JPH04216283A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To operate a noise canceler circuit at an optimum operating point corresponding to the envelop output of a magnetic head. CONSTITUTION:The regenerative video signal of a video head 101 is amplified by a preamplifier circuit 102 and supplied to filter groups 103, 104 and 105. The low-pass filter 103 separates a carrier chrominance signal from the video signal, and the high-pass filter 104 separates an FM luminance signal. After limiting the amplitude at an FM-AGC circuit 106, the above-mentioned FM luminance signal is demodulated to the luminance signal by an FM demodulation circuit 107 and further passed through a de-emphasis circuit 108, and the noise component is removed by a noise canceler circuit 109. On the other hand, the above-mentioned band pass filter 105 supplies the video signal to an envelop detector circuit 110 after separating the FM carrier component. The envelop detection of the FM carrier component is executed by this circuit 110, a direct current voltage in proportion to the amplitude is applied to the control input of the operating point of the noise canceler circuit 109, and the degree of canceling noise is controlled.

Description

[Detailed description of the invention]

0001 [Purpose of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling a noise canceller circuit of a video tape recorder or the like.

0003

2. Description of the Related Art Generally, a luminance signal reproduction processing system of a video tape recorder has a configuration as shown in the block diagram of FIG. A video head 401 reproduces a video signal from a magnetic tape (not shown), and the video signal is sent to a preamplifier 402.
The video signal supplied to the preamplifier 402 and amplified by the preamplifier 402 is sent to the next stage, a low-pass filter 403 and a high-pass filter 4.
04 and low-pass converted carrier color signals, F
It is separated into M luminance signals. FM brightness signal is FM-AGC
After the reproduced signal is adjusted to a constant amplitude in a circuit 405 to remove amplitude fluctuation components, the reproduced signal is demodulated into a luminance signal in an FM demodulation circuit 406. Next, in the demodulated luminance signal, the characteristics whose high frequencies were emphasized by the pre-emphasis circuit during recording are returned to the original characteristics by the de-emphasis circuit 407, and further,
After canceling noise that is easily noticeable to the human eye in a noise canceller circuit 408, the signal is supplied to a mixing circuit (not shown), mixed with the carrier color signal, and output as a composite color video signal.

By the way, the noise canceller circuit 408 has a function of removing minute noise components, but when removing it, it also removes a part of the signal representing the detail part of the image in the high frequency minute signal at the same time as the noise component. It has the disadvantage of being That is, the noise canceler circuit 408 generally eliminates noise by utilizing the characteristic that noise is concentrated in a low level portion of high frequencies. A method in which the high frequency component is passed through a slicing circuit to remove the low level part (noise component), and then the high frequency component is superimposed on the low frequency component and output.
Alternatively, you can separate the high-frequency components from the original signal with a high-pass filter, pass it through a limiter circuit to remove the large amplitude part, extract the noise component, and then reverse the polarity of the noise and superimpose it on the original signal. There is a method to cancel noise components. There is also a method that takes advantage of the fact that noise components have no horizontal correlation, extracts the uncorrelated part with a comb filter, limits the amplitude with a limiter circuit, and then subtracts it from the original signal to remove the noise component. Regardless of the method used, it still takes advantage of the fact that noise components are concentrated in the low-level portion of high frequencies.

Therefore, the optimal operating point of the noise canceller circuit 408 should be set depending on the amount of noise components during reproduction caused by the tape head system. However, since the operating point is usually fixed, it cannot be said that optimal operation is performed. Since tape performance has improved significantly in recent years, the noise level input to the noise canceller circuit 408 varies depending on the type of tape, and its fluctuation range is large. For example, the noise level is SV
HS tape or high grade normal tape and normal normal tape are 3 to 4 dB, sometimes 6 dB.
A difference of more than dB may occur.

