JPS6070498A - Digital equalizer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a digital equalizer, and particularly to a digital equalizer of a digital audio system that provides free characteristics.

[Prior Art] FIG. 1 is a circuit diagram of a conventional graphic equalizer. The acoustic signal input to the input terminal 1 is passed through n bandpass filters 2, each having a center frequency of n.
After frequency division by a, 2b, ... 2n, so that the characteristics of the graphic equalizer become the desired characteristics,
n gain controllers 3a, 3b..., 3Jn
As a result, the amplitudes of the frequency-divided signals in each band are adjusted by ξ and then added by the adder 4, and the output of this adder is outputted from the output terminal 5. This type of graphic equalizer has drawbacks such as riffling in frequency characteristics due to individual differences in element values, temperature fluctuations in element values, and the like.

[Summary of the Invention] Therefore, the main object of the present invention is to utilize the high degree of freedom in signal processing of a digital filter that applies moxibustion to digitized acoustic signals to create a digital signal that can have arbitrary frequency characteristics. It is to provide an equalizer.

To summarize this invention, a digitizer 1J' that digitizes line images, an inverse fast Fourier transform section (hereinafter referred to as FFT section) that performs inverse fast Fourier transform, and a storage device are used to create a finite impulse response type filter (hereinafter referred to as FIR type filter). ) is @Ifc, the output of this filter is multiplied by the output obtained by multiplying the digitized analog signal by the window number, and the sum is multiplied by the n-th power, and this is added by an adder. This is a digital equalizer that changes the spectrum of analog signals.

The above objects and other objects and features of the present invention will become more apparent from the detailed description given below with reference to the drawings.

Embodiment 1 of the Invention FIG. 2 is an external view of a first embodiment of the invention, in which a CRT 6 and operation buttons 8 are provided on the front of the device main body 9.
is provided, and the pen 7 is connected to the main body 9 of the i-device. Lie on CT' R6! - By inputting a desired frequency characteristic to Ben 7, it can be thought of as an amplifier whose frequency characteristic changes to the inputted desired frequency characteristic.

On the other hand, among digital filters, the FIR type filter converts the input desired frequency characteristics into inverse Fourier transform (
There is a characteristic that the impulse response obtained by fast Fourier transform (usually fast Fourier transform) can be used as is, and this invention makes effective use of this characteristic. Figure 3 is a circuit diagram of one embodiment of this invention. be.

In the figure, a light pen 7 is connected to an image input section 11.
Enter above. Image input section 1'l.

It is connected to a first RAM '+2 which records its output. The inputted figure representing the desired frequency characteristic is digitized and stored in the first RAM 12.
The CRT drive section 10 for driving the RT6 has a first R
Connected to AM12. CRT drive unit 10 (first
It receives information from the RAM 12 and displays the input figure on the CRTe. A light pen 7, an image input section 11,
The CRT 6 and the CRT drive section 10 constitute a digitizer that digitizes line images. The first RAM 12 has F[
-r section 13, and the FF7 section 13 is connected to the second RAM1
Connected to 4. The curve stored in the first RAM 12 is subjected to inverse fast Fourier transform in the FF7 section 13, and then
The output of the 7 section 13 is stored in the second RAM 14. A digitizer, a first RAM 12, an FFT section 13,
The second RAM 14 forms an FIH type filter, and F F
'The output of part 13 also has characteristics to be equalized')P
IF (becomes the coefficient of the type filter.

On the other hand, the digitized A-tio signal is input from the input 1J terminal '1. Input terminal 15 is window function generator 2
4, and the window function generator 24 is connected to the third RA~116.
It is connected to 1. The digitized A-dio signal is multiplied by the window function W (t) in the window function generator 24 and stored in the third RAM 16.

The second RAM 14 and the third RAM 16 are connected to a multiplier 17, and the multiplier 17 is connected to an adder 18.

The information stored in the first RAM 14 and the third RAM 140 is sequentially multiplied by the multiplier 17, and the adder 18 is
Add the output of xt unit 17 to I! II.

The adder 18 is connected to a fourth RAM 19 that temporarily stores the multiplication link when adding in the adder 18.
19 is foil tWti! It is connected to an output terminal 20 that outputs the i-result.

Now, when a desired frequency characteristic is given, the output signal of the FIR type filter with this desired frequency characteristic is the inverse transform of the input signal and this filter's Inno(Russian response), that is, the frequency characteristic of the filter. It is given by convolution with the signal.

The frequency characteristics of the filter input by CRT6 are 1+
−(ω), then the input pulse response H of this filter is
(t) is given by the following equation (1).

t1 (t)=F-'(h' (ω))FF
The output of section 7 13 is h(n
). If the input signal is × (n), the output signal @y
(n) is given by − in the following equation (2a). here,
n is the sample number, and N is the approximate number of input samples.

Also, the Zvi transformations of h (n), x (n), and y (n) are respectively) l (Z), X CZ'), Y (Z),! : Then, Y (Z)=X (Z) ・ l-1(Z) ・
(2b) Here, if 1-1(Z) is made longitudinally symmetrical with respect to the center cylinder of Z, the phase characteristic of the filter becomes a straight line. In such a case, the circuit can be simplified by utilizing the symmetry of H(Z).

FIG. 4 is a circuit diagram of another embodiment of the present invention in which the phase characteristic is linear C. In addition, in Fig. 4,
Parts similar to those in FIG. 3 are given the same reference numerals. In the figure, a calculation unit 21 is added to the third RAM 16 to perform the calculation shown in the following equation (3>0. Here, N is the total number of input samples.

Go x - (n) = Σ x (i) x (-i)...
・(3) t + 0 On the other hand, the number of coefficient points of the FI 11 type noilter stored in the second RAM 1.1 was also N points in the case of the embodiment shown in FIG. 3, but in this embodiment, it is N, ,' 2 Accumulate only one point x-(n) and output h(n) of FFT section 13.
He rides this and brightens that which has been ridden.

In the above embodiment, the waveform stored in the second RAM 14 was only one input waveform, but the number of waveforms stored in the second RAM 14 can be increased several times, for example, (1) Past frequencies Store characteristic setting examples and selectively recall them as needed.

(2) By storing a large number of slightly different frequency characteristics and recalling them at intervals slightly apart in time, it is possible to realize a wave number characteristic that changes by 1J over time.

be able to.

FIG. 5 shows a RAM that stores frequency characteristics according to the present invention.
FIG. 7 is a circuit diagram of still another embodiment in which the capacitance is increased. In FIG. 5, the same reference numbers are given to the same parts as in FIGS. 2, 3, and 4. The contents of the RAM 140 can be read out by the RAM controller 1-roller 22 by connecting the RΔM controller 22 and the operation button 23 to the RAM 140 having a large storage capacity.

In the above embodiment, a CRT and a light pen were used as waveform input devices, but other devices may be used as long as they can digitize figures, such as a tablet or a facsimile input unit equipped with an in-sensor. 1
．． It goes without saying.

[Effects of the Invention] As described above, according to the present invention, there is provided a digitizer that digitizes a line image, and a first digitizer that stores the output of the digitizer.
R/', M, an FFT section that performs inverse fast Fourier transform (inverse FFT) on the information in the first RAM, and a second RAM that stores the output of the FFT section, and performs this inverse fast Fourier transform (inverse FFT). ) By configuring an FIR type filter that uses the output as a coefficient, it can be applied to the spectrum of the digitized analog signal with arbitrary frequency characteristics
It is possible to create a digital equalizer based on Ifi.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional graphic equalizer. FIG. 2 is an external view of an embodiment of the present invention. FIG. 3 is a circuit diagram of an embodiment according to the present invention. FIG. 4 is a circuit diagram of another embodiment in which the phase characteristic is linear according to the present invention. FIG. 5 is a circuit diagram of still another embodiment in which the number of RAMs for storing frequency characteristics according to the present invention is increased by one step. In the figure, 6 is CRT, 7 is Light Ben, 10 is CR
T drive unit, 11 is an image input unit, 12 is a first RAM, 1
3 is the FFT section, 14 is the second RAM 1140 is the second RAM with a large capacity, 116 is the third RAM, 1
7 is a multiplier, 18 is an adder, 19 is a fourth RAM, 20
21 is an output terminal, 21 is a calculation section, and 22 is a RAM controller. Agent Masuo Oiwa Figure 1 Figure 2 (21 Figure 3 Figure 4)

Claims (5)

[Claims] (1) A digitizer that can digitize and input between line drawings, and a first record 41 that temporarily stores the output of the digitizer! ,
an inverse fast Fourier transform unit that performs inverse fast Fourier transform on information in the first storage device; and a second record 1! that temporarily stores the output of the inverse fast Fourier transform unit. ! an input terminal for receiving a signal obtained by digitizing an analog signal; a window function generation section for multiplying the output of the input terminal by a window function; and a third note for temporarily storing the output of the window function generation section. an @field device that sequentially multiplies the information in the first storage @ location and the information in the third storage M location; an adder that adds the outputs of the multiplier; and a multiplication field result of the multiplier. and a fourth storage device for storing the output of the digitizer, which is subjected to inverse fast Fourier transform by the digitizer, the first storage device, the inverse fast Fourier transform unit, and the second storage device. What is claimed is: 1. A digital equalizer comprising a finite impulse response filter having a coefficient of , and changing the spectrum of the digitized analog signal. (2) The digital equalizer according to claim 1, wherein the digitizer includes an image input means including a CRT and a light beam. (3) The digital equalizer according to claim 1, wherein the digitizer captures an image input means including a tablet. (4) The digital equalizer according to claim 1, wherein the digitizer includes an image input means including a line sensor and paper feed. (5) The value obtained by adding the first input sample and the sample input one step later among the digitized signals of analog signal 8 and dividing by 2 is set as the first sample, and then each adjacent sample is The value obtained by adding them together is used as the second sample, and then the sample next to each currently deduced glue → pull is deduced in the same way to create samples one after another, halving the number of samples, and then inverse fast Fourier 2. The digital equalizer according to claim 1, wherein only half of the output of the inverse fast Fourier transform unit is used.