JPH0720036B2 - Equalizer circuit, high fidelity reproduction amplifier equipped with equalizer circuit, and acoustic characteristic correction circuit in high fidelity reproduction amplifier - Google Patents

Description

TECHNICAL FIELD The present invention relates to an equalizer circuit that corrects the sound quality and frequency characteristics of a reproduced sound so that the reproduced sound is reproduced in a state close to the original sound in a reproduced sound field. The present invention relates to a high-fidelity reproduction amplifier including an equalizer circuit whose frequency characteristics and phase characteristics are flat over a wide range, and an acoustic characteristic correction circuit in a high-fidelity reproduction amplifier having ideal phase characteristics.

[Prior Art and Problems to be Solved by the Invention] Recently, an amplifier called a so-called audio amplifier, which can reproduce a sound with high fidelity, is generally used.

Since this audio amplifier is required to reproduce a sound with high fidelity, its frequency characteristic is made flat over as wide a range as possible.

FIG. 22 is a characteristic diagram showing frequency characteristics and phase characteristics of a general audio amplifier. As you can see,
The frequency characteristics of general audio amplifiers are almost flat from about 30Hz to about 10KHz, but in other frequency bands, the characteristics gradually drop as the frequency decreases or increases. . Further, the phase characteristic is such that it gradually delays as the frequency increases.

By the way, although the sound quality has been improved from the past, the improvement that has been conventionally performed is mainly in terms of how to reproduce a flat frequency characteristic in a sound field by using an equalizer amplifier or the like. It was the one. However, when higher-quality sound is required, it is required that the phase characteristic be flat in all frequency bands. Conventionally, correction such that the phase characteristic is flat in all frequency bands is performed. There was no improvement such as the one on the amplifier side. Further, due to the phase shift, the oscillation may occur when the reduction or the amplification in the higher range is performed.

In addition, in an audio amplifier for automobiles where the sound field is in the vehicle interior, the sound field characteristics peculiar to the vehicle interior are corrected so that the sound reproduced by the amplifier is reproduced in a state close to the original sound. It contains an equalizer circuit that corrects the characteristics.

As this equalizer circuit, an NFB type having an arrangement as shown in FIG. 17 is generally used.

This NFB type equalizer circuit is one in which a kind of filter circuit 2 having frequency selectivity is connected to the feedback circuit of the NFB amplifier 1, and the filter circuit 2 is provided with, for example, the eighteenth Various circuits constituted by R and C as shown in the figure or FIG. 19 are used.

Then, for example, when listening to an ideal sound close to the original sound in a room having a frequency characteristic as shown by the frequency characteristic curve A in FIG. The low-pass filter, band-pass filter, and high-pass filter with the configuration shown in
When connected as shown in FIGS. 20A and 20B and reproduced by an amplifier having an equalizer circuit having the characteristic shown by the frequency characteristic curve B in FIG. 21, the peak of the frequency characteristic curve in the room The part is corrected, and the sound is reproduced with a substantially flat frequency characteristic over a wide range of frequencies as shown by the frequency characteristic curve in FIG. 7C. In terms of frequency characteristic, reproduction in a state close to the original sound is performed. Done. As described above, conventionally, an equalizer circuit capable of correcting the sound field characteristic in the vehicle interior is provided in the amplifier, and even in a vehicle interior where conditions are not so good, it is possible to listen to music or the like in a relatively good state. I was able to do it.

However, such a conventional equalizer circuit can be made flat in terms of frequency characteristics, but is very unsatisfactory in terms of phase characteristics.

That is, in the case of this equalizer circuit, when the phase characteristic is measured with a measuring instrument by sequentially increasing or decreasing the frequency with a single tone composed of a sine wave, the phase characteristic curve shown by D in FIG. A characteristic that does not vary much over almost the entire area can be obtained. However, this phase characteristic is a curve obtained as a result of combining the phase characteristic curve E of the low-pass filter, the phase characteristic curve F of the band-pass filter, and the phase characteristic curve G of the high-pass filter. In the area where the phase characteristic curves of the filter of (1) overlap, phase distortion occurs due to the phase difference, resulting in deterioration of sound quality, turbidity, and unclear localization of sound image. This phase distortion becomes particularly large at the point where the frequency characteristic curves of the filters overlap, that is, near the dip point. This is also due to the fact that the equalizer circuit is a feedback circuit.

