JP6102360B2 - Channel divider and audio playback system including the same - Google Patents

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, an output signal to any speaker unit corresponding to a speaker system of 3 ways or more. The present invention relates to a channel divider that can appropriately change the reproduction sound quality of a multi-way speaker system without changing the amplitude frequency characteristics even when the phase is inverted.

  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).

  When the multi-way speaker system includes a woofer for low-frequency reproduction and a tweeter for high-frequency reproduction, and a squawker for mid-range reproduction (sometimes called a mid-range speaker or sometimes a full-range speaker). The channel divider needs to be able to set a BPF (band pass filter). In order to set the BPF, a first crossover frequency that defines the band division between the woofer and the squawker and a second crossover frequency that defines the band division between the squawker and the tweeter are determined. The BPF may be configured by deriving from the first crossover frequency and the second crossover frequency. However, the BPF is an HPF that sets the low frequency side crossover frequency and the low frequency side crossover frequency. An LPF for setting the over frequency may be connected in series. In the case of a 3 way or more multi-way speaker system, the output signal to each speaker unit is not phase-inverted, or the setting of each filter characteristic is complicated, and there are many combinations when the phase is inverted. Therefore, even if a smooth amplitude frequency characteristic is obtained at either the first crossover frequency or the second crossover frequency, a dip may occur at the other frequency and the amplitude frequency characteristic may change. There is a problem.

  In conventional channel dividers, the LPF on the low-frequency side, the BPF on the middle-frequency range side, and the HPF on the high-frequency range can be selected from several standard filter characteristics. A recursive filter (infinite length impulse response filter, IIR filter) 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 JP-A-6-97777 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 to provide a channel divider and an acoustic reproduction system for use in reproducing an audio signal by a multi-way speaker system. Corresponding to the above speaker system, the amplitude frequency characteristic does not change even if the phase of the output signal to any speaker unit is reversed, and the phase shift characteristic of the filter of the channel divider and the network circuit included in the speaker system An object of the present invention is to provide a channel divider and a sound reproduction system capable of appropriately changing the reproduction sound quality of a multi-way speaker system by converting the phase shift characteristic into a substantially linear phase.

  The channel divider of the present invention includes a low-pass filter unit that divides an input audio signal into a first output signal on the low frequency side and outputs the first output signal to a first output terminal, and an audio signal higher than the first output signal. A high-pass filter section that divides a band into second output signals on the sound range side and outputs the second output signal to the second output terminal; and a sound signal that is on the high sound range side of the first output signal and on the low sound range side of the second output signal A band-pass filter unit that divides a band into a third output signal and outputs the band-pass filter unit to a third output terminal, wherein the low-pass filter unit includes a first low-pass filter characteristic and a band-pass filter unit. A first high-pass filter having a filter characteristic including a product of a second low-pass filter characteristic that defines a low-pass characteristic, wherein the high-pass filter part defines the high-pass characteristic of the band-pass filter part Characteristics and second high-pass filter The bandpass filter unit includes at least the product of the first high-pass filter characteristic and the second low-pass filter characteristic, and the first low-pass filter characteristic and the second filter characteristic. The filter characteristic includes the sum of the product of the high-pass filter characteristic and the sum of the filter characteristic of the low-pass filter part, the filter characteristic of the high-pass filter part, and the filter characteristic of the band-pass filter part. Is substantially equal to the characteristics of the all-band pass filter, is the sum characteristic of the first low-pass filter characteristic and the first high-pass filter characteristic, and the second low-pass filter characteristic and the second high-pass filter characteristic. Is equal to the product of

  Preferably, in the channel divider of the present invention, the band-pass filter unit is composed of a plurality of N band filters for outputting a plurality of N (N: an integer of 2 or more) third output signals, and each of the plurality of band filters is provided. A filter including at least a product of a high-pass filter and a low-pass filter, a product of a low-pass filter and a low-pass filter, and a product of a high-pass filter and a high-pass filter The low-pass filter unit has a filter characteristic including a product of (N + 1) low-pass filter characteristics including the first low-pass filter characteristic and the second low-pass filter characteristic; The pass-pass filter unit is configured to have a filter characteristic including a product of (N + 1) high-pass filter characteristics including the first high-pass filter characteristic and the second high-pass filter characteristic.

  Preferably, in the channel divider according to the present invention, the first low-pass filter characteristic and the first high-pass filter characteristic define a band division between the first output signal and the third output signal, and the first crossover frequency. And the second low-pass filter characteristic and the second high-pass filter characteristic define the second crossover frequency by defining a band division between the third output signal and the second output signal.

  Preferably, in the channel divider of the present invention, the first low-pass filter characteristic, the first high-pass filter characteristic, the second low-pass filter characteristic, and the second high-pass filter characteristic each have an odd order. Amplitude frequency characteristics of the sum signal that is the sum of the first output signal, the second output signal, and the third output signal, and the first output signal, the second output signal, and the third output signal that match the filter characteristics of the Butterworth filter Both of the amplitude frequency characteristics of the phase inversion sum signal, which is the sum of the signal obtained by phase inversion of any one of the above and the other two signals that are not phase-inverted, coincide with the amplitude frequency characteristics of the audio signal.

