and output playback signals.

Of these, the video head 12. The switch 17 selects the playback signal output from the video head 12 or 13 that is tracing the magnetic tape 16, and the playback signal output from the video head 13 is sent to the output terminal 18 for video signal processing (not shown). It is supplied to a circuit and used for image display.

On the other hand, the switch 19 selects the reproduction signal output from the audio head 14 or 15 that is tracing the magnetic tape 16 as the reproduction signal output from the audio head 14 or 15. The switching operation of this switch 19 is controlled based on a head switching pulse output from a switching pulse generating circuit 20. In other words, this head switching pulse is applied to the audio head 1.
The polarity of the magnetic tape 16 is reversed in accordance with the cycle in which the magnetic tape 16 is alternately traced, and the switch 19 is changed depending on the polarity.

The reproduced signals guided by the switch 19 are supplied to band-pass filters 21 and 22 and band-limited, thereby extracting an L-channel audio reproduction signal and an R-channel audio reproduction signal. Of these, the L channel audio reproduction signal is supplied to a demodulation circuit 23 and demodulated, and is also supplied to a dropout detection circuit 24 to detect dropouts.

Here, if dropout has not occurred, the output signal of the demodulation circuit 23 is supplied to the dropout correction circuit 25, but passes through without undergoing any processing, and is then passed through the low-pass filter 26. The signal is output from the output terminal 29 via the noise reduction circuit 27 and the amplifier circuit 28, and is used for audio reproduction.

Then, the L output from the band pass filter 21 is
When a dropout occurs in the audio reproduction signal of the channel, a detection signal is output from the dropout detection circuit 24, and the dropout correction circuit 25 is driven. Therefore, the dropout portion of the output signal of the demodulation circuit 23 is corrected and supplied to the low-pass filter 26.

In addition, the R output from the band pass filter 22 is
The audio reproduction signal of the channel is transmitted through a demodulation circuit 30°, a dropout detection circuit 31. Dropout correction circuit 32. Low pass filter 33. The noise reduction circuit 34 and the amplification circuit 35 perform the same processing as described above depending on whether or not there is a dropout, and the signal is output from the output terminal 36 and used for audio reproduction.

Here, FIG. 6 shows a detailed configuration of the dropout correction circuit 25. Note that the dropout correction circuit 32 has a similar configuration, so a description thereof will be omitted. That is, 37 in FIG. 6 is an input terminal to which the output signal of the demodulation circuit 23 is supplied, and 38 in the figure
is an input terminal to which a detection signal output from the dropout detection circuit 24 is supplied.

First, a state where no dropout has occurred,
In other words, before time ti in FIG. 7, if the detection signal is at the L (low) level as shown in FIG. 7(a), the output of the mute detection circuit 39 is at the L level as shown in FIG. 7(b). The switch control circuit 40 is connected to the switch 4.
1 to the state shown in the figure.

Therefore, the demodulated output signal shown in FIG. 7(C) supplied to the input terminal 37 is transmitted to the switch 41. The signal is directly supplied to the low-pass filter 26 via the amplifier 42 and the output terminal 43, as shown in FIG. 4(d).

Here, as shown in FIG. 7, it is assumed that dropout occurs during a short period T1 from time tl to t2. Then, the detection signal supplied to the input terminal 38 becomes H (high) level for a period TI, as shown in FIG. 7(a). During this short period TI, the output of the mute detection circuit 39 maintains the L level, as shown in FIG. 7(b).

On the other hand, when the detection signal becomes H level, the switch control circuit 40 controls the sample and hold circuit 44 to be in a hold state, and switches the switch 41 to the sample and hold circuit 44 side. For this reason, the low-pass filter 45
The demodulated output signal that was being supplied to the sample-and-hold circuit 44 via is held at the level at time t1, and the output from the output terminal 43 becomes as shown in FIG. 7(d).
This will be corrected using a signal at a certain level.

Further, as shown in FIG. 7, it is assumed that dropout occurs during a long period T2 from time t3 to t5. Then, the detection signal supplied to the input terminal 38 is as shown in FIG.
), it becomes H (high) level for a period T.

In this case, until time t4 when period T3 has elapsed, the output of mute detection circuit 39 is as shown in FIG. 7(b).
Maintains L level.

Therefore, in this period T3, the above-mentioned
Sample and hold circuit 4 via low-pass filter 45
The demodulated output signal supplied to the output terminal 4 is held at the level at time t3, and the output of the output terminal 43 is corrected with a signal at a constant level, as shown in FIG. 7(d).

Then, when time t4 is reached, the output of the mute detection circuit 39 becomes H level as shown in FIG. 7(b). Then, the switch control circuit 40 switches the switch 4I to the constant voltage source 46 side. I #do.

Therefore, the output of the output terminal 43 is corrected by the output voltage level of the constant voltage source 46, as shown in FIG. 7(d). After that, the mute detection circuit 39 detects the signal at time t4.
At time t6, when a predetermined period including the chattering prevention period has elapsed, the output is set to L level.

(Problem to be Solved by the Invention) However, the conventional dropout correction means as described above still cannot be said to have sufficiently corrected the dropout, and may cause unnatural hearing to the user. The reality is that it is given.

Therefore, the present invention has been made in consideration of the above circumstances, and provides an extremely good dropout correction circuit that can correct the occurrence of dropout so as not to give the user an unnatural hearing sensation. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) That is, the dropout correction circuit according to the present invention has the following features:
An information signal read from a recording medium is converted into digital data, a dropout portion is detected, and the dropout portion is replaced with predetermined interpolated data and stored in a memory. Thereafter, the length of the dropout portion is detected by reading the digital data from the memory and detecting its interpolated data component.

On the other hand, data correction means with a number of stages capable of correcting the interpolated data portion based on the digital data before and after the interpolated data using different means are provided, and the number of stages can be adjusted according to the length of the dropout portion detected earlier. Select a desired data correction means from among the data h (i) and correct the interpolation data part.Then, this correction data is stored in the interpolation data storage position of the memory, and the data including the correction data is stored in the memory. It is designed to read out digital data and convert it into analog data.

(Function) According to the above configuration, data correction means suitable for the length of the dropout period is selected for correction, so even if dropout occurs, the data correction method is selected and corrected. , correction can be made so as not to give an unnatural sound to the user.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In this embodiment, the case where the dropout of the L channel audio reproduction signal output from the demodulation circuit 23 shown in FIG. To correct dropouts in the audio playback signal,
Since they are similar, their explanation will be omitted.

That is, in FIG. 1, the L channel audio reproduction signal supplied to the input terminal 47 is supplied to an A/D (analog/digital) conversion circuit 48 and converted into digital data, and then sent to an interpolation data insertion circuit 49. is supplied to A dropout detection signal output from the dropout detection circuit 24 is supplied to the interpolation data insertion circuit 49 via an input terminal 50. The interpolation data insertion circuit 49 functions to replace the digital data manually input during the generation of the dropout detection signal, that is, during the H level period, with predetermined interpolation data.

In this way, the digital data whose dropout portions have been replaced with interpolated data by the interpolated data insertion circuit 49 is supplied to the memory 52 via the switch 51 and stored therein. The digital data stored in the memory 52 is read out via the switch 53 and supplied to the interpolation data detection circuit 54, where the interpolation data added by the interpolation data insertion circuit 49 is detected.

Here, the interpolation data detection circuit 54 outputs the detected interpolation data to the dropout length detection circuit 55, and also outputs data necessary for correction among the digital data read from the memory 52 to the switch 56. Of these, the dropout length detection circuit 55 detects the dropout length by counting the number of samples of interpolated data, and generates a length detection signal. The switch 56 also connects the data output from the interpolation data detection circuit 54 to the least squares approximation circuit 57 based on the length detection signal output from the dropout length detection circuit 55. Average value approximation circuit 58. Pre-hold circuit 59
and selectively leads to the mute processing circuit 60.

In other words, a short dropout now occurs, and Figure 2 (
Assume that the dropout detection signal becomes H level as shown in a), and the data at the sampling point C of the audio reproduction signal is lost as shown in FIG. Then, the dropout length detection circuit 55 controls the switch 56 so that the data output from the interpolation data detection circuit 54 is supplied to the least squares approximation circuit 57.

