JPH0564288A - Scaling system - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a system in which the amplitude levels of all filters are almost the same when there are multiple filters. [Structure] After obtaining the amplitude frequency characteristics of a plurality of digital filters by FFT, the first scaling is performed to change the maximum amplitude value of each to a specified value. Next, a range is specified in the window for the characteristic after the first scaling, and the average value of the amplitude values within the range is obtained. The minimum value is calculated from the plurality of average values obtained from the plurality of filters, and the second scaling is performed on all the filters so that the average value of each of the previously obtained values is equal to this minimum value. To do.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scaling system, and more particularly to a means for processing data supplied to a sound reproduction signal processing device for a speaker.

[0002]

2. Description of the Related Art When an arithmetic operation using a digital filter is performed, the size of the value that can be handled is limited because the arithmetic operation is performed by an arithmetic unit having a finite word length. The coefficient value of the filter must be set so that it does not become larger (not overflow). Scaling means an operation of setting the coefficient value of the filter so that the arithmetic unit does not overflow while the characteristics of the filter are hardly changed.

First, the drawings will be described. FIG. 6 is a block diagram of a conventional scaling system, and FIG. 7 is an example of amplitude-frequency characteristics of a digital filter. FIG. 8 is an example in which the characteristics of FIG. 7 are scaled. In FIG. 6, 10 is a digital filter system, 11 is an FFT that obtains the frequency response of the digital filter from the coefficient values of the digital filter, and 12 is maximum value detection that detects the maximum amplitude of the frequency response of the digital filter obtained by the FFT 11. And 9 performs scaling operation so that the value obtained by the maximum value detector 12 does not exceed the specified value 4,
It is a third scaling device that supplies new coefficient values to the digital filter. In FIG. 7, reference numeral 4 is a prescribed value that indicates a limit within which the calculation result of the calculator does not overflow when the maximum amplitude value data that can be input to the digital filter is input and the filter calculation is performed. That is, overflow occurs in the frequency range in which the value is larger than the specified value 4.

Next, the operation will be described. First, the amplitude-frequency characteristic of the digital filter 10 is obtained by the FFT 11 using the coefficient value of the digital filter 10. The maximum value detector 12 calculates the maximum amplitude value from the calculated frequency response. The value calculated by the third scaling unit 9 so that the value calculated by the maximum value detector 12 becomes the specified value 4 is
The new coefficient value is supplied to the digital filter 10. When the scaling is performed in this way, the maximum amplitude of the frequency response does not exceed the specified value, and no arithmetic overflow occurs.

[0005]

In the conventional system as described above, a solution to the problem of arithmetic overflow can be seen. However, when using a plurality of digital filters at the same time, for example, in a stereo speaker system, the left and right speakers are filtered by digital filters for reproduction, and when left and right filters with different characteristics are used, There is a problem that the amplitude levels are different.

For example, when a filter having the characteristics shown in FIG. 2 is used for the left speaker and a filter having the characteristics shown in FIG. 3 is used for the right speaker, scaling with the maximum value as the prescribed value is performed, respectively. , As shown in FIG. When the speaker is reproduced with the same characteristics, the reproduced sound on the right side becomes louder and the left and right sound volumes are unbalanced.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a scaling system which makes mutual amplitude levels as uniform as possible when a plurality of filters are used. To aim.

[0008]

According to the scaling system of the present invention, a window is applied to the maximum amplitude value of the amplitude-frequency characteristics of a plurality of filters and a frequency range excluding the vicinity of the frequency of the maximum amplitude value. The average value of the amplitude levels is calculated, and the scaling processing is performed so that the maximum amplitude value does not exceed the specified value and the amplitude levels within the window range are almost the same.

[0009]

By using the scaling processing device as described above, it becomes possible to make the amplitude levels of a plurality of digital filters substantially the same. For example, when used in a stereo reproduction system, the level balance between the left and right speakers. Can be obtained.

[0010]

EXAMPLES Example 1. FIG. 1 is a diagram showing the configuration of one embodiment, in which 11 and 21 are digital filters 10 and 20, respectively.
FFT for obtaining the amplitude-frequency characteristic from the coefficient value of 1
Reference numerals 2 and 22 are maximum value detectors for obtaining the maximum amplitude value of the amplitude-frequency characteristics obtained by FFT, and 13 and 23 are maximum value detectors 1.
The first scaling device for performing scaling so that the value obtained in 2 and 22 becomes the specified value 4, 14 and 24 are frequencies excluding the frequency of the maximum amplitude value among the amplitude characteristics obtained in the first scaling devices 13 and 23. A window for designating a range, 15 and 25 are average value calculators for obtaining an average value of amplitude levels within the ranges specified by windows 14 and 24, and 5 is a minimum value obtained from the average value calculators 15 and 25. Minimum value detectors for detecting values, 16 and 26 are average value calculators 15 and 2
The result of No. 5 and the result of the minimum value detector 5 are scaled so that there is no difference, and the new coefficient value is supplied to the digital filter.
It is a scaler.

FIG. 2 shows the characteristics of the digital filter 10 before scaling, and FIG. 3 shows the characteristics of the digital filter 20 before scaling.
FIG. 4 shows the characteristics of the digital filter 10 when scaling is performed according to the present invention, and FIG. 5 shows the characteristics of the digital filter 20 after scaling.