  Preferably, the channel divider of the present invention is 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 sum signal or a phase inversion sum signal with respect to an audio signal. And an all-band pass filter unit that is an FIR filter, and an audio signal is input to the all-band pass filter unit, and an output signal from the all-band pass filter unit is replaced with the low-pass filter unit instead of the audio signal, respectively. The high-pass filter unit and the band-pass filter unit are input.

  Preferably, the channel divider of the present invention includes a level adjustment circuit for adjusting the level of the first output signal, the second output signal, or the third output signal, and the first output signal, the second output signal, or the third output signal. And a delay circuit that adjusts the delay time of the first output signal, the second output signal, or the third output signal.

  In addition, the sound reproduction system of the present invention corresponds to the above-described channel divider, an amplifier including an amplifier circuit corresponding to the first output terminal, the second output terminal, and the third output terminal of the channel divider, and at least the first output signal. And a speaker system including a tweeter corresponding to the second output signal, a tweeter corresponding to the third output signal, a squawker or a woofer, and capable of bi-wiring connection with the amplifier.

  The operation of the present invention will be described below.

  In the channel divider of the present invention, the input audio signal is divided into at least a first output signal on the low frequency side, a second output signal on the high frequency side of the first output signal, and a high frequency side of the first output signal. And band-dividing into a third output signal that is lower than the second output signal and outputting the result to the first output terminal, the second output terminal, and the third output terminal, respectively. The channel divider includes an amplifier including an amplifier circuit corresponding to each output terminal, a woofer or subwoofer corresponding to at least the first output signal, a tweeter corresponding to the second output signal, and a tweeter corresponding to the third output signal. Alternatively, a sound reproduction system including at least a squawker or a woofer and a speaker system capable of bi-wiring connection with an amplifier is configured. Note that the 3-way multi-way speaker system includes a case where a sub-woofer that reproduces the low-frequency side is added to a 2-way multi-way speaker system including a woofer and a tweeter. Therefore, the user can adjust the channel divider to change the frequency band and the reproduction level of each speaker unit that are reproduced in an overlapping manner, so that there is an advantage that the reproduction sound quality of the speaker system 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 of the present invention includes a low-pass filter unit that divides an input audio signal into a first output signal on the low frequency side and outputs the first output signal to a first output terminal, and an audio signal higher than the first output signal. A high-pass filter section that divides a band into second output signals on the sound range side and outputs the second output signal to the second output terminal; and a sound signal that is on the high sound range side of the first output signal and on the low sound range side of the second output signal A band-pass filter unit that divides the band into third output signals and outputs the third output signals to the third output terminal. The low-pass filter unit has a filter characteristic including a product of the first low-pass filter characteristic and the second low-pass filter characteristic that defines the low-pass characteristic of the band-pass filter unit, and the high-pass filter part Has a filter characteristic including a product of a first high-pass filter characteristic and a second high-pass filter characteristic that define the high-pass characteristic of the band-pass filter part, and the band-pass filter part has at least a first high-pass characteristic. It has a filter characteristic including the sum of the product of the band-pass filter characteristic and the second low-pass filter characteristic and the product of the first low-pass filter characteristic and the second high-pass filter characteristic.

  Here, the first low-pass filter characteristic of the low-pass filter unit and the first high-pass filter characteristic of the band-pass filter unit determine the band division between the first output signal and the third output signal, and the first cross Specifies the over frequency. The sum of the filter characteristics of the low-pass filter section, the filter characteristics of the high-pass filter section, and the filter characteristics of the band-pass filter section is substantially equal to the characteristics of the all-band filter, and the first low-pass filter section It is equal to the product of the sum characteristic of the pass filter characteristic and the first high-pass filter characteristic and the sum characteristic of the second low-pass filter characteristic and the second high-pass filter characteristic. As a result, when the channel divider of the present invention is designed for a low-pass filter unit, a high-pass filter unit and a band-pass filter unit so as to be suitable for a 3-way multi-way speaker system, the amplitude frequency characteristic does not change. There is no peak or dip near the crossover frequency.

  The third output signal that is the output of the band-pass filter unit may be further divided into a plurality of N (N: an integer of 2 or more). That is, in the channel divider, when the band-pass filter unit includes a plurality of N band filters that output a plurality of N third output signals, each of the plurality of band filters includes at least a high-pass filter and a low-pass filter. Low-pass filter with filter characteristics including the sum of the product of the band-pass filter, the product of the low-pass filter and the low-pass filter, and the product of the high-pass filter and the high-pass filter The filter unit has a filter characteristic including a product of (N + 1) low-pass filter characteristics including the first low-pass filter characteristic and the second low-pass filter characteristic, and the high-pass filter part is the first The filter is configured to have a filter characteristic including a product of (N + 1) high-pass filter characteristics including the high-pass filter characteristic and the second high-pass filter characteristic. Therefore, it is possible to deal with a multi-way speaker system of 4 Way (when N = 2) or more, and similarly, no peak or dip occurs near the crossover frequency without changing the amplitude frequency characteristic.

