JPH07170594A - Equalizer and audio device using the same - Google Patents

Abstract

PURPOSE:To improve the sound quality by produing a 1st control signal of a level corresponding to the sound quality enhancement when the enhancement is indicated and by producing a 2nd control signal corresponding to the sound quality attenuation when the attenuation is indicated. CONSTITUTION:In the emphasis adjustment state, the voltage generated by a variable resistor 12 becomes higher than the Vc and an inverter amplifier 26a accepts it so as to make the output voltage lower than the voltage Vref and V/I converter circuit 26b converts it into the current value. Thus, the current of the variable current source 5 id deteriorated lower than the prescribed value and the attenuation amount of an attenuation circuit 21 is deteriorated and the output is increased. In the attenuation state, the circuit 21 stops and only am attenuation circuit 22 is operated. The audio signal Vo is returned to the circuit 22 and the phase of the signal is inverted by an adder 23. The only signal whose phase in the specified frequency band is inverted through a filter 24 and is added to an original audio signal Vi. As the result, the level of the signal Vi is reeduced depending on the output level of the filter 24 and is attenuated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an equalizer and an audio device using the equalizer, and more particularly to an audio device having an equalizer therein such as a graphic equalizer or a surround processor.
The present invention relates to an audio device capable of improving the S / N ratio of the equalizer.

[0002]

2. Description of the Related Art FIG. 6 is an explanatory diagram of a cassette tape player having an equalizer as an example of a conventional audio device. The figure shows an outline of a reproduction circuit for one channel, and in a stereo device, a similar circuit has two left and right channels. Reference numeral 1 is a read head, 2 is a preamplifier, 10 is an equalizer, 3 is a main amplifier, and 4 is a speaker. This type of cassette tape recorder reads an audio signal magnetically recorded on a tape (not shown) with a reading head 1, amplifies the audio signal with a preamplifier 2, etc., and further adjusts the sound quality of the audio signal with an equalizer 10. The adjusted signal is added to the main amplifier 3, the power of the signal is amplified, and the speaker 4 outputs the sound. By operating the variable resistor 12 while listening to this, the listener changes the sound quality according to his / her preference.

The equalizer 10 is an operational amplifier (OP) 1
Non-inverting input terminal (hereinafter (+)
Input) and an inverting input terminal (hereinafter referred to as (-) input) which is a phase input on the negative side (variable resistor (VR) 1 of resistance R1)
2 is connected, and the variable terminal of VR 12 is grounded via the series resonance circuit 13 of LCr. The output signal (voltage signal) Vo of the operational amplifier 11 is fed back to the (−) input via the resistor Ro, and the input signal (voltage signal) Vi is supplied via the resistor Ri. Here, assuming that the open loop gain of the operational amplifier 11 is GA, GA >> 1, and the resistance values of the resistors Ri and Ro are Ri = Ro = R, the following relationship is established. However, Ri and Ro are resistance values of the resistance Ri and the resistance Ro, respectively. Further, both terminals of VR 12 are designated as points A'and B'as shown in the figure.

When the variable terminal of the variable resistor 12 is at the point A ', the input / output relationship at the resonance frequency fo of the series resonance circuit 13 is expressed by the following equation. Since the (+) input and the (-) input are virtual shorts, no current flows through the variable resistor 12 at this time. Therefore, the operational amplifier 11 becomes a buffer amplifier. Note that r is the resistance value of the resistor r in the resonance circuit 13. As a result, the output signal is attenuated with respect to the input signal. When the variable terminal of the variable resistor 12 is at the point B ′, the input / output relationship at the resonance frequency fo of the series resonance circuit 13 is as follows. Even at this time, no current flows through the variable resistor 12. Therefore, the operational amplifier 11 operates as a normal amplifier circuit. As a result, the output signal is amplified and emphasized with respect to the input signal. When the variable terminal of the variable resistor 12 is at the midpoint, the input / output relationship at the resonance frequency fo of the series resonant circuit 3 is Ri.
= Ro = R, the voltage ratio with respect to the input voltage applied to the (+) input becomes equal to the amplification factor of the operational amplifier 11, and the same input voltage V1 is generated at the (+) input and the (-) input, so that Vo = Vi. From the above relational expression, this circuit has the function of an equalizer centered on the resonance frequency fo.

The above is the case where there is one series resonance circuit 13. Usually, a CD radio cassette recorder, a component stereo device, or the like has a graphic equalizer circuit which divides an audio band into about 5 to 7 and handles the divided audio band. Each resonant circuit performs a filtering operation for attenuation or enhancement over a band having a specific center frequency. In this type of circuit, 5 to 7 series resonance circuits 13 and variable resistors 12 having different center frequencies fo are connected in parallel between the (+) input and the (-) input of the operational amplifier 11, respectively.

