JP2008193352A - Microphone filter circuit and microphone signal control circuit using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively reduce wind noise, solve problems that original signals, such as voice, are degraded caused by large wind noise and an SN ratio is decreased, and automatically achieve the same effects as a microphone using method which uses a proximity effect. <P>SOLUTION: A signal processing circuit 12 at least amplifies output signals from a filter circuit 11 which performs high-pass filtering signals from a microphone 2. The filter circuit 11 has sequentially-connected six-step element circuits N1 to N6, and each step of the element circuits N1 to N6 is composed of a CR filter. The sixth element circuit N6 includes a transistor Tr1 as a variable resistance means. When the amplitude of an output signal from the signal processing circuit 12 increases, a resistance control circuit 13 changes a resistance value of the transistor Tr1 so that a cut-off frequency of the filter circuit 12 increases with decreasing of the amplitude of the output signal from the filter circuit 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a microphone filter circuit and a microphone signal control circuit using the same.

  When the microphone is used outdoors or used as a vocal microphone, wind noise due to the surrounding wind or the breath of the user becomes a problem.

Patent Document 1 below discloses an apparatus that reduces wind noise by performing electrical processing on a signal from a microphone. This apparatus includes a preamplifier that preamplifies a signal from a microphone, an automatic gain control circuit that performs automatic gain control (AGF) on an output signal of the preamplifier, and an output signal of the automatic gain control circuit. A / D converter that performs A / D conversion of the sound and a wind noise reduction circuit that performs inherent wind noise reduction processing on the digital signal A / D converted by the A / D converter .
JP 2001-352594 A

  However, in the apparatus disclosed in Patent Document 1, a signal mixed with wind noise from the microphone is amplified by the preamplifier. Therefore, if the wind noise is large, the preamplifier becomes saturated, and the sound The original signal such as is deteriorated.

  Further, in the apparatus disclosed in Patent Document 1, automatic gain control is performed on the basis of a signal in which wind noise is mixed. Therefore, if the wind noise is large, the level of the original signal such as voice is reduced, The SN ratio is reduced.

  Furthermore, in the apparatus disclosed in Patent Document 1, the configuration of the wind noise reduction circuit is complicated, and thus an increase in cost is inevitable.

  Furthermore, the device disclosed in Patent Document 1 cannot intentionally bring the microphone close to or away from the mouth, the same effect as the method of using the microphone using the proximity effect as performed by a professional singer. It could not be realized automatically for beginners. Here, using the microphone using the proximity effect is to restrict the volume and clarify the voice (weaken the low frequency and emphasize the voice fault mantle) by keeping the microphone away from the mouth when speaking. It is a method of use that raises sensitivity and softens the voice (low tone emphasis by proximity effect) by bringing a microphone close to the mouth when speaking in a low voice.

  The present invention has been made in view of such circumstances, and while reducing wind noise effectively, an original signal such as voice or the like due to large wind noise is deteriorated or an SN ratio is lowered. An object of the present invention is to provide a microphone filter circuit that can reduce the noise and has a simple configuration and is inexpensive.

  In addition, the present invention can reduce wind noise and effectively reduce the deterioration of the original signal such as voice or the SN ratio due to the large wind noise, and the proximity. It is an object of the present invention to provide a microphone signal control circuit capable of automatic volume control that automatically realizes the same effect as that of the microphone using the effect.

  In order to solve the above-described problem, a microphone filter circuit according to a first aspect of the present invention is a microphone filter circuit that performs high-pass filtering on a signal from a microphone, and (i) four or more stages connected in sequence (Ii) The element circuit at each stage is a series circuit including a common connection portion, an input portion, a capacitor and a resistance portion, and the capacitor is on the input portion side. A series circuit connected between a common connection portion and the input portion, and an output portion connected to a connection point between the capacitor and the resistance portion or an intermediate connection point of the resistance portion, (Iii) The common connection parts of the four-stage element circuits are connected in common to each other, and a signal from the microphone is input to the input part of the first-stage element circuit of the four-stage or more element circuits. Input (Iv) the input part of the element circuit after the second stage among the element circuits of the four or more stages is connected to the output part of the element circuit of the preceding stage with respect to the element circuit, and (v) the four or more stages The output signal of the microphone filter circuit is output from the output portion of the last stage element circuit.