By the way, although sound quality has been improved from the past,
The improvement that has been made conventionally has been, as described above, in terms of how to reproduce level-flat frequency characteristics in the sound field. However,
When higher quality sound is required, the above phase distortion cannot be ignored. Since the phase of the reproduced sound is an important factor in the localization of the sound image, it is not a measuring instrument that there is a sense of realism, a sense of transparency, or fatigue even when listening for a long time. This is a particularly important improvement item in the case of pursuing a good sound in psychological aspects that cannot be measured, that is, a natural sound reproduction.

[Object of the Invention] The present invention has been made in order to solve the above conventional problems, and is an equalizer capable of reproducing natural sound without phase distortion by a relatively simple circuit. High fidelity reproduction amplifier with equalizer circuit that realizes flat phase characteristics and flat output level over a wide frequency band in addition to correction of circuit and phase distortion, and correction of low and high frequencies in addition to correction of phase distortion It is an object of the present invention to provide an acoustic characteristic correction circuit in the reproducing amplifier which makes full use of the acoustic characteristic.

[Outline of the Invention] Of the present invention that achieves the above object, the first invention is that the reproduced sound in various sound fields can be reproduced in a state close to the original sound, and the sound quality and frequency characteristics of the reproduced sound. An equalizer circuit that corrects; in a frequency range higher than around 1 KHz, the phase of an input audio signal has characteristics such that the phase advances as the frequency of the audio signal becomes higher, and a perspective is provided. If possible, wait for a circuit constant that relatively advances the phase of the frequency of about 1 KHz to 5 KHz, a mid-range correction and high-range correction circuit in which a resistor and at least an inductor are connected in series or in parallel, and about 1 KHz In the low frequency range, the phase of the input audio signal has a characteristic that it delays as the frequency of the audio signal decreases, and the characteristic is opposite to the peak of the resonance frequency of the reproduced sound field. With circuit constants such that, a resistor and a low-frequency correction circuit in which the inductor and is connected in parallel or in series is an equalizer circuit composed of interconnected.

In a second aspect of the invention, a phase correction circuit that corrects the phase characteristic of the amplification circuit over a wide frequency band is connected in front of the amplification circuit that amplifies a reproduced sound with high fidelity, and the phase correction circuit is further connected. Is a high-fidelity reproduction amplifier in which the equalizer circuit of the first invention is connected in the preceding stage and / or the subsequent stage.

Furthermore, a third invention is the equalizer circuit of the first invention,
This is an acoustic characteristic correction circuit that is connected to a front stage and / or a rear stage of the equalizer circuit and that is configured with an impedance conversion circuit that converts the impedance of the equalizer circuit into an appropriate value. In the third aspect of the invention, the mid-range, high-range and low-range correction circuits can also be composed of resistors and inductors.

In any of the above inventions, the equalizer circuit is the basis,
Phase distortion can be eliminated, the context of the sound source is clarified, and it becomes possible to make the sound more natural than ever before.

Embodiments of the Invention Embodiments of the present invention will be described in detail below with reference to the drawings.

1 to 4 show an embodiment of the equalizer circuit according to the first aspect of the present invention.

Fig. 1 shows the circuit configuration. As shown in the figure, this circuit is composed of a resistor and an inductor. The resistor R _2L and the inductor L _2L , the resistor R _3L and the inductor L _3L are connected in series on the left side. The high-pass filter of is composed of inductor L _2R and resistor R _2R , inductor L _3R and resistor R _3R
The high-pass filter on the right side is configured by the series circuit of. Then, the parallel circuit of the inductor L _1L and the resistor R _1L constitutes a left low-pass filter, and the parallel circuit of the inductor L _1R and the resistor R _1R constitutes a right low-pass filter. Of these resistors R and L, resistors R ₁ and L ₁ are the low range correction circuit, resistors R ₂ and L ₂ are the mid range correction circuit, and resistors R ₃
And inductor L ₃ form a high-frequency correction circuit, respectively. These high-pass filter and low-pass filter are connected to each other, and one end of the high-pass filter is grounded. If only one side of the circuit of FIG. 1 is shown, it is equivalently shown as in FIG.

