JPS62234495A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain digital signal processing with a the number of bits lower in degree than that in a case a digital signal processing is applied to the full frequency band of a brightness signal by separating the higher band of the brightness signal, and applying noise reduction processing by means of digital signal processing only to the said higher band. CONSTITUTION:A brightness signal is separated into the higher band including much noise components and the lower band by a high-pass filter circuit 14 and a low-pass filter circuit 15. And the noise is supplied to a noise reduction processing circuit 13 along with the higher band of brightness signal. The circuit 13 A/D converts the said components, then lets a field memory circuit 20a store the data in the unit of field. Based on the output of the circuit 20a, a noise detector circuit 19 detects the noise included in the brightness signal by making use of the field correlation. The detected noise is subtracted from the brightness signal by a noise subtracter 18, and D/A converted by a D/A converter 17. An output from the circuit 13 is added with thc lower band part of the brightness signal separatcd by the circuit 15 by an adder 24.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording/reproducing device that effectively removes noise contained in a luminance signal by digital signal processing.

[Prior Art] A magnetic recording/reproducing device such as a video tape recorder used for home use has a configuration in which a frequency-modulated luminance signal is frequency-multiplexed with a low-frequency converted color signal, but in the case of a luminance signal, If a signal with noise mixed in during the signal processing process during recording and playback is recovered as is, the higher the frequency, the more triangular noise (f) will occur in the frequency liquid/demodulation method. As shown in the conventional magnetic recording/reproducing device 1 shown in FIG. A method is used to cancel high-frequency emphasis using the de-emphasis circuit 2a.However, since the luminance signal that has passed through the de-emphasis circuit 2a also contains noise, in this example, the de-emphasis circuit 2a is equipped with a noise reduction circuit 3. The noise reduction circuit 3 extracts and removes noise components by using the difference in properties between a luminance signal with high line correlation and a noise component with almost no line correlation.The noise reduction circuit 3 uses line correlation to A noise detection circuit 3a that detects noise is connected to a subtracter 3c in parallel with the signal line 3b, and the subtracter 3c removes noise components from the luminance signal. The luminance signal is mixed with the color signal in the adder 4 at the next stage and output as a reproduced signal.

[Problems to be Solved by the Invention] The conventional magnetic recording/reproducing device 1 described above has a noise detection circuit 3a.
By delaying the luminance signal for one horizontal scanning line within the range and positively feeding back the delayed luminance signal to the luminance signal before the delay, the correlation between the luminance signals for several lines is taken, so the gain of positive feedback is The degree of SN improvement increases as the number of lines to be correlated is increased by increasing the number of lines to 1, but as long as the method utilizes line correlation, there is a limit to the degree of SN improvement. Therefore, if we take line correlation one step further and remove noise using field correlation, it is expected that the degree of SN improvement will be further improved, but if we prepare a field memory circuit that can store all luminance signals in field units, , it is necessary to use an 8-bit AD conversion circuit with at least 256 steps of amplitude resolution;
8-bit AD conversion circuit and 8-bit DA required for inverse conversion
Incorporating a conversion circuit poses a problem in that it is difficult to implement because it puts pressure on the product cost in terms of the manufacturing cost of these digital conversion elements.

[Means for Solving the Problems] The present invention solves the above problems. Among the brightness signals and color signals constituting the video signal, the brightness signals excluding the color signals are divided into high-frequency components and their high-frequency components.・The high frequency component of the luminance signal separated by this filtering method is converted into a digital signal, subjected to noise reduction processing to reduce noise, and then converted into an analog signal. The present invention is characterized in that it is constructed by providing a noise reduction processing circuit and an adder for adding the low frequency component of the luminance signal and the color signal separated by the above technique to the output of the noise reduction processing circuit.

[Operation] The present invention has a configuration in which the high-frequency component of the luminance signal is separated and noise reduction processing is performed by digital signal processing only on this high-frequency component, and the luminance signal is digitally processed over the entire band. To enable digital signal processing with a lower number of bits than the number of bits required for AD conversion or DA conversion.

[Example] Hereinafter, an example of the present invention will be described with reference to FIG. 1. FIG. 1 is a circuit diagram showing an embodiment of the magnetic recording/reproducing apparatus of the present invention.

In FIG. 1, a magnetic recording/reproducing device 11 is provided with a noise reduction processing circuit 13 downstream of a de-emphasis circuit (not shown) in a magnetic recording/reproducing circuit I2. In this embodiment, the noise reduction processing circuit 13 performs noise reduction processing only on the high frequency components of the luminance signal. It is separated into high frequency components, which contain many components, and low frequency components. In this embodiment, the cutoff frequency of both wave circuits 14 and 15 is set to I MHz, and noise components exceeding this cutoff frequency are supplied to the noise reduction processing circuit 13 together with the high frequency components of the luminance signal. .

The noise reduction processing circuit 13 aims to reduce noise by digital signal processing, and the high frequency is a wave circuit! A subtracter 18 that subtracts the noise component from the original signal is provided between the AD conversion circuit 16 that AD converts the output of 4 and the DA conversion circuit 17 that is the inverse conversion circuit. A noise detection circuit 19 is connected to the noise detection circuit 19.

The noise detection circuit I9 separates the luminance signal and the noise component based on the difference in field correlation.
Field memory circuit 2 that stores luminance data for two lines
The outputs of a correlation detection circuit 20 that positively feeds back the output of Qa to detect a signal with field correlation, and a subtracter 21 and a subtraction 121 that subtract a signal with high field correlation detected by the correlation detection circuit 20 from the original signal. It consists of an amplitude limiting circuit 22 that limits the amplitude and removes luminance signal components with little field correlation while leaving noise components.

The correlation detection circuit 20 has a positive feedback loop transfer gain K (K<
In order to compensate for the signal level being multiplied by 1/(1-K) due to 1), an attenuator circuit 20b having a gain of (1-K) is connected to the first stage. Attenuator circuit 20
b is connected to the serious crime field memory circuit 20a via an adder 20c and a signal line 20d with a forward transfer gain of I. An interpolation interpolation circuit 23 is connected to the field memory circuit 20a in order to obtain luminance data for 263 horizontal scanning lines. The interpolation circuit 23 is! A configuration is adopted in which a line memory circuit 23a that delays a signal for a horizontal scanning line and a signal line 23b that bypasses this are connected to an attenuator circuit 23d with a gain of 1/2 via an adder 23c. The interpolation circuit 23 is connected to the adder 20c via a gain attenuator circuit 20e.

24 is an adder that adds the output of the noise reduction processing circuit 13, the output of the low-frequency wave circuit I5, and the color signal.

Here, the gain of the attenuator circuit 20e is a guideline for setting up to how many fields of luminance signals are used for correlation detection, and the closer K is to 1, the more
The number of fields used for correlation detection increases, and S
The effect of improving the N ratio will increase. That is, adder 2
The luminance signal that is the input of 0c is cyclically added with signals from several fields before, so that signal components with field correlation are multiplied by 1/(1-k), and noise components with no correlation are multiplied by 1/(1-k). The amplitude increase is only about 0.7 times that amount. Therefore, the adder 20c extracts a luminance signal component with the noise component suppressed, and by subtracting this luminance signal component from the original signal in subtraction n21, a luminance signal component with little field correlation with the noise component is obtained. It will be done. Therefore, by amplitude-limiting the output of the subtracter 21 by the amplitude limiting circuit 22, the luminance signal component with little field correlation is suppressed, and only the noise component is obtained.

By the way, the AD conversion circuit 16 used in the noise reduction processing circuit I3 is a 6-bit one with an amplitude resolution of 1/64, and this AD conversion circuit 16 is operated at a sampling frequency rcp that is twice that of the color subcarrier. (455fo)
I am trying to drive it with. However, f u is the horizontal scanning frequency.

In this case, the field memory circuit 20a includes 25
It is sufficient to use 3 bit dynamic RAMs for 6. That is, the number of memories M required for the field memory circuit 201 is expressed as M=ntfcp. Here, n is the number of bits, and L is the memo. In this example, t = l / 59°94sec.

n=6. Since fcp=7.15909x108,
M=716,625.6 bits. Therefore, 256
786 obtained by using three bit RAMs in
, 432 bits of memory is sufficient.