Therefore, a large number of variable resistors 12 are connected to the input side of the operational amplifier 11. Since these variable resistors 12 are arranged and operated on the side of the operation panel, it is necessary to wire them. Moreover, since an audio signal flows through the variable resistor 12, this type of equalizer has a drawback that it is easily affected by noise due to such wiring. Therefore, Japanese Patent Laid-Open No. 63-276312 can be cited as a circuit that has improved such a drawback. This circuit, as shown in FIG.
The variable resistor 12 is not provided on the input side of. Instead, a voltage-current conversion circuit (hereinafter V / I conversion circuit) 3
0 and 31 are provided on the input side, and the current values of these circuits are controlled by the variable resistor 12. As a result, the variable resistor 12 for adjusting the sound quality is separated from the audio signal, so that noise is reduced.

The V / I conversion circuits 30 and 31 receive an input signal via the active filter 32 and convert a voltage signal in a predetermined frequency band into a current value. The current values converted here are added to the (+) input and the (−) input of the operational amplifier 11, respectively. As a result, a signal attenuated or emphasized with respect to the signal in the band extracted by the active filter 32 is obtained. The V / I conversion circuits 30 and 31
Are differentially operated with respect to each other in accordance with the operation of the circuit including the variable resistor 12. This circuit reduces the noise caused by the wiring between the variable resistor and the amplifier,
The S / N ratio is improved as compared with the circuit of FIG. However, this circuit requires a resistor Ri in series on the input side, and its value must be set to be approximately the same value as the feedback resistor Ro of the operational amplifier 11. This relationship imposes restrictions on the circuit design and limits the level of the input voltage Vi.
Therefore, depending on the bias voltage of the input signal, the dynamic range cannot be sufficiently taken and the S / N ratio is not sufficient.

Therefore, the applicant has proposed a circuit which is not easily limited by the bias of the input signal, has a large dynamic range, and has a good S / N ratio.
It has been filed as No. 51606. The circuit is shown in FIG. In FIG. 8, V / which receives the input signal Vi
An I conversion circuit 37, an active filter 33 that receives the output, an operational amplifier 11, a load resistor RL, a V / I conversion circuit 34a, and a V / I conversion circuit 35a are provided. The variable resistor 12 is controlled by the control circuit 36 to V
The I / I conversion circuits 34a and 35a are completely separated.

Here, the load resistance RL receives the output of the V / I conversion circuit 37. The operational amplifier 11 receives the voltage VL generated in the load resistance RL at its (+) input, and the output side is fed back to the (-) input via the feedback resistance Ro. The output side of the V / I conversion circuit 34a is connected to the (+) input of the operational amplifier 11 (= the voltage generation side of the load resistance RL), receives the output of the active filter 33, and responds to the current value of the variable current source 34b. The gain is controlled. The output side of the V / I conversion circuit 35a is connected to the (−) input of the operational amplifier 11, and the active filter 33
Of the variable current source 35b, and its gain is controlled according to the current value of the variable current source 35b. Then, the V / I conversion circuit 34a
And the variable current sources 34 of the V / I conversion circuits 35a.
The current values of b and 35b are controlled by the DC signal from the control circuit 36.

In this way, the V / I conversion circuit 37 is provided on the input side.
Is provided to receive the input signal Vi, and a current corresponding to the voltage level of the input signal Vi is passed through the load resistor RL to generate the voltage VL. Then, this voltage VL is applied to the operational amplifier 11. Further, the active filter 33 receives the current of the V / I conversion circuit 37 for attenuating and emphasizing a signal in a specific frequency band of the input signal, and generates a voltage signal corresponding to the frequency band, V / provided on the attenuation side and the emphasis side respectively
The I conversion circuits 34a and 35a convert the current values. Further, the current conversion output of the V / I conversion circuit 34a is added to the load resistance RL to form a voltage signal, which is added to the input signal Vi. The output of the V / I conversion circuit 34a is added to the (-) input of the operational amplifier 11 and subtracted from the input signal. With this configuration, the resistor R is connected in series with the input side.
You don't have to insert i. As described above, since the input side is the V / I conversion circuit, and the resistance is inserted in parallel to the input of the amplifier circuit such as the operational amplifier, there is a degree of freedom in setting the input bias, and the dynamic range is sufficient. Can be secured. Moreover, since the control is not based on the direct control by the variable resistance circuit but is based on the DC signal, a large S / N ratio can be obtained.