In the equalizer circuit according to the present embodiment, it is very important to determine the constants of the constituent elements.

Specifically, it is ideal that the above-mentioned dip point is determined so as to approximately match the resonance wave number in the room serving as the sound field or the vehicle interior. However, in the equalizer circuit of the present embodiment, the changes in the phase characteristics and the frequency characteristics are very smooth, so it is not necessary to make strict settings. The phase characteristic in the frequency band below the dip point should be delayed, and the level should be increased as the frequency is decreased. By doing so, the sense of localization in the left-right direction is improved, and the sound has a solemn feeling.
In the frequency band of the degree more than 5KH _z following dip point,
The phase characteristic is made to progress and the frequency characteristic level is raised. By doing so, the sense of localization in the front-back direction is improved. From 5KH _z 1
Frequency band around 2KH _z are the frequency band influencing the music of the richness, the same characteristics as described above, i.e.,
The phase characteristics are set to be progressive and the frequency characteristics are increased. 12KH _z equal to or greater than about frequency band, improvement of the atmosphere, is an important frequency range in order to get a more natural sound, also, the space required in order to eliminate the psychological feeling of oppression, such as the head is held down But also. Further, in the vicinity of the dip point, the characteristic is set to be opposite to the peak of the resonance frequency of the reproduced sound field (for example, the passenger compartment). Therefore, it is necessary to use a constant that satisfies the characteristics required for each of these frequency bands. An example of this characteristic is shown in FIG. The characteristics required for each frequency band described above are satisfied.

In implementing this circuit, it is necessary to take care not to couple the inductors to each other, pay attention to various inductions, and pay attention to the frequency characteristics and resonance frequency of each inductor itself.

Since various equalizer circuits shown in this embodiment are open loop circuits that are very simply configured, unlike conventional complicated circuits in which filters having various characteristics are serially connected, phase equalization It has a characteristic that even if a percussion instrument with a very small dynamic range and a large dynamic range that produces an instant sound is played back, there is no sound deviation.

Then, as a result of actually operating the equalizer circuit of the present invention, the psychological features that cannot be measured by the measuring instrument will be described in detail as follows.

(A) Since the phase distortion is reduced, the localization of the sound image is improved more than ever before, for example, even when reproducing sounds with different tones of the same frequency.

Specifically, for example, even when the sound of the violin and the sound of the piano emit the sound of the same frequency at the same time, the mutual positional relationship (front and rear, left and right) between the violin and the piano becomes very clear.

(B) The sound is very clear. In other words, it feels like the curtain has come off. This is natural because the phase distortion is reduced. Specifically, the sound of striking a string or the sound of rubbing can be heard well.

(C) The sound becomes realistic. More specifically, it feels as if you are on the side of the speaker or performer. This is considered to be a synergistic effect due to improved localization. To make this sense of reality even more specific, a nearby sound source is located in front of (close to) the speaker, a distant sound source is located farther than the speaker, and in the left-right direction, the azimuth angle of the speaker. Wider or narrower, reproduce the azimuth angle of each sound source. In other words, it is closer to the image of reproduction of the original sound field than the image of reproduction of the original sound.

(D) The sound did not get tired even after listening for a long time. It is considered that this is because the phase distortion remarkably decreased and the sound became closer to a natural sound. This psychological effect is especially important in car audio.

(E) When I listened to it in the passenger compartment, I felt as if I was listening to it in a large hall, and I no longer had the oppressive feeling of holding my head down. It can be considered that this is because the level up of the frequency band of 12 KHz or higher and the phase advance are combined to improve the low level feeling and the position of the sound image is clear.

(F) By adjusting the volume with the volume controller (volume), the entire sound image sounds as if approaching or moving away. Specifically, lowering the volume makes you feel as if you are playing far away, and raising it makes you feel that you are playing closer.

(G) When the output of the amplifier is saturated, the so-called flicker noise is reduced or eliminated.

FIG. 4 shows another example of the structure of the equalizer circuit, equivalently showing one side of the circuit. In this circuit, a series circuit of a capacitor C and a resistor R is supplementarily added to a circuit composed of a resistor R and an inductor L. Even with such a circuit configuration, the same effect as described above can be obtained.

5 to 10 show an embodiment of the high fidelity reproduction amplifier according to the second aspect of the present invention.

FIG. 5 shows only the phase correction circuit which constitutes this amplifier. The circuit in the figure is a circuit composed of transistors, and the phase correction circuit 1 is connected in two stages.

In this phase correction circuit 1, a low-pass filter is formed by a parallel circuit of an inductor L ₁ connected to the emitter of the transistor 10 and a resistor R ₁ , and an inductor L ₂ connected to the collector of the transistor 10 and a resistor. A high-pass filter is formed by the series circuit of the device R ₂ . It goes without saying that the constants of the respective circuit elements forming these filters are determined so as to compensate the phase characteristics of the amplifier. Capacitor C ₀₁ and capacitor C ₀₂ are capacitors for blocking DC of inductor L ₁ and inductor L ₂ , respectively. The resonance frequency of the inductor L ₁ and the capacitor C ₀₁ and the resonance frequency of the inductor L ₂ and the capacitor C ₀₂ need to be set outside the operating frequency band.

Then, a circuit configured in the same manner as this is connected to the subsequent stage in series with another stage, the output of which is amplified by the transistor 20 and output to the front stage of the amplifier. Therefore, the phase characteristic of the audio signal output from the amplifier is flat over a very wide range, and the frequency characteristic is flat over a very wide range.

Also, FIG. 6 shows a phase correction circuit having another circuit configuration. This circuit is also a circuit including transistors. In this circuit, resistor R ₁ and inductor L ₁
Form a low pass filter, and a series circuit of an inductor L ₂ and a resistor R ₂ form a high pass filter. The audio signal that has passed through these filters is amplified by the transistor 25 and the transistor 30 and output to the front stage of the amplifier. Also in this case, the constants of the respective circuit elements constituting these filters are determined so that the phase characteristics of the amplifier can be compensated. Therefore, the phase characteristic of the audio signal output from the amplifier has a flat characteristic over a very wide range, and the frequency characteristic has a flat characteristic over a very wide range.

Fig. 7 shows an example of embodying a phase correction circuit. A low pass filter consisting of a ₂₂ KΩ resistor R _.LPF and a 300 mH inductor circuit L _.LPF, and a 10 KΩ resistor R _.HPF 47
It is a circuit that is connected to a high-pass filter consisting of a μH inductor L _.HPF .

The frequency characteristic and the phase characteristic of this circuit are represented by the characteristic diagram shown in FIG. 8 and satisfy the above-mentioned characteristics.

That is, the frequency characteristic is such that, when 1000 Hz is used as a reference, the frequency gradually decreases from the lower frequency to about 200 Hz, and gradually increases from about 10 KHz to the higher frequency. Also, for the phase characteristics, 1000Hz as a reference,
At frequencies below about 1000 Hz, it lags as the frequency decreases, and at frequencies above 1000 Hz, it advances as the frequency rises.

Similar characteristics are possible in operational amplifiers and other amplifier circuits. Also in this case, it goes without saying that the circuit element constants constituting the high-pass filter and the low-pass filter are determined so that the phase characteristics of the amplifier can be compensated.

Then, the second invention is that the equalizer circuit according to the first invention is connected further before the amplifiers which are various phase correction circuits as described above. A concrete example of the second invention is shown in FIG. The structure of the equalizer circuit and the determination of the constants of each element forming the circuit are in accordance with the first invention. Further, the phase correction circuit uses the circuit shown in FIG. 7, but the circuit element constants and the phase characteristics of the amplifier are determined by the circuits shown in FIGS. 5 and 6 or an amplifier circuit such as an operational amplifier. Of course, it may be a circuit determined so as to be compensated.