  Further, the first low-pass filter characteristic, the first high-pass filter characteristic, the second low-pass filter characteristic, and the second high-pass filter characteristic are matched with the filter characteristics of the odd-order Butterworth filter, respectively. In the case where it is defined, since the first low-pass filter characteristic defining the first crossover frequency and the first high-pass filter characteristic are considered, the phase is shifted by 90 ° at the first crossover frequency. , Even if one of the phases is inverted, the sum frequency characteristic thereof does not change. The same applies to the second low-pass filter characteristic and the second high-pass filter characteristic that define the second crossover frequency. Therefore, in the channel divider of the present invention, the amplitude frequency characteristic of the sum signal, which is the sum of the first output signal, the second output signal, and the third output signal, the first output signal, the second output signal, and the third output signal. Both of the amplitude frequency characteristics of the phase inversion sum signal, which is the sum of the signal obtained by phase inversion of any one of the above and the other two signals that are not phase-inverted, coincide with the amplitude frequency characteristics of the audio signal. In other words, the channel divider of the present invention can peak or dip near the crossover frequency without changing the amplitude frequency characteristic even if the phase of the output signal to any speaker unit of the 3-way multiway speaker system is inverted. There is no end.

  The channel divider of the present invention includes a level adjustment circuit for adjusting the level of the first output signal, the second output signal, or the third output signal, and the phase inversion of the first output signal, the second output signal, or the third output signal. And a delay circuit that adjusts a delay time of the first output signal, the second output signal, or the third output signal. The range to adjust the playback sound quality will be expanded, and it will be compatible with various multi-way speaker systems.

  The channel divider of the present invention is an 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 phase shift characteristic of a sum signal or phase inversion sum signal with respect to an audio signal. A certain all-band pass filter unit may be further included. In this channel divider, an audio signal is input to an all-band pass filter unit, and an output signal from the all-band pass filter unit is replaced with an audio signal, respectively, a low-pass filter unit, a high-pass filter unit, and a band-pass filter. Input to the filter section. This FIR filter is an all-band pass filter (all-pass filter, APF) and has a constant and flat gain characteristic regardless of frequency. For example, a low-pass filter unit, a high-pass filter unit, a band-pass filter When a phase shift accompanied by a phase delay in a cyclic filter that constitutes each of the first and second components is targeted, an FIR filter coefficient obtained by inverting the time axis of a finite impulse response includes a predetermined phase advance. Realize phase characteristics.

  As a result, in the channel divider or audio reproduction system of the present invention, the phase shift characteristic is linearly phase-related with respect to the filters constituting the low pass filter unit, the high pass filter unit, and the band pass filter unit of the channel divider. Can be In audio playback systems including channel dividers and speaker systems, even if high-order nonlinear phase filters with steep gain characteristics are used, the phase delay characteristics and group delay characteristics are corrected by correcting phase shifts that vary greatly depending on the frequency. Since it is phased, it is possible to prevent distortion of the waveform of the output signal. Since the amplitude frequency characteristic of the sum signal, which is the sum of the first output signal, the second output signal, and the third output signal, matches the amplitude frequency characteristic of the input audio signal, the overall characteristic of the channel divider is the entire band. This is because it can be regarded as a pass filter. Therefore, if the all-band pass filter unit can define the phase shift characteristic of the sum signal or the phase inversion sum signal with respect to the audio signal, the phase shift characteristic can be linearized. Therefore, by obtaining the impulse response of this phase shift characteristic and obtaining a finite impulse response of a predetermined length, the FIR filter coefficient of the all-band pass filter that is time-axis inverted necessary for linear phase conversion is obtained. Can do.

  The channel divider and sound reproduction system of the present invention corresponds to a speaker system of 3 ways or more, and the phase of the channel divider filter does not change the amplitude frequency characteristic even if the phase of the output signal to any speaker unit is inverted. The reproduction characteristic of the multi-way speaker system can be appropriately changed by making the shift characteristic and the phase shift characteristic of the network circuit included in the speaker system into a substantially linear phase.

It is a figure explaining the sound reproduction system containing the amplifier apparatus 1 by preferable embodiment of this invention. (Example 1) 4 is a graph for explaining frequency characteristics (gain characteristics, group delay characteristics) of a low-pass filter LPF, a band-pass filter BPF, and a high-pass filter HPF of the channel divider 12 of the amplifier device 1. (Example 1) The sum signal obtained by adding the outputs of the low-pass filter LPF, the band-pass filter BPF and the high-pass filter HPF of the channel divider 12 of the amplifier device 1 or the phase-inverted sum signal obtained by adding a part of the outputs after phase inversion. It is a graph explaining a frequency characteristic (gain characteristic, group delay characteristic). It is a graph explaining the frequency characteristic (gain characteristic, group delay characteristic) at the time of operating the all-pass filter APF which makes a linear phase. (Example 2)

  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 illustrating the frequency characteristics (gain characteristics, group delay characteristics) of the low-pass filter unit 13, the band-pass filter unit 15, and the high-pass filter unit 14 of the channel divider 12 of the amplifier device 1. . 3 shows a sum signal obtained by adding the outputs of the low-pass filter unit 13, the band-pass filter unit 15 and the high-pass filter unit 14 of the channel divider 12 of the amplifier device 1, or a phase inversion of a part of the output. 6 is a graph for explaining frequency characteristics (gain characteristics, group delay characteristics) of phase-inverted sum signals added together. 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 3-way bi-wiring SS including a woofer WO, a squawker SQ, and a tweeter TW, 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 3-way bi-wiring SS including a woofer WO, a squawker SQ, and a tweeter TW, and includes a network circuit and an input terminal corresponding to each speaker unit. The low frequency range reproduction woofers WO of the left speaker 7L and the right speaker 7R are connected to the input terminal tL, respectively. Further, the squawker SQ for mid-range reproduction is connected to the input terminal tM. In addition, the tweeter TW for high sound range reproduction is connected to the input terminal tH.

  Since the woofer WO and the squawker SQ and the tweeter TW of the speaker system 7 mainly have predetermined frequency bands capable of reproducing sound, the crossover frequency fc1 between the woofer WO and the squawker SQ is between the squawker SQ and the tweeter TW. Is divided by a channel divider with the crossover frequency fc2 as a boundary. The woofer WO for low frequency reproduction mainly reproduces the frequency band below the crossover frequency fc1, the squawker SQ mainly reproduces the frequency band below the crossover frequency fc1 to fc2, and the tweeter TW represents the crossover frequency. A frequency band of fc2 or higher is mainly reproduced. The speaker system 7 is adjusted using a channel divider so as to realize a relatively flat synthesized sound pressure frequency characteristic.

  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 (DL 1, DL 2, DL 3, DR 1, DR 2, DR 3) for 6 channels of the channel divider 12 to the D / A converter 2. The channel divider 12 includes a low-pass filter unit 13, a band-pass filter unit 15, a high-pass filter unit 14, a first output adjustment circuit 13a, and a third output corresponding to the left signal L and the right signal R, respectively. An adjustment circuit 15a and a second output adjustment circuit 14a are included. The CPU 4 controls the filter settings of the low pass filter unit 13, the band pass filter unit 15 and the high pass filter unit 14 of the channel divider 12 of the DSP 10.

  The low-pass filter unit 13, the band-pass filter unit 15 and the high-pass filter unit 14 of the channel divider 12 of the present embodiment are respectively a low-pass filter LPF or a high-pass filter HPF or a band-pass filter constituted by IIR filters. It is a digital filter configured to include a filter BPF. 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. In addition, the band pass filter unit 15 divides the input audio signal into a third output signal that is higher in the frequency range than the first output signal and lower in the frequency range than the second output signal, and the third output terminal D3. Output to.

  Stereo signals L and R which are output signals of the decoder 11 of the DSP 10 are respectively input to the all-band pass filter unit 16 which is an FIR filter, and the output of the all-band pass filter unit 16 is the low-pass filter unit 13 or The signal is branched and input to the high-pass filter unit 14 or the band-pass filter unit 15. The all-band pass filter unit 16 having a flat amplitude frequency characteristic includes an all-band pass filter APF, and can change the phase characteristic (group delay characteristic) by changing the coefficient of the FIR filter. That is, the all-band pass filter unit 16 has a linear phase characteristic (group delay time is a constant value) or a non-linear phase characteristic (group delay time is not a constant value) like a simple delay element. Can be switched. In the first embodiment, the all-pass filter unit 16 has a simple delay element (coefficient is 1 at an arbitrary tap and coefficient is 0 at all other taps), and linear phase characteristics (group delay time is constant). Value). Therefore, in the present embodiment, the all-band pass filter unit 16 may be omitted.

  The output of the low-pass filter unit 13 is input to the first output adjustment circuit 13a and 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 14 is input to the second output adjustment circuit 14a and output to the output terminals (DL2, DR2) of the DSP 10 as the second audio output signal D2. The output of the band pass filter unit 15 is input to the third output adjustment circuit 15a, and is output to the output terminals (DL3, DR3) of the DSP 10 as the third audio output signal D3. The first output adjustment circuit 13a, the second output adjustment circuit 14a, and the third output adjustment circuit 15a expand the range for adjusting the reproduction sound quality so that the first sound output signal D1 can be applied to a wide range of speaker systems 7. Each of the second audio output signal D2 and the third audio output signal D3 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 shown in FIG. 2A, the frequency characteristics are illustrated in the graph of FIG. 2 (left: normalized amplitude frequency characteristics, right: normalized group delay characteristics). : Set the low-pass filter unit 13, FIG. 2 (b): the band-pass filter unit 15, and FIG. 2 (c): set the high-pass filter unit 14 to divide the input audio signal into bands. Can do. The filter characteristics of the low-pass filter unit 13, the band-pass filter unit 15 and the high-pass filter unit 14 shown in FIG. 2 are the respective output signals (first audio output) when an impulse is input as the input audio signal. Signal D1, second audio output signal D2, and third audio output signal D3). Here, the crossover frequency fc1 between the woofer WO and the squawker SQ is set to 300 Hz, and the crossover frequency fc2 between the squawker SQ and the tweeter TW is set to 1.2 kHz. As described above, the low-pass filter unit 13, the band-pass filter unit 15, and the high-pass filter unit 14 each include a low-pass filter LPF, a high-pass filter HPF, or a band-pass filter BPF configured by IIR filters. Therefore, the group delay characteristic does not become a constant value with respect to the frequency change, but changes so that inflection points appear in the vicinity of the crossover frequencies fc1 and fc2. That is, the low-pass filter unit 13, the band-pass filter unit 15, and the high-pass filter unit 14 are non-linear phase filters, respectively.