In this way, the magnetic recording/reproducing device 11 has a configuration in which the high frequency component of the luminance signal is separated in the high frequency wave circuit 14, and the noise reduction processing by digital signal processing is performed only on this high frequency component. Digital signal processing is possible with a lower number of bits than the number of bits required for AD conversion or DA conversion when digital signal processing is performed over the entire band of the luminance signal, and it is possible to perform digital signal processing with a lower number of bits than the number of bits required for AD conversion or DA conversion when performing digital signal processing on the luminance signal over the entire band. The number of bits required for the AD conversion circuit 16 or DA conversion circuit 17 can be kept to a low number of bits that has little impact on product costs in terms of manufacturing costs of digital ICs and the like.

Furthermore, the fact that the noise components are concentrated in the high range, I-
G) f: k%t - J-h, L: t'/l
flrF *jj')h -'II-r, -11,
It is possible to achieve almost the same effect as when digital signal processing is performed on the luminance signal over the entire band with a bit count of 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,0000 bits, and it is possible to reduce noise at a low cost without degrading the quality. .

Further, the noise reduction processing circuit 13 includes an AD conversion circuit 16 that AD converts the high frequency component of the luminance signal, a field memory circuit 20a that stores the output of this AD conversion circuit I6 in field units, and a field memory circuit 20a that stores the output of this AD conversion circuit I6 in units of fields. By being composed of a noise detection circuit 19 that detects noise included in a luminance signal based on the output using field correlation, and a subtracter 18 that subtracts the noise detected by this noise detection circuit 19 from the luminance signal. , it is possible to more accurately extract and remove noise components in a luminance signal using field correlation, and it is possible to achieve an SN improvement effect that is incomparable to conventional noise reduction processing using line correlation.

Note that in the above embodiment, the noise reduction processing is possible not only in the signal reproduction system but also in the signal recording system, and in that case, the noise reduction processing circuit 13 is preferably provided in the stage 11a of the pre-emphasis circuit.

[Effects of the Invention] As explained above, the present invention separates the high-frequency component of a luminance signal and performs noise reduction processing using digital signal processing only on this high-frequency component. Digital signal processing is possible with a lower number of bits than the number of bits required for AD conversion or DΔ conversion when performing digital signal processing over the entire band,
A required for digital signal processing in the noise reduction processing circuit
Considering the unit manufacturing cost of digital ICs, it is possible to keep the number of bits of the D conversion circuit or DA conversion circuit to a low-order bit number that has little impact on the product cost, and furthermore, noise components are concentrated in the high frequency range. Taking this into consideration, the noise reduction effect can be almost the same as when the luminance signal is digitally processed over the entire band using a high number of bits, and this reduces the quality. This provides excellent effects such as being able to reduce noise at a low cost.

Further, the present invention includes a noise reduction processing circuit that includes an AD conversion circuit that performs AD conversion on high-frequency components of a luminance signal, a field memory circuit that stores the output of this AD conversion circuit in field units, and an output of this field memory circuit. A noise detection circuit that detects noise contained in a luminance signal using field correlation based on Using this method, noise components in the luminance signal can be extracted and removed more accurately, and S is incomparable to conventional noise reduction processing using line correlation.
This has effects such as being able to improve N.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a magnetic recording/reproducing apparatus of the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional magnetic recording/reproducing apparatus. 11. , Magnetic recording and reproducing device, 13. ,, Noisy [E? (1hfLnfil Fuki IA
X bln door? h ril shi!
XIFζ3. Low range is wave circuit, +6. ,, AD conversion circuit. +7. , ,I) A conversion circuit, 20a, ,field memory circuit, 24. ,,Adder.

Claims (2)

[Claims] (1) A filtering means that separates the luminance signal excluding the color signal from among the luminance signal and color signal constituting the video signal into high-frequency components and other low-frequency components, and the luminance separated by the filtering means. Converts the high frequency components of the signal into a digital signal,
a noise reduction processing circuit that performs noise reduction processing to reduce noise and then converts it into an analog signal; and an addition that adds the low-frequency components and color signals of the luminance signal separated by the filtering means to the output of this noise reduction processing circuit. A magnetic recording/reproducing device comprising a container. (2) The noise reduction circuit converts the high-frequency components of the luminance signal into A
An AD conversion circuit that performs D conversion, a field memory circuit that stores the output of this AD conversion circuit in field units, and a field correlation based on the output of this field memory circuit to detect noise contained in the luminance signal. 2. The magnetic recording and reproducing apparatus according to claim 1, comprising a noise detection circuit and a subtracter for subtracting the noise detected by the noise detection circuit from the luminance signal.