JP2014007627A - Channel divider and sound reproduction system including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a channel divider capable of changing the reproduction sound quality of a multiway speaker system appropriately, by rendering the phase shift characteristics of a filter in a channel divider, and the phase shift characteristics of a network circuit included in a speaker system to substantially linear phase, and to provide an acoustic reproduction system.SOLUTION: In the channel divider, a low-pass filter section includes a first all-pass filter, i.e., an FIR filter having coefficients obtained by time axis inversion of a finite length impulse response of an all-pass filter having phase shift characteristics substantially equal to those of a low-pass filter having predetermined low-pass characteristics, and the high-pass filter section includes a second all-pass filter, i.e., an FIR filter having coefficients obtained by time axis inversion of a finite length impulse response of an all-pass filter having phase shift characteristics substantially equal to those of a high-pass filter having predetermined high-pass characteristics.

Description

  The present invention relates to a channel divider used for reproducing an audio signal by a multi-way speaker system and an audio reproducing system including the channel divider, and in particular, a phase shift characteristic of a filter of the channel divider and a phase shift of a network circuit included in the speaker system. The present invention relates to a channel divider capable of appropriately changing the reproduction sound quality of a multi-way speaker system by converting characteristics into a substantially linear phase.

  In a multi-way speaker system including a woofer for low-frequency range playback and a tweeter for high-frequency range playback, it is common to include a network circuit that divides the audio signal amplified by the amplifier in accordance with the playback frequency band of each speaker unit. It is. In recent years, a network system corresponding to a woofer and a network circuit corresponding to a tweeter can be independent of each other, and a speaker system corresponding to a bi-wiring connection provided with an input terminal connected to each of them has become widespread. In bi-wiring connection, bi-amp driving using a power amplifier connected to the network circuit of the woofer and another power amplifier connected to the network circuit of the tweeter is adopted.

  On the other hand, as a method of realizing multi-amplifier (bi-amplifier) driving without using the network circuit of the speaker system, there is a case where a channel divider is provided in front of the power amplifier and the audio signal is divided into bands by this channel divider. In the audio playback system of the multi-amplifier-multi-way speaker system as described above, the channel divider divides the input audio signal into at least a low-frequency side output signal and a high-frequency side output signal and outputs it to the multi-amplifier. To do. By using a channel divider, LPF (low-pass filter) or HPF (high-pass filter) having a steeper transition band than the network of the speaker system can be set, the crossover frequency can be set relatively freely, etc. (For example, patent document 1). In addition, when a channel divider is used, the low-frequency amplifier circuit and the high-frequency amplifier circuit are independent, reducing the cross-modulation distortion that occurs when the low-frequency component and the high-frequency component are superimposed, reducing the playback sound quality. It is said that there is an advantage that it is excellent.

  In recent years, there has been an attempt to give a DSP a channel divider function so that a speaker system without a network circuit can be connected using an AV receiver including a DSP and a multi-amplifier (Patent Document 2, Patent Document). 3). When the channel divider is realized by a digital filter, an FIR filter or an IIR filter may be used. In order to use the channel divider, it is necessary to appropriately set the crossover frequency by measuring the reproduction band of each speaker unit of the speaker system using a microphone or the like (Patent Documents 4 and 5).

  In the conventional channel divider, the LPF on the low frequency side and the HPF on the high frequency range can be selected from several standard filter characteristics, and a recursive filter having a non-linear phase phase shift characteristic (infinite Long impulse response filters, IIR filters) may be used. Specific examples of standard filter characteristics include various filters such as a Butterworth filter, a Bessel filter, and a Linkwitz-Riley filter. When setting the filter by increasing the order of the recursive filter, the gain characteristics of the transition band can be made steep in setting the pass band of the filter, the stop band, and the transition band between them. In some cases, the phase rotation increases and a delay occurs, and the phase delay characteristic and the group delay characteristic differ greatly depending on the frequency. On the other hand, when a non-recursive filter (finite length impulse response filter, FIR filter) is used, a filter having a phase shift characteristic of a linear phase can be set. In the case of the phase shift characteristic of the linear phase, the delay is constant with respect to the frequency, and the phase delay characteristic and the group delay characteristic are flat.

  However, in a filter having a non-linear phase phase shift characteristic, the waveform of the input signal is distorted in terms of time and output. Therefore, in the channel divider, for example, 96 dB / Oct. -192 dB / Oct. When a high-order non-linear phase IIR filter having a steep gain characteristic is used, there is a problem that the waveform of the output signal is greatly distorted and appears as a timbre change in reproduced sound. Further, since the filter of the network circuit of the speaker system is also a non-linear phase passive filter, it has the same problem when it has a steep gain characteristic. Therefore, it is preferable that the phase shift characteristic of the non-linear phase can be converted into a linear phase even when the desired gain characteristic is set in the filter of the network circuit of the channel divider and the speaker system.