The low-pass filter unit 13 includes a low-pass filter LPF having a filter characteristic H _LP (s) expressed by the following equation (1). Note that s means a Laplace operator.

H _LP (s) = G _LP 1 (s) G _LP 2 (s) (1)

That is, the low-pass filter unit 13 has a filter characteristic including a product of the first low-pass filter characteristic G _LP 1 and the second low-pass filter characteristic G _LP 2. The first low-pass filter characteristic G _LP 1 is a fifth-order Butterworth low-pass filter whose cut-off frequency is the crossover frequency fc1, while the second low-pass filter characteristic G _LP 2 is the crossover frequency fc2. Is a 15th-order Butterworth low-pass filter with a cutoff frequency. Therefore, the low-pass filter LPF can be configured as a total 20th-order IIR filter with multiple stages of IIR filters.

The high-pass filter unit 14 includes a high-pass filter HPF having a filter characteristic H _HP (s) expressed by the following equation (2).

H _HP (s) = G _HP 1 (s) G _HP 2 (s) (2)

That is, the high-pass filter unit 14 has a filter characteristic including a product of the first high-pass filter characteristic G _HP 1 and the second high-pass filter characteristic G _HP 2. The first high-pass filter characteristic G _HP 1 is a fifth-order Butterworth high-pass filter whose cut-off frequency is the crossover frequency fc1, while the second high-pass filter characteristic G _HP 2 is a crossover frequency fc2. Is a 15th-order Butterworth high-pass filter with a cutoff frequency. Therefore, the high-pass filter HPF can be configured as a total 20th-order IIR filter with multiple stages of IIR filters.

The band pass filter unit 15 is configured by a band pass filter BPF having a filter characteristic H _BP (s) expressed by the following equation (3).

H _BP (s) = G _HP 1 (s) G _LP 2 (s) + G _LP 1 (s) G _HP 2 (s) (3)

That is, the band-pass filter unit 15 includes the product of the first high-pass filter characteristic G _HP 1 and the second low-pass filter characteristic G _LP 2, and the first low-pass filter characteristic G _LP 1 and the second high-pass filter characteristic G _LP 2. It has a filter characteristic including the sum of the product of the band-pass filter characteristic G _HP 2. As described above, the first high-pass filter characteristic G _HP 1 and the first low-pass filter characteristic G _LP are fifth-order Butterworth filters having the crossover frequency fc1 as a cutoff frequency, while the second low-pass filter characteristic G _LP The filter characteristic G _LP 2 and the second high-pass filter characteristic G _HP 2 are 15th order Butterworth filters having the crossover frequency fc2 as a cutoff frequency. Therefore, the band pass filter BPF can be configured by providing IIR filters in multiple stages, providing two 20th-order IIR filters in parallel, adding their outputs, and outputting a sum signal.

  FIG. 3 shows a sum signal obtained by adding the outputs of the low-pass filter unit 13, the band-pass filter unit 15 and the high-pass filter unit 14 of the channel divider 12 of the amplifier device 1, or a phase of the output of a part of the output. It is a graph explaining the frequency characteristic (gain characteristic, group delay characteristic) of the added phase inversion sum signal. Specifically, FIG. 3A shows a sum signal (LPF + BPF + HPF) obtained by adding the output D1 of the low-pass filter unit 13, the output D3 of the band-pass filter unit 15, and the output D2 of the high-pass filter unit 14. It is. FIG. 3B shows a phase-inverted sum signal obtained by adding the phase-inverted output (−D1) of the low-pass filter unit 13, the output D3 of the band-pass filter unit 15, and the output D2 of the high-pass filter unit 14. This is the case of (−LPF + BPF + HPF). FIG. 3C shows a phase inversion sum obtained by adding the output D1 of the low-pass filter unit 13, the output (−D3) of the phase-inverted band-pass filter unit 15, and the output D2 of the high-pass filter unit 14. This is the case of the signal (LPF−BPF + HPF). FIG. 3D shows a phase inversion sum obtained by adding the output D1 of the low-pass filter unit 13, the output D3 of the band-pass filter unit 15, and the output (−D2) of the phase-inverted high-pass filter unit 14. This is the case of the signal (LPF + BPF-HPF).