[0011]

In such a conventional audio apparatus, the frequency of a certain band of the audio signal is extracted by a filter and divided into two, an attenuation system and an emphasis system, and a specific system is specified. It is an equalizer that generates a signal in which only the frequency band is attenuated or emphasized and adds or subtracts the signal from the original audio signal. As a result, the sound quality is improved over the conventional one.
However, from the user of the audio device, S
There is a demand to improve the / N ratio. An object of the present invention is to provide an equalizer having a good S / N ratio, which meets such a demand. Another object of the present invention is S
An object of the present invention is to provide an audio device capable of adjusting sound quality with a good / N ratio.

[0012]

The features of the equalizer of the present invention for achieving such an object are that an equalizer receives an audio signal as an input signal and generates a signal in a specific frequency band of the input signal. An equalizer that generates an audio signal adjusted to one of sound quality attenuation and sound quality enhancement by adding or subtracting this to or from the audio signal, receives the input signal and a first control signal, and receives the input signal. A first attenuator circuit for attenuating a signal according to the level of the first control signal, a filter of the specific frequency band for receiving an output of the first attenuator circuit, an output of the filter and the input signal Receiving the added signal and adding them to output the adjusted audio signal, and the adjusted audio signal and this signal from the adding circuit. Receiving a second control signal and any one of the signals corresponding to the above, attenuating any one of the signals according to the level of the second control signal, and transmitting a signal whose phase is inverted to the filter. And an attenuator circuit for receiving the sound quality adjustment signal, and when the sound quality adjustment signal indicates the sound quality enhancement, the first control signal having a level corresponding to the enhancement state is generated, and the sound quality adjustment signal is attenuated by the sound quality adjustment signal. , The second control signal having a level corresponding to the attenuation state is generated.

[0013]

By thus arranging the filter after the attenuating circuit, the attenuating circuit first performs the attenuation, and then the filter extracts the specific frequency band. As a result, the noise generated in the attenuating circuit is also processed by the filter, so that the frequency components of the noise generated in the attenuating circuit other than the specific frequency band are blocked by the filter. Therefore, the noise component included in the signal for adjusting the sound quality is reduced as compared with the related art by the cutoff amount. Furthermore, since the input signals of the first attenuator circuit and the second attenuator circuit are independent of each other, they are not influenced by each other. Further, a feedback loop is formed in the attenuation state in which the sound quality is deteriorated. These reduce noise. Therefore, the S / N ratio of the audio signal whose sound quality has been adjusted can be improved as compared with the related art. Further, if the operations of the first and second attenuating circuits are stopped in the sound quality unadjusted state, the original audio signal and the equalized signal are separated from each other, so that the sound quality is improved.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of a reproducing circuit for one channel in a cassette player, as in FIG. In a stereo device, a similar circuit has two left and right channels. In addition, the same components as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted. The difference between FIG. 6 and FIG. 1 is that an equalizer 20 is provided instead of the equalizer 10. The equalizer 20 includes an attenuation circuit 21, an attenuation circuit 22, an addition circuit 23, a filter 24, an addition circuit 25, and a control circuit 2.
It consists of 6 and 6. The control circuit 26 receives the sound quality adjustment signal from the variable resistor 12 arranged on the operation panel side, and controls the attenuation currents A and B (hereinafter control signals A and B) to the attenuation circuits 22 and 21 according to the voltage value thereof. Respectively. These control signals are DC signals resistant to noise. In addition,
The contents of the control signals A and B will be described later.

The attenuator circuit 21 receives the audio signal Vi as an input and at a conversion ratio according to the current level of the control signal A,
The input signal is attenuated and output. This output is added to the (+) input of the adder circuit 23. As a result, the output of the adder circuit 23 has the same phase as the original audio signal Vi, and this becomes an added signal when viewed from the original audio signal Vi to which it is added later. Therefore, the path passing through the attenuation circuit 21 becomes the emphasis system. The attenuation circuit 22 uses the audio signal V
With o as an input, the input signal is attenuated and output at a conversion ratio according to the current level of the control signal B. This output is added to the (−) input of the adder circuit 23. As a result, the output of the adder circuit 23 is inverted in phase with respect to the original audio signal Vi. Since the output of the adder circuit 23 is the phase-inverted output, it becomes a subtraction signal in view of the original audio signal Vi to which it is added later. Therefore, the path passing through the attenuation circuit 22 becomes an attenuation system.

