CN115835070A - Microphone bottom noise testing device - Google Patents
Microphone bottom noise testing device Download PDFInfo
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- CN115835070A CN115835070A CN202211380361.4A CN202211380361A CN115835070A CN 115835070 A CN115835070 A CN 115835070A CN 202211380361 A CN202211380361 A CN 202211380361A CN 115835070 A CN115835070 A CN 115835070A
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Abstract
The application discloses microphone end noise testing arrangement includes: the filter circuit module is used for respectively receiving input signals of a standard microphone and a microphone to be tested and outputting a filter signal after filtering; the amplifying circuit module receives the filtering signal and outputs an amplifying signal after amplification; and the oscilloscope reads the amplified signals of the standard microphone and the microphone to be tested and acquires an output signal, and calculates and acquires the background noise value of the microphone to be tested according to the known background noise value and the output signal of the standard microphone and the output signal of the microphone to be tested. The microphone bottom noise testing device has the advantages of more extensive requirements on the measuring environment, high testing efficiency and low cost. The bottom noise measuring device can be integrated into automatic test equipment, and the peak-to-peak value can be measured by the automatic test equipment with higher accuracy.
Description
Technical Field
The application relates to the technical field of microphone measurement, in particular to a microphone noise floor testing device.
Background
At present, in the process of testing the microphone noise floor, external sound and electromagnetic wave interference need to be isolated. Two ways of isolating ambient sound include: first, an anechoic chamber is constructed in which the noise floor of the microphone is measured. Second, since the transmission of sound waves requires a medium, a microphone test in a vacuum chamber can be used to isolate external sound wave interference. The two modes have high environmental cost, complex test and low test efficiency.
In order to make the requirements for the test environment more tolerant, patent CN104869519B proposes a noise test method based on an adaptive filter. This need design adaptive filter, the information that needs to carry out the contrast collection of background noise wave form is many, and the design degree of difficulty is big, and the calculated volume that needs is big, and is inefficient, is unfavorable for big batch test.
Disclosure of Invention
To the problem among the correlation technique, this application has provided a microphone bottom noise testing arrangement, can improve efficiency of software testing, reduces test cost.
The technical scheme of the application is realized as follows:
according to an aspect of the present application, there is provided a microphone noise floor test apparatus including:
the filter circuit module is used for respectively receiving input signals of a standard microphone and a microphone to be tested and outputting a filter signal after filtering;
the amplifying circuit module receives the filtering signal and outputs an amplifying signal after amplification;
and the oscilloscope is used for reading the amplified signals of the standard microphone and the microphone to be detected and acquiring an output signal, and calculating and acquiring the background noise value of the microphone to be detected according to the known background noise value and the output signal of the standard microphone and the output signal of the microphone to be detected.
The output signal of the standard microphone and the output signal of the microphone to be tested comprise the peak-to-peak value of a waveform signal displayed by the oscilloscope, the background noise value is an effective value of noise voltage, and the peak-to-peak value and the effective value are in a statistically linear proportional relationship.
Wherein the filter circuit module comprises a band pass filter for simulating A weighting to attenuate low and high frequency noise in the frequency band of 20 to 20 kHz.
The input signal comprises the noise of the microphone to be tested, the noise of the standard microphone and the circuit noise of the microphone bottom noise testing device.
Wherein the noise of the microphone to be tested, the noise of the standard microphone and the circuit noise of the microphone bottom noise test device are uncorrelated with each other and satisfy the relation:
e n1 is an effective value of the noise floor of the standard microphone,
e n2 is a significant value of the circuit noise of the microphone noise floor test device,
e nT is the total noise of the input signal and,
when 3. E n2 <e n1 And when the amplifying circuit module comprises a low noise amplifier, neglecting e n2 。
The microphone bottom noise testing device has the advantages of more extensive requirements on the measuring environment, high testing efficiency and low cost. The bottom noise measuring device can be integrated into automatic test equipment, and the peak-to-peak value can be measured by the automatic test equipment with higher accuracy.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required in the embodiments will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 illustrates a circuit diagram of a microphone noise floor test apparatus provided in accordance with some embodiments.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments that can be derived from the embodiments given herein by a person of ordinary skill in the art are intended to be within the scope of the present disclosure.
In microphone testing techniques, the background noise of a microphone is an effective value Vrms, which generally refers to the noise voltage, but the oscilloscope measures the peak-to-peak Vpp. When the noise is similar to white noise, a statistically linear proportional relationship exists between the peak-to-peak value and the effective value. Specifically, the method comprises the following steps:
1. the peak-to-peak value of a white noise signal statistically appears as a gaussian distribution curve that constitutes a probability density function. The probability distribution function is the integral of the probability density function.
2. According to the probability distribution function, the probability of detecting the peak-to-peak value of the noise voltage between +/-3 sigma (namely 6 sigma) is 99.7%, and the probability of detecting the peak-to-peak value of +/-3.3 sigma (namely 6.6 sigma) is 99.9%.
3. The input end of the filter circuit module 100 includes a dc blocking capacitor, i.e., a capacitor C4 in fig. 1), it can be assumed that the standard deviation δ is equal to the effective voltage Vrms, so under a certain standard deviation condition, a linear proportional relationship between the noise peak-to-peak value Vpp and the effective noise Vrms can be estimated. The ratio value can be calculated according to the peak-to-peak value and the background noise value of the standard microphone. And calculating to obtain the bottom noise value of the microphone to be detected based on the obtained proportional value and the peak-to-peak value of the microphone to be detected. The structure of the test apparatus will be described in detail below.
Referring to fig. 1, according to an embodiment of the present application, a microphone bottom noise testing apparatus is provided for testing the bottom noise of a microphone, the testing apparatus is relatively tolerant to the testing environment, the testing result is relatively accurate, the method is simple and convenient, the testing efficiency is high, and the testing apparatus is suitable for mass detection and can be integrated into an automatic testing device.
The microphone bottom noise testing device comprises a filter circuit module 100, an amplifying circuit module 200 and an oscilloscope for reading voltage signals.
The filter circuit module 100 receives input signals of the standard microphone and the microphone to be tested, and outputs a filtered signal after filtering. At the mic element shown in fig. 1, the standard microphone may be measured and the output signal of the standard microphone may be obtained, and then the microphone to be measured may be measured and the output signal of the microphone to be measured may be obtained.
The noise in the living environment is mostly low-frequency noise, such as a fan, an air conditioner and the like. Therefore, the input signal needs to be filtered. In some embodiments, the filtering circuit module 100 of fig. 1 is used to remove low frequency noise from the input signal. In some embodiments, the filtering circuit module 100 includes a band-pass filter for simulating a weighting to attenuate low-frequency and high-frequency noise in the frequency band of 20 to 20kHz, and the output signal obtained after filtering approximately satisfies the statistical rule of the linear relationship between the peak-to-peak value and the effective value of the signal.
The amplifying circuit module 200 receives the filtered signal and outputs an amplified signal after amplification. The background noise of a microphone is typically on the order of microvolts, whereas voltages on the order of millivolts are more easily detected by an oscilloscope. Therefore, the test apparatus needs to employ the amplifying circuit module 200 to amplify the filtered signal.
In some embodiments, the input signal includes noise of the microphone under test, noise of a standard microphone, and circuit noise of the microphone noise floor test device.
In some embodiments, the noise of the microphone under test, the noise of the standard microphone, and the microphone
The circuit noises of the noise floor test device are uncorrelated with each other and satisfy the relation:
e n1 is an effective value of the background noise of a standard microphone,
e n2 is a significant value of the circuit noise of the microphone noise floor test device,
e nT is the total noise of the input signal and,
when 3. E n2 <e n1 And when the amplifying circuit module 200 includes a low noise amplifier, e is ignored n2 ，
So that the noise signal can be considered to come from the microphone and not from the testing device.
And the oscilloscope reads the amplified signals of the standard microphone and the microphone to be tested and acquires an output signal, and calculates and acquires the background noise value of the microphone to be tested according to the known background noise value and the output signal of the standard microphone and the output signal of the microphone to be tested.
In some embodiments, the output signal of the standard microphone and the output signal of the microphone to be tested comprise a peak-to-peak value of a waveform signal displayed by an oscilloscope, the bottom noise value is an effective value of the noise voltage, and the peak-to-peak value and the effective value are in a statistically linear proportional relationship.
The principle of use of the test device will be described in detail below.
Step 1, determining a linear scale coefficient K according to the bottom noise value of the standard microphone and the measured peak-to-peak value.
And 2, calculating a bottom noise value Y of the microphone to be detected by using the proportionality coefficient K and the peak-to-peak value V of the microphone to be detected, wherein A is the amplification factor of the amplifying circuit module.
The testing device has the advantages of more tolerant requirements on the measuring environment, high testing efficiency and low cost. The bottom noise measuring device can be integrated into automatic test equipment, and the peak-to-peak value can be measured by the automatic test equipment with higher accuracy.
The following table shows the comparison of the measurement results obtained by the test device with the measurement results of a professional metering mechanism:
the present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (5)
1. A microphone noise floor testing device, comprising:
the filter circuit module is used for respectively receiving input signals of the standard microphone and the microphone to be tested and outputting a filter signal after filtering;
the amplifying circuit module receives the filtering signal and outputs an amplifying signal after amplification;
and the oscilloscope is used for reading the amplified signals of the standard microphone and the microphone to be detected and acquiring an output signal, and calculating and acquiring the background noise value of the microphone to be detected according to the known background noise value and the output signal of the standard microphone and the output signal of the microphone to be detected.
2. The microphone noise floor test device of claim 1, wherein the output signal of the standard microphone and the output signal of the microphone to be tested comprise a peak-to-peak value of a waveform signal displayed by the oscilloscope, the noise floor value is an effective value of a noise voltage, and the peak-to-peak value and the effective value are in a statistically linear proportional relationship.
3. The microphone noise floor test device of claim 1, wherein the filter circuit module comprises a band pass filter for simulating a-weighting to attenuate low and high frequency noise in the frequency band of 20 to 20 kHz.
4. The microphone noise floor test device of claim 1, wherein the input signal comprises noise of the microphone under test, noise of the standard microphone, and circuit noise of the microphone noise floor test device.
5. The microphone noise floor test device according to claim 4, wherein the noise of the microphone under test, the noise of the standard microphone, and the circuit noise of the microphone noise floor test device are uncorrelated with each other and satisfy the relation:
e n1 is an effective value of the noise floor of the standard microphone,
e n2 is a significant value of the circuit noise of the microphone noise floor test device,
e nT is the total noise of the input signal and,
when 3. E n2 <e n1 And when the amplifying circuit module comprises a low noise amplifier, neglecting e n2 。
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN202211380361.4A CN115835070A (en) | 2022-11-04 | 2022-11-04 | Microphone bottom noise testing device |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202211380361.4A CN115835070A (en) | 2022-11-04 | 2022-11-04 | Microphone bottom noise testing device |
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| CN115835070A true CN115835070A (en) | 2023-03-21 |
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