Patent Translate Powered by EPO and Google Notice This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate, complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or financial decisions, should not be based on machine-translation output. DESCRIPTION JP2005033307 The present invention provides a digital filter in which a composite output frequency characteristic is formed by a plurality of filters used in graphic equalizers and the like, wherein the influence of the adjacent band is extremely small without changing the characteristic of the conventional filter alone. Provided is a digital filter design method that can easily form approximate frequency characteristics. An inverse convolution operation is performed on a desired target frequency characteristic formed by a plurality of filters alone and a frequency characteristic of each of the filters alone, and each of the filters alone is determined by the inverse convolution. The coefficients of each filter are set according to the frequency characteristic setting value, and based on that, the combined output frequency characteristic is formed. [Selected figure] Figure 1 Digital filter design method The present invention relates to a digital filter used in circuits of audio equipment, video equipment, communication equipment and the like, and relates to a method of designing a digital filter which can obtain a desired frequency characteristic. [0002] Digital filters, for example, graphic equalizers used in audio circuits of audio equipment, have long been used as convenient tools for changing the frequency characteristics. However, it is also a fact that there is a big difference between the set value and the measured value of the frequency characteristic. In the prior art, the cause of the occurrence of the error of the frequency characteristic will be described in detail based on the frequency characteristic setting value graph and the actual value graph of the graphic equalizer configured by a plurality of digital filters. Conventional Example 1 When the amplitude characteristics of each filter unit 14 of the graphic equalizer 13 as shown in FIG. 10A are set as a frequency characteristic setting value graph, the measured values of FIG. 10B are obtained. It can be seen that a large error occurs in the curve of the frequency 08-05-2019 1 characteristic 15 according to the conventional design method realized as shown in the graph. Especially in the portion where the curve changes rapidly, the error is large and the set characteristics can not be realized. (Conventional Example 2) As in the frequency characteristic setting value graph shown in FIG. 11 (a), the amplitude is increased by only one band of the filter unit 14 according to the conventional design method of FIG. 11 (b) actual value graph. The frequency characteristic 16 can be confirmed. It can be seen from the frequency characteristics of this measured value graph that the amplitudes of not only the center frequency f0 but also the adjacent bands increase. Therefore, even if the amplitude of only one band of the filter unit 14 is raised, it can be confirmed that the amplitude increases in the range of several bands before and after and causes an error. (Conventional Example 3) As in the frequency characteristic setting value graph shown in FIG. 12 (a), when the amplitudes of the seven filter units 14 are equalized, the time of one band of the filter unit 14 and Similarly, the adjacent band is affected, and the characteristics on both sides are raised as shown in the frequency characteristic 17 according to the conventional design method of the actually measured value graph in FIG. Also, when the amplitudes of a plurality of bands are raised, the amplitude of the center frequency of each filter also becomes larger than the set value. This is because the bands affect each other and increase the amplitude. As described above, even if the frequency characteristic of the filter unit 14 is set as in the frequency characteristic setting value graph, not only the setting frequency but also the adjacent bands are respectively added, as shown in the actual value graph. The amplitudes of adjacent bands also increase or decrease, and desired frequency characteristics can not be obtained. In addition, even if a filter in which adjacent bands do not change is designed, a high-order filter is required and the filter becomes complicated, resulting in a large apparatus and an expensive cost burden. SUMMARY OF THE INVENTION In view of the above-described current situation, a method of designing a digital filter is provided which can obtain a desired combined output frequency characteristic without changing the characteristics of a conventional filter alone. Means for Solving the Problems In view of the above, the inventor of the present invention has solved the problem by the following means as a result of earnest research. (1) In a digital filter design method for forming a combined output frequency characteristic with a plurality of filters used for graphic equalizers etc., a desired target frequency characteristic formed with the plurality of filters alone, and a plurality of the plurality of filters. The inverse convolution operation is performed with the frequency characteristics of each filter alone, the coefficients of each filter alone are set according to the respective frequency characteristic setting values of the