CN115002640A - Sound field characteristic conversion method of microphone and capacitive type test microphone system - Google Patents
Sound field characteristic conversion method of microphone and capacitive type test microphone system Download PDFInfo
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Abstract
The application relates to a sound field characteristic conversion method of a capacitive test microphone and a capacitive test microphone system with freely changeable sound field characteristics.
Description
Technical Field
The present invention relates to the field of measuring microphone technology, and in particular, to a method for converting sound field characteristics of a capacitive test microphone and a capacitive test microphone system.
Background
A commonly used test microphone in acoustic testing is a capacitive type test microphone. In order to make the measured acoustic quantity uniform and transmittable, the national standard and the national standard stipulate the standard external dimensions (mainly diameters) of the test condenser microphone, and the external dimensions of the standard condenser type test microphone are three kinds of Φ 23.77, Φ 12.7, and Φ 6.3, which are the diameters of the condenser type test microphone.
When the capacitance type test microphone is placed in a field measurement, the capacitance type test microphone has a certain size which is close to the wavelength of sound waves at high frequency, so that the influence is caused on a sound field, and the influence is related to the size of the microphone. The higher the frequency of the sound wave, the shorter the wavelength, and the greater the effect of the microphone size on the sound field.
In order to compensate the influence, when the test condenser microphone is designed and produced, the high frequency response of the microphone is adjusted correspondingly according to different sound fields. In general acoustic testing, free field type microphones are used in free space, diffuse field type microphones are used in reverberation chambers, and pressure microphones are used in coupling cavities.
This results in the need to use different types of microphones in a non-acoustic environment, which greatly increases the cost of testing.
Disclosure of Invention
Based on this, it is necessary to provide a method for converting the sound field characteristics of a condenser type test microphone, aiming at the problem that the conventional condenser type test microphone requires different types of microphones under a non-sound field environment when in use, resulting in high test cost.
The application provides a sound field characteristic conversion method of a capacitance type test microphone, which comprises the following steps:
placing the capacitive type test microphone in a first sound field, and acquiring a frequency response curve of the capacitive type test microphone in the first sound field to obtain a first frequency response curve;
placing the capacitive type test microphone in a second sound field, and acquiring a frequency response curve of the capacitive type test microphone in the second sound field to obtain a second frequency response curve;
carrying out subtraction processing on the first frequency response curve and the second frequency response curve to obtain a frequency response compensation curve;
constructing a filter, and adjusting the transfer function of the filter to ensure that the frequency response curve of the filter is the same as the frequency response compensation curve;
the filter and the capacitive test microphone are connected.
The present application also provides a capacitive test microphone system in which sound field characteristics can be freely changed, including:
a capacitive test acoustic assembly comprising a capacitive test microphone and a filter; the filter is in communication connection with the capacitive test microphone;
the A/D converter is in communication connection with the capacitive type test sound transmission assembly;
the singlechip is in communication connection with the A/D converter; the single chip microcomputer is also in communication connection with the capacitive type test sound transmission assembly and is used for executing the sound field characteristic conversion method of the capacitive type test microphone.
The application relates to a sound field characteristic conversion method of a capacitive type test microphone and a capacitive type test microphone system with freely changeable sound field characteristics.
Drawings
Fig. 1 is a schematic flowchart of a sound field characteristic conversion method of a capacitive test microphone according to an embodiment of the present application.
Fig. 2 is a graph of frequency value versus frequency response in a free type acoustic field in a method for converting acoustic field characteristics of a condenser type test microphone according to an embodiment of the present application.
Fig. 3 is a graph of frequency value versus frequency response in a pressure type acoustic field in a method for converting acoustic field characteristics of a capacitive type test microphone according to an embodiment of the present application.
Fig. 4 is a frequency response compensation graph of a frequency value-frequency response curve in a pressure-type acoustic field and a frequency value-frequency response curve in a free-type acoustic field in a method for converting acoustic field characteristics of a condenser type test microphone according to an embodiment of the present invention.
Fig. 5 is a graph of frequency value versus amplitude-frequency response value in a sound field characteristic conversion method for a capacitive test microphone according to an embodiment of the present application.
Fig. 6 is a schematic structural diagram of a capacitive test microphone system with freely changeable sound field characteristics according to an embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
The application provides a sound field characteristic conversion method of a capacitive test microphone. It should be noted that the present application provides a method for converting the sound field characteristics of a condenser type test microphone, which is applied to a condenser type test microphone of any diameter.
Further, the sound field characteristic conversion method of the condenser type test microphone provided by the present application is not limited to its execution body. Alternatively, the main body of the implementation of the method for converting the sound field characteristics of the capacitive test microphone provided by the present application may be a single chip connected to the capacitive test microphone.
As shown in fig. 1, in an embodiment of the present application, the sound field characteristic conversion method of the capacitive type test microphone includes the following steps S100 to S500:
s100, placing the capacitive type test microphone in a first sound field, and acquiring a frequency response curve of the capacitive type test microphone in the first sound field to obtain a first frequency response curve.
Specifically, the abscissa of the frequency response curve is a frequency value, and the ordinate is an output voltage level corresponding to the frequency value. The output voltage stage is converted from the output voltage. Frequency response curve is frequency value-frequency response curve.
Alternatively, the first sound field may be a free-form sound field, and the resulting first frequency response curve is shown in fig. 2.
S200, placing the capacitive type test microphone in a second sound field, and acquiring a frequency response curve of the capacitive type test microphone in the second sound field to obtain a second frequency response curve.
Specifically, the second sound field is a sound field of a completely different type from the first sound field. The second acoustic field may be a pressure type acoustic field, and the resulting second frequency response curve is shown in fig. 3.
And S300, performing subtraction processing on the first frequency response curve and the second frequency response curve to obtain a frequency response compensation curve.
Specifically, the subtraction processing means that, for the same abscissa, that is, the frequency value, the corresponding ordinate, that is, the output voltage level, is taken from the first frequency response curve and the second frequency response curve, and the two ordinates are subtracted from each other to obtain a difference. It will be appreciated that the same process is performed for each abscissa, and a curve is finally obtained, which is a frequency response compensation curve.
S400, constructing a filter, and adjusting a transfer function of the filter to enable a frequency response curve of the filter to be the same as the frequency response compensation curve.
Specifically, as shown in fig. 1, it is difficult to avoid errors in the sound pickup of the capacitive test microphone, and the frequency response curve in the free-form sound field can be approximated as a straight line without considering the errors. In another pressure-type acoustic field, the frequency response curve is significantly warped after the 4k frequency value, as shown in fig. 2.
In order to make the frequency response curve under the free type sound field and the frequency response curve under the pressure type sound field identical, the two curves are a straight line. To achieve this, the present embodiment compensates for the capacitive test microphone by constructing the filter. Specifically, a method of obtaining a frequency response compensation curve and then adjusting a transfer function of the filter so that the frequency response curve of the filter is the same as the frequency response compensation curve is adopted.
And S500, connecting the filter with the capacitive test microphone.
Specifically, the filter has a circuit structure, and nominal values of resistors and capacitors in the filter can be calculated according to a transfer function of the filter, so that a complete filter is designed, and the filter is further connected with a capacitive test microphone to complete the method.
In the embodiment, a filter is introduced to be connected with the capacitive type test microphone, and the transfer function of the filter is controlled to enable the filter to compensate the frequency response of the microphone, so that the capacitive type test microphone can be used in different sound fields, and the use cost is greatly reduced.
In an embodiment of the present application, the first sound field is one of a free type sound field, a pressure type sound field, and a diffuse type sound field, and the second sound field is one of a free type sound field, a pressure type sound field, and a diffuse type sound field, and the first sound field and the second sound field are different.
Specifically, the present application provides a sound field characteristic conversion method of a condenser type test microphone, which can realize switching before any two different sound fields of a free type sound field, a pressure type sound field, and a diffusion type sound field.
In an embodiment of the present application, S100 includes the following S110 to S140:
s110, the capacitive type test microphone is placed in a noise elimination chamber, output voltage values of the capacitive type test microphone under different frequency values are obtained, and a frequency value-voltage value curve in a free type sound field is obtained.
Specifically, the present embodiment describes a case where the first sound field is a free-form sound field. The capacitive test microphone is placed in a noise elimination chamber, which is equal to the environment of a free sound field, and the output voltage value V of the capacitive test microphone under different frequency values is measured at the moment i And drawing a frequency value-voltage value curve.
And S120, converting each output voltage value into an output voltage level according to the formula 1, so as to convert the frequency value-voltage value curve into a frequency value-output voltage level curve.
K i ＝20log 10 (V i ) Equation 1
Wherein, V i Is the output voltage value. K i Is the output voltage level. i is the frequency value.
Specifically, the output voltage level is in dB, which is a pure unit of count. The dB objective is to represent the ratio of a very large (followed by a long string of 0's) or very small (preceded by a long string of 0's) in a relatively short way, for ease of calculation and statistics.
S130, selecting the output voltage level corresponding to the 250Hz frequency value as a reference value, and calculating the difference value between the output voltage level corresponding to each frequency value and the reference value. And further, taking the difference value as a frequency response parameter value corresponding to each frequency value to obtain a frequency value-frequency response curve in the free type sound field.
Specifically, the frequency value versus frequency response curve in the free-form acoustic field is shown in fig. 2.
And S140, taking a frequency value-frequency response curve in the free type sound field as a first frequency response curve.
Specifically, as shown in fig. 2, the frequency value-frequency response curve in the free-form acoustic field is approximated by a straight line.
In the embodiment, the capacitance type test microphone is arranged in the anechoic chamber, so that the environment of a free type sound field is created, and the frequency value-frequency response curve of the capacitance type test microphone in the free type sound field is smoothly obtained.
In an embodiment of the present application, S200 includes steps as S210 to S250:
s210, 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.
Specifically, the electrostatic actuator may apply an electrostatic field to the capacitive test microphone, which generates an attractive force that vibrates the diaphragm of the capacitor, which approximates a pressure response, thereby forming a pressure field.
S220, acquiring output voltage values of the capacitive type test microphone under different frequency values in the pressure type sound field to obtain a frequency value-voltage value curve in the free type sound field.
Specifically, the principle of S220 is similar to that of S110, and is not described here again.
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.
Specifically, the principle of S230 is similar to that of S120, and is not described here again.
S240, selecting an output voltage level corresponding to a 250Hz frequency value as a reference value, calculating a difference value between the output voltage level corresponding to each frequency and the reference value, and using the difference value as a frequency response parameter value corresponding to each frequency value to obtain a frequency value-frequency response curve in the pressure type sound field.
Specifically, the principle of S240 is similar to that of S130, and is not described here again. The frequency value versus frequency response curve in a pressure-type acoustic field is shown in fig. 3.
And S250, taking a frequency value-frequency response curve in the pressure type sound field as a second frequency response curve.
Specifically, the principle of S250 is similar to that of S140, and the description thereof is omitted here. As shown in fig. 3, the frequency value-frequency response curve in the pressure type acoustic field is not a straight line, and a kink occurs in the portion behind the 4kHz frequency value.
In the embodiment, the electrostatic exciter is introduced and coupled with the capacitive test microphone, so that an environment of a pressure type sound field is created, and a frequency value-frequency response curve of the capacitive test microphone in the pressure type sound field is smoothly acquired.
In an embodiment of the present application, the S300 includes the following S310 to S370:
s310, selecting N frequency values. N is a positive integer. And N is greater than or equal to 10.
S320, selecting a frequency value.
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.
S340, calculating the difference value 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.
And S350, returning to S320 until N frequency response compensation values are obtained.
And S360, forming a frequency response compensation point by each frequency value and the frequency response compensation value corresponding to the frequency value to obtain N frequency response compensation points.
And S370, smoothly connecting the N frequency response compensation points to obtain a frequency response compensation curve.
Specifically, the first frequency response curve shown in fig. 2 and the second frequency response curve shown in fig. 3 are subtracted, and S310 to S370 are executed to obtain the frequency response compensation curve shown in fig. 3. The frequency response compensation curve is the compensation target that we want to achieve. The frequency response compensation curve is shown in fig. 4.
In this embodiment, by 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 at each frequency value, a frequency response compensation value is obtained, and a frequency response compensation curve is drawn, so that a compensation target can be specifically presented, and a target is provided for a subsequent transfer function setting of the filter.
In an embodiment of the present application, including S400 includes the following S410 to S440:
s410, a filter is created.
Specifically, this step creates a filter in the analog domain.
And S420, setting a transfer function of the filter, wherein the transfer function expression of the filter is shown as formula 2.
Where H (S) is a transfer function. And S is an analog domain parameter. A is a first optimization coefficient. And B is a second optimization coefficient. C is a third optimization coefficient, and D is a fourth optimization coefficient. F is a fifth optimization coefficient.
Specifically, S and h (S) are data in the analog domain, which means that these data are continuous.
And S430, making S equal to j omega to convert the transfer function expression of the filter into a frequency response parameter expression of the filter. The frequency response parameter expression of the filter is shown in equation 3.
Where H (j ω) is a frequency response parameter. A is a first optimization coefficient. And B is a second optimization coefficient. And C is a third optimization coefficient. And D is a fourth optimization coefficient. F is a fifth optimization coefficient. j is the imaginary part of the complex number. ω is the angular frequency.
Specifically, the angular frequency is 2 π × frequency value.
And S440, adjusting the first optimization coefficient, the second optimization coefficient, the third optimization coefficient, the fourth optimization coefficient and the fifth optimization coefficient according to the formula 4, 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.
Where i is the frequency value. ω is the angular frequency. H (j ω) | is the modulus of the frequency response parameter. W (j omega) is the amplitude-frequency response value of the filter.
Specifically, H (j ω) is information having both a phase and an amplitude direction. And taking the modulus of H (j omega), namely extracting the amplitude information of H (j omega) to obtain | H (j omega) |. Then calculate 20log 10 The | H (j omega) converts | H (j omega) | into a unit which is the same as the vertical coordinate of the frequency response compensation curve, namely a unit dB of the frequency response compensation value, thereby unifying the unit dimension, facilitating the leveling of the amplitude-frequency response value and the frequency response compensation value and controlling the equality of the amplitude-frequency response value and the frequency response compensation value.
That is, the frequency response compensation curves of the frequency value-amplitude response curve shown in fig. 5 and the frequency value-frequency response curve shown in fig. 4 are close to completely coincide.
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.
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 an absolute value of a 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 obtain that the amplitude-frequency response value corresponding to each frequency value is completely equal to the frequency response compensation value corresponding to the frequency value, an error range of more than or equal to 0 and less than or equal to 0.5dB can be provided, which is more suitable for practical situations.
In this embodiment, the transfer function expression of the filter is first converted into a 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 equal to the frequency response compensation value corresponding to the frequency value, thereby implementing that the filter can implement a compensation function, so that the output result of the capacitive type test microphone in the second sound field is consistent with the output result of the first sound field, so that the capacitive type test microphone can be used in different sound fields, and the use cost is greatly reduced.
In an embodiment of the present application, after S500, the method for converting the sound field characteristics of the capacitive type test microphone includes the following steps:
s610, converting the simulation domain parameters into discrete domain expressions based on the formula 5.
Wherein S is a simulation domain parameter. Z is a predetermined plurality of re jΩ . And Ta is a preset sampling time interval.
Specifically, the present embodiment also converts the transfer function expression of the filter in the analog domain into the discrete domain form, so that the accuracy of data of the capacitive type test microphone and the stability of the capacitive type test microphone are better when used because the discrete domain form is a digital time series.
The value of the preset complex number is re j Ω It has an imaginary part j. Ta is a preset sampling interval, which may take 0.01 milliseconds.
And S620, substituting the formula 5 into the formula 2 to perform Z conversion on the transfer function expression of the filter by using a bilinear transformation method to obtain an expression of a discrete domain time sequence, wherein the expression of the discrete domain time sequence is shown as a formula 6.
Wherein Z is a predetermined plurality of re jΩ . H (Z) is Ta, which is a preset sampling time interval. a is 0 Is a first discrete domain parameter. a is 1 Is a second discrete domain parameter. a is a 2 Is a third discrete domain parameter. b 1 Is a fourth discrete domain parameter. b 2 Is a fifth discrete domain parameter.
Specifically, the diameters of the capacitive type test microphones may be 23.77 mm, 12.7 mm, and 6.3 mm. A 12.7 mm diameter capacitive test microphone is more common, and when the capacitive test microphone is 12.7 mm diameter, the first discrete domain parameter a 0 1.2533, a second discrete domain parameter a 1 0.0178, third discrete domain parameter a 2 0.0579, fourth discrete domain parameter b 1 Is 0.2105, a fifth discrete domain function b 2 Is 0.0501.
After the formula 5 is substituted into the formula 2, the formula 2 is converted into the formula 6, and 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 the formula 2 are naturally converted into the first discrete domain parameter a 0 Second discrete domain parameter a 1 The third discreteDomain parameter a 2 Fourth discrete domain parameter b 1 Fifth discrete Domain function b 2 . The meaning here is not to say that A is converted to a 0 B is converted to a 1 Instead, a occurs naturally when formula 6 is simplified after formula 2 is converted to formula 6 0 -b 2 Five parameters, a-F, disappeared.
In this embodiment, the accuracy of the data output after the sound field conversion of the capacitive test microphone and the stability of the data output after the sound field conversion of the capacitive test microphone are greatly improved by converting the transfer function expression of the filter in the analog domain into the discrete domain form.
In an embodiment of the present application, after S620, the method for converting a sound field characteristic of a condenser type test microphone further includes:
s630, placing the capacitive type test microphone in a first sound field, obtaining input sound signals picked up by the capacitive type test microphone at intervals of preset sampling time, and converting the input sound signals into a digital signal sequence X (t) through an A/D converter.
Specifically, the input acoustic signal is converted into an electrical signal by a microphone (which may be specifically a microphone), and then the electrical signal is converted into a digital signal sequence x (t) by an a/D converter, and the step of converting the electrical signal into the electrical signal is omitted in this step.
S640, substituting the digital signal sequence x (t) into formula 7 to obtain a digital signal sequence y (t) in the second sound field.
Where y (t) is a digital signal sequence within the second acoustic field. Y is t The voltage value at the moment t in the second acoustic field. Y is t-1 Is the voltage value at the time immediately preceding time t within the second acoustic field. X t Is the voltage value at time t within the first acoustic field. X t-1 Is the voltage value at the time immediately preceding time t within the first acoustic field. a is 0 Is a first discrete domain parameter. a is a 1 Is a second discrete domain parameter.a 2 As a third discrete domain parameter, b 1 Is a fourth discrete domain parameter, b 2 Is a fifth discrete domain parameter.
Specifically, when the digital signal sequence x (t) is substituted into equation 7 and Y (t) is solved, it can be seen that Y 1 ＝a 0 ×X 1 ，Y 2 ＝a 0 ×X 2 +a 1 ×X 1 -b 1 ×Y 1 ，Y 3 ＝a 0 ×X 3 +a 1 ×X 2 +a 2 ×X 1 -b 1 ×Y 2 +b 2 ×Y 1 From Y 3 At the beginning, calculate a Y t Substitution of 5 data, X respectively, is required t ，X t-1 ，X t-2 ，Y t-1 And Y t-2 . By analogy, the voltage value converted by the formula 7 at each time can be calculated, and the converted digital time series y (t) is converted into a digital signal series in the second acoustic field.
In this embodiment, the capacitive test microphone picks up the acoustic signal and converts the acoustic signal into an electrical signal, which enters the a/D converter and is converted into a digital time series. By converting the digital time series according to the formula 7, a new digital time series can be obtained, and the new digital time series is the test result after the digital time series is converted into the capacitive test microphone under the second sound field.
The application also provides a capacitive type test microphone system with freely changeable sound field characteristics.
As shown in fig. 6, in an 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.
The capacitive test acoustic assembly 100 includes a capacitive test microphone 110 and a filter 120. The filter 120 is in communication with the capacitive test microphone 110. The a/D converter 200 is in communication with the capacitive test acoustic assembly 100. The single chip microcomputer 300 is in communication connection with the a/D converter 200. The single chip microcomputer 300 is in communication connection with the capacitive type test microphone assembly 100. The single chip microcomputer 300 is used to execute the sound field characteristic conversion method of the capacitive type test microphone mentioned above.
Specifically, in the present application, the devices and elements are labeled only in the part of the test microphone system of the condenser type in which the sound field characteristics can be freely changed, and although the devices and elements of the same name appear in the respective embodiments of the sound field characteristic conversion method of the condenser type test microphone, no reference numeral is given in order to keep the line concise.
The diameters of the capacitive type test microphones may be 23.77 mm, 12.7 mm, and 6.3 mm.
Alternatively, the test microphone assembly 100 may only include the test microphone 110 and not include the filter 120, and the function of the filter 120 may be implemented by the single chip microcomputer 300 in a mathematical calculation manner, that is, the single chip microcomputer 300 calls a sound field characteristic conversion method of the test microphone to implement the function of the virtual filter.
The technical features of the embodiments described above may be arbitrarily combined, the order of execution of the method steps is not limited, and for simplicity of description, all possible combinations of the technical features in the embodiments are not described, however, as long as there is no contradiction between the combinations of the technical features, the combinations of the technical features should be considered as the scope of the present description.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is specific and detailed, but not construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.
Claims (7)
1. A sound field characteristic conversion method of a microphone, characterized by comprising:
placing the capacitive type test microphone in a first sound field, and acquiring a frequency response curve of the capacitive type test microphone in the first sound field to obtain a first frequency response curve;
placing the capacitive type test microphone in a second sound field, and acquiring a frequency response curve of the capacitive type 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 to ensure that the frequency response curve of the filter is the same as the frequency response compensation curve;
connecting the filter and a capacitive test microphone;
the subtracting the first frequency response curve and the second frequency response curve to obtain a frequency response compensation curve includes:
selecting N frequency values, wherein N is a positive integer and is more than or equal to 10;
selecting a frequency value;
acquiring an output voltage level corresponding to the frequency value in the first frequency response curve, and acquiring an output voltage level corresponding to the frequency value in the second frequency response curve;
calculating the difference value 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;
returning to the step of selecting a frequency value until N frequency response compensation values are obtained;
forming a frequency response compensation point by each frequency value and the frequency response compensation value corresponding to the frequency value to obtain N frequency response compensation points;
smoothly connecting the N frequency response compensation points to obtain a frequency response compensation curve;
the constructing a filter and adjusting the transfer function of the filter to make the frequency response curve of the filter the same as the frequency response compensation curve comprises:
creating a filter;
setting a transfer function of the filter, wherein the transfer function expression of the filter is shown as formula 2;
wherein H (S) is a transfer function, S is a simulation domain parameter, A is a first optimization coefficient, B is a second optimization coefficient, C is a third optimization coefficient, D is a fourth optimization coefficient, and F is a fifth optimization coefficient;
making S equal to j omega to convert the transfer function expression of the filter into a frequency response parameter expression of the filter, wherein the frequency response parameter expression of the filter is shown as a formula 3;
h (j omega) is a frequency response parameter, A is a first optimization coefficient, B is a second optimization coefficient, C is a third optimization coefficient, D is a fourth optimization coefficient, F is a fifth optimization coefficient, j is an imaginary part of a complex number, and omega is an angular frequency;
according to a formula 4, adjusting the first optimization coefficient, the second optimization coefficient, the third optimization coefficient, the fourth optimization coefficient and the fifth optimization coefficient to enable 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 to be more than or equal to 0 and less than or equal to 0.5 dB;
wherein i is a frequency value, ω is an angular frequency, | H (j ω) | is a modulus of the frequency response parameter, and W (j ω) is an amplitude-frequency response value of the filter.
2. The sound field characteristic conversion method of a microphone according to claim 1, wherein the first sound field is one of a free type sound field, a pressure type sound field, and a diffuse type sound field, and the second sound field is one of a free type sound field, a pressure type sound field, and a diffuse type sound field, and the first sound field and the second sound field are different.
3. The method for converting a sound field characteristic of a microphone according to claim 2, wherein the placing the condenser type test microphone in the first sound field and obtaining a frequency response curve of the condenser type test microphone in the first sound field to obtain the first frequency response curve comprises:
placing the capacitive test microphone in a noise elimination chamber, and obtaining output voltage values of the capacitive test microphone under different frequency values to obtain a frequency value-voltage value curve in a free type sound field;
converting each output voltage value into an output voltage level according to formula 1, so as to convert a frequency value-voltage value curve into a frequency value-output voltage level curve;
K i ＝20log 10 (V i ) Formula 1;
wherein, V i To output a voltage value, K i I is the frequency value for the output voltage level;
selecting an output voltage level corresponding to a 250Hz frequency value as a reference value, calculating a difference value between the output voltage level corresponding to each frequency value and the reference value as a frequency response parameter value corresponding to each frequency value, and obtaining a frequency value-frequency response curve in the free type sound field;
and taking a frequency value-frequency response curve in the free type sound field as a first frequency response curve.
4. The method for converting the sound field characteristics of a microphone according to claim 2, wherein the placing of the capacitive test microphone in the second sound field and the obtaining of the frequency response curve of the capacitive test microphone in the second sound field to obtain the second frequency response curve comprise:
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;
acquiring output voltage values of the capacitive type test microphone under different frequency values in a pressure type sound field to obtain a frequency value-voltage value curve in a free type sound field;
converting each output voltage value into an output voltage level according to formula 1 to convert a frequency value-voltage value curve into a frequency value-output voltage level curve;
selecting an output voltage level corresponding to a 250Hz frequency value as a reference value, calculating a difference value between the output voltage level corresponding to each frequency and the reference value, and taking the difference value as a frequency response parameter value corresponding to each frequency value to obtain a frequency value-frequency response curve in the pressure type sound field;
and taking the frequency value-frequency response curve in the pressure type sound field as a second frequency response curve.
5. The sound field characteristic conversion method of a microphone according to claim 3 or 4, characterized in that after the connection of the filter and the capacitive test microphone, the method further comprises:
converting the analog domain parameters into discrete domain expressions based on formula 5;
wherein S is an analog domain parameter, Z is a predetermined plurality of re jΩ Ta is a preset sampling time interval;
substituting the formula 5 into the formula 2 to perform Z conversion on the transfer function expression of the filter by using a bilinear transformation method to obtain an expression of a discrete domain time sequence, wherein the expression is shown in a formula 6;
wherein Z is a predetermined plurality of re jΩ H (Z) is Ta as the predetermined sampling time interval, a 0 Is a first discrete domain parameter, a 1 Is a second discrete domain parameter, a 2 Is a third discrete domain parameter, b 1 Is a fourth discrete domain parameter, b 2 Is a fifth discrete domain parameter.
6. The sound field characteristic conversion method of a microphone according to claim 5, characterized in that after obtaining the expression of the discrete domain time series, the method further comprises:
placing a capacitive type test microphone in a first sound field, acquiring an input sound signal picked up by the capacitive type test microphone at intervals of preset sampling time, 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 a formula 7 to obtain a digital signal sequence Y (t) in a second sound field;
wherein Y (t) is a digital signal sequence in the second sound field, Y t Is the value of the voltage at time t in the second acoustic field, Y t-1 Is the voltage value, X, in the second acoustic field at a time preceding time t t Is the voltage value at time t in the first sound field, X t-1 Is the voltage value at a time immediately preceding time t in the first sound field, a 1 Is a second discrete domain parameter, a 2 Is a third discrete domain parameter, b 1 Is a fourth discrete domain parameter, b 2 Is a fifth discrete domain parameter.
7. A condenser type test microphone system in which a sound field characteristic is freely changeable, comprising:
a capacitive test acoustic assembly comprising a capacitive test microphone and a filter; the filter is in communication connection with the capacitive test microphone;
the A/D converter is in communication connection with the capacitive type test sound transmission assembly;
the singlechip is in communication connection with the A/D converter; the single chip microcomputer is also in communication connection with the capacitive type test sound transmission assembly and is used for executing the sound field characteristic conversion method of the microphone according to any one of claims 1 to 6.
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