  Conventionally, with respect to a time axis inversion type linear phase filter having a configuration of an IIR type digital filter having a linear phase characteristic, a time axis inversion circuit and a time for inverting a signal in a unit of time about twice the impulse response period of the IIR filter There is one that attempts to realize a configuration in which two systems of IIR type filters for processing a signal whose axis has been inverted is prepared with a required amount of memory much smaller than that of the prior art (Patent Document 6). In addition, the impulse response of a cyclic digital filter that gives the desired frequency amplitude characteristics is measured, the impulse response is limited to a predetermined response time, the limited impulse response is obtained, and the time axis of the limited impulse response and the limited impulse response is reversed backwards and forwards. There is a design method for an acyclic digital filter in which the coefficients of the first and second acyclic digital filters are set so that the impulse response is an impulse response coefficient, respectively (Patent Document 7). An apparatus for removing ringing of a filtered ECG signal having an A / D converter for converting an analog input signal into a series of digital values and a filter unit connected to the output side of the A / D converter. The unit has a cyclic IIR filter and a subsequent all-pass filter with a phase shift equal to twice the phase shift of the IIR filter, and the all-pass filtering is performed with the time reversed in relation to the IIR filtering. There is an apparatus for removing ringing of a filtered ECG signal characterized in that (Patent Document 8).

JP 2005-109969 A JP 2002-111399 A JP 2005-184149 A Japanese Patent No. 4321315 Japanese Utility Model Publication No. 5-39097 Japanese Examined Patent Publication No. 7-107970 Japanese Examined Patent Publication No. 7-107970 JP-A-7-51236

  The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is a channel divider and an acoustic reproduction system used for reproducing an audio signal by a multi-way speaker system, and more particularly, a channel. A channel divider and sound reproduction system capable of appropriately changing the reproduction sound quality of the multi-way speaker system by making the phase shift characteristic of the filter of the divider and the phase shift characteristic of the network circuit included in the speaker system into a substantially linear phase. It is to provide.

  The channel divider according to the present invention divides the input audio signal into at least a first output signal on the low frequency range side and a second output signal on the high frequency range side than the first output signal, and each of the first output terminals. And a low-pass filter section and a high-pass filter section that output to the second output terminal, wherein the low-pass filter section has a phase of a low-pass filter having a predetermined low-pass characteristic. A first all-pass filter that is a FIR filter having a coefficient obtained by inverting the time axis of a finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to the shift characteristic, Finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to that of a high-pass filter having a high-pass characteristic Including a second all-pass filter is a FIR filter having coefficients obtained by time-axis inverted.

  Preferably, the channel divider of the present invention includes a first low-pass filter in which a low-pass filter unit and a high-pass filter unit of the channel divider are respectively connected in series to the first all-band filter, and a second all-band filter. A first high-pass filter connected in series with the filter.

  Preferably, the channel divider according to the present invention includes a level adjustment circuit for adjusting a level of the first output signal or the second output signal, a phase inversion circuit for performing phase inversion of the first output signal or the second output signal, A delay circuit for adjusting a delay time of the first output signal or the second output signal.

  According to another aspect of the present invention, there is provided an acoustic reproduction system including the channel divider, an amplifier including an amplifier circuit corresponding to the first output terminal and the second output terminal of the channel divider, a second low-pass filter corresponding to at least a woofer, A speaker system including a network circuit including a second high-pass filter corresponding to the tweeter and capable of bi-wiring connection.

  Preferably, in the sound reproduction system of the present invention, the first all-pass filter has a phase shift characteristic of the first low-pass filter, or a phase shift characteristic of the second low-pass filter, or the first low-pass filter. A phase-shift characteristic of a product of a band-pass filter and a second low-pass filter, and a FIR filter having a coefficient obtained by reversing a time axis of a finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to The second all-band filter has a phase shift characteristic of the first high-pass filter or a phase shift characteristic of the second high-pass filter or a product of the first high-pass filter and the second high-pass filter. The phase shift characteristic is a time-reversed finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to any of the phase shift characteristic and the phase shift characteristic. It is a FIR filter with.

  The operation of the present invention will be described below.

  The channel divider according to the present invention divides the input audio signal into at least a first output signal on the low frequency range side and a second output signal on the high frequency range side than the first output signal, and each of the first output terminals. And output to the second output terminal. The channel divider constitutes an acoustic reproduction system including an amplifier including an amplifier circuit corresponding to each output terminal of the channel divider and at least a woofer and a tweeter, and a speaker system capable of bi-wiring connection with the amplifier. . Therefore, the user can adjust the channel divider to change the frequency band and the reproduction level in which the woofer and the tweeter are reproduced in an overlapping manner, so that there is an advantage that the reproduction sound quality can be easily adjusted. The network circuit of a general speaker system is ± 6 to 18 dB / Oct. The channel divider LPF, BPF, and HPF are ± 24 to 96 dB / Oct. The above transition region characteristics are also possible, and by introducing a channel divider, the attenuation rate of the transition region and the stop region can be increased.

  The channel divider according to the present invention divides the input audio signal into at least a first output signal on the low frequency range side and a second output signal on the high frequency range side than the first output signal, and each of the first output terminals. And a low-pass filter unit and a high-pass filter unit that output to the second output terminal. The low-pass filter unit includes a FIR having a coefficient obtained by inverting the time axis of a finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to a phase shift characteristic of a low-pass filter having a predetermined low-pass characteristic. It includes a first all-pass filter that is a filter, and preferably includes a first low-pass filter connected in series to the first all-band pass filter. In addition, the high-pass filter unit has a coefficient obtained by inverting the time axis of a finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to the phase shift characteristic of a high-pass filter having a predetermined high-pass characteristic. And a first all-pass filter connected in series with the second all-band pass filter.

  That is, the channel divider according to the present invention includes an FIR filter in which the low-pass filter unit and the high-pass filter unit each have a coefficient obtained by inverting the time axis of the finite-length impulse response of the all-band pass filter having a predetermined phase shift characteristic. Is included. When this FIR filter is an all-band pass filter (all-pass filter, APF), the gain characteristic is constant and flat regardless of frequency, and a phase shift with a phase delay in a cyclic filter is targeted, A phase characteristic including a predetermined phase advance is realized by using an FIR filter coefficient obtained by inverting the time axis of a finite impulse response. Specifically, the first all-band pass filter includes a phase shift characteristic of the first low-pass filter of the low-pass filter unit, or a phase shift characteristic of the second low-pass filter of the network circuit of the speaker system, or And a coefficient obtained by reversing the time axis of a finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to any one of the product phase shift characteristics of the first low-pass filter and the second low-pass filter. In addition, the second all-band filter includes a phase shift characteristic of the first high-pass filter of the high-pass filter unit, or a phase shift characteristic of the second high-pass filter of the network circuit of the speaker system, or the first A coefficient obtained by inverting the time axis of a finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to any one of the phase shift characteristics of the product of the high-pass filter and the second high-pass filter.

  As a result, in the channel divider or audio reproduction system of the present invention, the phase shift characteristic of the non-linear phase can be linearized with respect to the filter of the network circuit of the channel divider and the speaker system. In a sound reproduction system including a channel divider and a speaker system having a network circuit, even if a high-order nonlinear phase filter having a steep gain characteristic is used, the phase delay characteristic and the group delay characteristic have a phase shift that varies greatly depending on the frequency. Since the phase is corrected to a linear phase, it is possible to prevent the waveform of the output signal from being distorted. The first all-band pass filter and the second all-band pass filter substantially match the order and the cut-off frequency (crossover frequency) of the target cyclic low-pass filter or high-pass filter, respectively. Phase shift characteristics can be assumed. Therefore, the impulse response of these cyclic low-pass filters or high-pass filters is obtained, and the finite-length impulse response of a predetermined length is obtained. The FIR filter coefficient of the band pass filter can be obtained.

  The channel divider includes a level adjustment circuit in which the low-pass filter unit and the high-pass filter unit adjust the level of the first output signal or the second output signal, and the phase inversion of the first output signal or the second output signal. And a delay circuit for adjusting the delay time of the first output signal or the second output signal, and the range for adjusting the reproduction sound quality is widened, and can be applied to various multi-way speaker systems. It becomes possible to respond.

  The channel divider and sound reproduction system of the present invention appropriately change the reproduction sound quality of the multi-way speaker system by making the phase shift characteristic of the filter of the channel divider and the phase shift characteristic of the network circuit included in the speaker system into a substantially linear phase. can do.