filter alone determined by the inverse convolution operation, and the combined output frequency characteristics are based thereon In the method of designing a digital filter, it is possible to easily form a characteristic similar to a target frequency characteristic, which has very little influence of adjacent bands, without changing the characteristic of a conventional filter alone. (2) A digital filter for setting a coefficient of each filter unit according to each frequency characteristic setting value of the filter unit determined by the inverse convolution calculation and forming a combined 08-05-2019 2 output frequency characteristic based on the set value is an audio signal. The method of designing a digital filter according to (1), which is applicable to a digital filter incorporated in an electronic device such as a device, a video device, and a communication device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on the drawings. FIG. 1 is an explanatory view for obtaining the frequency characteristic setting value of each filter by “inverse convolution calculation (* <− 1> mark)” from the target frequency characteristic of the cascade connection type filter of the embodiment of the present invention. Explanatory drawing which sets the coefficient of each cascade connection type | mold filter according to the frequency characteristic setting value of each filter calculated | required by "inverse convolution calculation" of an example, FIG. Fig. 5 is an explanatory diagram of a cascade connection type filter, and Fig. 6 is a flow chart of each filter of the cascade connection type filter from the target frequency characteristic of the cascade connection type filter for obtaining the frequency characteristic setting value of each filter by "inverse convolution operation" An explanatory view for obtaining a combined output frequency characteristic by “Convolution calculation (* mark)” from the frequency characteristic setting value, and FIG. 7 shows “Inverted from the combined output frequency characteristic of the cascade connection type filter obtained in FIG. Explanatory drawing which calculates | requires the frequency characteristic setting value of each filter by calculation (* <-1> mark), FIG. 8: the frequency characteristic of each filter calculated | required by the "inverse convolution operation" of the cascade connection type filter of this invention invention Example Comparison graph of actual measurement result 1 of synthetic output frequency characteristic by setting value and synthetic output frequency characteristic by setting the frequency characteristic of each filter by the conventional method, FIG. 9 is “reverse convolution of cascade connection type filter according to the embodiment of the present invention It is a comparison graph of the measurement result 2 of the synthetic | combination output frequency characteristic by the frequency characteristic setting value of each filter calculated | required by calculation ", and the synthetic | combination output frequency characteristic by the frequency characteristic setting value of each filter by a conventional system. First, based on the signal processing of the current graphic equalizer, a method of calculating the filter characteristic in consideration of the influence of the adjacent band will be described. The present embodiment will be described using an example of an IIR (Infinite Impulse Response / Recursive) filter system in which a single filter is composed of an adder, a plurality of delay units, and a multiplier based on digital signal processing. In FIG. 5, transfer functions H 1 (z) and H 2 (z) to Hn (z) of the cascade connection type filter 3 of 1 to n filters alone 1 are set. For example, a second-order band boost filter with a quality factor Q = 5 and a peak of +12 dB is set. Assuming that the input signal amplitude is X (z), the output signal amplitude is Y (z), and the transfer function of the filter is Hn (z), the transfer function H (z) can be expressed by the product of the transfer functions of the individual filters. Here, when the transfer function is decomposed into the amplitude and the phase, the amplitude characteristic M (ω) is in the form of a product, The 08-05-2019 3 phase characteristic θ (ω) can be expressed in the form of a sum. As described above, the amplitude characteristic at a certain frequency can be expressed by the product of the amplitude characteristics of all the filters. Here, the amplitude value is converted to a logarithmic scale to reduce the amount of calculation. By this conversion, the amplitude characteristic becomes the sum of all filter characteristics. <Img class = "EMIRef" id = "198843278-000005" /> [0018] Here, considering the frequency characteristic setting value of each filter and the frequency characteristic of a single filter, the synthesis of the graphic equalizer is performed. The output frequency characteristic is understood to be one in which the frequency characteristic of a single filter is moved and integrated on the frequency axis for each central frequency. Therefore, by converting the amplitude value of each filter into a logarithmic scale, it can be treated as an integral, and as shown in FIG. 6, the frequency characteristic setting value of each filter and the frequency characteristic 5 of the single filter unit have a relationship of "convolution". I understand that