This least squares approximation circuit 57
Samples, data at points A and B, and sampling point C
B is obtained by least squares approximation using the next three samples, that is, the data at points E and p.

The data at points C, D, and E are as shown in Figure 2 (c).
Correction is made by replacing the data with data indicated by points Bl, CL, Di, and E1.

Here, the least squares approximation circuit 57 corrects the interpolated data portion by least squares approximation calculation of a cubic equation as shown in the following equation.

Yoi-Σa ijY ij/ b i (tatashi, ai
j, bi are constants, Yij is human digital data, Yoi
is the first estimated data. ) In the above case, if the A-F points are respectively 1 to 6, then i-2, 3, 4, 5, j-1, 2, 4°5.6.

In addition, a dropout that is slightly longer than the above dropout occurs, and the dropout detection signal becomes H level as shown in Figure 3(a), and two samplings of the audio reproduction signal are detected as shown in Figure 3(b). Suppose that data at points B and C are missing. Then, the dropout length detection circuit 5
5 is a switch 5 so that the data output from the interpolation data detection circuit 54 or the average value approximation circuit 58 is supplied.
6 is switched and controlled.

This average value approximation circuit 58 is located at the sampling point B.

Using the data of the two samples before and after C, that is, the data of points A and D, the data of points B and C are calculated based on the average value as shown in Figure 3 (c
), the correction is made by replacing the data with the data shown at points BL and C1.

Furthermore, a long dropout occurs, and the dropout detection signal becomes H level as shown in FIG. 4(a).
Assume that data at a plurality of sampling points C-■ of the audio Ij raw signal is missing, as shown in FIG. 2B. Then, the dropout length detection circuit 55 controls the switch 56 so that the data output from the interpolation data detection circuit 54 is supplied to the pre-hold circuit 59.

This pre-hold circuit 59 holds the sample immediately before dropout occurs, that is, the data at point B, and uses that value to change the data at point C-1 to 01 as shown in FIG. 4(c). ~■ Replace with the data shown in 1. and,
The output of this pre-hold circuit 59 is supplied to a least squares approximation circuit 61 which operates in the same manner as the least squares approximation circuit 57 described above. This least squares approximation route 61 adds data at point L to the original digital data portion, that is, A, B, and J.
C[.

As shown in Fig. 4(d), the data of Dl and I1 points are
C2, D2. Correct by replacing with the data shown at point 12.

Further, when the dropout period is very long, the dropout length detection circuit 55
The switch 56 is controlled so that the data output from the mute processing circuit 60 is supplied to the mute processing circuit 60. This mute processing circuit 60 fixes the digital data to a constant value during the dropout period and applies so-called muting.

The output of the mute processing circuit 60 is then supplied to the least squares approximation circuit 61 and corrected so that the transition between the original digital data portion and the muted data portion becomes smooth.

As described above, depending on the length of the dropout period, the least squares approximation circuit 57. The data corrected by different correction means such as the average value approximation circuit 58, the pre-halt circuit 59 and the mute processing circuit 60 are switched based on the length detection signal output from the dropout length detection circuit 55. taken out by a switch 62 operated;
The interpolated data is stored again in the memory 52 via the switch 51 at the address where the interpolated data was previously stored.

Thereafter, the digital data including the corrected data is read out from the memory 52, and the D/
A (digital/analog) conversion circuit 63 is supplied with
The signal is converted into an analog audio reproduction signal and supplied to the low-pass filter 26 via an amplifier circuit 64 and an output terminal 65.

Here, the conversion operations of the A/D conversion circuit 48 and the D/A conversion circuit 63, the write and read operations of the memory 52, the switching operations of the switches 51 and 53, etc. are output from the timing generation circuit 66. It is controlled by various timing signals. Further, the address of the memory 52 is controlled by an address generation circuit 67 which is controlled by a timing signal output from the timing generation circuit 66.
is generated by.

Therefore, according to the configuration of the above embodiment, the optimum means is selected from among various correction means such as least squares approximation, average value approximation, pre-hold, and mute, depending on the length of the dropout period. Since dropout correction is performed by selecting , it is possible to perform correction that does not give the user an unnatural hearing sensation.