  According to the first aspect, since the element circuit is composed of four or more stages, the change in gain with respect to the frequency below the cutoff frequency is made steep enough to reduce wind noise. Wind noise can be effectively suppressed. As a result of the simulation to be described later, it is preferable that the number of stages of the component circuits constituting the microphone filter circuit is large, since the change in gain with respect to the frequency below the cut-off frequency can be made steeper. It was experimentally found that wind noise can be effectively suppressed.

  Further, the microphone filter circuit according to the first aspect is a passive filter, and before the signal from the microphone is amplified, the low-frequency component that is the main component of wind noise is removed by the microphone filter circuit. Therefore, even if wind noise is large, a situation in which an amplifier or the like is saturated and an original signal such as voice is deteriorated is reduced.

  Furthermore, according to the first aspect, since it is basically configured by a resistor and a capacitor, the configuration is simple and inexpensive.

  A microphone signal control circuit according to a second aspect of the present invention includes the microphone filter circuit according to the first aspect, and signal processing means for amplifying at least an output signal of the microphone filter circuit, and the four stages. Among the above element circuits, at least a part of the resistance section of at least one element circuit is configured by variable resistance means, and the resistance of the variable resistance means has an output signal amplitude of the signal processing means. When increasing, the amplitude of the output signal of the microphone filter circuit decreases and the cut-off frequency of the microphone filter circuit increases so that the cutoff frequency of the microphone filter circuit increases. It is.

  According to the second aspect, in addition to the advantages of the first aspect described above, the following advantages are also obtained. That is, according to the second aspect, the overall gain is automatically controlled on the basis of the output signal of the microphone filter circuit (that is, the signal after the main component of the wind noise is removed). Therefore, even if the wind noise is large, a decrease in the level of the original signal such as voice is reduced, and a decrease in the SN ratio is also reduced. According to the second aspect, when the amplitude of the output signal of the signal processing means is to increase, the amplitude of the output signal of the microphone filter circuit is reduced and the cutoff frequency of the microphone filter circuit is reduced. Since the resistance of the variable resistance means changes so as to increase, it is possible to perform automatic sound volume control having a function of automatically realizing the same effect as the method of using the microphone using the proximity effect.

  The microphone signal control circuit according to a third aspect of the present invention is the signal control circuit for a microphone according to the second aspect, wherein the signal processing means adds an acoustic effect (for example, an audio signal delayed for a predetermined time) to the signal from the microphone. And an acoustic effect imparting circuit that outputs a signal imparted with an echo addition function by combining them.

  According to the third aspect, since the automatic volume control is performed based on the total amplitude increased as a result of applying the acoustic effect, the automatic volume control with high quality can be performed.

  Advantageous Effects of Invention According to the present invention, it is possible to reduce an original signal such as a voice or a signal-to-noise ratio from being deteriorated due to a large wind noise while effectively reducing the wind noise, and the configuration is improved. A microphone signal control circuit that can provide a simple and inexpensive filter circuit for microphones and that can perform automatic volume control that automatically realizes the same effect as a microphone using the proximity effect is provided. can do.

  Hereinafter, a microphone filter circuit and a microphone signal control circuit using the same according to the present invention will be described with reference to the drawings.

  [First Embodiment]

  FIG. 1 is a circuit diagram showing a microphone signal control circuit 1 together with a microphone 2 according to a first embodiment of the present invention.

  The microphone 2 is used as a so-called vocal microphone, for example. The microphone 2 may be, for example, a condenser microphone or a dynamic microphone.

  The microphone signal control circuit 1 according to the present embodiment includes a microphone filter circuit 11 that performs high-pass filtering on a signal from the microphone 2, a signal processing circuit 12 that at least amplifies the output signal of the microphone filter circuit 11, and A resistance control circuit 13 that changes the resistance of the transistor Tr1 as a variable resistance means of the microphone filter circuit 11 in accordance with an output signal of the signal processing circuit 12 is provided.

  In the present embodiment, the microphone filter circuit 11 includes six stages of element circuits N1 to N6 that are sequentially connected. Each element circuit N1 to N6 has a common connection part connected in common to each other, and these are grounded. Input terminals A1 and A2 of the microphone filter circuit 11 are connected to both terminals of the microphone 2, respectively. The input terminal A2 is grounded.

  The input part of the first stage element circuit N1 is connected to the terminal A1. The first-stage element circuit N1 is a series circuit composed of a capacitor C1 and a resistor R1, and the first-stage element circuit N1 is arranged such that the capacitor C1 side is the input side of the first-stage element circuit N1. It has a series circuit connected between the input and ground.

  The midpoint of connection between the capacitor C1 and the resistor R1 is the output section of the first-stage element circuit N1, to which the input section of the second-stage element circuit N2 is connected. The second-stage element circuit N2 is a series circuit including a capacitor C2 and a resistor R2, and the second-stage element circuit N2 is arranged so that the capacitor C2 side is the input side of the second-stage element circuit N2. It has a series circuit connected between the input and ground.

  The midpoint of connection between the capacitor C2 and the resistor R2 is the output section of the second-stage element circuit N2, to which the input section of the third-stage element circuit N3 is connected. The third-stage element circuit N3 is a series circuit composed of a capacitor C3 and a resistor R3. The third-stage element circuit N3 has a capacitor C3 side as an input side of the third-stage element circuit N3. It has a series circuit connected between the input and ground.

  The midpoint of connection between the capacitor C3 and the resistor R3 is the output section of the third stage element circuit N4, to which the input section of the fourth stage element circuit N4 is connected. The fourth-stage element circuit N4 is a series circuit composed of a capacitor C4 and a resistor R4. The fourth-stage element circuit N4 is arranged so that the capacitor C4 side is the input side of the fourth-stage element circuit N4. It has a series circuit connected between the input and ground.

  The midpoint of connection between the capacitor C4 and the resistor R4 is the output section of the fourth-stage element circuit N4, to which the input section of the fifth-stage element circuit N5 is connected. The fifth-stage element circuit N5 is a series circuit composed of a capacitor C5 and a resistor R5. The fifth-stage element circuit N5 has a capacitor C5 side as an input side of the fifth-stage element circuit N5. It has a series circuit connected between the input and ground.

  The midpoint of connection between the capacitor C5 and the resistor R5 is the output section of the fifth stage element circuit N5, to which the input section of the sixth stage element circuit N6 is connected. The sixth-stage element circuit N6 is a series circuit composed of a capacitor C5 and a resistance section (resistance section consisting of resistors R6 and R7 and a transistor Tr1 as variable resistance means), and the capacitor C6 side is connected to the sixth-stage element circuit. It has a series circuit connected between the input part of the fifth stage element circuit N5 and the ground so as to be on the input part side of the circuit N6. A resistor R6 is connected between the capacitor C6 and the ground, and a series circuit of the resistor R7 and the transistor Tr1 is connected in parallel with the resistor R6. The collector of the transistor Tr1 is connected to the resistor R7, and the emitter of the transistor Tr1 is grounded. When the voltage applied to the base of the transistor Tr1 changes, the resistance between the collector and the emitter of the transistor Tr1 changes. Therefore, in this embodiment, the transistor Tr1 is used as variable resistance means. However, the variable resistance means used in this embodiment is not limited to a transistor. In the present embodiment, a capacitor C7 for cutting a signal in a frequency range (for example, 1 kHz or more) exceeding the audio frequency range is connected in parallel with the resistor R6. However, the capacitor C7 is not necessarily provided. A connection midpoint between the resistor R7 and the collector of the transistor Tr1 (an intermediate connection point between the resistors R6 and R7 and the transistor Tr1) B1 is an output portion of the sixth-stage element circuit N6, and thus a microphone filter. This is the output section of the circuit 11. One or both of the resistors R6 and R7 are not necessarily provided. In the present embodiment, an automatic volume control range can be set by appropriately setting the resistance value of the resistor R7.

  The input section of the signal processing circuit 12 is connected to the output section (connection midpoint B1) of the microphone filter circuit 11. The output portion of the signal processing circuit 12 is connected to one output terminal O1 of the microphone signal control circuit 1 according to the present embodiment, and the other output terminal O2 is grounded. For example, an input terminal of headphones or a recording cable terminal is connected between the output terminals O1 and O2.

  In the present embodiment, the signal processing circuit 12 includes a DC cut capacitor C11, an amplifier AP1, an acoustic effect applying circuit PS, and an amplifier AP2, which are sequentially connected between the input unit and the output unit. The amplifier AP1 receives the audio signal output from the output unit of the microphone filter circuit 11 via the capacitor C11 and amplifies the audio signal. The acoustic effect applying circuit PS outputs a signal in which, for example, an echo is added as an acoustic effect to the audio signal amplified by the amplifier AP1, and a commercially available IC can be used, for example. The amplifier AP2 amplifies the output signal of the acoustic effect applying circuit PS and outputs it from the output terminal O1. Although not shown in the drawing, on / off of the application of the acoustic effect by the acoustic effect applying circuit PS may be switched by an operating device such as a switch. Note that the signal processing circuit 12 does not necessarily include the acoustic effect applying circuit PS, and the acoustic effect applying circuit PS and the amplifier AP2 may be removed and the output unit of the amplifier AP1 may be connected to the output terminal O1.

  The input section of the resistance control circuit 13 is connected to the output section of the microphone filter circuit 11 (the output section of the amplifier A2). The resistance control circuit 13 includes a DC cut capacitor C21 connected to the input portion thereof, diodes D21 and D22, a capacitor C22 and a resistor R21 constituting an envelope detection circuit, resistors R22 and R23, and a transistor Tr2. ing. The transistor Tr2 is Darlington-connected to the transistor Tr1, and the emitter of the transistor Tr2 is connected to the base of the transistor Tr1. The base of the transistor Tr2 is connected to the output portion of the envelope detection circuit (the connection midpoint between the cathode of the diode D22 and the resistor R21) via the resistor R22. The collector of the transistor Tr2 is connected to the power supply Vcc via the resistor 23.

  Therefore, according to the resistance control circuit 13, when the amplitude of the output signal of the signal processing circuit 12 increases, the resistance between the collector and the emitter of the transistor Tr1 is reduced, while the amplitude of the output signal of the signal processing circuit 12 decreases. Then, the resistance between the collector and the emitter of the transistor Tr1 increases. As a result, since the transistor Tr1 is connected as described above in the sixth stage element circuit N6 of the microphone filter circuit 11, when the amplitude of the output signal of the signal processing circuit 12 is to be increased, the microphone filter circuit Thus, the resistance between the collector and the emitter of the transistor Tr1 as the variable resistance means changes so that the amplitude of the output signal of the transistor 11 is reduced and the cutoff frequency of the microphone filter circuit 11 is increased.

  FIG. 2 is a diagram schematically showing the characteristics of the microphone signal control circuit 1 according to the present embodiment. In FIG. 2, the horizontal axis indicates the frequency, and the vertical axis indicates the gain of the output signal output from between the output terminals O1 and O2 with respect to the signal from the microphone 2 input between the input terminals A1 and A2 (hereinafter referred to as “total”). May be referred to as “gain”). According to the present embodiment, as shown in FIG. 2, when the signal from the microphone 2 is increased, the total gain is automatically reduced, the volume is automatically reduced, and the cutoff frequency is automatically reduced. When the signal from the microphone 2 is reduced, the total gain is automatically increased and the sound volume is automatically clarified (the low frequency is weakened and the fault mantle of the voice is emphasized). Is automatically increased, and the sensitivity is increased and the sound is softened (bass emphasis by the proximity effect). Thus, according to the present embodiment, even if the user does not intentionally bring the microphone 2 close to or away from the mouth, the same effect as that of the microphone using method using the proximity effect is automatically realized. Automatic volume control can be performed.

  And according to this Embodiment, since the filter circuit 11 for microphones is comprised by the element circuit N1-N6 of 4 steps | paragraphs or more as mentioned above, to the extent sufficient to reduce a wind noise, A change in gain with respect to a frequency below the cutoff frequency can be made steep, and wind noise can be effectively suppressed. As a result of the simulation described later, it is preferable that the number of stages of the component circuits constituting the microphone filter circuit 11 is larger, because a change in gain with respect to the frequency below the cutoff frequency can be made steeper. It was found that wind noise can be effectively suppressed.

  Further, according to the present embodiment, the microphone filter circuit 11 is a passive filter, and the wind noise component is removed by the microphone filter circuit 11 before the signal from the microphone 2 is amplified by the signal processing circuit 12. Therefore, even if the wind noise is large, there is no situation where the amplifier or the like is saturated and the original signal such as voice is deteriorated.

  Furthermore, according to the present embodiment, since the total gain is automatically controlled on the basis of the output signal of the microphone filter circuit 11 (that is, the signal after the wind noise component is removed), the wind noise is reduced. Even if it is large, the level of the original signal such as voice does not decrease, and the SN ratio does not decrease.

  Furthermore, according to the present embodiment, as described above, the microphone filter circuit 11 is basically composed of a resistor and a capacitor, so that the configuration is simple and inexpensive.

  Here, the first simulation performed in connection with the present embodiment and the result thereof will be described with reference to FIGS. The first simulation is for examining the influence of the number of stages of element circuits in the microphone filter circuit.

  FIG. 3 and FIG. 4 are diagrams showing each microphone filter circuit used in the first simulation. 3 and 4, the same or corresponding elements as those in FIG. 1 are denoted by the same reference numerals. 3 and 4, e is a voltage source corresponding to the microphone 2, r1 is an internal impedance of the microphone 2, and R0 is an input impedance of the amplifier AP1.

  In the microphone filter circuit shown in FIG. 3A, the number of stages n of the element circuits is one, and this circuit is composed of capacitors C1 and R1. In the microphone filter circuit shown in FIG. 3B, the number n of element circuits is two, and this circuit is composed of capacitors C1 and C2 and resistors R1 and R2. In the microphone filter circuit shown in FIG. 3C, the number of stages n of the element circuits is three, and this circuit includes capacitors C1 to C3 and resistors R1 to R3. In the microphone filter circuit shown in FIG. 4A, the number of stages n of the element circuits is four, and this circuit includes capacitors C1 to C4 and resistors R1 to R4. In the microphone filter circuit shown in FIG. 4B, the number n of the element circuits is five, and this circuit includes capacitors C1 to C5 and resistors R1 to R5. In the microphone filter circuit shown in FIG. 4C, the number n of element circuits is six, and this circuit includes capacitors C1 to C6 and resistors R1 to R5 and R36. The resistor R36 corresponds to the resistor portion including the resistors R6 and R7 and the transistor Tr1 in FIG.

  In this first simulation, for each circuit shown in FIGS. 3 and 4, r1 = 600Ω, R0 = 10GΩ, C1 = 10 μF, C2 = 4.7 μF, C3 = 2.2 μF, C4 = 1 μF, C5 = 0. The characteristics of each circuit were determined by simulation when 22 μF, C6 = 0.1 μF, R1 = 1 kΩ, R2 = 2 kΩ, R3 = 4 kΩ, R4 = 8 kΩ, R5 = 16 kΩ, and R36 = 32 kΩ. The result of the simulation is shown in FIG. In FIG. 5, the horizontal axis indicates the frequency, and the vertical axis indicates the gain of the output signal output from between the terminals B1 and B2 with respect to the signal input between the input terminals A1 and A2.

  From FIG. 5, as the number of stages n of the element circuits constituting the microphone filter circuit increases, the gain change with respect to the frequency below the cut-off frequency can be made steeper, and wind noise is effective when the number is four or more. It can be seen that it can be suppressed. The wind noise is approximately 100 Hz or less.

  Next, the second simulation performed in connection with the present embodiment and the result thereof will be described with reference to FIGS. The second simulation is for examining the influence of the change in the resistance value of the variable resistance means in the microphone filter circuit.

  FIG. 6 is a diagram illustrating a microphone filter circuit used in the second simulation. In FIG. 6, elements that are the same as or correspond to the elements in FIG. In FIG. 6, e is a voltage source corresponding to the microphone 2, r1 is an internal impedance of the microphone 2, and R0 is an input impedance of the amplifier AP1.

  In the microphone filter circuit shown in FIG. 6, the number n of the element circuits is four, and this circuit includes capacitors C1 to C4 and resistors R1 to R3, R46, R47, and R. The resistors R46 and R47 correspond to the resistors R6 and R7 in FIG. 1, respectively, and the variable resistor R corresponds to the transistor Tr1 in FIG.

  In this second simulation, for the circuit shown in FIG. 6, r1 = 600Ω, R0 = 10GΩ, C1 = 10 μF, C2 = 4.7 μF, C3 = 2.2 μF, C4 = 1 μF, R1 = 1 kΩ, R2 = 2 kΩ, The characteristics when R3 = 3.9 kΩ, R46 = 10 kΩ, R47 = 1 kΩ and the variable resistance R is changed (when R = 10Ω, 100Ω, 1 kΩ, 1 MΩ) were obtained by simulation. . The result of the simulation is shown in FIG. In FIG. 7, the horizontal axis indicates the frequency, and the vertical axis indicates the gain of the output signal output from between the terminals B1 and B2 with respect to the signal input between the input terminals A1 and A2. In addition, black circles in FIG. 7 indicate cutoff frequencies when the value of the resistance R is changed.

  From FIG. 7, the smaller the value of the variable resistor R, the lower the gain and the higher the cut-off frequency. Conversely, the larger the value of the variable resistor R, the higher the gain and the lower the cut-off frequency. I understand that. This confirms that in the above-described embodiment, it is possible to perform automatic sound volume control that automatically realizes the same effect as the microphone utilization method using the proximity effect.

  [Second Embodiment]

  FIG. 8 is a circuit diagram showing the microphone signal control circuit 101 according to the second embodiment of the present invention together with the microphone 2. 8, elements that are the same as or correspond to those in FIG. 1 are given the same reference numerals, and redundant descriptions thereof are omitted. This embodiment is different from the first embodiment only in the points described below.

  In the present embodiment, in the second-stage element circuit N2, a resistor R92 is inserted between the capacitor C2 and the resistor R2, and a midpoint of connection between the resistors R2 and R92 (an intermediate portion of the resistor portion composed of the resistors R2 and R92). The connection point is an output part of the second stage element circuit N2, and the input part (one end of the capacitor C3) of the third stage element circuit N3 is connected thereto.

  In the present embodiment, the resistor R7 and the transistor Tr1 are removed from the sixth-stage element circuit N6, and the connection midpoint between the capacitor C6 and the resistor R6 is the output section of the sixth-stage element circuit N6. As a result, it is set as the output part of the filter circuit 11 for microphones, and the end of the capacitor | condenser C12 of the signal processing circuit 12 is connected there.

  Further, in the present embodiment, the resistor R4 is removed from the fourth-stage element circuit N4, and a resistor R94 and a transistor Tr1 are added instead. A series circuit of a capacitor C4 and a resistor part composed of a resistor R94 and a transistor Tr1 (between its collector and emitter) is connected between the input part of the fourth-stage element circuit N4 and the ground. A connection point (a connection midpoint between the resistor R94 and the collector of the transistor Tr1) is an output section of the fourth-stage element circuit N4.

  Also in this embodiment, the same advantages as those in the first embodiment can be obtained.

  8, a resistor corresponding to the resistor 94 may be inserted into any one or more element circuits in FIG. 1 in the same manner as the resistor 94 is inserted into the element circuit N2 at the second stage. In FIG. 1, the sixth stage element circuit N6 includes a transistor Tr1 as variable resistance means. In FIG. 8, the fourth stage element circuit N4 includes a transistor Tr1 as variable resistance means. Any one or more of the element circuits may include resistance means corresponding to the transistor Tr1.

  Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

  For example, the microphone filter circuit according to the present invention may be used only for reducing wind noise, and in that case, the variable resistance means may not necessarily be included.

It is a circuit diagram which shows the signal control circuit for microphones by the 1st Embodiment of this invention with a microphone. It is a figure which shows typically the characteristic of the signal control circuit for microphones by the 1st Embodiment of this invention. It is a circuit diagram which shows the filter circuit for microphones used in the 1st simulation. It is a circuit diagram which shows the filter circuit for other microphones used in the 1st simulation. FIG. 5 is a diagram illustrating a simulation result of characteristics of the circuit illustrated in FIGS. 3 and 4. It is a circuit diagram which shows the filter circuit for microphones used by the 2nd simulation. It is a figure which shows the simulation result of the characteristic of the circuit shown in FIG. It is a circuit diagram which shows the signal control circuit for microphones by the 2nd Embodiment of this invention with a microphone.

Explanation of symbols

1,101 Microphone signal control circuit 11 Microphone filter circuit 12 Signal processing circuit 13 Resistance control circuit N1 to N6 Element circuit

Claims (3)

A microphone filter circuit that performs high-pass filtering on a signal from a microphone,
It has four or more stages of element circuits connected in sequence,
The element circuit of each stage is a series circuit including a common connection portion, an input portion, a capacitor, and a resistance portion, and the common connection portion and the input portion are arranged so that the capacitor is on the input portion side. A series circuit connected in between, and an output part connected to a connection point between the capacitor and the resistance part or an intermediate connection point of the resistance part,
The common connection parts of the four-stage element circuits are connected in common to each other,
A signal from the microphone is input to the input unit of the first stage element circuit among the four or more stage element circuits,
The input part of the element circuit after the second stage among the element circuits of the four or more stages is connected to the output part of the element circuit of the preceding stage for the element circuit
The output signal of the microphone filter circuit is output from the output unit of the last stage element circuit among the four or more stage element circuits.
A filter circuit for a microphone. A microphone filter circuit according to claim 1;
Signal processing means for amplifying at least an output signal of the microphone filter circuit;
With
At least a part of the resistance portion of at least one element circuit of the four or more element circuits is configured by variable resistance means.
When the amplitude of the output signal of the signal processing means increases, the resistance of the variable resistance means decreases the amplitude of the output signal of the microphone filter circuit and increases the cutoff frequency of the microphone filter circuit. So as to change according to the output signal of the signal processing means,
A microphone signal control circuit.   3. The microphone signal control circuit according to claim 2, wherein the signal processing means includes an acoustic effect applying circuit that outputs a signal obtained by applying an acoustic effect to a signal from the microphone.

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