JPS63267007A - Octave multiplex filter - Google Patents

Abstract

PURPOSE:To designate the characteristic at a logarithmically uniform interval over a wide frequency band by specifying a delay time per one stage of a unit delay element of a filter in each filter group every time the filter number is decremented by one. CONSTITUTION:A delay time nT per one stage of unit delay element of digital filters LPF3-a, LPF3-b and BPF4 having the maximum number among numbers given to each filter of each digital filter group in the order of connection is set to a time being a sampling time interval T or over for an input signal. Moreover, the delay time of one stage of the unit delay element of the filter is decreased at a multiple of AB (A>1, B>0) for every decrement of each filter number and the delay time per one stage of unit delay element of a digital filter having a low pass characteristic of a number is selected as an integral number of multiple of the delay time per one stage of unit delay element of the digital filter having the band pass characteristic of the same number. Thus, the characteristic is designated at a nearly logarithmically uniform interval at the frequency region.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of an octave multiplex filter that is formed by combining a plurality of digital filter groups with band-pass characteristics and low-pass characteristics.

[Summary of the Invention] Each filter output of a first digital filter group having a low-pass characteristic connected in series is given to each filter of a digital filter group having a band-pass characteristic connected in parallel, The output of each of the above-mentioned amplitude and phase control circuits is added to each of the second digital filters having low-pass characteristics connected in series through the amplitude and phase control circuits, and taken out from the final stage. An octave multiple filter configured so that each phase is independently and adaptively controlled allows characteristics to be specified at almost logarithmically uniform intervals over a wide band in one frequency domain.The input data can also be specified by sequentially increasing the sampling time interval. This also makes it possible to reduce the number of arithmetic circuits.

[Prior art] Conventional digital filters operate at a predetermined clock frequency in order to process discrete sample values at equal time intervals, so characteristics in the frequency domain are specified at equal frequency intervals. I was worried.

For this reason, conventional filters that specify characteristics at logarithmic intervals over a wide band have only been realized by combining a plurality of analog filters.

[Problems to be Solved by the Invention] As mentioned above, the former digital filter uses a method of specifying characteristics at equal frequency intervals, so the resolution in the low range is too coarse, while the resolution in the high range is too fine than necessary. , it is extremely difficult to widen the bandwidth.

Generally, the characteristics of audio equipment are evaluated or specified in the frequency domain using logarithmic intervals. Therefore, when using conventional digital filters, such as FIR type (finite impulse response) filters, the characteristics are accurate in the low frequency range for the reasons mentioned above. could not be specified, and in the high range, the characteristics had to be specified with higher precision than necessary, which was extremely inefficient in terms of circuit implementation.

In particular, when attempting to realize something with complex frequency characteristics such as a graphic equalizer using a conventional FIR type filter, such restrictions can be avoided; in fact, a graphic equalizer using an FIR type filter has not yet been put to practical use. .

On the other hand, the latter filter uses an analog active filter addition or multiplication method.

There was interference between filters, and it was difficult to specify phase and amplitude independently. In particular, it has been extremely difficult to specify the phase characteristics arbitrarily.

SUMMARY OF THE INVENTION In order to solve the problems of the prior art, it is an object of the present invention to provide an octave multiple filter that can specify characteristics at logarithmically uniform intervals over a wide band in one frequency domain.

[Means for Solving the Problems] In order to achieve the above object, the present invention operates with a clock set at a time interval greater than or equal to the sampling time interval of the input signal, with respect to the sampling time interval of the input signal. The first one has a plurality of low-pass characteristics that
and a second digital filter group and a digital filter group having band-pass characteristics, the first and second digital filter groups having low-pass characteristics are each connected in series, and the digital filter groups having band-pass characteristics are each connected in parallel. The outputs of the first digital filters with low-pass characteristics are connected to each other, and the outputs of the first digital filters with low-pass characteristics are applied to the second digital filters with low-pass characteristics through the amplitude and phase control circuit. The delay time per stage of the unit delay element of the digital filter with the largest number among the numbers assigned to each filter in each filter group in the order of connection. is set to be greater than or equal to the sampling time interval of the input signal, and each time the filter number decreases by one in each filter group, the delay time per unit delay element stage of the filter increases AB (A) 1, B>0) times. and the delay time per stage of a unit delay element of a digital filter with a low-pass characteristic having a certain number is configured to operate at an integral multiple of the delay time per stage of a unit delay element of a digital filter having a band-pass characteristic having the same number. It is characterized by