In addition to the above-mentioned four types of means for correcting the data in the dropout period, for example, when the dropout period is long, writing of new data to the memory 52 is stopped and data already stored in the memory 52 is corrected. Possible methods include means for repeatedly reading out the data stored in the memory 52, and means for clearing the joints of the data repeatedly read from the memory 52 using least squares approximation.

Furthermore, when the dropout period is long and the high-fidelity audio reproduction signal obtained from the aforementioned audio head 14 or 15 is muted, a normal audio reproduction signal output from the fixed audio head is generated. Possible means include means for automatically switching between the two, and means for approximating the seam between the high-fidelity audio reproduction signal and the normal audio reproduction signal when switching by this means.

In addition, if data correction processing takes a long time (for example, if software processing is performed on a microcomputer), the correction processing may not be completed in time if dropouts occur frequently. It may also be possible to detect this and automatically switch to a correcting means that requires a shorter processing time.

In addition, as for multiple correction means, by making some or all of them common and changing the given parameters,
The characteristics may also be switched.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without departing from the scope of the invention.

[Effects of the Invention] Therefore, as detailed above, according to the present invention, when dropout occurs, it is possible to perform extremely good dropout correction that can be corrected so as not to give audible unnaturalness to the user. The circuit can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing an embodiment of a dropout correction circuit according to the present invention, FIGS. 2 to 4 are timing diagrams for explaining the operation of the same embodiment, and FIG.
The figure is a block diagram showing an audio reproduction system of a high-fidelity VTR, and FIGS. 6 and 7 are block diagrams showing a conventional dropout correction means and timing diagrams for explaining its operation, respectively. 11... Rotating drum, 12. 13... Video head, 14° 15... Audio head, 1B... Magnetic tape, ■7... Switch, 18... Output terminal, 19
...Switch, 2o...Switching pulse generation circuit, 21
．． 22... Band pass filter, 23... Demodulation circuit, 24... Dropout detection circuit, 25... Dropout correction circuit, 26... Low pass filter, 27
...Noise reduction circuit, 28...Amplification circuit,
29... Output terminal, 30... Demodulation circuit, 31...
Dropout detection circuit, 32... Dropout correction circuit, 33... Low pass filter, 34... Noise reduction circuit, 35... Amplification circuit, 36...
Output terminal, 37.38... Input terminal, 39... Mute detection circuit, 40... Switch control circuit, 41...
・Switch, 42...Amplifier, 43...Output terminal,
44... Sample hold circuit, 45... Low pass filter, 4G... Constant voltage source, 47... Input terminal,
48... A/D conversion circuit, 49... Interpolation data insertion circuit, 50... Input terminal, 51... Switch, 52
...Memory, 53...Switch, 54...Interpolation data detection circuit, 55...Dropout length detection circuit, 5G...Switch, 57...Least squares approximation circuit,
58... Average value approximation circuit, 59... Pre-hold circuit, 60... Mute processing circuit, 61... Least squares approximation circuit, 62... Switch, 63... D/A conversion Circuit, 64... Amplification circuit, 65... Output terminal, 66
...Timing generation circuit, 67...Address generation circuit. Applicant's agent Patent attorney Takehiko Suzue (α) Figure 2 Figure 3

Claims (1)

[Claims] A signal reproducing device that reads an information signal from a recording medium on which the information signal is recorded includes an analog-to-digital conversion means for converting the information signal read from the recording medium into digital data, and an output from the analog-to-digital conversion means. data interpolation means for detecting dropout portions of digital data and replacing the dropout portions with predetermined interpolation data; storage means for storing digital data output from the data interpolation means; and digital data stored in the storage means. detection means for reading data and detecting the interpolation data component in the read digital data to detect the length of the dropout portion; a plurality of data correction means capable of correcting the dropout portion; and a desired data correction means is selected from among the plurality of data correction means according to the length of the dropout portion detected by the detection means, and the interpolated data is selection means for correcting the portion and storing the correction data in the storage position of the interpolation data of the storage means; and reading out the digital data stored in the storage means including the correction data obtained by the selection means and converting it into analog data. 1. A dropout correction circuit comprising digital-to-analog conversion means for converting.