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 JP2013168706 PROBLEM TO BE SOLVED: To include a filter section constituted by connecting in series one or a plurality of stages of IIR type filters having a shelf type characteristic (or step characteristic), and the phase characteristic θ of this filter section has a phase frequency close to almost linear Provided are a digital signal processing device and a digital signal processing method capable of correcting response characteristics. SOLUTION: A digital signal processing device comprises a filter unit constituted by an M-order (M: integer) Butterworth IIR filter Sn having a shelf-shaped characteristic Hn indicating a cutoff frequency fcn and a gain gn, and a filter unit. And a phase correction filter unit connected in series to correct the phase characteristic θ of the filter unit to be close to a linear phase, and the phase correction filter unit is a 2Mth or 4Mth order corresponding to a Butterworth IIR type filter Sn It is comprised by IIR type filter An. [Selected figure] Figure 1 Digital signal processing apparatus and digital signal processing method [0001] The present invention relates to a digital signal processing apparatus and a digital signal processing method for giving a predetermined frequency response characteristic to an audio signal, and in particular, to an IIR type filter (Shelving Filter) having a shelf type characteristic (or step characteristic). The present invention relates to a digital signal processing device and a digital signal processing method that include a filter unit configured by connecting stages or stages in series, and that can correct the phase characteristic θ of the filter unit to a phase frequency response characteristic close to a substantially linear phase. [0002] 08-05-2019 1 In an audiovisual apparatus such as an AV receiver that reproduces an audio signal, or an electronic computer such as a personal computer, an equalizer that achieves a predetermined frequency response characteristic to an audio signal by inputting a plurality of sets of desired frequency values and gain values is realized. Some include digital signal processors or digital signal processing methods. As an equalizer that provides a predetermined frequency response characteristic, there is a graphic equalizer whose frequency is typically fixed, and a parametric equalizer whose frequency can be varied. These equalizers often include a plurality of band pass filters (or peaking filters). [0003] However, in a parametric equalizer using a conventional band pass filter, individual attempts may be made to realize an equalizer having a desired frequency response characteristic by freely setting plural sets of setting values consisting of arbitrary frequency value and gain value combinations. In some cases, the band pass filters in the above may affect each other, and it may not be possible to realize frequency response characteristics passing through these set values. That is, in the configuration using a plurality of band pass filters for passing a predetermined band, there is a band in which the pass frequency bands overlap with each other between filters, so an arbitrary frequency value and gain at one point with frequency response characteristics Even if the values are passed, they may deviate from arbitrary frequency values and gain values at other points. [0004] For example, conventionally, the gain is variably set for each of a plurality of predetermined frequency bands of the input signal so that the gain adjustment is performed so that the target characteristic can be appropriately obtained even when the leakage gain from another band is affected. In order to obtain a target gain for each of the frequency bands, the gain setting means configured as described above, in the case where at least one of the frequency bands adjacent to each other has a target gain value set, Process for obtaining a leakage gain value to the frequency band and updating the gain value to be set to the other frequency band based on the leakage gain value from the one frequency band to the other frequency band as the updating process And the leak gain value from the other frequency band when the updated gain value is set. Gain adjustment means for adjusting the gain value to be set for each frequency band by the gain setting means based on the result of alternately repeating the process of updating the gain 08-05-2019 2 value to be set to one frequency band; There is a signal processing apparatus characterized by including (Patent Document 1). [0005] Also, conventionally, in place of the band pass filter, a plurality of shelving filters having shelf type characteristics (or step characteristics) are connected in series to pass a plurality of set values consisting of an arbitrary set of frequency values and gain values. Patent Document 2 discloses an equalizer that realizes frequency response characteristics. In the equalizer in which a plurality of shelving filters of Patent Document 2 are connected in series, a frequency response passing a plurality of set values consisting of an arbitrary frequency value and a set of gain values than in the case of a conventional band pass filter or peaking filter There is an advantage that it is easy to realize the characteristics. [0006] Also, conventionally, a plurality of shelving filters connected in series, for example, a low-pass filter and a high-pass filter in which shelving filters are connected in parallel, are divided by n-1 frequency limit points In an equalizer for digital signals having n adjacent frequency ranges, the equalizer comprises n-1 filter circuits connected in cascade and a control unit, said n-1 connected in cascade. Each of the filter circuits is provided corresponding to each one of the n-1 frequency limit points, and each filter circuit has one frequency limit point corresponding to the filter circuit as a frequency limit. Of digital low-pass filters and one digital high-pass filter in parallel. Each of the digital high-pass filters has a complementary transfer function, and the gains of the digital low-pass and digital high-pass filters passbands are adjustable by means of weighting their outputs, and each filter circuit is further And a combining stage for combining the output of the digital low pass filter output in parallel with the output of the digital high pass filter through the weighting means and outputting the result as the output of the filter circuit, the control unit being connected in cascade. Configured to control the weight addition of the outputs of the digital low pass filter and the digital high pass filter provided in each of n-1 filter circuits, in two adjacent frequency ranges on both sides of each frequency limit point Increases the amplitude in the increased frequency range of the frequency When the control unit makes the output signal from the digital high pass filter of the filter circuit corresponding to the frequency limit point more weight than the output signal from the digital low pass filter by the control unit, the adjacent two sides of each frequency limit point The output signal from the digital low-pass filter of the filter circuit corresponding to the frequency limit point is reduced by the control unit from the output signal from the digital high-pass filter when the amplitude is reduced by the increased 08-05-2019 3 frequency range of the frequency in one frequency range. There is also an equalizer configured to be able to assign a large weight (Patent Document 3). [0007] Patent documents 1: JP 2007-166195 A (FIGS. 1 to 10) WO 2009/112825 pamphlet (FIGS. 1 to 11) Patent No. 4 25 6626 (FIGS. 1 to 10) [0008] However, it is known that linear phase characteristics can not be realized in the case of connecting IIR filters in series in the equalizer design method of the above-mentioned patent document. The linear phase characteristic filter has an advantage that the signal of another band is not delayed with respect to the signal of a certain band because the difference of the phase delay does not occur depending on the frequency of the signal (group delay is constant). Therefore, when the shelving filter is realized by the IIR type filter, there is a problem that a phase delay occurs in a frequency band higher than the vicinity of the transient region (cutoff frequency of the shelving filter). Although the FIR filter may be used in the prior art to correct the phase characteristic to a linear phase, there is a problem that a large number of taps is required when the low-pass phase characteristic is corrected by the FIR filter. In addition, in the conventional IIR all-pass filter (All Pass Filter), there is a problem that it is difficult to match phase characteristics. [0009] The present invention has been made to solve the above-mentioned problems of the prior art, and its object is to construct an IIR type filter having a shelf type characteristic (or step characteristic) by connecting one or more stages in series. It is an object of the present invention to provide a digital signal processing device and a digital signal processing method that can correct the phase characteristic θ of the filter unit to a phase frequency response characteristic close to a substantially linear phase. [0010] 08-05-2019 4 The digital signal processing apparatus according to the present invention is a digital signal processing apparatus for giving a predetermined frequency response characteristic to an audio signal, and an input unit for inputting the audio signal and an input side are connected to the input unit, and the cutoff frequency fcn and A filter unit composed of an M-order (M: integer) Butterworth IIR filter Sn having a shelf-shaped characteristic Hn indicating a gain gn and a filter unit connected in series, the phase characteristic θ of the filter unit approaches a linear phase And an output unit connected to the output side of the phase correction filter unit to output an audio signal, and the phase correction filter unit corresponds to the Butterworth IIR filter Sn. It is configured by the next or 4Mth-order IIR type filter An. [0011] Preferably, in the digital signal processing device according to the present invention, the filter unit is configured by serially connecting a plurality of N stages (N: an integer of 2 or more) of Morder Butterworth type IIR filters Sn, and the phase correction filter unit It is configured by