That is, based on the frequency characteristic setting values 4a to i of each filter shown in the frequency characteristic setting value graph of each filter in FIG. 6A and the frequency characteristic 5 of the single filter in FIG. If "*" is selected, the composite output frequency characteristic 6 is calculated as a result of the "convolution" calculation result shown in FIG. 6 (c). Here, if the frequency characteristic of the graphic equalizer is determined by the relation of “folding”, it becomes possible to obtain the frequency characteristic setting value of each filter from the combined output frequency characteristic. Since “combined” (the “*” mark) indicates that the frequency characteristic setting values 4a to i of each filter and the frequency characteristic 5 of the filter unit are “combined”, the composite output frequency characteristic 6 is obtained. It is obvious that the result of “reversing” (characters * <− 1>) in the characteristic 5 is the frequency characteristic setting values 4a to i of each filter. The situation is shown in FIG. Based on the combined output frequency characteristic 6 according to the “convoluted” calculation result shown in FIG. 7C and the frequency characteristic 5 of the single filter of FIG. 7B, “inverse operation (* <− 1> mark 6A, the frequency characteristic setting of each filter of FIG. 7A is the same as the frequency characteristic setting values 4a to i of each filter shown in the frequency characteristic setting value graph of each filter of FIG. 6A. Frequency characteristic set values 4a to i of the respective filters shown in the value graph are calculated. Here, based on the combined output frequency characteristic, “inverse convolution operation (* <− 1> mark)” is performed based on the target frequency characteristic 7 of FIG. 1 (a) and the frequency characteristic 5 of the filter unit of FIG. 1 (b). For example, as in the frequency characteristic setting value graph of each filter in FIG. 1C, the frequency characteristic setting values 8a to 8i of each filter considering the influence on the adjacent band are obtained. Furthermore, each filter of the frequency characteristic setting value graph of each filter of FIG. 2A obtained by “inverse convolution calculation (* <− 1> mark)” from the target frequency characteristic 7 of FIG. 1A The coefficients of each filter unit 1 of the cascade connection type filter 3 are set as shown in FIG. 2 (b) according to the frequency characteristic setting values 8a 08-05-2019 4 to i of FIG. Can be realized. That is, in FIG. 3, as one example, the filter unit 1 is an input of the multiplier a1 and the multiplier a1 in which the input signal X (z) is connected in series with the multiplier a0 and the delay device Z <−1>. Is connected to the adder 18 via each of the multipliers a2 connected in series to the delay device Z <−1> connected to the output signal Y (z) connected in series to the delay device Z <−1> The multiplier b1 is connected to the adder 18 via the multiplier b2 connected in series to the delay device Z <-1> connected to the input of the multiplier b1. Here, as described above, the frequency characteristic setting value graph of each filter of FIG. 2 (a) obtained from the target frequency characteristic 7 of FIG. 1 (a) by "inverse convolution calculation (* <-1> mark)" By setting the frequency characteristic setting values 8a to 8 of the respective filters as the coefficients of the multipliers a0, a1, a2, b1 and b2 forming the characteristics of the single filter 1, it is possible to realize a filter which does not include an error. FIG. 4 is a flowchart for obtaining the frequency characteristic setting value of each filter by “inverse convolution operation” from the target frequency characteristics of the cascade connection type filter according to the embodiment of the present invention, wherein “inverse convolution operation” is cascaded The procedure applied to the filter is as follows. After the setting procedure “START”, “set target frequency characteristics” and “convert amplitude values to logarithms” and “set frequency characteristics of filter alone” and “convert amplitude values to logarithms”. Subsequently, the frequency characteristics to be set for each filter obtained by “inverse convolution operation” of the two are input to a graphic equalizer or other IIR digital filter design tool or the like, and finally “filter coefficients of each filter Calculate "" and "STOP". As a result, it is possible to realize a combined output frequency characteristic that approximates the target frequency characteristic. The measurement result of the filter which realized the complicated transfer function by this design method is shown. (Measured result 1) In FIG. 8, this figure is actually measured data in the case of setting to raise the amplitude of seven bands of single filter, and compared with synthesized output frequency characteristic 9 by the conventional design method. It can be seen that the frequency characteristic 10 has a frequency characteristic similar to the target frequency characteristic in which the influence of the adjacent band is extremely small. (Result of Measurement 2) In FIG. 9, the figure shows the measurement data when setting the amplitude of 5 bands out of 10 bands of the filter alone to lower the amplitude of 5 bands in the same manner as described above. It can be seen that the combined