The effects of the noise canceller circuit 408 depending on the type of tape will be explained in more detail with reference to FIGS. 5 and 6. (a) of FIG. 5 shows the reproduction output of the normal tape video head, that is, the envelope output, and (b) shows the reproduction output signal before input to the noise canceller circuit 408, that is, the level of the FM demodulated luminance signal. (C) shows the frequency characteristics of the brightness signal level and the noise level output from the noise canceller circuit 408. Note that in (C), the arrow indicates the noise canceling effect of the noise canceller circuit 408. Similarly, (a) in FIG. 6 shows the playback output of the video head of a high-grade normal tape, and (
b) and (c) show the frequency characteristics of the luminance signal level and noise level before and after the input/output of the noise canceller circuit 408, respectively.

As can be seen from FIGS. 5 and 6 (a),
The envelope output of a high-grade normal tape is larger than that of a normal tape, and when it comes to the stage where it is FM demodulated and input to the noise canceller circuit 408, (
As shown in b), the noise level of the high-grade normal tape is lower than that of the normal tape, resulting in a large difference in the noise level. This is a natural result since the high-grade normal tape has a large envelope output, so the S/N ratio of the FM luminance signal is good, and therefore the S/N ratio of the demodulated luminance signal is also good.

As described above, the noise canceler circuit 408 has a fixed operating point for luminance signals having different noise levels.
When the noise is canceled by , its output is (c
), the normal tape has an insufficient degree of noise cancellation, and therefore has a poor S/N ratio, while the high-grade normal tape has an excessive degree of noise cancellation, and it is difficult to cancel high-frequency minute signals. This also removes some of the signal representing the details of the image. That is, depending on the type of tape, the noise canceler circuit 408
does not operate at the optimal cancellation operating point, the signal S
This has the drawback that the /N ratio decreases, or the degree of cancellation is applied too much than necessary, and minute signals are removed unnecessarily, resulting in deterioration of image quality during reproduction.

[0009]

[Problems to be Solved by the Invention] As mentioned above, the noise canceller circuit of the conventional magnetic recording/reproducing device has a fixed cancellation operating point, so when the noise level is high, the degree of cancellation is shallow, and therefore ,S/N
On the other hand, when the noise level is low, the degree of cancellation is deep, and therefore, there is an inconvenience that minute signals are removed unnecessarily. The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a magnetic recording/reproducing device in which a noise canceler circuit operates at an optimal operating point depending on the noise level, so that high-quality images can always be obtained. shall be.

0010 [Structure of the invention]

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a reproducing means for reproducing a video signal including an FM-modulated luminance signal from a magnetic recording medium on which the video signal is recorded; a preamplifying means for amplifying the video signal, and an FM signal from the video signal amplified by the preamplifying means.
a separating means for separating a luminance signal; an amplitude limiting means for converting the FM luminance signal into an FM luminance signal having a constant amplitude; an FM demodulating means for demodulating the FM luminance signal having a constant amplitude; and the preamplifying means. bandpass filtering means for separating an FM carrier component from the amplified video signal; envelope detection means for detecting the envelope of the signal from the bandpass filtering means; and removing noise from the luminance signal demodulated by the FM demodulation means. The present invention provides a magnetic recording/reproducing apparatus characterized by comprising a noise removing means for changing an operation level in response to the output signal of the envelope detection means.

0012

[Operation] The FM carrier component of the reproduced video signal is separated from the output signal of the preamplification means, which has an extremely high correlation with the noise level, by passing through the bandpass filtering means, and the amplitude of the FM carrier component is detected by the envelope detection means. The noise removal means is detected by envelope detection, and the operation level of the noise removal means is controlled according to the detection result. Therefore, the reproduced luminance signal can be optimally noise-removed by the noise removing means with the operating level controlled as described above, and the reproduced image quality is improved.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 1 is a block diagram showing an embodiment of a magnetic recording/reproducing apparatus according to the present invention. A video head 10 that converts video signals magnetically recorded on a magnetic tape into electrical signals.
1 is connected to a preamplifier 102 that amplifies the video signal, and the preamplifier 102 includes a low-pass filter 103 that separates a carrier color signal that has been low-pass converted from the amplified video signal, and a high-pass filter that separates an FM luminance signal. 1
04 and a bandpass filter 105 that separates the FM carrier component of the FM luminance signal. The high-pass filter 104 is sequentially connected to a noise canceller circuit 109 via an FM-AGC circuit 106, an FM demodulation circuit 107, and a de-emphasis circuit 108.