serially connecting a 2M or 4Mth order IIR filter An of one or more stages and N or less stages. [0012] The digital signal processing method according to the present invention is a digital signal processing method for giving a predetermined frequency response characteristic to an audio signal, which is a Butterworth IIR filter Sn having a shelf characteristic Hn indicating a cutoff frequency fcn and a gain gn. Step of configuring the filter portion by the step of configuring the phase correction filter portion with the 2M or 4Mth order IIR filter An corresponding to the Butterworth IIR type filter Sn, and connecting the phase correction filter portion in series to the filter portion Correcting the phase characteristic θ of the filter unit to be close to a linear phase, in the phase correction filter unit, approximating each IIR filter An with a first-order polynomial or second-order polynomial of Laplace variable s And asking. [0013] Preferably, in the digital signal processing method of the present invention, the step of configuring the filter unit includes the step of configuring an M-order Butterworth IIR filter Sn in series connection of a plurality of N stages (N: integer of 2 or more). And a step of forming a phase correction filter by connecting in series one or more and a plurality of N or less 2M order or 4M order IIR filters An. [0014] Hereinafter, the operation of the present invention will be described. 08-05-2019 5 [0015] The digital signal processing apparatus and the digital signal processing method of the present invention are M-th order having a shelf type characteristic Hn indicating a cutoff frequency fcn and a gain gn so as to give a predetermined frequency response characteristic to an input audio signal and output it. A (M: integer) IIR type filter Sn is connected in one stage, or a plurality of N stages (N: an integer of 2 or more) are connected in series to configure a filter section. The filter unit sets a plurality (N + 1) of set values (Fn, Gn) consisting of a set of a frequency value Fn and a gain value Gn and sets a desired frequency response characteristic D of the filter, and a desired characteristic setting unit The cutoff frequency fcn and the gain gn may be determined corresponding to the setting values (Fn, Gn) of the characteristic setting unit, and the filter setting unit may set the respective IIR type filters Sn of the filter unit. [0016] For example, when the user sets a plurality (N + 1) of set values (Fn, Gn) and sets the desired frequency response characteristic D of the filter, the digital signal processing apparatus and the digital signal processing method An IIR type filter having an error calculation unit that calculates H and calculates an error E between desired frequency response characteristic D and realized frequency response characteristic H, and calculates a slope of desired frequency response characteristic D at frequency value fn By selecting the order M of Sn, the filter unit can be set to reduce the error E. The filter setting unit receives the output from the error calculation unit, calculates the correction value Tn so as to reduce the error E, and corrects the gain value gn of the plurality of IIR filters Sn of the digital filter unit using the correction value Tn Do. [0017] Further, the digital signal processing apparatus and the digital signal processing method of the present invention include a phase correction filter unit connected in series to the filter unit to correct the phase characteristic θ of the filter unit so as to approach a linear phase. 08-05-2019 6 The phase correction filter unit is configured by serially connecting a 2M-order or 4M-order IIR filter An corresponding to the Butterworth IIR filter Sn in one or more stages and a plurality of N stages or less. Specifically, in the phase correction filter unit, one of 2M-order or 4M-order IIR-type filters An corresponding to the Butterworth-type IIR-type filter Sn in the filter unit is connected in one stage, or a predetermined number of N stages or less It connects in series and comprises a phase correction filter part. Then, in the phase correction filter unit, each IIR filter An is obtained by approximating it to a linear polynomial or a quadratic polynomial of Laplace variable s. As a result, when the phase correction filter unit is connected in series to the filter unit, the phase characteristic θ of the filter unit can be corrected so as to approximate a substantially linear phase. Since the phase correction filter unit is configured by serially connecting IIR type filters An with small calculation load, it is possible to realize arbitrary frequency response characteristics and to realize linear phase characteristics by further reducing the calculation load of the filter. it can. [0018] The digital signal processing apparatus and the digital signal processing method according to the present invention may be a filter section formed by connecting in series one or a plurality of stages of IIR type filters having shelf type characteristics (or step characteristics). The phase characteristic θ of the filter can be made to be a phase frequency response characteristic close to a substantially linear phase by reducing