JPH0230909Y2 - - Google Patents

Description

[Detailed Description of the Invention] 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 enhancement or attenuation 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 and high-pass filter, and the multiplication coefficients of calculation circuits 3 and 8 are changed while keeping the 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 + jω ^T/K /1 + jωTe ₁ (3), and by adjusting K in the range of 0<k≦1, the bending frequency can be adjusted. A constant low frequency attenuation characteristic can be obtained. An example of this is the frequency characteristic curves a, b, and
It is shown as c, d (broken line approximate curve). Curve a is K=
1, and as K becomes smaller than 1, the curves become like b, c, d, but the bending point P
The frequency of 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 cutoff frequency is lowered in inverse proportion to the value of K in the multiplication coefficient (that is, whose cutoff 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, low-frequency enhancement characteristics as 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, when obtaining the aforementioned low-frequency enhancement characteristic, the cutoff frequency of filter 2 is raised in proportion to the value of K (in other words, the cutoff frequency is set to K/2πT). (b) can be obtained by using a filter 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+jω ^T/K e ₁ =1+jωT/1+jω ^T/K e ₁ (6). FIG. 4 is a polygonal approximate curve diagram showing an example of the high frequency enhancement and attenuation characteristics obtained in this manner. Curve a is for K=1, and as K becomes larger than 1, curves e', f', and g'appear; as K becomes smaller than 1, curves b', c', and
d', but the frequency at the bending point Q is constant at 1/2πT.

FIG. 5 is a circuit diagram showing an example of a low frequency sound quality adjustment circuit according to the present invention. In the figure, parts corresponding to those in FIG. 1 are given the same or similar symbols. Further, 6 is an adder, 7 and 9 are inverting amplifiers, and 10 is an inverter. X and Y indicate interlocking variable resistors and their resistance values, and are configured as shown in FIG. 6, for example. As shown in the figure, the variable resistor Y is assumed to have a good conductor portion such as a copper foil, and the total resistance value of the portion of the variable resistor X corresponding to this good conductor portion is set to be r. Note that r in Figure 5
And, R ₁ is a resistor and its resistance value, and C ₁ is a capacitor and its capacitance value. In this example, T = C ₁ (R ₁ +Y) at the cutoff frequency 1/2πT of the high-pass filter 2, and the multiplication coefficient (1-K) of the arithmetic circuit 3 becomes 1 at the output terminal of the adder 6. -X/r, and the multiplication coefficient K of the arithmetic circuit 8 is K=X/r. Therefore, in the case of low frequency attenuation, 0<K≦1
For this purpose, the adjustment should be made within the range of 0<X≦r, as indicated by the solid line arrow in FIG. In Fig. 6, when adjusting _{the variable} resistor The cutoff frequency is constant at 1/2πC ₁ R ₁ , and therefore the frequency at the bending point is constant. In addition, in the case of low frequency enhancement, the adjustment is made within the range of K≧1, so
It may be adjusted within the range of ≧r. However, in order to set the cutoff frequency to 1/2πKC ₁ R ₁ , it is necessary to set R ¹ +Y=KR ₁ , that is, Y=(K-1)R ₁ . now,
When adjusting in the range of X≧r in Fig. 6, the resistance value of the part of the resistance X shown in the figure where X≧r
Then, K=X/r=r+x/r=x/r+1.

On the other hand, from the above condition Y=(K-1)R ₁ , K=
We get Y/R ₁ +1. Therefore, from both equations, we obtain the relationship x/r=y/R ₁ , that is, Y/x=R ₁ /r. Therefore, if the variable resistors X and Y are configured to maintain this relationship, the cutoff frequency of the filter 2 can be set to 1/2πKC ₁ R ₁ , and as mentioned above, the frequency at the bending point is 1/2πKC 1 R 1. It becomes constant at 2πC ₁ R ₁ .

As mentioned above, a high-pass filter is used for low-frequency adjustment, and a low-pass filter is used for high-frequency adjustment, so use an appropriate switch to switch between the two for low and high frequencies. It may be configured as follows. Since such a switch can be easily constructed, illustration and description thereof will be omitted. In addition, 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 low-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 low or high frequency range. This has the advantage of making it easy to adjust the sound quality.

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 the low-frequency attenuation and enhancement characteristics of the present invention. Diagram showing an example of
5 is a diagram showing an example of high frequency attenuation and enhancement characteristics, FIG. 5 is a circuit diagram showing an example of the low frequency sound quality adjustment circuit according to the present invention, and FIG. 6 is a connection diagram showing an interlocking variable resistor. 1...Input terminal, 2...High pass filter, 3, 8
...Arithmetic circuit, 4...Adder, 5...Output terminal, X, Y
... Cutoff frequency variable means.

Claims (1)

[Scope of utility model registration request] By adding the input signal to a signal obtained through a series connection circuit of a high-pass filter and the first calculation means and the signal obtained from the input signal to the second calculation means to obtain an output signal, the frequency characteristics can be changed. 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 above arithmetic circuit. When the value of K 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 variable in inverse proportion to the value of K. A frequency characteristic adjustment circuit comprising means.