JPH04362571A - Drop-out compensation device - Google Patents

Abstract

PURPOSE:To improve the detection sensitivity of drop-out in the drop-out compensation device of a device recording/reproducing a video signal. CONSTITUTION:A drop-out detection means 3 is provided before a frequency conversion means composed of a balanced modulator 1 and HPF 2 and a drop- out detection means 6 is provided after the frequency conversion means. Drop- out whose frequency difference between drop-out and an FM signal is enlarged when a reproduced FM signal is converted into the high frequency is detected in the detection means 6 and drop-out whose difference with the FM signal is larger in the case of the low freqeuncy is detected in the detection means 3. Respective detection outputs are added in an addition means 7 and a drop-out compensation means 5 is controlled by the output of the addition means 7. Thus, detection sensitivity can be improved even if the frequency difference between drop-out and the reproduction FM singal is small.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to video equipment for recording and reproducing video signals, and more particularly to a dropout compensation device for reproduced FM signals.

0002

[Background Art] In recent years, the recording media of video equipment that records and plays back video signals have been improved, and dropouts due to scratches, dust, etc. during the manufacturing process of the recording media have been reduced, but this does not mean that they will be completely eliminated. Correct playback will not be possible unless dropout compensation is performed. Therefore, in order to increase the detection sensitivity of dropouts, it has been conventionally possible to improve the detection sensitivity by using an envelope detection circuit or a dropout frequency detection circuit that detects frequencies other than the deviation frequency band of the FM signal. I'm trying.

[0003] Hereinafter, a conventional embodiment of the above-described dropout detection means will be described with reference to the drawings. FIG. 3 shows a conventional dropout compensator. In FIG. 3, 8 is a balanced modulator, 9 is a high-pass filter, 10 is dropout detection means, 11 is FM demodulation means, and 12 is dropout compensation means. The dropout detection means No. 10 uses methods such as frequency detection and envelope detection that detect portions other than a predetermined pulse width using a monomulti. The dropout compensation device configured as described above detects dropouts in the reproduced FM signal before frequency conversion by methods such as envelope detection or frequency detection, or by detecting pulse-like dropouts with a comparator, and detects dropouts in the 1H Dropout compensation is performed by replacing the dropout period with a delayed signal.

0004

[Problems to be Solved by the Invention] However, in a dropout compensation device having a conventional configuration, especially in the case of a device using frequency detection, in the case of a dropout at a frequency close to the frequency of the reproduced FM signal, the frequency difference is small, so the FM Since it is difficult to distinguish from the FM signal and there is a high possibility of false detection, the detection sensitivity is not increased much, and the sensitivity is set to detect only dropouts that have a large frequency difference from the FM signal. Therefore, it has been difficult to increase the detection sensitivity of dropout. In view of the above-mentioned problems, it is an object of the present invention to provide a dropout compensating device that can set dropout detection sensitivity higher than that of conventional devices, especially in devices using frequency detection.

[0005]

[Means for Solving the Problems] In order to achieve this object, the dropout compensation device of the present invention provides that the frequency-converted FM signal has dropouts that are easy to detect because the frequency difference between the signal and the dropouts is increased. Focusing on that,
Dropout detection means are provided before and after the frequency conversion means for the reproduced FM signal, and addition means is provided for adding the outputs of both detection means, and dropout compensation for the demodulated signal is performed using the output of the addition means. It has a structure.

[0006]

[Operation] With this configuration, if the frequency difference between the frequency-converted FM signal and the dropout increases and the dropout is easier to detect, the dropout detection means after the frequency conversion will detect it, and vice versa. In the case of dropouts that are easier to detect in the unconverted signal, the dropout detection sensitivity can be increased by detecting them using the dropout detection means before frequency conversion and adding the detection outputs of both. It is.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A dropout compensating device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a dropout compensator according to an embodiment of the present invention. In FIG. 1, 1 is a balanced modulator, 2 is a high pass filter (HPF), 3 and 6 are dropout detection means, 4 is FM demodulation means, 5 is dropout compensation means, and 7 is addition means.

The operation of the dropout compensating device configured as above will be explained. First, the F of regeneration
The M signal is converted to a high frequency by a frequency conversion means consisting of a balanced modulator 1 and a high-pass filter 2, and in the case of a dropout in which the frequency difference between the dropout and the FM signal is expanded, the dropout detection means 3 is used.
If the frequency difference between the dropout and the FM signal is larger at lower frequencies, the dropout detection means 6
The outputs of the dropout detecting means 3 and 6 are added by the adding means 7, and the dropout compensating means 5 is controlled by the output of the adding means 7 to compensate for the dropout. Dropout detection sensitivity can be increased by performing dropout detection before and after frequency conversion and adding the outputs.

The reason why the detection sensitivity of the dropout compensator of the present invention is increased will be explained below with reference to the drawings. In Figure 2, A, C, H, and G are waveforms when detecting dropout before frequency conversion, and B, D, H, and F are waveforms when detecting dropout after frequency conversion to a higher frequency. It is. C, D, G, and C are the waveforms of A, B, E, and F, respectively. First, a case where detection is better when converted to a higher frequency will be described. Figure 2
In the case of dropouts like (a) and (b), converting the frequency of the FM signal to a frequency with a higher width (frequency) of the period during which the FM signal is missing will increase the frequency difference between the FM signal and the dropout. This can be seen from the pulse waveforms c and d. On the other hand, in the case of pulse-like dropouts such as E and F, it can be seen that the lower the frequency, the greater the frequency difference with the FM signal, making it easier to detect. As described above, by using the dropout detection means for the FM signal after frequency conversion and the dropout detection means for the FM signal before frequency conversion together, it is possible to prevent dropouts such as signal loss and noise mixture. Good dropout detection sensitivity can be achieved even when the signal form and influence differ due to differences in causes.

[0010] In the above explanation, the frequency conversion means is explained using an example of converting to a high frequency, but the invention is not limited to this, and furthermore, although it was explained using an example of a video signal, other FM modulation may be used. It is obvious that the scope of the present invention is to apply the present invention to signals in which the demodulated signal has periodicity and restoration by interpolation is practical.

[0011]

According to the present invention, in dropout detection of video equipment for recording and reproducing video signals, dropout detection means are provided before and after the frequency conversion means, and addition means for adding both detection outputs is provided. This provides an excellent dropout compensation device that can increase the sensitivity of dropout detection even when the form and influence on the signal differs due to differences in dropout causes such as signal loss and noise contamination. However, the effects of its implementation are significant.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a dropout compensation device in one embodiment of the present invention.

FIG. 2 is a waveform diagram illustrating that dropout detection sensitivity is increased according to the present invention.

FIG. 3 is a block diagram showing a conventional dropout compensation device.

[Explanation of symbols]

1, 8...Balanced modulator 2, 9...High pass filter (HPF) 3, 6, 10...
... Dropout detection means 4, 11 ... FM demodulation means 5, 12 ... Dropout compensation means 7 ... Addition means a, c ... Reproduction FM signals b, d ... Single carrier A, E ... Reproduction FM Signal B, F... Frequency converted FM signal, C, G... Waveform shaping output of A, E. Waveform shaping output of 2, CH... B, F.

Claims (1)

[Claims] 1. A first dropout detection means for detecting a dropout, which is a dropout of a signal, from a reproduced FM signal; a frequency conversion means for converting the frequency of the FM signal; A second dropout detection means for detecting dropout from the FM signal, and an addition means for adding the outputs of the first and second dropout detection means, and a dropout compensation means using the output of the addition circuit. A dropout compensator characterized in that it performs control.