JPH0230908Y2 - - Google Patents

Description

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

Generally, the sound quality of an audio device or the like is adjusted by enhancing or attenuating the low or high range, but this also changes the frequency at the bending point of the frequency characteristic, making adjustment difficult.
The present invention aims to provide a frequency characteristic 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
and 10 are filters, 3 is an arithmetic circuit that multiplies an input signal by a constant, 4 is an adder, and 5 is an output terminal. In this circuit, the filters 2 and 10 are low-pass and high-pass filters, or high-pass and low-pass filters, and the multiplication coefficient of the arithmetic circuit 3 is changed while keeping their cut-off frequencies at constant constant values, and the filters 2 and 10 are By changing the cutoff frequencies of 1 and 10 in relation to the multiplication coefficient, 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, high-pass and low-pass filters with a cutoff frequency of 1/2πT as shown in FIGS. 2 and 3 are used as filters 2 and 10, respectively.

Now, if the input signal is e ₁ , the output of filter 2 is e ₂
is e ₂ =jωT/1+jωTe ₁ …(1). Further, when the multiplication coefficient of the arithmetic circuit 3 is K, the output signal e ₃ of the arithmetic circuit 3 becomes e ₃ =K/1+jωTe ₁ (2). Therefore, if the composite output signal is e ₀ , then e ₀ = b ₂ + e ₃ = k1 + jω ^T/K /1 + jωTe ₁ ...(3), and if k is adjusted within the range of 0<k≦1, the bending point can be found. A low-frequency attenuation characteristic with a constant frequency can be obtained. An example of this is the frequency characteristic curve a in Figure 4.
Indicated by b, c, d (broken line approximate curve). Curve a is for k=1, and as k becomes smaller than 1, the curve becomes like b→c→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, high-pass and low-pass filters are used as filters 2 and 10, respectively, and the cutoff frequency is lowered in inverse proportion to the value of the multiplication coefficient k (that is, the cutoff frequency is 1/2πkT). )do. In the same manner as described above, the output signal e ₂ of the filter 2, the output signal e 3 of the arithmetic circuit ₃ , and the composite output signal
When calculating e ₀ , e ₂ = jωkT/1+jωkTe ₁ …(4) e ₃ = k/1+jωkTe ₁ …(5) e ₀ = e ₂ +e ₃ = k1+jωT/1+jωkTe ₁ …(6), and k≧ If the adjustment is made within the range of 1, low frequency enhancement characteristics as shown by the polygonal approximation curves a, e, f, and g in FIG. 4 can be obtained. 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, low-pass and high-pass filters may be used as filters 2 and 10, respectively. First, high-frequency attenuation characteristics can be obtained by keeping the cut-off frequencies of filters 2 and 10 constant at 1/2πT and adjusting k in the range of 0<k≦1, in the same way as when obtaining low-frequency attenuation characteristics. It will be done. That is, the combined output signal e ₀ is e ₀ =1/1+jωTe ₁ +jωT/1+jωT·k·e ₁ =1+jωkT/1+jωTe ₁ (7). In addition, for the high-frequency enhancement characteristic, when obtaining the low-frequency enhancement characteristic, the cutoff frequencies of filters 2 and 10 are raised in proportion to the value of k (in other words, the cutoff frequency is set to k/2πT). ) by using a filter and adjusting k in the range k≧1. In other words, the composite output signal e ₀ is e ₀ =1/1+jω ^T/K e ₁ +jω ^T/K /1+jω ^T / _K・k・e
₁ = 1 + jωT/1 + jω ^T/K e ₁ …(8). FIG. 5 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; as k becomes larger than 1, curve e'→f'→g'; as k becomes smaller than 1, curve b'→c'→
d', but the frequency at the bending point Q is constant at 1/2πT.

FIG. 6 is a circuit diagram showing an embodiment of the 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, 7 indicates an inverting amplifier, and 8 indicates an inverter. X, Y, and Z indicate interlocking variable resistors and their resistance values, and are configured as shown in FIG. 7, for example.
As shown in the figure, variable resistors Y and Z are made of a good conductor such as copper foil between their mechanical midpoint D and one terminal A of each, and a resistor such as carbon is made between the other terminal B. Made from the body. Further, the total resistance value of the portion of the variable resistor X corresponding to the above-mentioned good conductor portion is set to be r. Note that r, R ₁ , and R ₂ represent resistors and their resistance values, and C ₁ and C ₂ represent capacitors and their capacitance values. In this example, the cutoff frequencies of the low-pass and high-pass filters 10' and 2' are 1/2πC ₁ (R ₁ +Y) and 1/2πC ₂ (R ₂ +Z),
The multiplication coefficient k of the arithmetic circuit 3 is k=X/r. Therefore, in the case of low-frequency attenuation, adjustment is made within the range of 0<k≦1, but for this purpose, it is sufficient to adjust within the range of 0<X≦r, as shown by the solid line arrow in Figure 7. .
In Fig. 7, when adjusting _{the variable} resistor
= C ₂ R ₂ , the cutoff frequency of filters 10' and 2' is constant at 1/2πC ₁ R ₁ (=1/2πC ₂ R ₂ ), and therefore the frequency at the bending point is constant.

