JPS6041886B2 - noise reduction device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a device for reducing noise.

Most of the noise reduction devices conventionally used for the purpose of improving the S/N ratio of tape recorders use a compression/expansion method.

When the compression/expansion method described above is used, the noise is reduced by the amount of signal expansion during reproduction, so the larger the amount of companding, the greater the SN ratio can be improved.

However, these companding devices have the problem that distortion occurs unless the compression characteristics during recording and the expansion characteristics during reproduction have completely complementary characteristics both statically and dynamically. Hereinafter, the problems of the conventional device will be explained in more detail with reference to the drawings.

Figures 1 to 4 are diagrams showing typical characteristic examples of conventional devices. This is an example of frequency characteristics (emphasis characteristics), and is shown using one signal level as a parameter.

In general, most companding devices have complex companding characteristics as shown in Figures 1 and 2, so in order to maintain the complementary characteristics described above, it is necessary to set the threshold value of the compression characteristics and the expansion characteristics. It was necessary to match the threshold accurately, which was a very difficult problem. As a way to solve the above problems,
An apparatus having linear companding characteristics as shown in FIG. 3 can be used.

However, when this type of companding device is used in a tape recorder, there is a problem in that the more system noise there is, the more noise fluctuations occur depending on the operation during decompression. One way to solve this noise fluctuation phenomenon is to control the amount of pre-emphasis and de-emphasis according to the signal level, as shown in Figure 4, and this is recognized to be very effective. . However, when using this variable emphasis, since it is of a level response type, there remains the problem that the threshold value as described above must be adjusted accurately. The present invention eliminates all the drawbacks and problems of conventional devices,
Hereinafter, the present invention will be explained in detail based on illustrated embodiments.
FIG. 5 is a block diagram showing one embodiment of the present invention.

In FIG. 5, 1 is an input terminal of the compression device, 2 is a variable pre-emphasis circuit, 3 is a divider, and 4 is a level sensor, and the divider 3 is controlled according to this level. 5 is a high-pass filter, 6 is a low-pass filter, 7 and 8 are level sensors,
Reference numeral 9 denotes an amplitude ratio detector, which is a means for extracting an output signal according to the amplitude ratio of two signals applied to two independent input terminals.

10 is a signal transmission system, which corresponds to a tape recorder or the like.

11 is a multiplier, 12 is a variable de-emphasis circuit, 13
is the output terminal of the decompressor.

Here, the variable gain amplifier composed of the divider 3 and the level sensor 4 is well-known, and
Obtain an output proportional to /2.

This characteristic is shown in Figure 3 a. Ru. On the other hand, the variable gain amplifier composed of the multiplier 11 and the level sensor 4 is also well-known, and is
It is possible to obtain an output proportional to the power of

This characteristic is as shown in Fig. 3b. On the other hand, the variable pre-emphasis circuit 2 and the variable de-emphasis circuit 12 are configured so that the emphasis characteristics are controlled according to the component ratio of the high-frequency signal component and the low-frequency signal component included in the signal. That is, the high frequency signal component is separated by the high frequency filter 5 and its level is detected by the level sensor 7, and the low frequency signal component is separated by the low pass filter 6 and its level is detected by the level sensor 8. . Then, the output levels of the level sensors 7 and 8 are respectively applied to the amplitude ratio detector 9, and a signal corresponding to the signal level ratio of the high frequency signal component and the low frequency signal component is extracted from the amplitude ratio detector 9. It's summery. The amount of emphasis is controlled by the control signal from the amplitude ratio detector 9 obtained in this way.

It goes without saying that the emphasis characteristics of the variable pre-emphasis circuit 2 and the variable de-emphasis circuit 12 have complementary characteristics. An example of the emphasis characteristic is shown in FIG. It is most effective to configure this emphasis characteristic so that it changes more as the high-frequency signal components E, h become smaller than the low-frequency signal component Efe, that is, as the ratio of Efe/Efh increases. The emphasis characteristics are shown in Figure 7.
As shown in FIG. 8, as Efe/E,h becomes larger, the cutoff frequency can be increased or the amount of emphasis can be increased. Further, a bandpass filter may be used as a filter for separating high-frequency signal components and low-frequency signal components.

As a specific method for implementing the amplitude ratio detector, a method can be used in which two signals divided into high and low frequencies are logarithmically compressed, and then the level difference between the two signals is extracted using a differential amplifier.

In any case, any circuit can be used as long as it extracts the signal level ratio between the two. As described above, the noise reduction device according to the present invention uses a linear companding type compandor and further includes a variable emphasis that is controlled according to the content ratio of high-frequency signal components and low-frequency signal components. ,
It is possible to completely eliminate the part where the companding characteristics change depending on the level, which has been a problem in the past. Therefore, there is no need to match threshold values during use, and more perfect complementary characteristics can be obtained. Furthermore, since it uses a variable emphasis circuit that is always controlled by the content ratio of high and low frequency signal components even when the signal level changes, it has many excellent features such as effectively suppressing noise fluctuation phenomena. be.

[Brief explanation of the drawing]

1, 2, and 3 are compression/expansion characteristic diagrams (input/output characteristic diagrams) of a conventional noise reduction device, FIG. 4 is an emphasis characteristic diagram of a conventional device, and FIG. 5 is an embodiment of the present invention. The basic diagrams, FIGS. 6, 7, and 8 are examples of the emphasis characteristics of the apparatus of the present invention. 2...Variable pre-emphasis circuit, 3...
...Divider, 4...Level sensor, 5...
High-pass filter, 6...Low-pass filter, 7, 8...
...Level sensor, 9...Amplitude ratio detector, 1
1... Multiplier, 12... Variable de-emphasis circuit.

Claims (1)

[Scope of Claims] 1. A noise reduction device having a variable emphasis means and a linear compression/expansion means, wherein the emphasis characteristic of the variable emphasis means is determined by the ratio of two signal components of a high frequency component and a low frequency component of a signal. What is claimed is: 1. A noise reduction device comprising: control means for controlling the noise to change according to the noise. 2. In the description of claim 1, the control means includes a filter means for separating a signal into two components, a high frequency component and a low frequency component, and a level sensor means for detecting the signal level obtained from the filter means. and amplitude ratio detection means for detecting the output voltage ratio of the level sensor means, and the variable emphasis means is configured to have a relation to the ratio of the high frequency signal component voltage and the low frequency signal component voltage obtained from the amplitude ratio detection means. 1. A noise reduction device characterized in that the noise reduction device is configured to be controlled using a signal obtained by 3. In claim 2, the amplitude ratio detection means includes a differential amplifier, and the differential amplifier has a logarithmic value of the level of the high-frequency signal component and the level of the low-frequency signal component. A noise reduction device configured to be supplied with. 4. In the statement of claim 1, the emphasis characteristic of the variable emphasis means is such that the high frequency signal component becomes smaller than the low frequency signal component as the ratio of both components increases. A noise reduction device characterized in that it is configured such that the amount of emphasis changes in an increasing direction.