The FM-AGC circuit 106 limits the amplitude of the FM luminance signal and removes amplitude fluctuation components, and the FM demodulation circuit 107 demodulates the FM luminance signal into a luminance signal.
Then, the de-emphasis circuit 108 restores the high-frequency emphasized characteristics by a pre-emphasis circuit (not shown) to the original characteristics during recording, and the noise canceler circuit 109 extracts the noise using a high-pass filter, for example, and converts this noise into the original. The noise component is removed by multiplying the signal by the opposite phase and the same amplitude. On the other hand, the bandpass filter 105 is connected to the noise canceller circuit 109 via an envelope detector circuit 110 that performs envelope detection of the FM carrier component of the FM luminance signal. The envelope detector circuit 110 is F
By applying a DC voltage proportional to the amplitude (envelope) of the M carrier wave component to the operating points of the noise canceller circuit 109, that is, the control inputs such as the slice level, limiter level, and amplitude amplification degree, the degree of noise cancellation is changed. It is something that makes you

That is, when the amplitude of the FM carrier component is large, the output voltage of the envelope detector circuit 110 becomes large, and the noise canceller circuit 109 operates at an operating point where the degree of noise cancellation is shallow. On the other hand, F.M.
When the amplitude of the carrier wave component is small, the output voltage of the envelope detector circuit 110 becomes small, and the noise canceller circuit 109 operates at an operating point that increases the degree of noise cancellation.

Next, the operation of the above embodiment will be explained with reference to FIGS. 1 to 3. The video signal reproduced by the video head 101 is amplified by the preamplifier 102 and supplied to the next stage low-pass filter 103, high-pass filter 104, and band-pass filter 105, respectively. The low-pass filter 103 separates the low-pass converted carrier color signal from the video signal, the high-pass filter 104 separates the FM luminance signal, and the band-pass filter 105 separates FM carrier components within a predetermined range. The FM luminance signal is processed by the FM-AGC circuit 1 as in the conventional luminance signal processing system.
After the amplitude of the FM luminance signal is limited in step 06 and the amplitude fluctuation component is removed, it is demodulated into a luminance signal in the next stage FM demodulation circuit 107, and is further demodulated into a luminance signal by a de-emphasis circuit 108 during recording. The emphasized characteristics are returned to their original characteristics, and a high-pass filter in the noise canceller circuit 109 extracts the noise component.
The noise is removed by multiplying the original signal by this noise with an opposite phase and the same amplitude.

On the other hand, the bandpass filter 105 separates the carrier component within a predetermined range of the FM luminance signal, that is, the FM carrier wave component, and supplies this component to the envelope detector circuit 110 at the next stage. The envelope detector circuit 110 performs envelope detection of the FM carrier wave component, and detects the envelope,
That is, a DC voltage proportional to the amplitude is applied to the operating point control input of the noise canceller circuit 109 to control the degree of noise cancellation. The operation of controlling the degree of cancellation of the noise canceller circuit 109 according to the result of the envelope detection will be described with reference to FIGS. 2 and 3. Figure 2
3, (a) shows the playback output, that is, the envelope output, and (b) shows the playback output signal before being input to the noise canceller circuit, that is, of a normal tape or a high-grade normal tape, respectively. The frequency characteristics of the level of the FM demodulated luminance signal and the noise level are shown, and (c) shows the frequency characteristics of the level of the brightness signal and the noise level output from the noise canceller circuit. Note that in (C), the arrow indicates the noise canceling effect of the noise canceller circuit 109.

