JPH01209392A - Frequency spectrum analyzer - Google Patents

Abstract

PURPOSE:To secure the optimum display screen regardless of the type of displays, by always holding the intensity of emission for the entire tube surface of a graphic display within a fixed range. CONSTITUTION:An acoustic signal is applied to a fast Fourier transformer 20 through an A/D converter 10 to be converted into a signal of a frequency area, which is smoothed with a smoothing processor. Then, it is so converted with a display area converter 40 to enter the optimum display intensity range and a display conversion signal is outputted. The display conversion signal is supplied to a graphic display 60 as display signal through a display controller 50.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency spectrum analysis device suitable for optimally displaying a portion with a poor signal-to-noise ratio in frequency analysis of a passive sonar or the like.

[Conventional technology]

As described in Japanese Patent Publication No. 58-19208, the conventional apparatus does not have a display conversion table section and is designed to be displayed on a recorder. Also, JP-A-59-
In the technique described in No. 221681, the display brightness is made brighter for signals with higher signal levels than those with lower signal levels.

[Problem to be solved by the invention]

The above conventional technology does not take into consideration the optimal display of areas with poor signal-to-noise ratios, and when displayed on a display using the conventional technology, the display becomes difficult to read, and the problem is that staring at the spectrum for a long time causes eye fatigue. was there.

An object of the present invention is to optimally display a spectrum with a poor signal-to-noise ratio on a display.

(Means for solving ialM) When noise in water or the like is subjected to frequency analysis and smoothing processing, its level distribution shows a shape that follows the Habo-Leley distribution. By giving the average value, the Rayleigh distribution can be expressed by the average value of the smoothing process.

Furthermore, in order to display the smoothed data on a graphic display, it is necessary to clip the maximum value of the data to a certain value. At this time, if the clipping value is small compared to the smoothing average value, the distribution will deviate from the Rayleigh distribution, but experiments have shown that this does not become a problem as long as the clipping value is about twice the smoothing average value or more. It turned out to be true.

By the way, in order to display smoothed data on a graphic display, it is necessary to give a display strength (L) to the smoothed data level (x). It has been experimentally determined that the display will be optimal if this function L'(X) is given under the following conditions.

5A-x-20≦L≦5th breath, x(1)x
xi: smoothing average value (0x9:≦50) X: smoothing data level (D≦X≦
21) L: Display intensity (0≦L≦100) 22. Display intensity (L) corresponds to luminance in a monochrome display, and corresponds to the total intensity of luminance, hue, and saturation in a color display. For monochrome displays, L
If the display intensity is set to be maximum when =O, the light emission in the spectral part to be viewed is low, making it less tiring. Although it is unavoidable that a color display is more tiring than a monochrome display, the display intensity can be set to the minimum when L=O, and the maximum luminous intensity should be set to a weak value. Furthermore (1
), the following relationship must also be maintained:

L(2・x')≦L(x) −(2)2××≦100 L(xl)≦L(X,) −(3)X<x.

It was also confirmed that although equation (1) is the optimal display range, it can be extended to the following range if some quality deterioration is allowed.

51t, x 3(, ≦L≦-5=Ω-+10- (4
) x
x [Operation] By limiting the function L (x), the luminous intensity of the entire screen surface of the graphic display can be kept within a constant range. Therefore, an optimal display screen can be obtained no matter which display is used.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a block diagram of the frequency spectrum analysis device of this embodiment. In this figure, the acoustic signal is quantized by an A/D converter 10. The sampling frequency of this A/D converter 1o needs to be twice or more the band of the acoustic signal 1. The digital acoustic signal 2 after A/D conversion is converted into a frequency domain signal by a fast Fourier transformer 20 and becomes an FFT signal 3. Furthermore, the envelope in the frequency axis direction is flattened by the smoothing processor 30, and a smoothed signal 4 is obtained. Then, the display conversion signal 5 is outputted by the display data converter 4o such that it falls within the above-mentioned optimum display range.
get. The display controller 50 converts the display conversion signal 5 into an RGB signal or a luminance signal as a display signal for the graphic display 60. Note that an example of data conversion from an acoustic signal to a smoothed signal is shown below the signal name in the figure. As shown in the figure, the acoustic signal is converted into a frequency domain signal whose average level is approximately constant.

FIG. 2 is a detailed block diagram of display data converter 40 of FIG. The smoothed signal 4 is taken into an internal memory by the input taking part 41 and stored as a smoothed signal X. Then, the signal level determiner 42 determines that X is 2.
Luminance calculation unit (1) 4
3 or (2) sent to 44. Note that Ma is a smoothed average value.

Here, the function of the brightness calculation unit (1) 43 is:

L=2・x+80 (x: smoothed signal, i: smoothed average value L: brightness signal), and the function of the brightness calculation unit (2) 44 is L=↓・X+
It is 80. Furthermore, the output of the brightness calculation unit (2) 44 is input to a brightness level determiner 45, which classifies whether L is greater than or equal to 0 or less than 0. When L is 0 and there are no drops, the brightness calculation unit (3) 46 sets L=0. Each result is sent by the display output section 47 to the display controller as a display conversion signal 5.

FIG. 3 is a graph of the smoothed signal-display intensity function of this embodiment, where the solid line is the luminance function and the broken line is the optimum display range. As shown in the figure, the smoothed average value in this example is 25%.

Figure 4 shows an example of the output results of this example.
4(a) is a case where the spectrum is below the optimal display lower limit function, and the spectrum display is too weak; FIG. 4(b) is a case where the spectrum is above the optimal display upper limit function, and the noise is too strong, making the spectrum difficult to see. FIG. 4(C) is within the optimal display function, and noise and spectrum are displayed appropriately.

〔Effect of the invention〕

According to the present invention, it is possible to always provide an optimal display on a graphic display, which has the effect of improving the visibility of the spectrum on the display. It also has the effect of reducing the burden on the eyes.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention,
Figure 2 is a block diagram of the display data converter, Figure 3 is a luminance function graph of this embodiment, and Figures 4 (a) to (C).
) is a diagram showing the output results of this example. 10... A/D converter, 20... Fast Fourier transform processor, 30... Smoothing processor, 40... Display data converter, 50... Display controller, 60... Graphic display, 41... signal acquisition section, 42.
...Signal level determination section, 43...Brightness calculation section 1.44
... Brightness calculation unit 2.45 ... Brightness level determiner, 4
6... Brightness calculation unit 3.47... Display signal output unit.

Claims (1)

[Claims] 1. A calculation unit that outputs the frequency analysis result of an acoustic signal in water etc. as a digital quantity, a smoothing processing unit that averages the envelope of the calculation output to an arbitrary value, and a parameter that uses the average value of the smoothing processing. The display data converter is comprised of a display data converter that allocates the display intensity to a display intensity, a display control unit that represents the display data in shades of gray and displays them temporally shifted, and a graphic display, and the display data converter optimally displays parts with poor signal-to-noise ratios. A frequency spectrum analysis device characterized by having display conversion characteristics as follows.