It is a figure explaining the sound reproduction system containing the amplifier apparatus 1 by preferable embodiment of this invention. Example 1 It is a graph explaining the sound pressure frequency characteristic of the speaker system 7, and the frequency characteristic of the low-pass filter LPF2 or the high-pass filter HPF2 of the network circuit. Example 1 4 is a graph illustrating frequency characteristics (gain characteristics, phase characteristics) of a low-pass filter LPF1 and a high-pass filter HPF1 of the channel divider 12 of the amplifier device 1. Example 1 6 is a graph for explaining frequency characteristics (gain characteristics, phase characteristics) of the all-pass filter APF1 and the all-pass filter APF2 of the channel divider 12 of the amplifier device 1. Example 1 6 is a graph for explaining output characteristics (first output signal D1 and second output signal D2) of the channel divider 12 of the amplifier device 1; Example 1

  Hereinafter, a channel divider and an audio reproduction system including the same according to preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

  FIG. 1 is a diagram illustrating a sound reproduction system according to a preferred embodiment of the present invention. Specifically, the sound reproduction system includes an amplifier device 1 including a channel divider and speaker systems 7L and 7R connected to the amplifier device 1, and FIG. 1 is a block diagram showing the internal configuration of each. FIG. 2 is a graph for explaining the sound pressure frequency characteristics of the speaker system 7 and the frequency characteristics of the low-pass filter LPF2 or the high-pass filter HPF2 of the network circuit, and FIG. It is a graph explaining the frequency characteristic (gain characteristic, phase characteristic) of the low-pass filter LPF1 and the high-pass filter HPF1 of the divider 12. FIG. 4 is a graph illustrating frequency characteristics (gain characteristics and phase characteristics) of the all-pass filter APF1 and the all-pass filter APF2. FIG. 5 is a graph illustrating the output characteristics (first output signal D1 and second output signal D2) of the channel divider 12 of the amplifier device 1. In addition, illustration and description are abbreviate | omitted about the one part structure unnecessary for description, an internal structure, etc.

  The sound reproduction system includes an amplifier device 1 and speaker systems 7L and 7R connected to the amplifier device 1, converts digital signal data data input to the amplifier device 1 into stereo audio signals L and R, and the amplifier device. This is a sound reproduction system for reproducing stereo sound by a speaker system 7 composed of two speakers 7L and 7R after being amplified at 1. The amplifier device 1 includes a DSP and a multi-amplifier, and can be connected to a multi-amplifier that operates a channel divider. The speaker system 7 is a 2-way bi-wiring SS including a woofer WO and a tweeter TW, respectively, and is bi-wiring connected to the amplifier device 1 by a speaker cord. Therefore, the user who uses the amplifier device 1 can adjust the reproduction quality of the speaker system 7 by adjusting the channel divider to change the frequency band and the reproduction level in which the woofer and the tweeter overlap and reproduce. Become.

  The amplifier device 1 includes a DSP (digital signal processor) 10 that performs signal processing of digital signal data data, a D / A converter 2 that receives outputs from the DSP 10 for four channels, and converts them into analog signals, and these analog signals. And an amplifier circuit 3 for amplifying each of the signals and outputting them to the speaker system 7. The stereo audio signals L and R may be supplied to the DSP 10 via an A / D converter (not shown) as stereo signals (left signal L and right signal R) supplied in analog. The amplifier device 1 includes a CPU 4 that is a control circuit that controls the whole, an operation unit 5 that is connected to the CPU 4 and receives an instruction input from a user, and a display circuit 6 that includes a display. Specifically, the amplifier device 1 can be configured by a DSP that supports multi-channel sound, an AV receiver that incorporates a multi-channel amplifier circuit, and the like. The operation unit 5 includes an input device such as a switch, a jog dial, or a remote control device. The display circuit 6 may be a built-in FL display, a liquid crystal display, or the like, or a display device connected to another. Of course, the amplifier device 1 may be constituted by another sound reproducing device including the DSP 10, the D / A converter 2, the multi-channel amplifier circuit 3, and the CPU 4 such as a microcomputer. Further, the DSP 10 included in the amplifier device 1 may be independent as a single channel divider device.

  The speaker system 7 is a 2-way bi-wiring SS including a woofer WO and a tweeter TW, and includes a network circuit and an input terminal corresponding to each speaker unit. The woofer WO for reproducing the low sound range of the left speaker 7L and the right speaker 7R is connected to the input terminal tL and the network circuit LPF2. Further, the tweeter TW for high-frequency range reproduction is connected to the input terminal tH and the network circuit HPF2. The network circuit LPF2 constitutes a low-pass filter that passes the low sound range together with the woofer WO. The network circuit HPF2 constitutes a high-pass filter that passes the high-frequency range together with the tweeter TW. The network circuits LPF2 and HPF2 are analog filters configured to include a coil, a resistor, and a capacitor.