As shown in FIG. 3A, in the channel divider 12 of the amplifier device 1 of the present embodiment, the sum of the filter frequency dividing frequency characteristics that can be said to be the overall characteristics of the channel divider 12 becomes flat, and the gain Becomes a constant value regardless of the frequency. That is, the amplitude frequency characteristic of the sum signal, which is the sum of the first output signal D1, the second output signal D2, and the third output signal D3, matches the amplitude frequency characteristic of the audio signal input to the channel divider 12. Become. This means that the filter characteristics H _LP (s) (= Equation (1) = G _LP 1 (s) G _LP 2 (s)) of the corresponding low-pass filter LPF and the filter characteristics of the high-pass filter HPF, respectively. H _HP (s) (= Equation (2) = G _HP 1 (s) G _HP 2 (s)) and the filter characteristic H _BP (s) of the bandpass filter BPF (= Equation (3) = G _HP 1 ( s) G _LP 2 (s) + G _LP 1 (s) G _HP 2 (s)) and the sum (H _LP (s) + H _HP (s) + H _BP (s)) This is equivalent to showing that the characteristics of the all-band pass filter that are constant without being shifted are substantially equal. The sum of the filter characteristic H _LP (s) of the low-pass filter LPF, the filter characteristic H _HP (s) of the high-pass filter HPF, and the filter characteristic H _BP (s) of the band-pass filter BPF is: (G _LP 1 (s) G _LP 2 (s) + G _HP 1 (s) G _HP 2 (s) + G _HP 1 (s) G _LP 2 (s) + G _LP 1 (s) G _HP 2 (s) since it described by the formula of the sum of which is the sum characteristics of the first low-pass filter characteristic _(G LP 1 _(s)) and the first high pass filter characteristic _{(G HP 1 (s))} (G LP 1 (S) + G _HP 1 (s)), and the sum characteristic (G of the second low-pass filter characteristic (G _LP 2 (s)) and the second high-pass filter characteristic (G _HP 2 (s)) _{LP 2 (s) + G HP} 2 (s)), the product _{(G LP 1 (s) +} G HP 1 (s) _{· (G LP 2 (s)} + G HP 2 (s)) be equal in its expansion into equation sum calculated is the arithmetic evident.

This is because the first low-pass filter characteristic G _LP 1 of the low-pass filter unit 13 defining the first crossover frequency fc1 and the first high-pass filter characteristic G _HP 1 of the band-pass filter unit 15 are 5 respectively. are defined to match the characteristics of the following Butterworth filter, further, the band pass filter section 15 which defines the second cross-over frequency fc2 of the second low-pass filter characteristic G _{LP 2} and the high pass filter unit 14 This is because the second high-pass filter characteristics G _HP 2 are defined so as to coincide with the characteristics of the 15th-order Butterworth filter. Therefore, at the output stage of the channel divider 12, the amplitude frequency characteristic does not change, and no peak or dip occurs near the crossover frequencies fc1 and fc2, and the reproduction sound quality of the 3-way speaker system 7 is appropriately changed. can do.

  On the other hand, as shown in FIGS. 3B to 3D, in the channel divider 12 of the amplifier device 1 of the present embodiment, one of the filters to be band-divided is phase-inverted to obtain the other. When the phase is not inverted, the sum amplitude frequency characteristic including the phase inversion of each filter characteristic becomes flat, and the gain becomes a constant value regardless of the frequency. That is, the amplitude of the phase-reversed sum signal, which is the sum of a signal obtained by phase inverting one of the first output signal D1, the second output signal D2, and the third output signal D3 and the other two signals that are not phase-inverted. Both of the frequency characteristics coincide with the amplitude frequency characteristics of the audio signal input to the channel divider 12.

This is because the first low-pass filter characteristic G _LP 1 of the low-pass filter unit 13 defining the first crossover frequency fc1, the first high-pass filter characteristic G _HP 1 of the band-pass filter unit 15, and the second The second low-pass filter characteristic G _LP 2 of the band-pass filter unit 15 that defines the crossover frequency fc2 and the second high-pass filter characteristic G _HP 2 of the high-pass filter unit 14 are respectively odd-order Butterworth filters. This is because the frequency characteristics of the sum do not change even if one of them is phase-inverted because it is defined to match the characteristics.

  Therefore, at the output stage of the channel divider 12, the amplitude frequency characteristic does not change, and no peak or dip occurs near the crossover frequencies fc1 and fc2, and the reproduction sound quality of the 3-way speaker system 7 is appropriately changed. can do. That is, in the audio reproduction system using the amplifier device 1 including the channel divider 12, the output signal to any speaker unit of the 3-way multi-way speaker system 7 is inverted in phase (or any speaker unit's Even if the connection is phase-inverted), there is an advantage that the amplitude frequency characteristic does not change and a peak or dip does not occur near the crossover frequency.

  The channel divider 12 is not limited to the one applied to the 3-way bi-wiring SS including the woofer WO, squawker SQ, and tweeter TW as in the above embodiment. The 3-way multi-way speaker system includes a case where a sub-woofer for reproducing the low frequency range is further added to a 2-way multi-way speaker system including a woofer and a tweeter. In that case, the first output signal D1 divided into the low sound band side is output to the subwoofer, and the second output signal D2 divided into the high sound band side is output to the tweeter of the 2-way multi-way speaker system. The third output signal D3 divided into bands between them may be output to the woofer of the 2-way multi-way speaker system.