[Function] In the octave multiplex filter of the present invention having the above-described configuration, each output signal from the first digital filter group having a low-pass characteristic passes through each filter in series, so that the band is sequentially narrowed and each The low-pass output signal of is multiplied by the band-pass characteristic and given to the amplitude and phase control circuit to adaptively control its amplitude and phase, and is added to each of the second digital filter group having the low-pass characteristic to cut noise. Ru.

[Examples] The present invention will be described below with reference to examples shown in the drawings.
FIG. 1 shows an embodiment of an octave multiplex filter (4 octaves) according to the present invention. In the figure, IN is an input terminal for an analog signal such as an audio signal, OUT is an output terminal, and A/D is an A-D Converter, D/A is DA converter, L
PF is a normal analog type low pass filter, LP
FI-a ” LPFI-a and LPFI-b
-LPF3-b is a group of first and second digital filters having low-pass characteristics using, for example, an FIR type filter; BPFI to BPF4 are digital filter groups having band-pass characteristics using similar filters; AD
Dl to ADD3 are adder circuits, C0EFFI to C0EF
F4 is an amplitude phase control circuit, and C0NT is an adaptive control circuit.

The adaptive control circuit C0NT is configured as shown in FIG. 2, for example. In the figure, DET is a band component detector, PROC is a microprocessor, and COM is a control signal generation circuit.

The FIR type filter consists of a delay element SR, a coefficient multiplier ML, and an adder AD, as shown in FIG. The coefficients a-, .about.a of the coefficient multiplier ML are set so that - Figure 3 (a) is the desired frequency characteristic (low-pass characteristic)
The figure (b) shows the time domain function obtained by inverse Fourier transform of the first and second digital filter groups LPFI-aNLPF3- having low-pass characteristics.
a, LPFI-b"LPF3-b are each connected in series and are a digital filter group B having bandpass characteristics.
PFI-BPF4 are each connected in parallel, and a first digital filter LPFI-a with low-pass characteristics
Each output of the LPF3-a is given to each of the digital filter groups BPFI to BPF4 with bandpass characteristics, and each output is applied to the amplitude phase control circuit C0EFFI to
It is added to each of digital filters LPFI-b to LPF3-b with low-pass characteristics through C0EFF4, and taken out from the final stage, PF3-S.

In each digital filter group, among the numbers assigned to each filter in the order of connection, the digital filters LPF3-a, LPF3-b, and B with the highest numbers
When the delay time nT per unit delay element stage of PF4 is set to be greater than or equal to the sampling time interval T of the input signal, and each time the number of each filter decreases by one, the delay time per unit delay element stage of the filter becomes A. ” (A>1.B
>O), and the delay time per stage of a unit delay element of a digital filter with a low-pass characteristic of a certain number operates at an integral multiple of the delay time per stage of a unit delay element of a digital filter with a band-pass characteristic of the same number. It looks like this.

Furthermore, the adaptive control circuit C0NT controls each output B of a digital filter with a bandpass characteristic as shown in FIG.
By detecting PI to BP4 with the band component detector DET, the microprocessor PLOC detects each amplitude phase control circuit C0EFFI according to the component in each band.
The amplitude and phase coefficients of ~C0EFF4 are calculated, and predetermined control signals are sent to each coefficient unit to control each coefficient.

The amplitude and phase control circuit 1 is made up of a RAM, a multiplier MUL, and a delay element SR, as shown in FIG. The phase is changed by offsetting the timing at which the output is taken out from the delay element SR, and the RA
The coefficients extracted from M are BPFIed by the multiplier MUL.
The amplitude is changed by multiplying each output of the BPF 4, and the delay element SR can also be used in common with the RAM of a digital filter with bandpass characteristics.

In this embodiment, each coefficient is BPFI to BPF4 as described above.
The output of each coefficient multiplier is changed according to the output of the coefficient multiplier, but in the configuration shown in FIG. 1, no feedback is applied, and the system is stable.

Now, in the octave multiple filter configured as described above, the input analog signal applied to the input terminal IN is A-D.
A-converted by a converter A/D at a sampling frequency fe (sampling rate 1/f, 5ac),
It is added to the digital filters LPF3-a and BPF4 having the maximum number of low-pass characteristics and band-pass characteristics. This filter, for example, LPFl-a, has a delay time of 1/f, 2""sea for each stage of the delay element constituting it.
Usually, a digital filter having this configuration is used with a clock frequency of f,2-''7, and a sampling frequency of an input signal of f,2-''Hz. However, since the clock frequency and the sampling frequency of the above-mentioned digital filter are different, the desired processing cannot be performed as is. Therefore, as mentioned above, first, the coefficients of the FIR type filter are set by setting the unit delay time l/f, 2-"see. Actual sampling interval 1/f, se
For the input signal of a, set the clock frequency to f, Hz,
And the coefficient is set so that the delay time per stage of the unit delay element nT=1/fo2-"sec.

The digital filters of other stages are set in the same manner.

Each digital filter BPF4 to BPFI and L P
The characteristic of F 3- a = L P F 1- b is the fourth
They are as shown in Figures (a) to (1), and the output signals of the digital filters LPF 3-a and NLPF 1-a, each having a low-pass characteristic whose band is successively narrowed, are connected to BPF4 to BPFI. are multiplied by each bandpass characteristic, and each amplitude and phase is independently controlled by the amplitude phase control circuits COE F F 1 to COE F F4t, and is input to LPFI-b to LPF3-b to cut noise. By doing so, an output with the desired characteristics as shown in FIG. 4(m) can be obtained.

[Effects of the Invention] As is clear from the above explanation, according to the present invention, by having the above-mentioned configuration, the frequency domain (on the frequency axis)
The characteristics can be specified at logarithmically uniform intervals, and the resolution can be improved because the band can be widened in the low frequency direction.However, the amplitude and phase can be controlled adaptively, and the sampling time interval can be gradually lengthened. By spreading the data, the number of calculations can be reduced.

Thus, by combining these effects, you can achieve various noise reductions and
It is compatible with systems such as enhancers, and can also have special effects such as automatic sound field correction and surround sound field.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a block diagram showing an example of the configuration of an adaptive control circuit, FIG. 3 is a diagram showing an example of the configuration of the FIR filter used in the above embodiment, and FIG. 4 is a characteristic diagram of the filter.
FIG. 5 is a diagram showing an example of the configuration of an amplitude phase control circuit, and FIG. 6 is an output characteristic diagram of the digital filter with each bandpass characteristic in the above embodiment. LPFI-aNLPF3-b...Digital filter with low-pass characteristics, BPFI-BPF4...Digital filter with band-pass characteristics, C0EFFI-C0EFF4---Amplitude phase control circuit, ADD1-ADD3...Addition circuit, C0NT ...Adaptive control circuit. Patent Applicant Kyocera Corporation Figure 3 Figure 5 C0NT Procedural Amendment October 1985 lQ Date of 1988 Patent Application No. 101461 2 Title of Invention Octave Multiplex Filter 3 Amendment Person Case Relationship Patent Applicant Address Name (663) Kyocera Corporation 4, Agent Address 105 Address Shiba 3-chome Building, 3-2-14 Shiba, Minato-ku, Tokyo Phone: (03) 455-8746 Claim for patent in the specification The scope of the invention, the detailed description of the invention, the brief description of the drawings, and the drawings (1) The claims of the present application are amended as follows. [A plurality of first and second digital filter groups having low-pass characteristics and a plurality of digital filter groups having band-pass characteristics are provided that operate with a time interval equal to or longer than the sampling time interval of the input signal as a clock.] , the first and second digital filter groups with low-pass characteristics are each connected in series, the digital filter groups with band-pass characteristics are each connected in parallel, and the outputs of the first digital filter groups with low-pass characteristics are each connected in series. and each output thereof is added to each of the second digital filter groups having a low-pass characteristic via an amplitude phase control circuit and outputted from the final stage, Among the numbers assigned to each filter in each filter group in the order of connection, the delay time per unit delay element stage of the digital filter with the largest number is set to be longer than the sampling time interval of the input signal, and the Each time the number decreases by one, the delay time per unit delay element stage of the filter increases AB (A>
1. B>O), and the delay time per stage of a unit delay element of a digital filter with a low-pass characteristic of a certain number operates at an integral multiple of the delay time per stage of a unit delay element of a digital filter with a band-pass characteristic of the same number. An octave multiplex filter, characterized in that the octave multiplex filter is characterized by comprising control means for controlling the amplitude coefficient and phase coefficient of each of the amplitude and phase control circuits in accordance with the output signal of the digital filter having each bandpass characteristic. (2) "Amplitude and phase" on page 3, line 9 of the specification shall be corrected to "amplitude coefficient and phase coefficient." (3) In lines 9 and 10 of the same page of the same book, "independently and adaptively" is amended to "independently and adaptively." (4) Same book, page 5, lines 12-13 “Input signal...
Delete "for...". (5) Correct “PRoC” on page 8, line 8 of the same book to rMPUJ. (6) Delete "rcOM is a control signal generation circuit" on the 9th line of the same page of the same book. (7) Same book, page 9, lines 10-11 [for each...
..." is corrected to "It is added to each output and taken out." (8) Correct rPROcJ to rMPUj on page 10, line 9 of the same book. (9) Correct "amplitude and phase coefficient" in line 11 of the same page of the same book to "amplitude coefficient and phase coefficient". (10) The same book, page 11, line 3 rRAMJ is defined as “delay element S
Correct to RJ. (1'l) Ibid., page 11, line 16, line 12, line 3. 7th line r l/f, 2””J to r1/(f, ・2
-”) Corrected to J. (12) Ibid., page 11, lines 17 and 19 rf, 2-J
is corrected to "f, 2-2". (13) Delete "Bandpass characteristics" in the second line of page 14 of the same book. (14) Correct Figure 1 as shown in the attached sheet. (15) Correct Figure 6 as shown in the attached sheet.

Claims (1)

[Claims] A plurality of first and second digital filter groups having low-pass characteristics and a plurality of digital filter groups having band-pass characteristics are provided that operate with a time interval equal to or longer than the sampling time interval of the input signal as a clock, The first and second digital filter groups with low-pass characteristics are each connected in series, the digital filter groups with band-pass characteristics are each connected in parallel, and each output of the first digital filter group with low-pass characteristics has band-pass characteristics. are applied to each of the second digital filter groups, and each output is added to each of the second digital filter groups with a low-pass characteristic via an amplitude phase control circuit and output from the final stage. Among the numbers assigned to each filter in the filter group in the order of connection, the delay time per unit delay element stage of the digital filter with the highest number is set to be longer than the sampling time interval of the input signal, and the filter number in each filter group Each time decreases by one, the delay time per unit delay element stage of the filter becomes A^B (A>1
. 1. An octave multiplex filter, comprising: control means for controlling the amplitude and phase coefficient of each of the amplitude and phase control circuits in accordance with the output signal of the digital filter having each bandpass characteristic.