  FIG. 2 is a graph for explaining the sound pressure frequency characteristics of the speaker system 7. In the woofer WO and the tweeter TW of the speaker system 7 of the present embodiment, the frequency band for mainly reproducing sound is divided by the network circuits LPF2 and HPF2 with the crossover frequency fc as a boundary. The network circuit LPF2 has a frequency higher than the crossover frequency fc at −12 dB / Oct. It is a 2nd order LPF filter which shows the transition region characteristic of this. The network circuit HPF2 has a frequency lower than the crossover frequency fc at 12 dB / Oct. It is a 2nd-order HPF filter which shows the transition region characteristic. Therefore, the woofer WO for low-frequency range reproduction mainly reproduces the frequency band below the crossover frequency fc, and the tweeter TW mainly reproduces the frequency band above the crossover frequency fc. When the same signal is input using the network circuits LPF2 and HPF2 (that is, when the input terminals tL and tH are connected), the speaker system 7 has a relatively flat synthesized sound pressure frequency characteristic (illustrated). Adjusted to realize (WO + TW). In this embodiment, the crossover frequency fc is about 2.0 kHz. Since the network circuits LPF2 and HPF2 of the speaker system 7 are second-order filters exhibiting gentle transition band characteristics, as shown in FIG. 2, the reproduced sound of the speaker system 7 near the crossover frequency fc is The reproduced sound from the woofer WO and the reproduced sound from the tweeter TW overlap widely. In the case of a 2-way speaker system, the crossover frequency fc is generally set between about 1 to 8 kHz.

  The DSP 10 includes therein a decoder 11 that converts input data data into stereo signals L and R, and a channel divider 12 that includes a digital filter. The DSP 10 outputs the output terminals (DL1, DL2, DR1, DR2) for four channels of the channel divider 12 to the D / A converter 2. Channel divider 12 includes a low-pass filter unit 13, a high-pass filter unit 14, a first output adjustment circuit 15, and a second output adjustment circuit 16 corresponding to the left signal L and the right signal R, respectively. . Filter settings and the like of the low-pass filter unit 13 and the high-pass filter unit 14 of the channel divider 12 of the DSP 10 are controlled by the CPU 4.

  The low-pass filter unit 13 and the high-pass filter unit 14 of the channel divider 12 according to the present embodiment are respectively an all-pass filter APF1 or APF2 that is an FIR filter and a low-pass filter LPF1 or HPF1 configured by an IIR filter. Are digital filters configured by being connected in series. The low-pass filter unit 13 band-divides the input audio signal into a first output signal on the low-frequency range side, and outputs the first output signal to the first output terminal D1. The high-pass filter unit 14 divides the input audio signal into a second output signal on the high-frequency range side, and outputs the second output signal to the second output terminal D2. The low-pass filter LPF1 and the high-pass filter HPF1 may be any cyclic filter having a non-linear phase phase shift characteristic, such as a Butterworth filter or a Linkwitz-Riley filter.

  The output of the low-pass filter unit 13 is input to the first output adjustment circuit 15, and is output to the output terminals (DL1, DR1) of the DSP 10 as the first audio output signal D1. The output of the high-pass filter unit 11 is input to the second output adjustment circuit 16 and output to the output terminals (DL2, DR2) of the DSP 10 as the second audio output signal D2. The first output adjustment circuit 15 and the second output adjustment circuit 16 expand the range for adjusting the reproduction sound quality so as to be compatible with a wide range of speaker systems 7, and the first audio output signal D1 and the second audio output signal D2. Each includes a level adjustment circuit that performs level adjustment, a phase inversion circuit that performs phase inversion, and a delay circuit that adjusts the delay time.

  In the channel divider 12 of the present embodiment, for example, as illustrated in the graph of FIG. 3A, the low-pass filter LPF1 has a frequency higher than the crossover frequency fc at −12 dB / Oct. It is possible to set to a second-order LPF filter showing the transition band characteristics. Therefore, the phase characteristic of the low-pass filter LPF1 is almost positive phase below the crossover frequency fc, becomes phase delayed by −90 degrees at the crossover frequency fc, and is low at a frequency higher than the crossover frequency fc. It has a phase shift characteristic that the phase is inverted with respect to the frequency band to be reversed. Further, as shown in the graph of FIG. 3B, the high-pass filter HPF1 has a frequency lower than the crossover frequency fc at 12 dB / Oct. It is possible to set to a second-order HPF filter showing the transition band characteristics. Therefore, the phase characteristic of the high-pass filter HPF1 is almost opposite in phase below the crossover frequency fc, becomes phase delayed at the crossover frequency fc to +90 degrees, and is low at a frequency higher than the crossover frequency fc. It has a phase shift characteristic that the phase is inverted with respect to the band to become a positive phase.

  In the channel divider 12 of this embodiment, the cutoff frequency of the low-pass filter LPF1 is set equal to the crossover frequency fc of the network circuit of the speaker system 7, and the cutoff frequency of the high-pass filter HPF1 is set to crossover. Set equal to the frequency fc. The output levels of the low-pass filter LPF1 and the high-pass filter HPF1 are decreased by -6 dB from 0 dB in the pass band at the crossover frequency fc. Further, the phase shift characteristics of the low-pass filter LPF1 and the high-pass filter HPF1 are in the same relationship as the change in the phase characteristics only in an anti-phase relationship. Therefore, in the case of the combination of the low-pass filter LPF1 and the high-pass filter HPF1, the phase of the output signal is inverted by either the first output adjustment circuit 15 or the second output adjustment circuit 16. The addition characteristic can be made flat.

  In the channel divider 12, the CPU 4 controls the low-pass filter LPF1 and the high-pass filter HPF1 by ± 96 dB / Oct. ~ ± 192 dB / Oct. It is possible to use a high-order nonlinear phase IIR filter having such a steep gain characteristic. The high-order nonlinear phase IIR filter has a phase shift characteristic as shown in FIG. 3 substantially equal to a phase shift characteristic in which a plurality of stages are connected in series and phase rotation increases. Therefore, when the IIR filter having the phase shift characteristic of the non-linear phase is set to the low-pass filter LPF1 and the high-pass filter HPF1, the all-pass filter APF1 or APF2 is provided to make the phase shift characteristic linear phase. It is possible to prevent the waveform distortion of the input signal from increasing.

  FIG. 4 is a graph illustrating frequency characteristics (gain characteristics and phase characteristics) of the all-pass filter APF1 of the low-pass filter unit 13 and the all-pass filter APF2 of the high-pass filter unit 14. Each of the all-pass filters APF1 and APF2 is, for example, an FIR filter having a tap length of 4096 tap at a sampling frequency of 48 kHz, and is an all-band filter (all-pass filter, APF) that has a constant and flat gain characteristic regardless of the frequency. In addition, the phase characteristics of the all-pass filters APF1 and APF2 are substantially positive phase at the crossover frequency fc or lower, cause phase advance at the crossover frequency fc to +90 degrees, and are low at frequencies higher than the crossover frequency fc. It has a phase shift characteristic including a phase advance that is reversed in phase with respect to the frequency band, and in the case of the present embodiment, these are the same. Note that the phase characteristics shown in FIGS. 4 and 5 are normalized and displayed so as to exclude a constant phase rotation due to a time reversal delay.

  That is, the all-pass filters APF1 and APF2 have substantially the same phase shift characteristics as those obtained by inverting the phase shift characteristics of the low-pass filter LPF1 or the high-pass filter HPF1 on the time axis. The coefficients of the FIR filters of the all-pass filters APF1 and APF2 are obtained as impulse responses of the all-pass filters that are substantially equal to the phase shift characteristics of the low-pass filter LPF1 and the high-pass filter HPF1, and they are finite length (this embodiment In this case, it is obtained by reversing these on the time axis by limiting them to 4098 tap). In a cyclic filter having a phase shift characteristic of a non-linear phase that is selected from predetermined filter characteristics, the cutoff frequency and the order of the cyclic filter are determined regardless of low-pass or high-pass. The phase characteristic is uniquely determined. Therefore, if the all-pass filter, which is a recursive filter, is set to the same cutoff frequency and the same recursive filter order, the impulse response of the all-band pass filter can be obtained.

  In this embodiment, the low-pass filter LPF1 or the high-pass filter HPF1 is a second-order cyclic filter. However, if the low-pass filter LPF1 is a high-order cyclic filter, the all-pass filter of this embodiment is What is necessary is just to comprise so that it may connect in multistage. Further, the length of the impulse response and the tap length of the FIR filter may be any length as long as the impulse response of the target filter sufficiently converges according to the cutoff frequency and the order of the recursive filter. It can be set. The cut-off frequency, the order of the cyclic filter, and the tap length of the FIR filter may be set by the CPU 4 based on a user operation on the operation unit 5 or may be obtained by other automatic measurement. Further, in the configuration of the channel divider 12 shown in FIG. 1, the all-pass filters APF1 and APF2 are configured separately, but in the case where they have the same filter characteristics as in the present embodiment, they are shared. The signal flow may be changed to be used.