  The channel divider 12 is a 4-way or higher multi-way speaker (not shown) including a subwoofer and / or a mid-range (squaker) and / or a super tweeter. A configuration including a divided output may be used. Of course, the channel divider 12 of this embodiment is also effective in the case of a multi-way speaker including a network circuit. Similarly, the channel divider 12 is effective when the speaker system 7 includes a full range speaker. When a substantial crossover frequency fc with another speaker is set in response to a level drop caused by the limit of the reproduction sound pressure frequency characteristics of a full range speaker or a speaker such as a woofer, squawker, and tweeter. In addition, a low-pass filter unit, a band-pass filter unit, or a high-pass filter unit of the channel divider 12 can be set in accordance with this.

  When the multi-way speaker system of 4 Way or more is supported, the channel divider 12 causes the band pass filter unit 15 to further divide the third output signal D3 into a plurality of N (N: integer of 2 or more) (not shown). ) A plurality of N band division filter units may be configured. In this case, the low-pass filter unit 13 that outputs the first output signal D1 is a product of (N + 1) low-pass filter characteristics including the first low-pass filter characteristic and the second low-pass filter characteristic. Is set to have a filter characteristic including The high pass filter unit 14 that outputs the second output signal D2 includes a product of (N + 1) high pass filter characteristics including the first high pass filter characteristic and the second high pass filter characteristic. It is set to have characteristics. Further, the bandpass filter unit 15 that outputs the third output signal D3 includes a plurality of N bandpass filters, at least a product of a high-pass filter and a low-pass filter, and a low-pass filter and a low-pass filter. It is set to have a filter characteristic including the product of the filter and the sum of the product of the high-pass filter and the high-pass filter. In the channel divider of the present invention, the range for adjusting the reproduction sound quality is widened, and it becomes possible to cope with various multi-way speaker systems.

  In the above embodiment, the all-pass filter unit 16 included in the channel divider 12 of the amplifier device 1 is a case where the all-band pass filter unit 16 is a simple delay element and has a linear phase characteristic (group delay time is a constant value). However, in the second embodiment, the coefficient of the FIR filter is changed to set the phase characteristic (group delay characteristic) to a non-linear phase characteristic, and the low-pass filter unit 13 included in the channel divider 12 and the high-pass filter unit 14 and the band-pass filter unit 15 are linearly phased (group delay characteristics are made constant). Therefore, the description and illustration common to the above embodiment are omitted.

  As shown in FIG. 2, the channel divider 12 is configured such that the CPU 4 converts the low-pass filter unit 13, the high-pass filter unit 14, and the band-pass filter unit 15 into a high-order filter having a steep gain characteristic. It can be set to use a non-linear phase IIR filter. The phase characteristic of the high-order nonlinear phase IIR filter has a large phase rotation, and the amount of change with respect to the frequency also increases as the group delay characteristic. Therefore, when the IIR filter having the phase shift characteristic of the non-linear phase is set to the low pass filter unit 13, the high pass filter unit 14, and the band pass filter unit 15, the all pass filter unit 16 is provided. Therefore, the phase shift characteristic can be converted to a linear phase, and the waveform distortion of the input signal can be prevented from increasing.

  FIG. 4 is a graph for explaining the frequency characteristics (gain characteristics, group delay characteristics) when the APF of the all-pass filter unit 16 for linear phase operation is operated. That is, the sum signal (LPF + BPF + HPF) is obtained by adding the output D1 of the low-pass filter unit 13, the output D3 of the band-pass filter unit 15, and the output D2 of the high-pass filter unit 14. As shown in FIG. 4, in the channel divider 12 of the amplifier device 1 of this embodiment, the amplitude frequency characteristic of the sum of the respective filter characteristics to be divided into bands, which can be said to be the overall characteristic of the channel divider 12, becomes flat, and the gain becomes the frequency. Regardless, it becomes a constant value. That is, the amplitude frequency characteristic of the sum signal, which is the sum of the first output signal D1, the second output signal D2, and the third output signal D3, matches the amplitude frequency characteristic of the audio signal input to the channel divider 12. Become. Further, in the case of the present embodiment, since the APF of the all-pass filter unit 16 is operated, the normalized group delay characteristic is a constant value regardless of the frequency, and linear phase conversion is realized. ing.

  That is, the all-pass filter APF of the all-pass filter unit 16 sets the phase characteristic corresponding to the time characteristic when the sum signal of the respective filter characteristics to be band-divided has a group delay characteristic as shown in FIG. It is set so as to have substantially the same phase characteristics as when inverted by the axis. The coefficient of the FIR filter of the all-pass filter APF of the all-pass filter unit 16 obtains the impulse response of the all-band pass filter that is substantially equal to the phase characteristic of the signal of the sum of the filter characteristics to be divided into bands, and limits them to a finite length. Then, these can be obtained by inverting these on the time axis. 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. The length of the impulse response of the all-pass filter APF of the all-pass filter unit 16 and the tap length of the FIR filter are within a range in which the impulse response of the target filter sufficiently converges according to the cutoff frequency and the order of the recursive filter. It only needs to be long and can be set arbitrarily. 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.