The attenuator circuit 21 comprises a variable current source 5 whose current value is controlled according to the value of the control signal A, and a V / I conversion circuit 6 for attenuating operation having the variable current source 5, and the attenuator circuit 22.
Is a variable current source 7 whose current value is controlled according to the value of the control signal B and a V / I conversion circuit 8 for attenuation operation having the variable current source 7.
Composed of and. The V / I conversion circuits 6 and 8 decrease the V / I converted output current in accordance with the increase in the current of the variable current source. These are the same as the configuration of the V / I conversion circuit 34a and its variable current source 34b in FIG. 8, but the control operation thereof is different. Normally, in the V / I conversion circuit, the conversion current increases as the current of the current source increases. Therefore, when the attenuation operation is performed, the conversion current is decreased according to the decrease in the current, but the attenuation circuits 21 and 22 perform the opposite operations. The reason will be described later.

Here, the filter 24 is arranged after the adder circuit 23 and receives the output of the adder circuit 23.
As a result, of the signal components of the output of the adder circuit 23, only the frequency component of the specific frequency band determined by the filter characteristic is output. Frequency components other than that band are blocked. As a result, noise can be reduced more than ever before. The same applies to noise superimposed on the output of the attenuation circuit 22. The output of the filter 24 is added to the (+) input of the adder circuit 25. The audio signal Vi is added to the other (+) input of the adder circuit 25.
The addition result of the two signals of the adder circuit 25 is output as the audio signal Vo. The control circuit 26 includes a inverting amplification amplifier 26a and a V / I conversion circuit 26b for generating a control signal A, a normal amplification amplifier 26c, and a V / I conversion circuit 26b.
I conversion circuit 26d and a control signal B generation circuit, and an inverting amplification amplifier 26a and a non-inversion amplification amplifier 2 are provided.
6c and 6c respectively receive the voltage value of the sound quality adjustment signal from the variable resistor 12.

First, when the setting of the variable resistor 12 is at the midpoint, that is, when the sound quality is not adjusted, the current amounts of the control signals A and B are set to predetermined values and the variable current sources 5 and 5 are set.
The current of 7 is set to a predetermined value I or more so that the attenuation amount of each of the attenuating circuits 21 and 22 is infinite and the respective outputs are stopped. As a result, the outputs of the adder circuit 23 and the filter 24 become "0". As a result, the attenuation circuit 2
The outputs of 1 and 22 become "0". Here, the variable resistor 1
Assuming that the voltage at the middle point of 2 is Vc, the inverting amplification amplifier 26a and the non-inversion amplification amplifier 26c of the control circuit receive it and generate the voltage Vref respectively. This is the V / I conversion circuit 26
The b and V / I conversion circuits 26d respectively convert the current values. Thereby, the currents of the variable current sources 5 and 7 are set to the predetermined value I or more.

In the damping adjustment state when the variable resistor 12 is operated below the midpoint, the voltage generated by the variable resistor 12 becomes Vc or less. Sometimes, the control signal A
Is set to the predetermined value or more, and the current level of the control signal B is increased according to the operation amount from the middle point to the lower side of the variable resistor 12. That is, the variable resistor 12
If the voltage of V is less than Vc, the inverting amplification amplifier 26a of the control circuit receives it and raises the output voltage to Vref or more. This is converted into a current value by the V / I conversion circuit 26b.
As a result, the current of the variable current source 5 is set to I or more.
On the other hand, when the voltage of the variable resistor 12 becomes Vc or less, the non-inverting amplifier 26c of the control circuit receives this and sets the output voltage to the voltage Vref or less. This is converted into a current value by the V / I conversion circuit 26b. As a result, the current of the variable current source 7 drops below the predetermined value I. Therefore, the amount of attenuation of the attenuation circuit 22 decreases and the output increases. Since this is a subtraction amount with respect to the original audio signal, the output Vo is attenuated by this. In this case, the voltage of the variable resistor 12 decreases according to the operation amount, so that the audio signal whose sound quality has been adjusted attenuates according to the operation amount. At this time, the attenuation circuit 21 stops operating. By the way, when the voltage of the variable resistor 12 is Vc or less, the output of the inverting amplification amplifier 26a is changed to Vre.
A circuit that clamps to f may be added to this. As a result, the current value of the current source 5 is fixed to I in the above case.