  FIG. 5 is a graph for explaining the output characteristics (first output signal D1 and second output signal D2) of the channel divider 12 of the amplifier device 1. The first output signal D1 that is the output of the low-pass filter unit 13 has the same gain characteristic as the low-pass filter LPF1, and the phase characteristic is linearized. Further, the second output signal D2 that is the output of the high-pass filter unit 14 has the same gain characteristic as that of the high-pass filter HPF1, and the phase characteristic is linearized. Therefore, even if a high-order nonlinear phase filter having a steeper gain characteristic than in the present embodiment is used for the low-pass filter unit 13 and the high-pass filter unit 14 of the channel divider 12, the phase delay characteristic and Since a phase shift in which the group delay characteristic varies greatly depending on the frequency is corrected to form a linear phase, it is possible to prevent the waveform of the output signal from being distorted. Of course, the addition characteristic of the first output signal D1 and the second output signal D2 can be made flat.

  The channel divider 12 is not limited to the one applied to the 2-way bi-wiring SS including the woofer WO and the tweeter TW as in the above embodiment. The channel divider 12 is a 3-5 way multi-way speaker including a subwoofer and / or a mid range and / or a super tweeter (not shown) to 3-5 for 3-5 way to accommodate bi-wiring SS. A configuration including an output obtained by dividing a band may be used. The band pass filter BPF may be configured by connecting another low pass filter HPF or another low pass filter LPF in series to the low pass filter LPF and the high pass filter HPF.

  Of course, the channel divider 12 of this embodiment is also effective in the case of a multi-way speaker including a woofer and a tweeter that does not include a network circuit. Similarly, the channel divider 12 is effective when the speaker system 7 includes a full range speaker. Even when a substantial crossover frequency fc with other speakers is set in response to a decrease in level due to the limit of the reproduction sound pressure frequency characteristics of full range speakers or speakers such as woofers and tweeters, A low-pass filter LPF or a high-pass filter HPF of the channel divider 12 can be set in accordance with this.

  In the above embodiment, the all-pass filters APF1 and APF2 included in the channel divider 12 of the amplifier device 1 linearize the nonlinear phase shift characteristics of the non-circular low-pass filter LPF1 or high-pass filter HPF1. In the case of the present embodiment, the all-pass filters APF1 and APF2 linearize the phase shift characteristics of the nonlinear phase with respect to the filters LPF2 and HPF2 of the network circuit of the speaker system 7. Therefore, common description and illustration are omitted.

  That is, the first all-pass filter APF1 that is an FIR filter uses the finite-length impulse response of the all-band pass filter having a phase shift characteristic substantially equal to the phase shift characteristic of the low-pass filter LPF2 of the network circuit of the speaker system 7 in time. Set to have a coefficient that is inverted. The second all-pass filter APF2, which is an FIR filter, outputs the finite-length impulse response of the all-band filter having a phase shift characteristic substantially equal to the phase shift characteristic of the high-pass filter HPF2 of the network circuit of the speaker system 7 over time. Set to have a coefficient that is inverted.

  The crossover frequency and order of the network circuit of the speaker system 7 can be easily known from the circuit configuration. For example, when the crossover frequency of the network circuit of the speaker system 7 and the crossover frequency of the channel divider 12 are set to be approximately equal, the network circuit of the speaker system 7 is ± 24 dB / Oct. In this case, the all-pass filters APF1 and APF2 have a phase characteristic such that the phase shift characteristic substantially equal to the phase shift characteristic of the fourth order cyclic filter is time-reversed. That's fine. Even if the crossover frequencies of the low-pass filter LPF1 and the high-pass filter HPF1 set by the channel divider 12 are slightly different from the crossover frequency of the actual speaker system 7, the order of the filters of the network circuit is the same. If there is, the phase can be linearized so that the normalized phase characteristic converges to approximately 0 degrees even if the frequency changes.

  In the above two embodiments, the all-pass filters APF1 and APF2 included in the channel divider 12 of the amplifier device 1 are the acyclic low-pass filter LPF1 or the high-pass filter HPF1, or the filter of the network circuit of the speaker system 7. In this example, the all-pass filters APF1 and APF2 are all-pass filters APF1 and APF2 included in the channel divider 12; Regarding the synthesis characteristic of the network circuit of the speaker system 7 with the filters LPF2 and HPF2, the phase shift characteristic of the non-linear phase is linearized. Therefore, common description and illustration are omitted.

  That is, the first all-pass filter APF1 which is an FIR filter has a phase shift characteristic substantially equal to the phase shift characteristic of the product of the low-pass filter LPF1 of the channel divider 12 and the low-pass filter LPF2 of the network circuit of the speaker system 7. The finite-length impulse response of the all-band pass filter is set to have a coefficient obtained by inverting the time axis. The second all-band pass filter APF2 which is an FIR filter has a phase shift characteristic substantially equal to the phase shift characteristic of the product of the high pass filter HPF1 of the channel divider 12 and the high pass filter HPF2 of the network circuit of the speaker system 7. The finite-length impulse response of the all-band pass filter is set to have a coefficient obtained by inverting the time axis.

  For example, if the low-pass filter LPF1 and the high-pass filter HPF1 of the channel divider 12 are configured with a fourth-order IIR filter, and the network circuit of the speaker system 7 has a second-order filter configuration, the all-pass filter APF1 and APF2 only need to have a phase characteristic such that the phase shift characteristic substantially equal to the phase shift characteristic of the sixth-order cyclic filter is time-reversed. Of course, the all-pass filters APF1 and APF2 are for all-pass filters configured by integrating all-pass filters corresponding to the channel divider 12 and the network circuit of the speaker system 7, respectively, and have a phase substantially equal to this phase shift characteristic. What is necessary is just to make it have the phase characteristic which time-reversed the shift characteristic. In the entire audio reproduction system including the amplifier device 1 and the speaker system 7 of the present embodiment, the phase delay characteristic and the group delay characteristic are corrected to a phase shift so as to be linearly phased, so that the waveform of the output signal is distorted. Can be prevented, and good audio reproduction is possible.

  In addition, the objects for which the all-pass filters APF1 and APF2 of the channel divider 12 are to be linearly phased are not limited to the configurations described and illustrated in the above embodiments. That is, if the woofer WO and the tweeter TW of the speaker system 7 include a phase shift characteristic of a non-linear phase, it may be converted into a linear phase including this. In the audio reproduction system including the amplifier device 1 and the speaker system 7 of the above embodiment, the phase shift characteristic can be made substantially linear phase, so that the user can easily overlap the reproduction sounds from the woofer and the tweeter near the crossover frequency. In other words, the playback sound quality of the multi-way speaker system can be changed.

  The channel divider of the present invention can be applied not only to a stereo apparatus that reproduces a stereo audio signal, but also to an audio reproduction system including a multi-channel surround sound reproduction apparatus.

DESCRIPTION OF SYMBOLS 1 Amplifier apparatus 2 D / A converter 3 Amplifier circuit 4 CPU
5 Operation unit 6 Display circuit 7 Speaker system 10 DSP
DESCRIPTION OF SYMBOLS 11 Decoder 12 Channel divider 13 Low-pass filter part 14 High-pass filter part 15 1st output adjustment circuit 16 2nd output adjustment circuit

Claims (5)

The input audio signal is band-divided into at least a first output signal on the low-frequency range side and a second output signal on the high-frequency range side relative to the first output signal, and is divided into the first output terminal and the second output terminal, respectively. A channel divider including a low-pass filter unit and a high-pass filter unit for outputting,
The low-pass filter unit has a coefficient obtained by inverting the time axis of a finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to a phase shift characteristic of a low-pass filter having a predetermined low-pass characteristic. Including a first all-band pass filter that is an FIR filter;
The high-pass filter unit has a coefficient obtained by inverting the time axis of a finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to a phase shift characteristic of a high-pass filter having a predetermined high-pass characteristic. Including a second all-pass filter that is a FIR filter;
Channel divider. The low pass filter unit and the high pass filter unit of the channel divider are connected in series to the first low pass filter and the second all band pass filter, respectively, connected in series to the first all band pass filter. A first high pass filter,
The channel divider according to claim 1. A level adjustment circuit for adjusting a level of the first output signal or the second output signal; a phase inversion circuit for performing phase inversion of the first output signal or the second output signal; and the first output signal or the second output signal. A delay circuit for adjusting a delay time of the two output signals;
The channel divider according to claim 2.   The channel divider according to any one of claims 1 to 3, an amplifier including an amplifier circuit corresponding to the first output terminal and the second output terminal of the channel divider, and a second low-pass signal corresponding to at least a woofer A sound reproduction system including a network circuit including a second high-pass filter corresponding to a filter and a tweeter, and a speaker system capable of bi-wiring connection with the amplifier. The first all-band pass filter includes a phase shift characteristic of the first low-pass filter, or a phase shift characteristic of the second low-pass filter, or the first low-pass filter and the second low-pass filter. A FIR filter having a coefficient obtained by inverting the time axis of a finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to any of the phase shift characteristics of the product of the pass filter,
The second all-band pass filter includes a phase shift characteristic of the first high-pass filter, or a phase shift characteristic of the second high-pass filter, or the first high-pass filter and the second high-pass filter. A FIR filter having a coefficient obtained by inverting the time axis of a finite-length impulse response of an all-band pass filter having a phase shift characteristic substantially equal to any of the phase shift characteristics of the product of the pass filter,
The audio reproduction system according to claim 4.

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