As shown in FIG. 2(a), in the case of a normal tape, the amplitude of the envelope output is small, whereas as shown in FIG. 2(b), the noise level is high. At this time, the output voltage of the envelope detector circuit 110, which is proportional to the envelope of the carrier signal, that is, the amplitude, is low, the degree of cancellation of the noise canceller circuit 109 becomes deep, and a large amount of noise is removed, resulting in the S This results in a luminance signal with an improved /N ratio. On the other hand, as shown in FIG. 3(a),
In the case of a high-grade normal tape, the amplitude of the envelope output is large, whereas the noise level is small as shown in (b). At this time, contrary to the above case, the output voltage of the envelope detector circuit 110 is high, the degree of cancellation of the noise canceller circuit 109 is shallow, and the noise component is appropriately removed, resulting in a moderate S/R as shown in (C). N ratio, and a minute signal that is lost in a fixed operating point noise canceller circuit can be obtained.

In this way, the envelope detector circuit 1
Noise canceller circuit 109 according to the envelope detection of 10
The luminance signal from which noise components have been appropriately removed is supplied to a mixing circuit (not shown), where it is mixed with the carrier color signal and output as a composite color video signal.

As detailed above, since the amount of noise cancellation of the noise canceler circuit 109 is controlled according to the envelope detection of the envelope detector circuit 110,
When the envelope output is small, a large amount of noise is removed; conversely, when the envelope output is large, a small amount of noise is removed. Therefore, when the noise level is high, the obtrusive background noise disappears and a clear image is obtained.
On the other hand, when the noise level is low, a high-quality image can be obtained without losing signals representing detailed parts of the image in the high-frequency minute signals.

[0021]

As described in detail above, according to the present invention, the noise canceler circuit can be operated at an optimal operating point depending on the performance of various magnetic tapes, and therefore the S/N ratio of the luminance signal can be improved. This has the excellent effect of improving image quality and always providing high-quality images without unnecessary removal of minute signals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a reproduction brightness signal processing system of a magnetic recording and reproducing apparatus according to the present invention.

FIG. 2 is a characteristic diagram showing frequency characteristics of the envelope output of a normal tape, the level of a luminance signal before and after input/output of the noise canceller circuit of FIG. 1, and the noise level.

3 is a characteristic diagram showing the envelope output of a high-grade normal tape and the frequency characteristics of the luminance signal level and noise level before and after input and output of the noise canceller circuit of FIG. 1; FIG.

FIG. 4 is a block diagram showing a reproduction brightness signal processing system of a conventional magnetic recording and reproduction device.

5 is a characteristic diagram showing the frequency characteristics of the envelope output of a normal tape, the level of a luminance signal before and after input and output of the noise canceller circuit of FIG. 4, and the noise level.

6 is a characteristic diagram showing frequency characteristics of the envelope output of a high-grade normal tape, the brightness signal level before and after input/output of the noise canceller circuit of FIG. 4, and the noise level.

[Explanation of symbols]

101...video head, 102...preamplifier circuit, 10
3...Low pass filter circuit, 104...High pass filter circuit, 105...Band pass filter circuit, 106...FM
-AGC circuit, 107...FM demodulation circuit, 109...noise canceller circuit, 110...envelope detector circuit.

Claims (1)

[Claims] 1. Reproducing means for reproducing a video signal including an FM-modulated luminance signal from a magnetic recording medium on which the video signal is recorded; preamplifying means for amplifying the reproduced video signal; separation means for separating the FM luminance signal from the video signal amplified by the digital amplification means; amplitude limiting means for converting the FM luminance signal into an FM luminance signal having a constant amplitude; and demodulating the FM luminance signal having a constant amplitude. FM demodulation means; bandpass filtering means for separating an FM carrier component from the video signal amplified by the preamplification means; envelope detection means for performing envelope detection of the signal from the bandpass filtering means;
1. A magnetic recording and reproducing apparatus, comprising: noise removing means for removing noise from a luminance signal demodulated by a demodulating means, and changing an operating level in accordance with an output signal of the envelope detecting means.