In the emphasis adjustment state when the variable resistor 12 is operated above the midpoint, the voltage generated by the variable resistor 12 becomes Vc or more. Sometimes, the control signal B
Is set to the predetermined value or more, and the current level of the control signal A is increased according to the operation amount from the midpoint to the upper side of the variable resistor 12. That is, the variable resistor 12
If the voltage of Vc becomes Vc or more, the inverting amplification amplifier 26a of the control circuit receives this and reduces the output voltage to Vref or less. This is converted into a current value by the V / I conversion circuit 26b.
As a result, the current of the variable current source 5 drops below the predetermined value I. On the other hand, if the voltage of the variable resistor 12 becomes Vc or more,
The normal amplification amplifier 26c of the control circuit receives this and raises the output voltage to the voltage Vref or higher. This is the V / I conversion circuit 26
Convert to a current value with b. As a result, the current of the variable current source 7 is set to I or higher. Therefore, the amount of attenuation of the attenuation circuit 21 decreases and the output increases. This is an addition amount with respect to the original audio signal, so that the output Vo becomes large. In this case, the voltage of the variable resistor 12 rises according to the operation amount, so that the audio signal whose sound quality is adjusted is emphasized according to the operation amount. At this time, the attenuation circuit 22
Has stopped working.

By the way, in the same manner as described above, the variable resistor 12
A circuit for clamping the output of the non-inverted amplification amplifier 26c to Vref when the voltage is higher than Vc may be added thereto. As a result, the current value of the current source 7 is fixed to I in the previous period. As a result, the variable resistor 12 enables sound quality adjustment including attenuation adjustment, non-adjustment, and enhancement adjustment by the same operation as in the conventional case. The relationship between the operation of the equalizer 20 having such a configuration and noise will be described. First, when the sound quality is not adjusted by the variable resistor 12, the output level of the filter 24 becomes "0", so the audio signal Vi becomes the audio signal Vo as it is without adjustment. Therefore, the influence of noise due to the equalizer can be eliminated, and a signal with high sound quality is output.

Next, when the damping state is set, the damping circuit 21 stops and only the damping circuit 22 operates. The audio signal Vo is returned to the input of the attenuation circuit 22, and the attenuation signal is phase-inverted by the addition circuit 23 and added to the filter 24. Then, only the signal whose phase is inverted in a specific frequency band through the filter 24 is the original audio signal Vi.
Added to. As a result, the level of the audio signal Vi is reduced and attenuated according to the output level of the filter 24. Moreover, in the circuit in this case, since the attenuation is adjusted by the feedback system, the influence of noise is reduced as compared with the case of FIG. In the emphasized state, the damping circuit 22 stops and only the damping circuit 21 operates. Then, the attenuated signal is added to the original audio signal Vi only via the adder circuit 23 and the filter 24, in-phase signal of a specific frequency band. As a result, the level of the audio signal Vi is increased and emphasized according to the output level of the filter 24.

In the above case, the emphasizing circuit and the attenuating circuit are independent from each other and the signal input sides are independent of each other, so that they are not easily affected by noise. By the way, if the V / I conversion circuits 6 and 8 are configured to increase the conversion current in accordance with the increase in the current of the current source, the above-mentioned control is performed by changing the current of the current sources 5 and 7 in the sound quality unadjusted state. The control is such that the current is increased to 0 "and the current is increased according to the operation of the variable resistor 12. Although such control is possible, even if the current of the current source is set to "0", there is a leak, and it is difficult to completely stop the operation of the attenuation circuits 21 and 22. Therefore,
From the viewpoint of reducing noise, the above control is preferable.

The configuration of FIG. 1 shows a circuit for adjusting only one frequency band for an audio signal of only one channel. This is the basic minimum configuration. As described above, in a CD radio cassette recorder, a component stereo device, etc., the equalizer circuit is
It is responsible for dividing the audio band into about 5 to 7. Therefore, the circuit of FIG. 1 includes the attenuation circuits 22 and 21, and the control circuit 2.
By providing a plurality of 6, adder circuits 23, filters 24, etc. in parallel according to the number of divisions, it can be applied as a graphic equalizer for various audio devices. FIG. 4 shows the graphic equalizer and its control circuit 27 'in such a case. Each equalizer 20a, 20b,
..., 20n are addition circuits 2 in the equalizer 20.
5 and the control circuit 26 are equalizer circuits, and their respective filters 24a, 24b, ..., 24n
Have different center frequencies with respect to the filter 24 so as to correspond to the respective sound quality adjustment signals. The control circuit 26 is replaced with a control circuit 27 ', and each of the control circuits 27' has an equalizer 20a, 20b, ...
.., variable resistors 12a, 12b, ...
., 12n to receive the respective sound quality adjustment signals, and generate control signals A and B to the equalizers having filters corresponding to the respective sound quality adjustment signals.

FIG. 2 shows a practical circuit of the equalizer 20. This is basically the same as the circuit of FIG. In this circuit, the attenuation circuit 21 for receiving the audio signal Vi of FIG. 1 is composed of a V / I conversion circuit section 27 and an attenuation circuit section 21a, and the V / I conversion circuit section 27 and its active loads LA, LB, The transistors Q1 and Q2 of the attenuation circuit section 21a which receives the output from these loads form a V / I conversion section. The variable current source comprises a transistor Q3 having its emitter connected to the emitter of the transistor Q1, Q4 having its emitter connected to the emitter of the transistor Q2, and a variable voltage circuit V1. In this current source, the base voltages of the transistors Q3 and Q4 are controlled by the control signal A of the control circuit 26 via the variable voltage circuit V1, and the collector currents of the transistors Q1 and Q2 are controlled by this. The collector currents of the transistors Q1 and Q2 are converted current values, and the current mirror circuit 23 of the adding circuit 23
a, 23b.

Here, the input signals Vi are mutually 18 due to the active loads LA and LB of the V / I conversion circuit section 27.
It is converted into two current values having different 0 ° phases. These are added to the emitters of the transistors Q1 and Q2, respectively, and the remaining current of these currents minus the current value supplied by the transistors Q3 and Q4 is the transistor Q1.
It is generated as the collector output of 1 and Q2. Similarly, the transistors Q9 and Q10 and the current mirror circuits 25a and 25b provided in the adder circuit 25 have V / V for the output Vo.
In the I conversion circuit section, two currents which are inverted with respect to the output Vo and are 180 ° out of phase with each other are taken out, and these currents are used as input signals for the attenuation circuit section 22a.
To the emitters of the transistors Q5 and Q6. Here, the transistors Q9 and Q10 and the current mirror circuit 25
a, 25b, and V due to the transistors Q5 and Q6
The / I conversion part is configured. The variable current source comprises a transistor Q7 whose emitter is connected to the emitter of the transistor Q5, Q8 whose emitter is connected to the emitter of the transistor Q6, and a variable voltage circuit V2.

The specific operation is the above-mentioned transistor Q1.
, Q2, Q3, and Q4 are transistors Q5 and Q6, respectively.
, Q7, Q8, the variable voltage circuit V2 corresponds to the variable voltage circuit V1 and the input signal is the signal on the output side, the attenuating circuit section 22a differs from the attenuating circuit section 21a. Do the same. I will omit the detailed explanation. The variable voltage circuits V1 and V2 are composed of I / V conversion circuits that convert the current values of the control signals A and B into voltage values.

The adder circuit 23 includes transistors Q1 and Q2.
, Q5 and Q6 collector outputs are taken as mutually opposite phase outputs via the current mirror circuits 23a and 23b. Then, the current mirror circuit 23c takes out these added outputs. At this time, the outputs of the transistors Q5 and Q6 are 180 ° in phase with the input signal Vi.
Since they are different, they are subtracted with respect to the input signal Vi. A current-voltage conversion circuit (I / V conversion circuit) 28 is provided in front of the filter 24 that receives the output of the addition circuit 23. Further, the adder circuit 25 that receives the output of the filter 24 is provided with a V / I conversion circuit on its input side. Filter 24 may be an active filter, but in this embodiment filter 24 is not an active filter. Therefore, the I / V conversion circuit 28
The current signal is converted into a voltage signal by and the converted signal is applied to the CR filter. Then, a V / I conversion circuit is provided on the input side of the adder circuit 25 to convert the voltage signal obtained from the CR filter into a current signal again.

The adder circuit 25 includes a transistor Q9 whose output is the filter 24 and whose load is the current mirror circuit 25a.
And the input signal Vi is received by the transistor Q10 having the current mirror circuit 25b as a load. Then, the added output of these input signals is sent from the current mirror circuit 25a to the current mirror circuit 25c, and is further converted into a voltage value by the load resistor R. Then, this voltage value is applied to the buffer amplifier 29, and the output voltage Vo is obtained at the output of the buffer amplifier 29. Here, because the current signal is generated as the output signal to be sent to the subtraction circuit section 22a by the addition circuit 25, the current mirror circuit 2
An I / V conversion circuit including 5c, a load resistor R, and a buffer amplifier 29 is provided in front of the main amplifier 3. The current signal fed back to the input of the attenuation circuit 22 is obtained by converting the audio signal Vo into a current value,
It is a signal equivalent to the audio signal Vo. Further, the attenuator circuit in this embodiment has a V / V
It is a V / I conversion circuit composed of an I conversion circuit part.

Now, when the variable resistor 12 is in the sound quality unadjusted state at the intermediate position, the control circuit 26 applies the voltages of the variable voltage circuits V1 and V2 to the transistors Q1, Q2, Q5,
A control signal A having a current value for setting a high predetermined voltage level for maintaining Q6 in the OFF state is generated. At this time the load L
The current drawn into A and LB becomes the current from the transistors Q2 and Q4 of the current source, and the output of the attenuation circuit 21 stops. Similarly, at this time, the current mirrors 25a, 2
The current drawn into 5b is the current source transistor Q7.
, Q8, the output of the attenuation circuit 22 is stopped. When the variable resistor 12 is operated above its center position, the control circuit 26 receives a voltage value higher than the intermediate position, and the control circuit 26 sets a voltage level lower than the predetermined voltage level according to the operation amount. A control signal A having a current value to be set is applied to the variable voltage circuit V1. In response to this, the collector currents of the transistors Q1 and Q2 increase, and the output of the attenuation circuit 21 increases. At this time, the control signal B is
A current value set above a predetermined voltage level is generated to maintain the transistors Q5 and Q6 in the OFF state.

On the other hand, when the variable resistor 12 is operated below the central position, the control circuit 26 receives a voltage value lower than the intermediate position and the control circuit 26 controls the operation amount lower than the predetermined voltage level. A control signal B having a current value for setting a voltage level according to the above is applied to the variable voltage circuit V2. In response to this, the collector currents of the transistors Q5 and Q6 increase, and the output of the attenuation circuit 22 increases. At this time, the control signal A generates a current value to be set to a predetermined voltage level or higher and maintains the transistors Q1 and Q2 in the OFF state. With the above operation, control from attenuation to enhancement is performed according to the operation of the variable resistor 12.

By the way, in the above-mentioned embodiment, one variable resistor 12 is provided and the sound quality is emphasized when the middle point position is not adjusted and the sound quality is emphasized, and the sound quality is attenuated when it is operated downward. However, the variable resistor for setting the emphasized state and the variable resistor for setting the attenuated state may be separately provided and each voltage may be input to the control circuit 26. FIG. 5 shows this embodiment. The voltage input to the inverting amplifier 26a is the variable resistor 1
2a, the voltage input to the non-inverting amplifier 26c is only the voltage from the variable resistor 12b, and the control signals A and B generated by the control circuit 26 are the same as above. .

FIG. 3 shows another embodiment. This is
While the equalizer 20 in 2 is configured by using two attenuating circuits, the equalizer 200 uses only one attenuating circuit 21 in FIG. Therefore, a phase inversion circuit 201 and a switching circuit 202 are provided. The audio signal Vo is inverted by the phase inverting circuit 201 and output to the switching circuit 202. The switching circuit 202 includes the control circuit 26a.
The control signal C is received from the input terminal and the input is switched to either the output of the phase inverting circuit 201 or the audio signal Vi.

When the operation position of the variable resistor 12 is in the emphasized state, the control circuit 26a generates the control signal C, which causes the switching circuit 202 to switch to the audio signal Vi side input, and the output of the damping circuit 21. It is input. On the other hand, when the operation position of the variable resistor 12 is in the attenuated state, the control signal C from the control circuit 26a is stopped or inverted and the phase inversion circuit 2 is operated according to this signal.
The output of 01 is selected as the input. At this time, the audio signal Vo inverted by the phase inversion circuit 201 becomes the input of the attenuation circuit 21. And in any case,
The output of the attenuation circuit 21 passes through the filter 24 and the addition circuit 25.
And is added to the audio signal Vi. In addition,
The control signal 26a in this case is provided with a circuit for generating the control signal C in the control circuit 26 and a circuit for ORing the control signals A and B and outputting the result to the attenuation circuit 21.

Although the control signals A and B in the embodiment have been described as current signals respectively as described above, it goes without saying that they may be voltage signals. Further, of the attenuation circuits 21 and 22, the attenuation circuit 2 of the sound quality enhancement system.
1 may have not only attenuation but also a function of amplifying an input signal.

[0036]

As can be understood from the above description, in the present invention, since the filter is arranged after the attenuating circuit, the attenuating circuit first performs the attenuating, and then the filter causes the specific frequency to be reduced. Band extraction is performed. As a result, the noise generated in the attenuating circuit is also processed by the filter, so that the frequency components of the noise generated in the attenuating circuit other than the specific frequency band are blocked by the filter. Therefore, the noise component included in the signal for adjusting the sound quality is reduced as compared with the related art by the cutoff amount. Furthermore, since the input signals of the first attenuator circuit and the second attenuator circuit are independent of each other, they are not influenced by each other. Further, a feedback loop is formed in the attenuation state in which the sound quality is deteriorated. These reduce noise. As a result, the S / N ratio of the audio signal whose sound quality has been adjusted can be improved as compared with the related art. Furthermore, with no sound quality adjustment,
If the operations of the first and second attenuating circuits are stopped, the original audio signal and the equalized signal are separated, so that the sound quality is improved.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a cassette tape player having an equalizer of the present invention.

FIG. 2 is a detailed circuit diagram of the equalizer.

FIG. 3 is a block diagram of another embodiment of the cassette tape player having the equalizer of the present invention.

FIG. 4 is an explanatory diagram when the equalizer of the present invention is applied to a graphic equalizer having a large number of equalizers.

FIG. 5 is an explanatory diagram of a case where variable resistors for enhancing sound quality and for reducing sound quality are provided independently of each other.

FIG. 6 is a schematic diagram of a conventional cassette tape player.

FIG. 7 is a circuit diagram of an example of a conventional graphic equalizer.

FIG. 8 is a circuit diagram of the graphic equalizer of the Japanese application filed previously.

[Explanation of symbols]

1 ... Read head, 2 ... Preamplifier, 3 ... Main amplifier,
4 ... Speaker, 5, 7 ... Variable current source, 6, 8 ... I conversion circuit, 10, 20 ... Equalizer, 12 ... Variable resistor, 2
1, 22 ... Attenuation circuit, 24 ... Filter, 23, 25 ... Addition circuit, 26 ... Control circuit, 26a ... Inversion amplification amplifier, 2
6b, 26d ... V / I conversion circuit, 26c ... Forward amplification amplifier.

Claims (4)

[Claims] 1. An audio signal is received as an input signal, a signal of a specific frequency band of the input signal is generated, and the signal is added to or subtracted from the audio signal to perform sound quality attenuation or sound quality enhancement. An equalizer for generating an audio signal adjusted to the sound quality of the first, receiving the input signal and a first control signal, and attenuating the input signal according to the level of the first control signal.
Attenuator circuit, a filter of the specific frequency band that receives the output of the first attenuator circuit, an adder that receives the output of the filter and the input signal, adds them, and outputs the adjusted audio signal. A circuit and a second control signal and one of the adjusted audio signal and a signal corresponding to the adjusted audio signal from the adder circuit, and the one of the signals is attenuated according to the level of the second control signal. A second attenuator circuit for transmitting a signal whose phase has been inverted to the filter, and a first control signal having a level corresponding to the emphasized state when the sound quality adjustment signal is received and indicates the sound quality enhancement. And a control circuit which, when the sound quality adjustment signal indicates the sound quality attenuation, generates the second control signal of a level according to the attenuation state, Equalizer. 2. The first and second control signals further include:
The equalizer according to claim 1, wherein when the sound quality adjustment signal indicates that sound quality is not adjusted, the signal has a level at which the operations of the first and second attenuation circuits are stopped. 3. The first and second attenuating circuits each include a current source, and the first and second control signals are current signals, respectively. The current value of each of the current sources increases and the output current value of each of the first and second attenuation circuits decreases in accordance with an increase in the amount of current, and the first and second attenuation circuits are provided. 3. The equalizer according to claim 2, wherein each of the equalizers is composed of a voltage / current conversion circuit for attenuation operation including the current source, and an adder circuit is provided between the first and second attenuation circuits and the filter. 4. An audio signal is received as an input signal, a signal in a specific frequency band of the input signal is generated, and the signal is added or subtracted from the audio signal to perform sound quality attenuation or sound quality enhancement. An audio device for generating an audio signal adjusted to the sound quality of 1st, receiving the input signal and a first control signal, and attenuating the input signal according to the level of the first control signal.
Attenuator circuit, a filter of the specific frequency band that receives the output of the first attenuator circuit, an adder that receives the output of the filter and the input signal, adds them, and outputs the adjusted audio signal. A circuit and a second control signal and one of the adjusted audio signal and a signal corresponding to the adjusted audio signal from the adder circuit, and the one of the signals is attenuated according to the level of the second control signal. A second attenuator circuit for sending a signal whose phase is inverted to the filter, a variable resistor for generating a sound quality adjustment signal at a variable terminal, and a reception of the sound quality adjustment signal, which indicates the sound quality enhancement. Occasionally, the first control signal having a level corresponding to the emphasized state is generated, and when the sound quality adjustment signal indicates the sound quality attenuation, the level according to the attenuation state is generated. Audio apparatus comprising a control circuit for the generation of said second control signal.