The characteristic diagram of the circuit shown in FIG. 9 is shown in FIG. This tenth
As is clear from the characteristic diagram in the figure, the characteristic diagram of the equalizer circuit shown in FIG. 3 and the characteristic diagram of the phase correction circuit shown in FIG. 8 are almost combined.
Then, the second invention is applied to a general amplifier (this characteristic is
See figure. ), That is, when it is passed through a general amplifier, it appears as a characteristic diagram shown in FIG. As is clear from this characteristic diagram, it can be seen that the frequency characteristic level and the phase characteristic are flat characteristics over a wide range.

Although the equalizer circuit according to the second aspect of the invention is connected to the front stage of the phase correction circuit 1 in the above embodiment, the equalizer circuit may be connected to the rear stage or both front and rear stages of the phase correction circuit 1. It is possible.

Therefore, according to the second aspect of the present invention, since the phase distortion is small and the phase characteristic and the frequency characteristic of the audio signal output from the amplifier are flat over the range, the sound can be made closer to a natural sound. It was

12 to 16 show an embodiment of the acoustic characteristic correction circuit according to the third aspect of the present invention.

Of these, FIGS. 12 to 14 show a first embodiment of the third aspect of the present invention, and FIG. 12 shows a block diagram of the circuit.

This circuit consists of the equalizer circuit 50 and this equalizer circuit 50.
The impedance conversion circuit 60 is connected in series before and / or before and after. The equalizer circuit 50 is
As shown in the figure, it consists of a resistor and a capacitor.Capacitor C _2L and resistor R _2L , capacitor C _3L and resistor R
The parallel circuit of _3L constitutes the left high-pass filter, and the parallel circuit of the capacitor C _2R and the resistor R _2R , the capacitor C _3R and the resistor R _3R constitutes the right high-pass filter. Then, the capacitor C _1L , the capacitor C _4L, and the resistor R _1L constitute a low-pass filter on the left side, and the capacitor C _1R , the capacitor C _4R, and the resistor R 1
_{The 1R} constitutes the low-pass filter on the right side.
Of these resistors R and C, resistor R ₁ and capacitors C ₁ and C ₄ are the low-frequency correction circuit, resistor R ₂ and capacitor C ₂
Is a mid range correction circuit, and resistor R ₃ and capacitor C ₃ are high range correction circuits, respectively. These high pass filter and low pass filter are connected to each other, and one end of the low pass filter is grounded. If only one side of this circuit is shown, it is equivalently shown in FIG. In the equalizer circuit 50, it is very important to determine the constants of the respective elements that make up the equalizer circuit 50. The constants are determined according to the equalizer circuit in the first invention.

The impedance circuit 60 connected to the front stage and / or the rear stage of the equalizer circuit 50 is provided in order to sufficiently exhibit the characteristics of the equalizer circuit 50 (the characteristics described in the constant determination in the equalizer circuit of the first invention). It is provided.

That is, the characteristics of the equalizer circuit 50 are shown in FIG. 3, but the equalizer circuit 50 has a delicate relationship with the impedance of the other party that inputs to or outputs from this, and depending on the value of this impedance. May affect the frequency characteristics and phase characteristics in the low range or high range. Specifically, there is no problem when the output impedance of the preceding stage (not shown) of the equalizer circuit 50 is lower than the input impedance of the equalizer circuit 50, but when it is high, the characteristic diagram of FIG. At
At the same time, the lower frequency level does not rise sufficiently, and at the same time, the phase characteristic is not sufficiently delayed in the low frequency range. Therefore, the above-mentioned acoustic characteristics in the low range cannot be utilized. Also, if it is higher than the output impedance of the equalizer circuit 50, there is no problem, but if it is low, in the characteristic diagram, the higher frequency level rises too much, and at the same time, the phase characteristics advance faster in the high frequency range. Pruning. Therefore, in this case, the above-mentioned acoustic characteristics in the high range cannot be utilized. The impedance conversion circuit 60 has a function of sufficiently exhibiting the acoustic characteristics of the equalizer circuit 50 in these low and high frequencies. The impedance conversion circuit 60 may be either at the front stage or the rear stage of the equalizer circuit 50. For such an impedance conversion circuit 60, for example, an emitter follower, an operational amplifier or the like is used.

The equalizer circuit 50 may use the inductor L ₃ for a part of the equalizer circuit 50 to emphasize the phase correction and to correct the frequency characteristic, as shown equivalently on one side in FIG. In this example, the inductor L ₃ is used for high frequency phase correction (enhancement). However, in this case, it is necessary to bring the resonance frequency due to the relationship between the inductor and each element of the circuit to outside the band of the used frequency band.

15 and 16 show a second embodiment of the third invention. The equalizer circuit 70 in this embodiment is
This is a configuration in which an inductor is connected to a resistor and conforms to the equalizer circuit (FIGS. 1 and 2) in the first invention. Further, the determination of the constants of the respective elements forming the equalizer circuit 70 also conforms to the first invention. The other structure is similar to that of the first embodiment. However, the acoustic characteristic correction in the low and high frequencies by the impedance conversion circuit 60 in the equalizer circuit 70 is slightly different from that in the equalizer circuit 50, and the input impedance of the subsequent circuit (not shown) of the equalizer circuit 70 is lower than the output impedance. In addition, in the characteristic diagram of FIG. 3, it serves to correct the lowering of the higher frequency level and at the same time to correct the delay of the advance of the phase characteristic in the high frequency range.

Therefore, according to the third aspect of the present invention, in addition to the effect of the first aspect of the invention, the acoustic characteristics in the low and high frequencies can be fully utilized, and it becomes possible to bring the sound closer to a natural sound.

In the above three inventions, each filter is exemplified by one resistor and one inductor (a resistor and a capacitor or an inductor in the third invention), but the invention is not limited to this, and an equivalent circuit is also provided. If so, it goes without saying that an equalizer circuit (for example, π-type connection or the like) configured by a complicated circuit that eventually becomes the circuit of the present invention may be used. Further, the equalizer circuit of the present invention can be applied to various amplifiers such as an audio amplifier normally used indoors and an audio amplifier mounted in a passenger car.

The above inventions can, of course, be combined with each other.

[Effects of the Invention] As is clear from the above description, according to the equalizer circuit of the first aspect of the present invention, phase distortion can be eliminated, and reproduced sound can be brought closer to natural sound.

Further, according to the high fidelity reproduction amplifier of the second invention, in addition to the effect of the first invention, the phase characteristic and the frequency characteristic are flattened over a wide range, so that further reduction amplification and higher frequency Amplification was possible and it was possible to get closer to the natural sound.

According to the acoustic characteristic circuit of the third invention, in addition to the effect of the first invention, the acoustic characteristics of the equalizer circuit in the low and high frequencies are fully utilized, so that the reproduced sound is more natural in the low and high frequencies. It became possible to approach the sound.

Further, in any of the above-mentioned inventions, it is used in an audio circuit such as a home stereo, a CD player, a record player, a tape player, an FM receiver (audio after FM detection), a loudspeaker, etc. I was able to reproduce the place. As for the FM car radio, I could listen to it without feeling tired, as if I was in a packaging studio or a performance hall, without any support while running.

[Brief description of drawings]

FIG. 1 is a block diagram of an equalizer circuit according to the first invention, FIG. 2 is a block diagram of one side of the equalizer circuit shown in FIG. 1, and FIG. 3 is a block diagram according to the first invention. FIG. 4 is a characteristic diagram of the equalizer circuit, FIG. 4 is a configuration diagram showing another example of the equalizer circuit, and FIG. 5 is a diagram of a phase correction circuit constituting the high fidelity reproduction amplifier with an equalizer circuit according to the second invention. Circuit diagram, FIG. 6 is another phase correction circuit diagram, FIG. 7 is a circuit diagram showing a specific example of the same phase correction circuit, and FIG. 8 is a characteristic line of an amplifier using the circuit of FIG. FIG. 9, FIG. 9 is a circuit diagram according to the second invention, FIG. 10 is a characteristic diagram showing phase and frequency characteristics by the circuit of FIG. 9, and FIG. 12 is a characteristic diagram when applied to the audio amplifier of FIG. 12, FIG. 12 is a circuit diagram according to the first embodiment of the third invention, and FIG. 13 is a circuit diagram of FIG. Schematic of only one side of the circuit, 14th
The figure is a block diagram of only one side showing another example of the third invention,
FIG. 15 is a circuit diagram according to a second embodiment of the third invention,
FIG. 16 is a block diagram of only one side of the circuit of FIG. 15, FIG. 17 is a schematic block diagram of one filter which constitutes a conventional equalizer circuit, and FIGS. 18 and 19 are shown in FIG. The specific circuit diagram of the filter circuit shown, FIGS. 20A and 20B,
FIG. 21 is a schematic diagram showing the configuration of a conventional equalizer circuit,
FIG. 22 is a characteristic diagram of a commonly used amplifier, and FIG. 22 is a characteristic diagram of a commonly used equalizer circuit. R ₁ , C ₁ , L ₁ : Low range correction circuit, R ₂ , C ₂ , L ₂ : Middle range correction circuit, C ₃ , R ₃ , L ₃ : High range correction circuit, 50, 70: Equalizer circuit, 60 : Impedance conversion circuit.

Claims (3)

[Claims] Claim: What is claimed is: 1. An equalizer circuit for correcting the sound quality and frequency characteristics of a reproduced sound in a variety of sound fields so that the reproduced sound can be reproduced in a state close to the original sound. In the above, there is a characteristic that the phase of the input audio signal advances as the frequency of the audio signal becomes higher, and the phase of the frequency of about 1 KHz to 5 KHz is relatively advanced to give a sense of perspective. In the mid-range correction and high-range correction circuits, in which resistors and inductors are connected in series or in parallel, with a constant circuit constant, and in the frequency range lower than about 1 KHz, the phase of the input audio signal is the audio A resistor and an inductor are connected in parallel with a characteristic such that the signal delays as the frequency decreases, and has a circuit constant that is the characteristic opposite to the peak of the resonance frequency of the reproduced sound field. There is an equalizer circuit, characterized in that the low-frequency correction circuit connected in series, which are interconnected. 2. A phase correction circuit for correcting the phase characteristic of the amplification circuit over a wide frequency band is connected to the front stage of the amplification circuit for amplifying a reproduced sound of high fidelity, and the front stage of the phase correction circuit is further connected. And / or in the subsequent stage, in the frequency range higher than around 1 KHz, the phase of the input audio signal has a characteristic of advancing as the frequency of the audio signal becomes higher, and it is necessary to provide a sense of perspective. 1KHz to 5K
In the mid-range correction and high-range correction circuits, in which resistors and inductors are connected in series or in parallel, and which have a circuit constant that relatively advances the phase of the frequency of Hz, and in the frequency range lower than about 1 KHz, , Has a circuit constant such that the phase of the input audio signal is delayed as the frequency of the audio signal becomes lower, and has a characteristic opposite to the peak of the resonance frequency of the reproduced sound field. , A high-fidelity reproduction amplifier having an equalizer circuit, which is characterized by connecting an equalizer circuit in which a low-frequency correction circuit in which a resistor and an inductor are connected in parallel or in series is connected. 3. An equalizer circuit that corrects the sound quality and frequency characteristics of reproduced sound in various sound fields so that the reproduced sound can be reproduced in a state close to the original sound, and has a frequency range higher than about 1 KHz. In the above, there is a characteristic that the phase of the input audio signal advances as the frequency of the audio signal becomes higher, and the phase of the frequency of about 1 KHz to 5 KHz is relatively advanced to give a sense of perspective. In the mid-range correction and high-range correction circuits, in which resistors and capacitors or inductors are connected in series or in parallel, which have different circuit constants, and in the frequency range lower than about 1 KHz, the phase of the input audio signal is A resistor and a capacitor, which have characteristics such that they are delayed as the frequency of the audio signal becomes lower, and have a circuit constant that is the characteristic opposite to the peak of the resonance frequency of the reproduced sound field. An equalizer circuit in which a low-frequency correction circuit in which a sensor or an inductor is connected in parallel or in series is connected to each other, and is connected to a front stage and / or a rear stage of the equalizer circuit to convert the impedance of the equalizer circuit to an appropriate value. An acoustic characteristic correction circuit for a high-fidelity reproduction amplifier, characterized by comprising an impedance conversion circuit.