Further, in FIG. 2 to FIG.
Reference numeral 4 is a designated range designated by the windows 14 and 24.

Next, the operation will be described. The FFT 11 is used to find the amplitude-frequency characteristics of the digital filter 10 from the coefficient values of the digital filter 10 to find the maximum amplitude value.

The amplitude characteristic obtained by the FFT 11 is the characteristic shown in FIG. 2, and based on the value obtained by the maximum value detector 12, the first characteristic is obtained.
When scaling is performed by the scaler 13, the characteristics are similar to those of FIG. 9 shown in the conventional example. The range indicated by 14 in FIG. 9 is specified in the window 14, and the average value of the amplitude values is calculated by the average value calculator 15 in the specified frequency range. The calculated average value is input to the minimum value detector 5. Here, the minimum value detector 5 includes a digital filter 2
Since the same calculation is performed from 0, the input is obtained from the average value calculators 15 and 25. Then, the minimum value is detected from the average values input from them.

When the minimum value is detected, the calculation result of the first scaling 13 is calculated so as to eliminate the difference between the value calculated by the average value calculator 15 and the value calculated by the minimum value detector 5. The scaling is performed by the 2 scaling unit 16, and the coefficient value as a result of the scaling is supplied to the digital filter 10. The filter characteristics based on the supplied filter coefficients are as shown in FIG.

In this embodiment, the digital filter is
Since two are used as shown by 10 and 20, the same operation is performed for both of them.

That is, the digital filter 20 is similar to the digital filter 10, and the amplitude characteristic obtained by the FFT 21 is as shown in FIG. 3, which is scaled by the first scaling device 23 as in the conventional example shown in FIG. become. Further, the result of performing the necessary scaling operation in the second scaling unit 26 is shown in FIG. 5, which is supplied to the digital filter 20 as a new coefficient value.

In the present embodiment, the values input to the maximum value detector 5 are the average value in the range specified in the window 14 in FIG. 9 and the average value in the range specified in the window 24 in FIG. In this case, as can be seen from the figure, the average value specified in the window 14 of FIG. 9 was the minimum value.

In this way, the coefficients of the two filters can be scaled to make the amplitude characteristics of the two filters substantially the same.

Although only two filters are used in this embodiment, the number of filters is arbitrary, and FFT, window, maximum value detector, average value calculator, first and second filters are provided as many as the number of filters. All you need is a scaling device.

Further, in this embodiment, the scaling processing is made to exist independently for all the filters, but one scaling processing system may be used and the calculation may be performed in a time division manner.

[0022]

As described above, according to the present invention, by performing the scaling while monitoring the mutual levels of a plurality of filters, the amplitude levels of all the filters are substantially the same even if a plurality of filters exist. There is an effect such as being able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a scaling system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a characteristic of a filter according to a coefficient input in advance to the digital filter 10 of FIG.

FIG. 3 is a diagram showing a characteristic of a filter based on a coefficient input in advance to a digital filter 20 of FIG.

FIG. 4 is a diagram showing a filter characteristic of a digital filter 10 used in an embodiment after performing a scaling process according to the present invention.

FIG. 5 is a diagram showing filter characteristics of a digital filter 20 used in an embodiment after performing a scaling process according to the present invention.

FIG. 6 is a configuration diagram of a conventional scaling system.

FIG. 7 is a diagram showing characteristics of a filter according to a coefficient input in advance to the digital filter 10 of FIG.

FIG. 8 is a diagram showing characteristics of the digital filter 10 when scaling processing is performed by a conventional method.

FIG. 9 is a diagram showing characteristics of one filter when scaling of a plurality of filters is performed by a conventional method.

FIG. 10 is a diagram showing characteristics of another certain filter when scaling of a plurality of filters is performed by a conventional method.

[Explanation of Codes] 5 Minimum Value Detector 10 Digital Filter 11 FFT 12 Maximum Value Detector 13 First Scaling Device 14 Window 15 Average Value Calculator 16 Second Scaling Device

Claims (3)

[Claims] 1. A digital filter system for audio reproduction, comprising: an FFT for obtaining an amplitude frequency characteristic from a coefficient value of the digital filter; a maximum value detecting means for detecting a maximum value of the amplitude characteristic; and a detected maximum value system. The first scaling means for changing to the specified value, the window means for extracting only the designated frequency region with respect to the result of changing the amplitude characteristic by the first scaling means, and the window means designated by the window means. Average value calculating means for obtaining the average value of the amplitude values of the region, minimum value detecting means for detecting the minimum value of the results of the average value calculating means for a plurality of filters, and the first scaling means for changing the amplitude characteristic. A second characteristic for changing the amplitude characteristic so that the result of the average value computing means for the filter characteristic is the same as the value obtained by the minimum value detecting means. And a scaling system. 2. The scaling system according to claim 1, wherein the window means according to claim 1 extracts data in a specified frequency range from data for each sample of the FFT operation result. 3. The scaling system according to claim 1, wherein the window means according to claim 1 performs a convolution operation on the characteristic of the digital filter and the characteristic of a bandpass filter that defines a frequency range.