Furthermore, in the case of low frequency enhancement, since the adjustment is made within the range of k≧1, the adjustment may be made within the range of X≧r as indicated by the dashed-dotted line arrow in FIG. However, in order to set the cutoff frequency to 1/2πkC ₁ R ₁ (=1/2πkC ₂ R ₂ ), R ¹ +Y= kR ₁ , R ₂ +Z=kR ₂ and C ₁ R ₁ =C ₂ R ₂ , that is, Y
= (k-1) R ₁ , Z = (k-1) R ₂ and C ₁ R ₁ =
It needs to be C ₂ R ₂ . Now, when adjusting in the range of X≧r in Fig. 7, the resistance x shown in the figure,
Letting the resistance values of the y and z portions be x, y, and z, k=X/r=r+x/r=x/r+1. On the other hand, from the above condition Y=(k-1)R ₁ , k=Y/R ₁ + 1=y/R ₁ +1 is obtained. Therefore, from both equations, x/r=y/
We obtain the relationship R ₁ , that is, y/x=R ₁ /r. Similarly, z/x=R ₂ /r is obtained. Therefore, if variable resistors X, Y, and Z are configured to maintain such a proportional relationship, the cutoff frequency of filters 10' and 2' can be reduced to 1/2πkC ₁ R ₁ (=1/2πkC ₂ R ₂ ), and as mentioned above, the frequency at the bending point is constant at 1/2πC ₁ R ₁ (= 1/2πC ₂ R ₂ ).

Note that the output of the inverting amplifier 7 does not necessarily have to be inverted by the inverter 8 as shown in FIG. It is also possible to add the output. That is, referring to FIG. 6, first, the inverter 8 may be removed and this portion short-circuited, and the inverter 8 may be inserted between the filter 2' and the adder 4 instead. Even in this case, the same low frequency enhancement/attenuation characteristics as described above can be obtained.

As mentioned above, in the case of low-frequency adjustment, high-pass and low-pass filters are used as filters 2 and 10, respectively, and in the case of high-frequency adjustment, low-pass and high-pass filters are used, respectively. A configuration may be adopted in which both filters are switched between low frequency and high frequency. Since such a switch can be easily constructed, illustration and description thereof will be omitted. Furthermore, when the output impedance of the filter affects the gain of the arithmetic circuit (including an amplifier), a buffer amplifier is inserted after the filter.

It goes without saying that each variable resistor may be one in which a desired resistance value is selected from among a large number of fixed resistors by means of a changeover switch.

As explained above, according to the present invention, it is possible to obtain a frequency characteristic 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, thereby improving the sound quality. This has the advantage of being easy to adjust.

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 stated in the claims for utility model registration.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the basic configuration of the present invention, Figs. 2 and 3 are diagrams showing an example of filter characteristics used in the invention, and Fig. 4 shows an example of low frequency attenuation and enhancement characteristics. 5 is a diagram showing an example of high frequency attenuation and enhancement characteristics, and FIGS. 6 and 7 are a schematic circuit diagram showing an example of a low frequency sound quality adjustment circuit according to the present invention and its variable resistor, respectively. Connection diagram. 1... Input terminal, 2, 10... Low-pass or high-pass filter, 3... Arithmetic circuit, 4... Adder, 5
...Output terminal, X, Y, Z... Cutoff frequency variable means.

Claims (1)

[Scope of utility model registration request] a low-pass filter and a high-pass filter to which a common input signal is applied; an arithmetic means for multiplying the output of the low-pass filter by a variable coefficient K; and an output of the arithmetic means and the high-pass filter. and means for adding the output of the filter, and the coefficient K
When the coefficient K is 0<K≦1, the cutoff frequencies of the two filters are kept substantially constant, and when the coefficient K is K≧1, the cutoff frequencies of the two filters are varied in inverse proportion to the value of K. A frequency characteristic adjustment circuit comprising: