Microphone sound field characteristic conversion method and capacitive test microphone system

Abstract

The present application relates to a method for converting the sound field characteristics of a capacitive test microphone and a capacitive test microphone system with freely convertible sound field characteristics. By introducing a filter to connect the capacitive test microphone and controlling the transfer function of the filter so that the filter can compensate for the frequency response of the microphone, a capacitive test microphone can be used in different sound fields, thereby greatly reducing the cost of use.

Description

Technical Field

[0001] The present application relates to the technical field of measuring microphones, and in particular to a method for converting the sound field characteristics of a capacitive test microphone and a capacitive test microphone system. Background Art

[0002] The commonly used test microphone in acoustic testing is the condenser test microphone. In order to make the measured acoustic values ​​uniform and transferable, the national standard and the national standard stipulate the standard external dimensions (mainly the diameter) of the test condenser microphone. The standard external dimensions of the condenser test microphone are Φ23.77, Φ12.7, and Φ6.3, which are the diameters of the condenser test microphone.

[0003] When a capacitive test microphone is placed on-site for measurement, it has a certain size, which is close to the wavelength of the sound wave at high frequencies, thus affecting the sound field. The magnitude of this effect is related to the size of the microphone. The higher the frequency of the sound wave and the shorter the wavelength, the greater the effect of the microphone size on the sound field.

[0004] In order to compensate for this effect, when testing condenser microphones, the high-frequency response of the microphones will be adjusted accordingly according to the different sound fields used during design and production. In general acoustic tests, free-field microphones are used in free space, diffuse-field microphones are used in reverberation chambers, and pressure microphones are used in coupled chambers.

[0005] This results in the need to use different types of microphones in different sound field environments, greatly increasing the testing cost. Summary of the invention

[0006] Based on this, it is necessary to provide a method for converting the sound field characteristics of a capacitive test microphone to address the problem that different types of microphones need to be used in different sound field environments when traditional capacitive test microphones are used, resulting in high testing costs.

[0007] The present application provides a method for converting the acoustic field characteristics of a capacitive test microphone, the method comprising:

[0008] Placing a capacitive test microphone in a first sound field, and obtaining a frequency response curve of the capacitive test microphone in the first sound field to obtain a first frequency response curve;

[0009] Placing the capacitive test microphone in the second sound field, and obtaining a frequency response curve of the capacitive test microphone in the second sound field to obtain a second frequency response curve;

[0010] Subtracting the first frequency response curve from the second frequency response curve to obtain a frequency response compensation curve;

[0011] Constructing a filter, and adjusting the transfer function of the filter so that the frequency response curve of the filter is the same as the frequency response compensation curve;

[0012] The filter and a capacitive test microphone are connected.

[0013] The present application also provides a capacitive test microphone system with freely changeable sound field characteristics, comprising:

[0014] A capacitive test microphone assembly, comprising a capacitive test microphone and a filter; the filter is communicatively connected with the capacitive test microphone;

[0015] An A / D converter is communicatively connected to the capacitive test microphone assembly;

[0016] A single chip microcomputer is communicatively connected to the A / D converter; the single chip microcomputer is also communicatively connected to the capacitive test microphone assembly, and the single chip microcomputer is used to execute the sound field characteristic conversion method of the capacitive test microphone as mentioned above.

[0017] The present application relates to a method for converting the sound field characteristics of a capacitive test microphone and a capacitive test microphone system with freely convertible sound field characteristics. By introducing a filter to connect the capacitive test microphone and controlling the transfer function of the filter so that the filter can compensate for the frequency response of the microphone, a capacitive test microphone can be used in different sound fields, thereby greatly reducing the cost of use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic flow chart of a method for converting the acoustic field characteristics of a capacitive test microphone provided in one embodiment of the present application.

[0019] Figure 2 A frequency value-frequency response curve in a free sound field in a method for converting sound field characteristics of a capacitive test microphone provided in an embodiment of the present application.

[0020] Figure 3 A frequency value-frequency response curve in a pressure-type sound field in a method for converting sound field characteristics of a capacitive test microphone provided in an embodiment of the present application.

[0021] Figure 4 A frequency response compensation curve diagram of a frequency value-frequency response curve in a pressure sound field and a frequency value-frequency response curve in a free sound field in a sound field characteristic conversion method of a capacitive test microphone provided in an embodiment of the present application.

[0022] Figure 5 A frequency value-amplitude-frequency response value curve diagram in a method for converting the sound field characteristics of a capacitive test microphone provided in an embodiment of the present application.

[0023] Figure 6 A schematic structural diagram of a capacitive test microphone system with freely changeable sound field characteristics provided in one embodiment of the present application. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0025] The present application provides a method for converting the acoustic field characteristics of a condenser test microphone. It should be noted that the method for converting the acoustic field characteristics of a condenser test microphone provided by the present application is applicable to condenser test microphones of any diameter.

[0026] In addition, the method for converting the acoustic field characteristics of a capacitive test microphone provided in the present application does not limit its execution subject. Optionally, the method for converting the acoustic field characteristics of a capacitive test microphone provided in the present application may be executed by a single chip microcomputer connected to the capacitive test microphone.

[0027] like Figure 1 As shown, in one embodiment of the present application, the method for converting the sound field characteristics of the capacitive test microphone includes the following steps S100 to S500:

[0028] S100, placing a capacitive test microphone in a first sound field, and acquiring a frequency response curve of the capacitive test microphone in the first sound field to obtain a first frequency response curve.

[0029] Specifically, the horizontal axis of the frequency response curve is the frequency value, and the vertical axis is the output voltage level corresponding to the frequency value. The output voltage level is converted from the output voltage. The frequency response curve is the frequency value-frequency response curve.

[0030] Optionally, the first sound field may be a free sound field, and the first frequency response curve obtained is as follows: Figure 2 shown.

[0031] S200, placing a capacitive test microphone in a second sound field, and acquiring a frequency response curve of the capacitive test microphone in the second sound field to obtain a second frequency response curve.

[0032] Specifically, the second sound field is a sound field of a completely different type from the first sound field. The second sound field may be a pressure-type sound field, and the obtained second frequency response curve is as follows: Figure 3 shown.

[0033] S300, performing subtraction processing on the first frequency response curve and the second frequency response curve to obtain a frequency response compensation curve.

[0034] Specifically, the subtraction process means that for the same horizontal coordinate, that is, the frequency value, the corresponding vertical coordinate, that is, the output voltage level, is taken in the first frequency response curve and the second frequency response curve, respectively, and the two vertical coordinates are subtracted to obtain a difference. It can be understood that if the same process is performed on each horizontal coordinate, a curve will eventually be obtained, and this curve is the frequency response compensation curve.

[0035] S400: construct a filter, and adjust the transfer function of the filter so that the frequency response curve of the filter is the same as the frequency response compensation curve.

[0036] Specifically, Figure 1 As shown in the figure, it is difficult to avoid errors in the pickup of capacitive test microphones. Without considering the errors, the frequency response curve in a free sound field can be approximated as a straight line. Figure 2 As shown in the figure, under another pressure-type sound field, the frequency response curve has an obvious bend after the 4k frequency value.

[0037] In order to make the frequency response curve in the free sound field and the frequency response curve in the pressure sound field the same as a straight line. In order to achieve this purpose, this embodiment constructs a filter so that the filter compensates the capacitive test microphone. Specifically, a method is adopted in which a frequency response compensation curve is first obtained and then the transfer function of the filter is adjusted so that the frequency response curve of the filter is the same as the frequency response compensation curve.

[0038] S500, connecting the filter and a capacitive test microphone.

[0039] Specifically, the filter has a circuit structure. According to the transfer function of the filter, the nominal values ​​of the resistors and capacitors in the filter can be calculated, thereby designing a complete filter, and then further connecting the filter to a capacitive test microphone to complete the method.

[0040] In this embodiment, by introducing a filter connected to the capacitive test microphone and controlling the transfer function of the filter so that the filter can compensate for the frequency response of the microphone, a capacitive test microphone can be used in different sound fields, thereby greatly reducing the cost of use.

[0041] In one embodiment of the present application, the first sound field is one of a free sound field, a pressure sound field and a diffuse sound field, the second sound field is one of a free sound field, a pressure sound field and a diffuse sound field, and the first sound field and the second sound field are different.

[0042] Specifically, the present application provides a method for converting the sound field characteristics of a capacitive test microphone, which can realize switching between any two different sound fields among a free sound field, a pressure sound field and a diffuse sound field.

[0043] In one embodiment of the present application, S100 includes the following S110 to S140:

[0044] S110, placing a capacitive test microphone in an anechoic chamber, and obtaining output voltage values ​​of the capacitive test microphone at different frequency values ​​to obtain a frequency value-voltage value curve in a free sound field.

[0045] Specifically, this embodiment introduces the case where the first sound field is a free sound field. Placing the capacitive test microphone in an anechoic chamber is equivalent to an environment of a free sound field. At this time, the output voltage value V of the capacitive test microphone at different frequency values ​​is measured. i , and draw the frequency value-voltage value curve.

[0046] S120, converting each output voltage value into an output voltage level according to Formula 1, so as to convert the frequency value-voltage value curve into a frequency value-output voltage level curve.

[0047] K i =20log 10 (V i ) Formula 1

[0048] Among them, V i K is the output voltage value. i is the output voltage level. i is the frequency value.

[0049] Specifically, the unit of output voltage level is dB, which is a pure counting unit. The purpose of dB is to express a very large (followed by a long string of 0s) or very small (preceded by a long string of 0s) number in a relatively short manner, which is convenient for calculation and statistics.

[0050] S130, selecting the output voltage level corresponding to the 250 Hz frequency value as a reference value, calculating the difference between the output voltage level corresponding to each frequency value and the reference value, and further using the difference as the frequency response parameter value corresponding to each frequency value to obtain a frequency value-frequency response curve in the free sound field.

[0051] Specifically, the frequency value-frequency response curve in the free sound field is as follows: Figure 2 shown.

[0052] S140: Taking the frequency value-frequency response curve in the free sound field as a first frequency response curve.

[0053] Specifically, Figure 2 As shown, the frequency value-frequency response curve in the free sound field is approximately a straight line.

[0054] In this embodiment, the capacitive test microphone is placed in an anechoic chamber, thereby creating a free sound field environment, thereby successfully obtaining the frequency value-frequency response curve of the capacitive test microphone in the free sound field.

[0055] In one embodiment of the present application, S200 includes S210 to S250:

[0056] S210, coupling the electrostatic actuator to the capacitive test microphone, and controlling the electrostatic actuator to apply an electrostatic field to the capacitive test microphone to form a pressure-type sound field.

[0057] Specifically, the electrostatic actuator can apply an electrostatic field to the capacitive test microphone. The electrostatic field generates an attractive force, which causes the diaphragm of the capacitor to vibrate, which is similar to a pressure response, thereby forming a pressure field.

[0058] S220, obtaining output voltage values ​​of the capacitive test microphone at different frequency values ​​in the pressure-type sound field, and obtaining a frequency value-voltage value curve in the free-type sound field.

[0059] Specifically, the principles of S220 and S110 are similar and will not be described in detail here.

[0060] S230, converting each output voltage value into an output voltage level according to Formula 1, so as to convert the frequency value-voltage value curve into a frequency value-output voltage level curve.

[0061] Specifically, the principles of S230 and S120 are similar and will not be described in detail here.

[0062] S240, selecting the output voltage level corresponding to the frequency value of 250 Hz as a reference value, calculating the difference between the output voltage level corresponding to each frequency and the reference value as the frequency response parameter value corresponding to each frequency value, and obtaining a frequency value-frequency response curve in the pressure-type sound field.

[0063] Specifically, the principle of S240 is similar to that of S130, and will not be described here. The frequency value-frequency response curve in the pressure-type sound field is as follows: Figure 3 shown.

[0064] S250: Taking the frequency value-frequency response curve in the pressure-type sound field as a second frequency response curve.

[0065] Specifically, the principles of S250 and S140 are similar and will not be described in detail here. Figure 3 As shown in the figure, the frequency value-frequency response curve in the pressure-type sound field is not a straight line, and there is a bend after the 4kHz frequency value.

[0066] This embodiment introduces an electrostatic actuator and couples the electrostatic actuator with a capacitive test microphone, thereby creating a pressure-type sound field environment, thereby successfully obtaining the frequency value-frequency response curve of the capacitive test microphone in the pressure-type sound field.

[0067] In one embodiment of the present application, the S300 includes the following S310 to S370:

[0068] S310, select N frequency values, where N is a positive integer and is greater than or equal to 10.

[0069] S320, select a frequency value.

[0070] S330, obtaining an output voltage level corresponding to the frequency value in the first frequency response curve, and obtaining an output voltage level corresponding to the frequency value in the second frequency response curve.

[0071] S340, calculating a difference between an output voltage level corresponding to the frequency value in the first frequency response curve and an output voltage level corresponding to the frequency value in the second frequency response curve to obtain a frequency response compensation value.

[0072] S350, returning to S320, until N frequency response compensation values ​​are obtained.

[0073] S360: Each frequency value and the frequency response compensation value corresponding to the frequency value form a frequency response compensation point, and obtain N frequency response compensation points.

[0074] S370: smoothly connect the N frequency response compensation points to obtain a frequency response compensation curve.

[0075] Specifically, Figure 2 The first frequency response curve shown is Figure 3 The second frequency response curve is subjected to subtraction processing, and S310 to S370 are executed to obtain Figure 3 The frequency response compensation curve is shown in Figure 1. The frequency response compensation curve is the compensation target we want to achieve. Figure 4 shown.

[0076] In this embodiment, by calculating the difference between the output voltage level corresponding to the frequency value in the first frequency response curve and the output voltage level corresponding to the frequency value in the second frequency response curve at each frequency value, a frequency response compensation value is obtained, and a frequency response compensation curve is drawn, so that a specific presentation of the compensation target can be achieved, providing a target for the subsequent transfer function setting of the filter.

[0077] In one embodiment of the present application, the S400 includes the following S410 to S440:

[0078] S410, creating a filter.

[0079] Specifically, this step creates a filter in the analog domain.

[0080] S420, setting the transfer function of the filter, the transfer function expression of the filter is shown in Formula 2.

[0081]

[0082] Wherein, H(S) is the transfer function, S is the simulation domain parameter, A is the first optimization coefficient, B is the second optimization coefficient, C is the third optimization coefficient, D is the fourth optimization coefficient, and F is the fifth optimization coefficient.

[0083] Specifically, S and H(S) are data in the analog domain, which means that these data are continuous.

[0084] S430, let S equal to jω, so as to convert the filter transfer function expression into the filter frequency response parameter expression. The filter frequency response parameter expression is shown in Formula 3.

[0085]

[0086] Wherein, H(jω) is the frequency response parameter. A is the first optimization coefficient. B is the second optimization coefficient. C is the third optimization coefficient. D is the fourth optimization coefficient. F is the fifth optimization coefficient. j is the imaginary part of the complex number. ω is the angular frequency.

[0087] Specifically, the angular frequency is 2π×the frequency value.

[0088] S440, according to formula 4, adjusting the first optimization coefficient, the second optimization coefficient, the third optimization coefficient, the fourth optimization coefficient and the fifth optimization coefficient, so that the amplitude-frequency response value corresponding to each frequency value is equal to the frequency response compensation value corresponding to the frequency value.

[0089]

[0090] Where i is the frequency value. ω is the angular frequency. |H(j ω)| is the modulus of the frequency response parameter. W(jω) is the amplitude-frequency response value of the filter.

[0091] Specifically, H(jω) has information in both phase and amplitude. Taking the modulus of H(jω), that is, extracting the amplitude information of H(jω), we get |H(j ω)|. Then by calculating 20log 10 |H(j ω) converts |H(j ω)| into the same unit as the vertical coordinate of the frequency response compensation curve, that is, the unit of the frequency response compensation value, dB. This unifies the unit dimension and facilitates the leveling of the amplitude-frequency response value and the frequency response compensation value, and controls the two to be equal.

[0092] Our goal is to make Figure 5 The frequency value-amplitude frequency response value curve and Figure 4 The frequency response compensation curve of the frequency value-frequency response curve shown is close to being completely consistent.

[0093] In this step, the first optimization coefficient, the second optimization coefficient, the third optimization coefficient, the fourth optimization coefficient and the fifth optimization coefficient are adjusted so that the amplitude-frequency response value corresponding to each frequency value is equal to the frequency response compensation value corresponding to the frequency value.

[0094] Optionally, the first optimization coefficient, the second optimization coefficient, the third optimization coefficient, the fourth optimization coefficient and the fifth optimization coefficient are adjusted so that the absolute value of the difference between the amplitude frequency response value corresponding to each frequency value and the frequency response compensation value corresponding to the frequency value is greater than or equal to 0 and less than or equal to 0.5 dB. Because it is difficult to make the amplitude frequency response value corresponding to each frequency value completely equal to the frequency response compensation value corresponding to the frequency value, an error range of greater than or equal to 0 and less than or equal to 0.5 dB can be given, which is more in line with the actual situation.

[0095] In this embodiment, the transfer function expression of the filter is first converted into the frequency response parameter expression of the filter, and then the first optimization coefficient, the second optimization coefficient, the third optimization coefficient, the fourth optimization coefficient and the fifth optimization coefficient are adjusted so that the amplitude-frequency response value corresponding to each frequency value is consistent with the frequency response compensation value corresponding to the frequency value, so that the filter can realize the compensation function, so that the output result of the capacitive test microphone in the second sound field is consistent with the output result of the first sound field, so that the capacitive test microphone can be used in different sound fields, which greatly reduces the use cost.

[0096] In one embodiment of the present application, after S500, the method for converting the sound field characteristics of the capacitive test microphone includes the following steps:

[0097] S610: Based on Formula 5, convert the simulation domain parameters into discrete domain expressions.

[0098]

[0099] Where S is the simulation domain parameter. Z is the preset complex number re jΩ . Ta is the preset sampling time interval.

[0100] Specifically, this embodiment also converts the transfer function expression of the filter in the analog domain into a discrete domain form. This is because the discrete domain form is a digital time series, which has better accuracy of the data of the capacitive test microphone and stability of the capacitive test microphone when used.

[0101] The value of the preset complex number is re j Ω, which has an imaginary part j. Ta is a preset sampling time interval, which can be 0.01 milliseconds.

[0102] S620, substitute Formula 5 into Formula 2 to perform Z-transform on the filter transfer function expression using a bilinear transformation method to obtain a discrete domain time series expression, and the discrete domain time series expression is shown in Formula 6.

[0103]

[0104] Where Z is the preset complex number re jΩ H(Z) is Ta is the preset sampling time interval. a0 is the first discrete domain parameter. a1 is the second discrete domain parameter. a2 is the third discrete domain parameter. b1 is the fourth discrete domain parameter. b2 is the fifth discrete domain parameter.

[0105] Specifically, the diameter of the capacitive test microphone can be 23.77 mm, 12.7 mm, and 6.3 mm. A capacitive test microphone with a diameter of 12.7 mm is more common. When the capacitive test microphone has a diameter of 12.7 mm, the first discrete domain parameter a0 is 1.2533, the second discrete domain parameter a1 is 0.0178, the third discrete domain parameter a2 is 0.0579, the fourth discrete domain parameter b1 is 0.2105, and the fifth discrete domain parameter b2 is 0.0501.

[0106] After substituting Formula 5 into Formula 2, Formula 2 is transformed into Formula 6. The first optimization coefficient A, the second optimization coefficient B, the third optimization coefficient C, the fourth optimization coefficient D, and the fifth optimization coefficient F in Formula 2 are naturally transformed into the first discrete domain parameter a0, the second discrete domain parameter a1, the third discrete domain parameter a2, the fourth discrete domain parameter b1, and the fifth discrete domain function b2. This does not mean that A is transformed into a0 and B is transformed into a1, but that after Formula 2 is transformed into Formula 6, when Formula 6 is simplified and sorted, the five parameters a0-b2 naturally appear, and the five parameters AF disappear.

[0107] In this embodiment, by converting the transfer function expression of the filter in the analog domain into a discrete domain form, the accuracy and stability of the data output after the capacitive test microphone sound field conversion are greatly improved.

[0108] In one embodiment of the present application, after S620, the method for converting the sound field characteristics of the capacitive test microphone further includes:

[0109] S630, placing a capacitive test microphone in a first sound field, acquiring an input sound signal picked up by the capacitive test microphone at every preset sampling time interval, and converting the input sound signal into a digital signal sequence X(t) through an A / D converter.

[0110] Specifically, the input sound signal is first converted into an electrical signal through a microphone (specifically a microphone), and then the electrical signal is converted into a digital signal sequence X(t) through an A / D converter. This step omits the step of converting into an electrical signal.

[0111] S640, substituting the digital signal sequence X(t) into Formula 7 to obtain the digital signal sequence Y(t) in the second sound field.

[0112]

[0113] Wherein, Y(t) is the digital signal sequence in the second sound field. t Y is the voltage value at time t in the second sound field. t-1 is the voltage value at the moment before moment t in the second sound field. t is the voltage value at time t in the first sound field. t-1 is the voltage value at the moment before the moment t in the first sound field. a0 is the first discrete domain parameter. a1 is the second discrete domain parameter. a2 is the third discrete domain parameter. b1 is the fourth discrete domain parameter. b2 is the fifth discrete domain parameter.

[0114] Specifically, when substituting the digital signal sequence X(t) into Formula 7 and solving for Y(t), we can see that Y1=a0×X1, Y2=a0×X2+a1×X1-b1×Y1, Y3=a0×X3+a1×X2+a2×X1-b1×Y2+b2×Y1. Starting from Y3, we calculate a Y t Five data are required, namely X t , X t-1 , X t-2 , Y t-1 and Y t-2 By analogy, the voltage value converted by formula 7 at each moment can be calculated, and the converted digital time series Y(t) is the digital signal sequence converted into the second sound field.

[0115] In this embodiment, the acoustic signal is picked up by the capacitive test microphone and then converted into an electrical signal, and the electrical signal enters the A / D and is converted into a digital time series. By converting the digital time series according to Formula 7, a new digital time series can be obtained, and the new digital time series is the test result after being converted into the capacitive test microphone under the second sound field.

[0116] The present application also provides a capacitive test microphone system with freely changeable sound field characteristics.

[0117] like Figure 6As shown, in one embodiment of the present application, the capacitive test microphone system with freely changeable sound field characteristics includes a capacitive test microphone assembly 100 , an A / D converter 200 and a single-chip microcomputer 300 .

[0118] The capacitive test microphone assembly 100 includes a capacitive test microphone 110 and a filter 120. The filter 120 is connected to the capacitive test microphone 110 in communication. The A / D converter 200 is connected to the capacitive test microphone assembly 100 in communication. The single chip microcomputer 300 is connected to the A / D converter 200 in communication. The single chip microcomputer 300 is connected to the capacitive test microphone assembly 100 in communication. The single chip microcomputer 300 is used to execute the sound field characteristic conversion method of the capacitive test microphone mentioned in the above content.

[0119] Specifically, in the present application, only the devices and components in the part of the capacitive test microphone system whose sound field characteristics can be freely changed are labeled. Although devices and components with the same names appear in various embodiments of the sound field characteristic conversion method of the aforementioned capacitive test microphone, they are not labeled to keep the text concise.

[0120] The diameters of condenser test microphones are available in 23.77 mm, 12.7 mm and 6.3 mm.

[0121] Optionally, the capacitive test microphone assembly 100 may only include the capacitive test microphone 110 but not the filter 120. The function of the filter 120 may be implemented by the single-chip microcomputer 300 using mathematical calculations, that is, the single-chip microcomputer 300 calls the sound field characteristic conversion method of the capacitive test microphone to implement the function of the virtual filter.

[0122] The technical features of the above-described embodiments may be arbitrarily combined, and the execution order of the method steps is not limited. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0123] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for converting the sound field characteristics of a microphone, characterized in that: The method comprises: Placing a capacitive test microphone in a first sound field, and obtaining a frequency response curve of the capacitive test microphone in the first sound field to obtain a first frequency response curve; Placing the capacitive test microphone in the second sound field, and obtaining a frequency response curve of the capacitive test microphone in the second sound field to obtain a second frequency response curve; Subtracting the first frequency response curve from the second frequency response curve to obtain a frequency response compensation curve; Constructing a filter, and adjusting the transfer function of the filter so that the frequency response curve of the filter is the same as the frequency response compensation curve; Connecting the filter to a capacitive test microphone; Subtracting the first frequency response curve from the second frequency response curve to obtain a frequency response compensation curve includes: Select N frequency values, where N is a positive integer and N is greater than or equal to 10; Select a frequency value; Obtaining an output voltage level corresponding to the frequency value in the first frequency response curve, and obtaining an output voltage level corresponding to the frequency value in the second frequency response curve; Calculating the difference between the output voltage level corresponding to the frequency value in the first frequency response curve and the output voltage level corresponding to the frequency value in the second frequency response curve to obtain a frequency response compensation value; Return to the step of selecting a frequency value until N frequency response compensation values ​​are obtained; Each frequency value and the frequency response compensation value corresponding to the frequency value form a frequency response compensation point, and N frequency response compensation points are obtained; Smoothly connect N frequency response compensation points to obtain a frequency response compensation curve; The step of constructing a filter and adjusting the transfer function of the filter so that the frequency response curve of the filter is the same as the frequency response compensation curve comprises: Create a filter; Setting a transfer function of the filter, wherein the transfer function expression of the filter is shown in Formula 2; Formula 2: Wherein, H(S) is the transfer function, S is the simulation domain parameter, A is the first optimization coefficient, B is the second optimization coefficient, C is the third optimization coefficient, D is the fourth optimization coefficient, and F is the fifth optimization coefficient; Let S be equal to jω to convert the filter transfer function expression into the filter frequency response parameter expression. The filter frequency response parameter expression is shown in Formula 3. Formula 3: Wherein, H(jω) is the frequency response parameter, A is the first optimization coefficient, B is the second optimization coefficient, C is the third optimization coefficient, D is the fourth optimization coefficient, F is the fifth optimization coefficient, j is the imaginary part of the complex number, and ω is the angular frequency; According to formula 4, the first optimization coefficient, the second optimization coefficient, the third optimization coefficient, the fourth optimization coefficient and the fifth optimization coefficient are adjusted so that the absolute value of the difference between the amplitude-frequency response value corresponding to each frequency value and the frequency response compensation value corresponding to the frequency value is greater than or equal to 0 and less than or equal to 0.5 dB; Formula 4: Where i is the frequency value, ω is the angular frequency, is the modulus of the frequency response parameter, W(jω) is the amplitude-frequency response value of the filter; After connecting the filter and the capacitive test microphone, the method further comprises: Based on formula 5, the simulation domain parameters are converted into discrete domain expressions; Formula 5: Among them, S is the simulation domain parameter, Z is the preset complex number , Ta is the preset sampling time interval; Substitute Formula 5 into Formula 2 to perform Z-transform on the filter transfer function expression using the bilinear transformation method to obtain the expression of the discrete domain time series, as shown in Formula 6; Formula 6: Where Z is a preset complex number , H(Z) is Ta is the preset sampling time interval, a0 is the first discrete domain parameter, a1 is the second discrete domain parameter, a2 is the third discrete domain parameter, b1 is the fourth discrete domain parameter, and b2 is the fifth discrete domain parameter.

2. The method for converting the sound field characteristics of a microphone according to claim 1, characterized in that: The first sound field is one of a free sound field, a pressure sound field and a diffuse sound field, the second sound field is one of a free sound field, a pressure sound field and a diffuse sound field, and the first sound field and the second sound field are different.

3. The method for converting the sound field characteristics of a microphone according to claim 2, characterized in that: Placing a capacitive test microphone in a first sound field and obtaining a frequency response curve of the capacitive test microphone in the first sound field to obtain a first frequency response curve includes: The capacitive test microphone is placed in an anechoic chamber, and the output voltage values ​​of the capacitive test microphone at different frequency values ​​are obtained to obtain a frequency value-voltage value curve in a free sound field; Convert each output voltage value into an output voltage level according to Formula 1, so as to convert the frequency value-voltage value curve into a frequency value-output voltage level curve; Formula 1; Among them, V i is the output voltage value, K i is the output voltage level, i is the frequency value; The output voltage level corresponding to the frequency value of 250 Hz is selected as a reference value, and the difference between the output voltage level corresponding to each frequency value and the reference value is calculated as the frequency response parameter value corresponding to each frequency value, so as to obtain a frequency value-frequency response curve in a free sound field; The frequency value-frequency response curve in the free sound field is taken as the first frequency response curve.

4. The method for converting the sound field characteristics of a microphone according to claim 2, characterized in that: Placing the capacitive test microphone in the second sound field and obtaining a frequency response curve of the capacitive test microphone in the second sound field to obtain a second frequency response curve includes: coupling an electrostatic actuator with a capacitive test microphone, and controlling the electrostatic actuator to apply an electrostatic field to the capacitive test microphone to form a pressure-type sound field; Obtaining output voltage values ​​of the capacitive test microphone at different frequency values ​​in a pressure-type sound field, and obtaining a frequency-voltage curve in a free-type sound field; Convert each output voltage value into an output voltage level according to Formula 1, so as to convert the frequency value-voltage value curve into a frequency value-output voltage level curve; The output voltage level corresponding to the frequency value of 250 Hz is selected as the reference value, and the difference between the output voltage level corresponding to each frequency and the reference value is calculated as the frequency response parameter value corresponding to each frequency value, so as to obtain the frequency value-frequency response curve in the pressure-type sound field; The frequency value-frequency response curve in the pressure-type sound field is used as the second frequency response curve; Placing a capacitive test microphone in a first sound field and obtaining a frequency response curve of the capacitive test microphone in the first sound field to obtain a first frequency response curve includes: Convert each output voltage value into an output voltage level according to Formula 1, so as to convert the frequency value-voltage value curve into a frequency value-output voltage level curve; Formula 1; Among them, V i is the output voltage value, K i is the output voltage level, i is the frequency value; the unit of the output voltage level in Formula 1 is dB.

5. The method for converting the sound field characteristics of a microphone according to claim 1, characterized in that: After obtaining the expression of the discrete domain time series, the method further includes: Placing a capacitive test microphone in a first sound field, acquiring an input sound signal picked up by the capacitive test microphone at every preset sampling time interval, and converting the input sound signal into a digital signal sequence X(t) through an A / D converter; Substituting the digital signal sequence X(t) into Formula 7, the digital signal sequence Y(t) in the second sound field is obtained; Formula 7: Among them, Y(t) is the digital signal sequence in the second sound field, Y t is the voltage value at time t in the second sound field, Y t-1 is the voltage value at the moment before time t in the second sound field, X t is the voltage value at time t in the first sound field, X t-1 is the voltage value at the moment before the moment t in the first sound field, a1 is the second discrete domain parameter, a2 is the third discrete domain parameter, b1 is the fourth discrete domain parameter, and b2 is the fifth discrete domain parameter.

6. A capacitive test microphone system with freely changeable sound field characteristics, characterized in that: include: A capacitive test microphone assembly, comprising a capacitive test microphone and a filter; The filter is communicatively connected to a capacitive test microphone; An A / D converter is communicatively connected to the capacitive test microphone assembly; A single chip microcomputer is communicatively connected to the A / D converter; the single chip microcomputer is also communicatively connected to the capacitive test microphone assembly, and the single chip microcomputer is used to execute the sound field characteristic conversion method of the microphone as described in any one of claims 1-5.

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