output frequency characteristic 12 according to the design method of the present invention has a frequency characteristic similar to the target frequency characteristic with very little influence of the adjacent band compared to the combined output frequency characteristic 11 according to the conventional design method. Although the example of the IIR filter system has been described above, the present invention may be applied to a design tool of an FIR (Finite Impulse Response / non-recursive) filter system. Moreover, it is also possible to apply to a parallel connection type filter. According to the design method of the digital filter, the coefficients of each filter unit are set according to the respective frequency 08-05-2019 5 characteristic setting values of the filter unit determined by the inverse convolution operation, and the combined output frequency characteristic is formed based on the set coefficients. The present invention is applicable to all digital filters incorporated in electronic devices such as audio devices, video devices, communication devices and the like. According to the present invention, the following effects are exhibited. 1) Even if the target transfer function is complicated, filter coefficients can be easily calculated. 2) The operation time does not depend on the complexity of the transfer function. 3) A desired combined output frequency characteristic can be obtained only by changing the frequency characteristic setting value of each filter unit. From the above, it is possible to easily form a digital filter having a frequency characteristic close to the target frequency characteristic, which is hardly influenced by the adjacent band, without changing the characteristic of the conventional filter alone. 4) The digital filter design method can be applied to all digital filters incorporated in electronic devices such as audio devices, video devices, communication devices and the like. BRIEF DESCRIPTION OF THE DRAWINGS [FIG. 1] A description for obtaining the frequency characteristic setting value of each filter by "inverse convolution operation (* <-1> mark)" from the target frequency characteristic of the cascade connection type filter of the embodiment of the present invention. Figure. FIG. 2 is an explanatory view for setting coefficients of cascade-connected filters according to frequency characteristic setting values of the filters obtained by “inverse convolution operation” in the embodiment of the present invention. FIG. 3 is a circuit example block diagram of a single filter. FIG. 4 is a flow chart for obtaining a frequency characteristic setting value of each filter by “inverse convolution operation” from the target frequency characteristic of the cascade connection type filter of the embodiment of the present invention. FIG. 5 is an explanatory view of a cascade connection type filter. FIG. 6 is an explanatory diagram for obtaining a combined output frequency characteristic by “convolution calculation (* mark)” from the frequency characteristic setting value of each filter of the cascade connection type filter. FIG. 7 is an explanatory view for obtaining frequency characteristic setting values of the respective filters by “inverse convolution calculation (* <− 1> mark)” from the combined output frequency characteristics of the cascade connection type filter obtained in FIG. 6; FIG. 8 is a combined output frequency characteristic according to the frequency characteristic setting value of each filter determined by “inverse convolution operation” of the cascade connection type filter according to the embodiment of the present invention, and a combined output according to the frequency characteristic setting value according to the conventional method The comparison graph of measurement result 1 with a frequency characteristic. FIG. 9 is a combined output frequency characteristic according to the frequency characteristic setting value of each filter determined by “inverse convolution operation” of the cascade connection type filter according to the embodiment of the present invention, and a combined output according to the frequency characteristic setting value according to the conventional method The comparison graph of measurement result 2 with a frequency characteristic. FIG. 10 is an explanatory diagram of a frequency characteristic setting value graph (a) of a graphic equalizer according to 08-05-2019 6 Conventional Example 1 and an actually measured value graph (b). FIG. 11 is an explanatory diagram of a frequency characteristic setting value graph (a) of a graphic equalizer according to Conventional Example 2 and an actually measured value graph (b). FIG. 12 is an explanatory diagram of a frequency characteristic set value graph (a) of a graphic equalizer according to Conventional Example 3 and an actually measured value graph (b). [Description of the code] 1: Filter alone 2: Transfer function 3: cascaded filter 4: Frequency characteristics setting value 5: Frequency characteristics of a single filter 6: Synthetic output frequency characteristics 7: Target frequency characteristics 8: Frequency characteristics setting values 9 11, 15, 16, 17: Synthesized output frequency characteristic by the conventional design method 10, 12: Synthesized output frequency characteristic by the present invention design method 13: Graphic equalizer 14: Filter unit 18: Adder 08-05-2019 7

1/--страниц