the calculation load of the filter. [0019] FIG. 1 is a block diagram for explaining a digital signal processing device 1 according to a preferred embodiment of the present invention. (Example 1) FIG. 7 is a diagram for explaining the operation of a plurality of shelf-type filters 08-05-2019 7 connected in series in the filter unit 4 of the digital signal processing apparatus 1 according to a preferred embodiment of the present invention. (Example 1) A graph showing an example of an amplitude frequency characteristic and a phase delay frequency characteristic of the filter part 40s in the equalizer part 4 of the digital signal processing device 1 according to a preferred embodiment of the present invention. (Example 1) In the equalizer unit 4 of the digital signal processing apparatus 1 according to a preferred embodiment of the present invention, an example of the amplitude frequency characteristic and the phase delay frequency characteristic of the filter unit 40s and the phase correction filter unit 40a connected in series thereto is shown. It is a graph. (Example 1) It is a graph explaining the phase characteristics of IIR type filters Sn and An in the equalizer unit 4 of the digital signal processing device 1 according to a preferred embodiment of the present invention. Example 1) [0020] Hereinafter, although a digital signal processing apparatus and a digital signal processing method according to preferred embodiments of the present invention will be described, the present invention is not limited to these embodiments. [0021] FIG. 1 is a block diagram for explaining a digital signal processing apparatus 1 according to a preferred embodiment of the present invention. For example, the digital signal processing apparatus 1 is an electronic computer such as a personal computer (not shown), and when reproducing a content file including an audio signal, the user uses a GUI to obtain a desired frequency value and gain value. It includes an equalizer program which inputs a plurality of sets and gives a predetermined frequency response characteristic to an audio signal. The equalizer program is executed by the central processing unit (CPU) (not shown) or digital signal processor (DSP) of the personal computer, and one or more N stages of IIR filters with shelf characteristics are connected in series The digital signal processing method which comprises the equalizer part 4 is included. In addition, in order to make a figure and description intelligible, illustration of the whole structure of a personal computer (not shown) and the one part structure unnecessary to description of the digital signal processing apparatus 1 is abbreviate | omitted. [0022] 08-05-2019 8 The digital signal processing device 1 includes an input unit 2 for inputting an audio signal, an output unit 3 for outputting an audio signal, an equalizer unit 4 connected between the input unit and the output unit, and a desired frequency of the equalizer unit 4 It has a desired characteristic setting unit 5 for setting the response characteristic D, and a filter setting unit 6 for setting each Butterworth IIR filter Sn of the equalizer unit 4. The input unit 2 may include a DIR circuit if the audio signal is a digital signal, and an A / D circuit if it is an analog signal. In addition, the output unit 3 may include a D / A circuit that converts a digital signal output from the equalizer unit 4 into an analog signal. [0023] The equalizer unit 4 is configured to include a CPU or a DSP. The equalizer unit 4 is connected in series to a filter unit 40s configured by connecting in series one or a plurality of N stages of IIR filters Sn having shelf-type characteristics, and the filter unit 40s, and the phase characteristic θ of the filter unit 40s is linear And a phase correction filter unit 40a that corrects the phase to be close to the phase. The phase correction filter unit 40a is configured by serially connecting an IIR type filter An corresponding to the Butterworth type IIR type filter Sn in a predetermined number of stages equal to or less than the number N of IIR type filters Sn in the filter section 40s. . The IIR filter An is a filter having a filter characteristic substantially similar to an all-pass filter (all pass filter: APF) with only phase rotation, since the gain characteristic is almost flat as described later. [0024] The desired characteristic setting unit 5 includes a GUI (not shown), and a setting unit 51 for setting a plurality of (IIR type filter Sn stage number + 1) set values (Fn, Gn) consisting of a set of frequency value Fn and gain value Gn. And an operation unit 52 which calculates the desired frequency response characteristic D of the filter unit 40s. The user can freely set the desired desired frequency response characteristic D on the screen (not shown) by operating a key or the like. [0025] Further, the filter setting unit 6 determines the cut-off frequency fcn and the gain gn of each of 08-05-2019 9 the IIR filters Sn corresponding to the setting values (Fn, Gn) of the desired characteristic setting unit 5, and the filter unit of the equalizer unit 4 A setting unit 61 for setting each of the IIR filters Sn for 40 seconds, a calculation unit 62 for