  As a result, in the output stage of the channel divider 12, the addition characteristics of the first output signal D1, the second output signal D2, and the third output signal D3 can be flattened, and the crossover is performed without changing the amplitude frequency characteristics. A peak or dip does not occur in the vicinity of the frequencies fc1 and fc2, and the reproduction sound quality of the 3-way speaker system 7 can be appropriately changed. Further, even if a high-order nonlinear phase filter having a steep gain characteristic is used for the low-pass filter unit 13, the high-pass filter unit 14, and the band-pass filter unit 15 of the channel divider 12, the phase delay characteristic and the group Since the phase shift is corrected to correct the phase shift whose delay characteristic greatly varies depending on the frequency, the waveform of the output signal can be prevented 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 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 13a 1st output adjustment circuit 14 High pass filter part 14a 2nd output adjustment circuit 15 Band pass filter part 15a 3rd output adjustment circuit 16 All band pass filter part

Claims (7)

A low-pass filter unit that divides the input audio signal into a first output signal on the low-frequency range and outputs the first output signal to the first output terminal; and a second high-frequency-side filter for the audio signal. A high-pass filter section that divides the output signal into a band and outputs the output signal to the second output terminal; and a third high-frequency filter side of the audio signal that is higher than the first output signal and lower than the second output signal. A band divider including a band-pass filter unit that divides the output signal into a band and outputs it to the third output terminal,
The low-pass filter unit has a filter characteristic including a product of a first low-pass filter characteristic and a second low-pass filter characteristic defining the low-pass characteristic of the band-pass filter unit;
The high-pass filter unit has a filter characteristic including a product of a first high-pass filter characteristic and a second high-pass filter characteristic that define the high-pass characteristic of the band-pass filter part;
The band-pass filter unit includes at least a product of the first high-pass filter characteristic and the second low-pass filter characteristic, and the first low-pass filter characteristic and the second high-pass filter characteristic. Has a filter characteristic including the sum of products,
The sum of the filter characteristics of the low-pass filter section, the filter characteristics of the high-pass filter section, and the filter characteristics of the band-pass filter section is a constant value regardless of the frequency of the amplitude frequency characteristics. substantially equal to the characteristic of the all-pass filter becomes, and the sum characteristics of the first low-pass filter characteristic and the first high-pass filter characteristics, and, second low-pass filter characteristic and the second Equal to the product of the sum characteristic with the high-pass filter characteristic,
Channel divider. The band pass filter unit includes a plurality of N band filters that output a plurality of N (N: integer greater than or equal to 2) third output signals, and each of the plurality of band filters includes at least a high pass filter. Having a filter characteristic including the sum of the product of the low-pass filter, the product of the low-pass filter and the low-pass filter, and the product of the high-pass filter and the high-pass filter,
The low-pass filter unit has a filter characteristic including a product of (N + 1) low-pass filter characteristics including the first low-pass filter characteristic and the second low-pass filter characteristic;
The high-pass filter unit is configured to have a filter characteristic including a product of (N + 1) high-pass filter characteristics including the first high-pass filter characteristic and the second high-pass filter characteristic. ,
The channel divider according to claim 1.
Channel divider. The first low-pass filter characteristic and the first high-pass filter characteristic define a first crossover frequency by defining a band division between the first output signal and the third output signal;
The second low-pass filter characteristic and the second high-pass filter characteristic define a second crossover frequency by defining a band division between the third output signal and the second output signal;
The channel divider according to claim 1 or 2. The first low-pass filter characteristic, the first high-pass filter characteristic, the second low-pass filter characteristic, and the second high-pass filter characteristic respectively match the filter characteristics of the odd-order Butterworth filter. ,
An amplitude frequency characteristic of a sum signal that is a sum of the first output signal, the second output signal, and the third output signal, and any of the first output signal, the second output signal, and the third output signal The amplitude frequency characteristic of the phase inversion sum signal, which is the sum of the signal obtained by inverting one of the two signals and the other two signals that are not phase-inverted, coincides with the amplitude frequency characteristic of the audio signal.
The channel divider according to any one of claims 1 to 3. All band pass which is a FIR filter having a coefficient obtained by inverting the time axis of a finite impulse response of an all band pass filter having a phase shift characteristic substantially equal to the phase shift characteristic of the sum signal or the phase inversion sum signal with respect to the audio signal. A filter unit;
The audio signal is input to the all-band pass filter unit, and the output signal from the all-band pass filter unit is replaced by the low-pass filter unit, the high-pass filter unit, Input to the band pass filter section,
The channel divider according to any one of claims 1 to 4. A level adjusting circuit for adjusting a level of the first output signal or the second output signal or the third output signal; and a phase for performing phase inversion of the first output signal, the second output signal or the third output signal. An inverting circuit; and a delay circuit that adjusts a delay time of the first output signal, the second output signal, or the third output signal.
The channel divider according to any one of claims 1 to 5.   The channel divider according to any one of claims 1 to 6, an amplifier including an amplifier circuit corresponding to the first output terminal, the second output terminal, and the third output terminal of the channel divider, and at least the first A speaker system including a woofer or subwoofer corresponding to an output signal, a tweeter corresponding to the second output signal, and a tweeter, squawker or woofer corresponding to the third output signal, and capable of bi-wiring connection with the amplifier. And an audio playback system including: