JPS63252010A - Octave multiple filter - Google Patents

Abstract

PURPOSE:To specify characteristics logarithmically at uniform intervals by providing a group of digital filters which operate according to sampling time intervals of an input signal as a clock and have band-pass characteristics and low-pass characteristics. CONSTITUTION:The input signal supplied to an input terminal IN is A/D- converted by an A-D converter A/D at a sampling frequency and applied to digital LPF4 and BP5 with low-pass characteristics and band-pass characteristics. The output signal of the A/D converter A/D is supplied to a delay circuit DELAY as well. The respective outputs of the digital filters LP1-LP4 are supplied to digital filters BP1-BP4 respectively. The output signals of the digital filters BP1-BP5 are added to and subtracted from the output signal of a delay circuit DELAY by an adding and subtracting circuit AS through amplitude coefficient multipliers COB1-COE5 and also supplied to an adaptive control circuit CONT.

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 series-connected digital filter group having a low-pass characteristic is given to each filter of a parallel-connected digital filter group having a band-pass characteristic, and the output of the filter is They are added together through an amplitude coefficient unit and taken out as shown below.
In the octave multiplex filter configured such that the amplitude coefficient of each amplitude coefficient unit is adaptively controlled according to each large sword, a delay circuit is connected in parallel to the digital filter group having low-pass and band-pass characteristics. The output of the octave multiple filter is added to or subtracted from the output signal of the delay circuit.

[Prior Art] The present inventor previously proposed a novel octave multiple filter in Japanese Patent Application No. 194039/1982, and the present invention further improves this.

[Problems to be solved by the invention: Although the octave multiple filter of the above-mentioned prior application is excellent in that it is possible to specify characteristics at logarithmically uniform intervals over a wide band in the frequency domain, However, there were still some problems as described below.

First of all, in the octave multiplex filter mentioned above, the output of each digital filter is superimposed and output, so when boosting or cutting is not performed, each digital filter is It must be considered that the shape of the overlapping portion of each amplitude-frequency characteristic has a Nyquist slope, and the shape of the amplitude-frequency characteristic of the digital filter becomes uniform.

Furthermore, even when boosting and cutting are not performed, in-band ripples occur due to the overlapping of the above-mentioned characteristics of the digital filter, and due to this influence, the amplitude frequency characteristics of the output cannot be made flat.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an octave multiplex filter that can specify characteristics at logarithmically uniform intervals by improving the problems of the prior application described above.

[Means for Solving the Problems] In order to achieve the above object, the octave multiplex filter of the present invention uses a digital filter with band-pass characteristics and low-pass characteristics that operates with the sampling time interval of an input signal as a clock. The digital filter groups with low-pass characteristics are connected in series, the digital filters with band-pass characteristics are connected in parallel, and the delay circuits are connected in parallel to these filter groups. The output signal of the filter is given to each digital filter with a bandpass characteristic, and each output signal is added to and subtracted from the output signal of the delay circuit through an amplitude control coefficient device and taken out. Among the numbers assigned to each filter in the order of connection, the delay time per stage of unit delay element of the digital filter with the highest number is set to be longer than the sampling time interval of the input signal, and the number of filters in each filter group is one. Each time the delay time per unit delay element of the filter decreases AB
(A>1.B>0), and the delay time per stage of a unit delay element of a digital filter with a low-pass characteristic of a certain number is the delay time per stage of a unit delay element of a digital filter with a band-pass characteristic of the same number. The present invention is characterized in that it operates at an integer multiple of , and includes a control means for controlling the amplitude coefficient of each amplitude coefficient unit in accordance with the output signal of the digital filter having each bandpass characteristic.

[Function] Since the output signal of the octave multiple filter section of the prior application is configured to change its amplitude frequency characteristics by being added to or subtracted from the output signal of the delay circuit, 1. each pass band of the octave multiple filter of the present invention. The digital filter group that determines the frequency characteristics of can have a characteristic shape with a large degree of freedom, and can have changes in sharpness, center frequency, etc., and when the output signal of the octave multiple filter section is 0, Since nothing is added to the input signal and it is output as is, the overall amplitude-frequency characteristic becomes flat.

[Example] The present invention will be described below with reference to the embodiments shown in the drawings.
FIG. 1 shows an embodiment of an octave multiple filter (5 octaves) according to the present invention. In the same figure, IN is an input terminal, OUT is an output terminal, A/D is an A-D converter, and D/D is an input terminal, OUT is an output terminal,
A is a DA converter, LPF is a normal analog type low-pass filter, LPI to LP4 are digital filters with low-pass characteristics using, for example, FIR type filters, and BPI to BP5 are band-pass filters using similar filters. Digital filter with characteristics.

D is an adder circuit, C0EI to C0E5 are amplitude coefficient units, C0
NT is an adaptive control circuit DELAY is a delay circuit, A
S is an addition/subtraction 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-s to aG of the coefficient multiplier ML are set so as to obtain the following.

Figure 4 (a) shows the desired frequency characteristics (low-pass characteristics)
, and FIG. 3(b) shows a time-domain function obtained by inverse Fourier transform.

Digital filter groups BPI to BP5 and LPI to L having band-pass characteristics and low-pass characteristics configured as described above.
Digital filter groups LPI to LP4, which are composed of P4 and have low-pass characteristics, are connected in series, and digital filters BPI to BP5, which have band-pass characteristics, are connected in parallel, and a delay circuit DELAY is connected in parallel to these digital filter groups. connected to LP
Each output of 1 to LP4 is given to each of BPI to BP5, and each output signal of BPI to BP5 is sent to an amplitude coefficient multiplier C0E.
The signals are added by the adder circuit via I to C0E5, added to and subtracted from the output signal of the delay circuit DELAY, and taken out by the adder/subtractor circuit AS, and also given to the adaptive control circuit C0NT. The amplitude constant of each of the amplitude coefficient multipliers C0EI to C0E5 is adaptively controlled.

In each digital filter group, among the numbers given to each filter in the order of connection, the digital filter LP4. When the delay time nT per unit delay element stage of BP5 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 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 is the delay time per stage of a unit delay element of a digital filter with a band-pass characteristic of the same number. It is designed to work with integer multiples of .

Furthermore, the adaptive control circuit C0NT detects each of the outputs BPI to BP5 of the digital filter with bandpass characteristics using a band component detector DET, thereby converting the outputs BPI to BP2, for example, BPI and BF2. BF2. The microprocessor PLOC calculates the amplitude coefficients of the amplitude coefficient units C0E1 to C0E5 according to the components in the respective bands, and in response to the calculation results, the control signal generation circuit COM sends a predetermined control signal to each amplitude coefficient unit to control each coefficient.

Note that the coefficient multiplier is, for example, RA as shown in FIG.
M and a multiplier MUL, each coefficient is set in the RAM, and the amplitude is changed by multiplying each output of BPI to BP5 by the coefficient taken out in response to the control signal in the multiplier MUL. In this embodiment, as described above, each coefficient is changed according to the output of BPI to BP5 to change the output of each coefficient multiplier, but in the configuration shown in FIG. 1, no feedback is applied. The system is stable.

Seventh, in the octave multiple filter configured as described above, the input signal applied to the input terminal IN is sent to the A-D converter A.
/D at a sampling frequency fe (sampling rate 1/f, 5ec), and a digital filter LP4. 'Added to LP5. This filter, for example LP4, has a delay time of 1/(2-"·f, )see for each stage of the delay element that constitutes it. Usually, a digital filter with this configuration has a clock frequency of 2-2·f.
foHz, and the sampling frequency of the input signal is also used as 2-2·f, )Iz. However, since the clock frequency and the sampling frequency of the digital filter are different, the desired processing cannot be performed as is. For this reason, first, as mentioned above, the coefficient of the FIR type filter is determined by setting the unit delay time to 1/2"2・f osee, and then the actual sampling interval L/f
For an input signal of f1 sec, the clock frequency is f. 7, and the coefficient is set so that the delay time per stage of the unit delay element nT=1/2"·f, sec. Similarly, the digital filters of the other stages are set.

Each digital filter BP5 to BPI and LP4 to LP
The characteristics of I are as shown in Figure 6 (a) to (i),
BP5 is applied to the output signals of digital filters LP4 to LP1 having low-pass characteristics whose bands are successively narrowed.
The bandpass characteristics of ~BPI and the coefficients of each coefficient multiplier are multiplied to obtain the desired output as shown in FIG. 6(j).

Now, in the octave multiple filter of the present invention described above, the output signal of the A/D converter A/D is given to the delay circuit DELAY, and the output signal of each amplitude coefficient unit COE 1 to C0E5 is supplied to the output signal of the DELAY. The delay circuit DELAY is used to match the delay time with that of the digital filter group with low-pass and band-pass characteristics.

Therefore, the digital filter BPF with each band-pass characteristic can have a large degree of freedom in the shape of its amplitude-frequency characteristic, for example, as shown in FIG. 7. In the figure, (a) is the frequency characteristic of the output signal OD of the delay circuit DE LAY, (b) is the frequency characteristic of the signal OC6, which is the composite of the coefficient multipliers C0E1 to C0E5 and the teno output signals oC1 to OC5, and (C) is the frequency characteristic of the output signal OD of the delay circuit DE LAY. represent the frequency characteristics of the composite output signal OUT of the signals OD and OC6, respectively.

In order to control the amplitude of the composite output signal by adding or subtracting the amplitude frequency as shown in (b) to the flat amplitude frequency characteristic (a) as shown in Fig. 7, the digital filter of each bandpass characteristic is used. There is no need to consider the overlap between one band and another band, and amplitude-frequency characteristics can be controlled with a large degree of freedom.

[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. When the output signal of each amplitude coefficient unit is zero, its amplitude frequency characteristics are flat. Ripples as described above do not occur. In addition, since it is not necessary to consider the overlap between digital filters of each bandpass characteristic with adjacent bands, the sharpness and center frequency of the digital filter group that determines the shape of each passband can be freely set.

Thus, by using the octave multiple filter of the present invention,
By preparing various coefficient calculation programs, it is possible to support various systems such as noise reduction and enhancer, and furthermore, it is possible to provide special effects and functions such as automatic sound field correction and surround sound field.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the configuration of an adaptive control circuit, and FIG. 3 is a block diagram showing an example of the configuration of an FIR filter used in the above embodiment. 4 is a characteristic diagram of the filter, FIG. 5 is a diagram showing an example of the configuration of a coefficient unit, and FIGS. 6 and 7 are the outputs and composite outputs of each digital filter and delay circuit in the above embodiment. It is a characteristic diagram. LPI to LP4...Digital filters having low-pass characteristics, BPI to BP5...Digital filters having band-pass characteristics, C0E1 to C0E5...Amplitude coefficient multipliers. AS...addition/subtraction circuit. D...addition circuit, DELAY...delay circuit, C0NT...adaptive control circuit.

Claims (1)

[Claims] A plurality of digital filter groups with band-pass characteristics and low-pass characteristics are provided that operate with the sampling time interval of the input signal as a clock, and each digital filter group with low-pass characteristics is connected in series, and the digital filter groups with band-pass characteristics The digital filters are connected in parallel, a delay circuit is connected in parallel to these filter groups, and the output signal of each digital filter with low-pass characteristics is given to each digital filter with band-pass characteristics, and each output signal is The output signal of the delay circuit is added to and subtracted from the output signal of the delay circuit through the amplitude control coefficient, and the unit delay of the digital filter with the largest number among the numbers assigned to each filter in each filter group in the order of connection. The delay time per stage of element 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 stage of unit delay element of the filter becomes A^B(A >1, B>0), and the delay time per stage of a unit delay element of a digital filter with a low-pass characteristic with a certain number is an integer of the delay time per stage of a unit delay element of a digital filter with a band-pass characteristic with the same number. 1. An octave multiplex filter, characterized in that the octave multiplex filter is operable at a frequency of 1 to 2, and includes control means for controlling the amplitude coefficient of each amplitude coefficient unit according to the output signal of the digital filter having each bandpass characteristic.