calculating the realized frequency response characteristic H of the filter unit 40s, and an error E between the desired frequency response characteristic D and the realized frequency response characteristic H And an error calculation unit 63. The filter setting unit 6 sets the filter unit 40 s of the equalizer unit 4 so as to reduce the error E in response to the output from the error calculation unit 63 as described later. [0026] FIG. 2 is a diagram for explaining the operation of a plurality of rack-type filters Sn connected in series in the equalizer unit 4 of the digital signal processing apparatus 1. In FIG. 2, as shown in the figure, when realizing a filter of the desired frequency response characteristic D passing through three sets of setting values (Fn, Gn), (Fn + 1, Gn + 1), (Fn + 2, Gn + 2), gn and Two shelf filters Sn and Sn + 1 having gn + 1 as a gain are connected in series. The frequency characteristic of the shelf filter Sn is Hn, and the cutoff frequency fcn is an intermediate value on the octave scale of the frequency values Fn + 1 and Fn, and the gain thereof is gn. The frequency characteristic of the second rack type filter Sn + 1 is Hn + 1, and the cutoff frequency fcn + 1 is an intermediate value on the octave scale of the frequency values Fn + 1 and Fn + 2, and the gain thereof is gn + 1. In the method of connecting the shelf type filters in series, adjacent shelf type filters interfere with each other only in the vicinity of the illustrated frequency value Fn + 1, so the product (gn) * (gn + 1) of the gains of these two shelf type filters By setting the same to the desired gain (Gn + 2), it is possible to make the realized frequency response characteristic H close to the desired frequency response characteristic D. [0027] FIG. 3 is a graph showing an example of the amplitude frequency characteristic and the phase delay frequency characteristic of the filter unit 40s portion in the case (N = 9) in the equalizer unit 4 of the digital signal processing apparatus 1. The filter unit 40s is configured by serially connecting a plurality of N stages of IIR filters Sn having shelf-type characteristics, and the desired frequency setting unit 5 and the filter setting unit 6 determine the amplitude frequency characteristics and the phase delay frequency characteristics. . Specifically, all of the IIR filters Sn having a shelf type characteristic are M (integer) -order IIR filters, so that the amplitude frequency characteristics pass through a plurality of points shown in FIG. Each filter Sn is set. Further, in the graph of the phase delay shown in FIG. 3B, the horizontal axis represents the phase delay time [sec] calculated by dividing the phase angle [[Rad] by the angular frequency ω 08-05-2019 10 [Rad / sec], and the horizontal axis represents the frequency. It is plotted against. Therefore, in the case of a linear phase filter, the phase delay frequency characteristic is a flat graph because it has a delay time of a fixed time. In the filter unit 40 s of this example, since the IIR type filters Sn having shelf-type characteristics are connected in series, the absolute value of the phase delay time is large in a low frequency band of 65 Hz or less. [0028] FIG. 4 is a graph showing an example of the amplitude frequency characteristic and the phase delay frequency characteristic of the filter unit 40s and the phase correction filter unit 40a connected in series to the filter unit 40s in the equalizer unit 4 of the digital signal processing apparatus 1. That is, in addition to the case of the filter unit 40s described in FIG. 3, the phase correction filter unit 40a is further connected in series. The phase correction filter unit 40 a corrects the phase characteristic θ of the filter unit 40 s as shown in the graph of the phase delay of FIG. 3B so as to approach a substantially constant phase delay. As shown in FIG. 4B, when the phase correction filter unit 40a is used, the absolute value of the phase delay time decreases in the low frequency band of 65 Hz or less, and the difference with the high frequency band is almost eliminated. That is, the phase correction filter unit 40 a corrects the phase characteristic of the filter unit 40 s so that it approaches a substantially linear phase. In this embodiment, an IIR type filter A1 corresponding to a Butterworth type IIR type filter S1 having a shelf type characteristic is provided in the lowest frequency band (32 to 65 Hz) of the filter section 40s. [0029] Here, a method of deriving an IIR type filter An that corrects the phase characteristic so as to approach a substantially constant phase delay will be described, corresponding to the Butterworth type IIR type filter Sn having a shelf type characteristic. The phase correcting IIR type filter An may increase or decrease the order M approximated by the macro-phosphorus expansion according to the gain of the IIR type filter Sn in the low frequency region. The Butterworth type IIR filter Sn having a shelf type characteristic can be expressed as Expression (1) when normalized with a cutoff frequency ωc = 1. Here, M is an order and is an integer greater than or equal to 1, g is a gain (linear scale), and the equation is modified using the symmetry arrangement of poles on the s-plane. [0030] 08-05-2019 11 Equation (2) shows the phase characteristics of equation (1), that is, the phase characteristics θ of the Butterworth IIR filter Sn. Therefore, an all-pass filter that corrects the phase characteristic θ of the Butterworth IIR filter Sn to a linear phase is derived as shown in equation (3). [0031] However, since S-Z conversion can not be performed using bilinear conversion as in this equation (3), it can not be realized as a digital filter. Therefore, equation (3) is approximated as a polynomial of the Laplace variable s by using arctan (z) and exp (z) as in equation (4) and using the macrolin expansion. When both atan (z) and exp (z) are approximated to the first order, Expression (5) is obtained. Furthermore, when V and V2 are given as in equation (6), the integration term of equation (3) can be transformed as in equation (7). [0032] When approximating equation (3) as a polynomial of Laplace variable s, if exp (z) is approximated to the second order in equation (4), equation (8) is obtained. B1 to B7 in the formula (8) are as described in the formula (9). [0033] Then, using the bilinear transformation described in the equation (10), the equation (7) or the equation (8) is modified to obtain the phase characteristics of the Butterworth IIR filter Sn having a shelf characteristic of the cutoff frequency Ωc. It can be converted to a digital filter to be corrected. That is, by approximating the IIR type filter An which performs the phase correction of Expression (3) as a polynomial of S, it can be made an approximate full band pass filter, and can be realized as a digital filter. [0034] As is clear from the above equation (7) or (8), the IIR type filter An constituting the phase 08-05-2019 12 correction filter unit 40a has the 2Mth or 4Mth order corresponding to the Mth-order Butterworth type IIR type filter Sn. It can be constructed by approximating with an IIR type filter. The IIR filter An, which is approximately configured, has an amplitude characteristic that is substantially flat, and a phase characteristic that is substantially inverse to that of the Butterworth IIR filter Sn of M-th order. [0035] FIG. 5 is a graph for explaining phase characteristics of the IIR filters Sn and An in the equalizer unit 4. Specifically, in the case of a single-stage Butterworth IIR filter Sn of order M = 8 and gain g = 2 (6 dB), the corresponding phase correction IIR filter An is used, and the macrolin expansion is It is a case where it approximates and comprises by said Formula (7) approximated as a polynomial of degree. In the graph of FIG. 5, the phase characteristics of the shelf-type IIR filter Sn, the phase characteristics of the IIR filter An serving as an almost all band pass filter, and the case where the IIR filter Sn and the IIR filter An are connected in series Phase characteristics (Sn * An) of. Since the IIR filter An constructed by approximating is almost the reverse of the phase characteristics of the Butterworth IIR filter Sn of the M-th phase characteristic, the corrected phase characteristic becomes flat around 0 degrees. ing. [0036] Therefore, an IIR filter constructed by approximating when the phase characteristic θ of the filter unit 40s composed of M-th (M: integer of 2 or more) Butterworth IIR type filter Sn having the shelf type characteristic Hn is not linear phase The phase correction filter unit 40a made of An can be corrected so as to approach a linear phase. When the order M of the Butterworth IIR filter Sn is not large, the order of the IIR filter An is also only 2M or 4M. Therefore, the equalizer unit 4 having substantially linear phase characteristics as a practically usable digital filter Can be realized. [0037] As in the above embodiment, the phase correction filter An corresponding to only the low frequency IIR type filter Sn where the absolute value of the phase delay time becomes large may be provided. Of course, in the case where the filter unit 40s is configured by serially connecting a plurality of N stages (N: an integer of 2 or more) of M-order Butterworth IIR filters Sn, the phase 08-05-2019 13 correction filter unit 40a includes one or more stages of N A second stage or second stage IIR type filter IIR may be connected in series. That is, an IIR type filter An corresponding to each Butterworth type IIR type filter Sn may be prepared. The phase correction filter An may not necessarily be provided in a high frequency region in which the absolute value of the phase delay time decreases. [0038] The present invention is not limited to the above embodiment. The digital signal processing apparatus and the digital signal processing method can be applied not only to an electronic computer such as a personal computer but also to an audiovisual apparatus that realizes arbitrary frequency response characteristics passing an arbitrary plurality of set values. [0039] DESCRIPTION OF SYMBOLS 1 digital signal processing apparatus 2 input part 3 output part 4 equalizer part 40s filter part 40a phase correction filter part 5 desired characteristic setting part 6 filter setting part 08-05-2019 14

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