JPH0328588Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a frequency characteristic adjustment circuit used, for example, in a sound quality adjustment circuit of an audio device.

Generally, sound quality is adjusted by enhancing or attenuating the low or high frequencies, but this also changes the frequency at the bending point of the frequency characteristics, making adjustment difficult. The present invention aims to provide a sound quality adjustment circuit in which the frequency at the bending point of the frequency characteristic is held constant regardless of the amount of attenuation of the amount of enhancement in the low or high frequencies. Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing the basic configuration of the circuit of the present invention. In the figure, 1 is an input terminal, 2
is a filter, 3 and 8 are arithmetic circuits, 4 is an adder,
5 is an output terminal. In this circuit, filter 2 is a low-pass or high-pass filter, and the multiplication coefficients of arithmetic circuits 3 and 8 are changed while keeping its cutoff frequency constant, or the cutoff frequency of filter 2 is changed in relation to the multiplication coefficient. By doing so, it is possible to enhance or attenuate the low or high range without changing the frequency at the bending point.

First, the case of attenuating the low range will be explained.
In this case, a high-pass filter with a cutoff frequency of 1/2πT as shown in FIG. 2 is used as the filter 2. Now, if the input signal is e ₁ , the multiplication coefficients of calculation circuits 3 and 8 are 1-K and K, and the output signals of calculation circuits 3 and 8 are e ₃ and e ₈ , then e ₃ = (1-K)jωT/ 1 + jωTe ₁ …(1) e ₈ = Ke ₁ …(2). Therefore, if the composite output signal is e ₀ , then e ₀ = e ₃ + e ₈ = K1 + jωT/K/1 + jωTe ₁ (3), and if K is adjusted within the range of 0<K≦1, the frequency at the bending point can be adjusted as follows. A constant low frequency attenuation characteristic can be obtained. An example of this is the frequency characteristic curve a in Figure 3.
Indicated by b, c, d (broken line approximate curve). Curve a is for K=1, and as K becomes smaller than 1, the curves become like curves b, c, and d, but the frequency at the bending point P is constant at 1/2πT.

Next, the case of enhancing the low frequency range will be explained.
In this case, a high-pass filter whose cut-off frequency is lowered in inverse proportion to the value of K in the multiplication coefficient (that is, whose cut-off frequency is 1/2πkT) is used as the filter 2. In the same manner as described above, when the composite output signal e ₀ is obtained from the output signals e ₃ and e ₈ of the arithmetic circuits 3 and 8, e ₃ = (1-K) jωkT/1 + jωKTe ₁ e ₈ = Ke ₁ e ₀ = e ₃ +e ₈ =K1+jωT/1+jωKTe ₁ ...(4) If K is adjusted within the range of K≧1, the low-frequency enhancement characteristics shown by the approximate curves a, e, f, and g in Figure 3 can be obtained. It will be done. Curve a is for K=1, and as K becomes larger than 1, curve e,
f, g, but the frequency at the bending point P is constant at 1/2πT.

On the other hand, in order to obtain high-frequency enhancement and attenuation characteristics, a low-pass filter may be used as the filter 2.

First, the high-frequency attenuation characteristic can be obtained by keeping the cut-off frequency of filter 2 constant at 1/2πT and adjusting K in the range of 0<K≦1, in the same way as when obtaining the low-frequency attenuation characteristic described above. It will be done. That is, the combined output signal e ₀ is e ₀ =Ke ₁ +1/1+jωT(1-K)e ₁ =1+jωKT/1+jωTe ₁ (5). In addition, for the high-frequency enhancement characteristic, the cutoff frequency of filter 2 is lowered in proportion to the value of K (in other words, the cutoff frequency is K/2πT), contrary to when obtaining the low-frequency enhancement characteristic described above. This can be obtained by using a filter (such as ) and adjusting K within the range of K≧1. That is, the combined output signal e ₀ is e ₀ =Ke ₁ +1−K/1+jωT/Ke ₁ =1+jωT/1+jωT/Ke ₁ (6). FIG. 4 is a folded line approximate curve diagram showing an example of high frequency enhancement and attenuation characteristics obtained in this manner. Curve a is for K=1, and as K becomes larger than 1, the curves become like e', f', g',
As K becomes smaller than 1, the curves become like curves b', c', and d', but the frequency at the bending point Q is constant at 1/2πT.

FIG. 5 is a schematic circuit diagram showing an embodiment of the high frequency sound quality adjustment circuit according to the present invention. In the figure, filter 2 is a low pass filter. C ₁ is a capacitor and its capacitance value, R ₁ is a resistor and its resistance value, and Z is a variable resistor linked to X and its resistance value. In this example, T=C ₁ (R ₁ Z) at the cutoff frequency 1/2πT of the filter 2, and K is equal to X/r. The interlocking variable resistors X and Z are configured as shown in FIG. 6, for example. As shown in the figure, the total resistance value of the left side portion of the variable resistor X is r, and the corresponding portion of the variable resistor Z is left open. In Figure 6, in the case of high frequency attenuation, 0<K
≦1, that is, 0<X≦r. At this time, the slider of the variable resistor Z is opened as shown by the solid arrow in Fig. 6, and Z=∞, so the cutoff frequency of the filter 2 is It becomes constant at 1/2πC ₁ R ₁ , and the frequency at the bending point also becomes constant at 1/2πC ₁ R ₁ . In addition, in the case of high frequency enhancement, adjustment is made within the range of K≧1, that is, X≧r, but in this case, the cutoff frequency of filter 2, 1/2πC ₁ (R ₁ Z), is set to K/2πT, that is, K/2πC ₁ R ₁ Therefore, it is necessary to set R ₁ Z=R ₁ /K, that is, Z=R ₁ /K-1. Now, when adjusting in the range of X≧r in Fig. 6, as shown in the figure,
If x is the resistance value of the resistor x portion of the variable resistor X excluding the portion corresponding to the open portion of the variable resistor Z, then K=X/r=r+x/r=x/r+1.
On the other hand, from the condition Z=R ₁ /K-1, K=R ₁ /Z+1 is obtained. Therefore, from both equations, we obtain the relationship R ₁ /Z=x/r, that is, xZ=rR ₁ . Therefore, if variable resistors X and Z are configured to maintain this relationship, the cutoff frequency can be set to K/2πC ₁ R ₁ , and the frequency at the bending point is constant at 1/2πC ₁ R _1. becomes.

FIG. 7 is a connection diagram showing another example of interlocking variable resistors X and Z. In this example, the resistor R ₁ is included in the variable resistor Z', and the total resistance value of the variable resistor Z' is made equal to R ₁ . In this case, the resistor _R1 of FIG. 5 is unnecessary. 0 for high frequency attenuation
≦K≦1, that is, when adjusting in the range of 0<X≦r, the cutoff frequency of filter 2 where Z'=R ₁ is 1/2πC ₁ R ₁ , and the frequency at the bending point is also 1/2πC ₁ R It becomes constant at ₁ . In addition, in the case of high frequency enhancement, it is sufficient to adjust within the range of K≧1, that is, X≧r, and in this case, it is necessary to adjust so that Z'=R ₁ /K, that is, Z=R ₁ /Z'. , the cutoff frequency of the filter 2 is constant at 1/2πC ₁ R ₁ . In this case, since it is X/r, it is sufficient to maintain the relationship XZ'=rR ₁ .

As mentioned above, a high-pass filter is used for low-pass adjustment, and a low-pass filter is used for high-pass adjustment, so use an appropriate switch to switch between the low-pass and high-pass filters. It may be configured like this. Since such a switch can be easily constructed, illustration and description thereof will be omitted. Also, the output impedance of the filter is determined by the calculation circuit (including the amplifier).
If the gain of the filter is affected, insert a buffer amplifier after the filter.

Note that adder 4 and adder 6 in FIG. 5 may be combined. That is, in this case, the adder 6 may be omitted and the input terminals of the adder 4 may be of a three-input type.

As explained above, according to the present invention, it is possible to obtain a high-frequency sound quality adjustment circuit in which the frequency at the bending point of the frequency characteristic is kept constant regardless of the amount of enhancement or attenuation in the high-frequency range. This has the advantage of making it easier.

It should be noted that the present invention is not limited to the above-described embodiments, and can be modified and changed in various ways without departing from the gist of the invention as set forth in the claims for utility model registration.

[Brief explanation of the drawing]

Figure 1 is a block diagram for explaining the basic configuration of the circuit of the present invention, Figure 2 is a diagram showing an example of filter characteristics used in the present invention, and Figure 3 is an example of low-frequency attenuation and enhancement characteristics. FIG. 4 is a diagram showing an example of the high frequency attenuation and enhancement characteristics according to the present invention, FIG. 5 is a schematic circuit diagram showing an example of the high frequency sound quality adjustment circuit according to the present invention, and FIGS. The figure is a connection diagram showing an example of an interlocking variable resistor. 1...Input terminal, 2...Low pass filter,
3, 8... Arithmetic circuit, 4... Adder, 5... Output terminal, X, Z, Z'... Cutoff frequency variable means.

Claims (1)

[Scope of utility model registration request] The frequency characteristic is determined by adding the input signal through a series connection circuit of a low-pass filter and the first calculation means and the signal obtained through the input signal through the second calculation means to obtain an output signal. In the circuit to be adjusted, when the multiplication coefficient of the second arithmetic circuit is K, the multiplication coefficient of the first arithmetic circuit is 1-K, and the cutoff frequency of the filter is set to K in the multiplication coefficient of the multiplication circuit of the arithmetic circuit. When the value is 0<K≦1, the cutoff frequency is constant, and when the value of K in the multiplication coefficient of the arithmetic circuit is K≧1, the cutoff frequency of the filter is changed in proportion to the value of K. A frequency characteristic adjustment circuit comprising: