TW202338369A - Audio signal processing method and audio signal processing device - Google Patents

Abstract

An audio signal processing method includes: obtaining an audio frequency spectrum of an acoustic wave; determining a target frequency corresponding to a target acoustic pressure value higher than an acoustic pressure threshold value in the audio frequency spectrum; obtaining a frequency range corresponding to the target frequency and including an upper-frequency limit and a lower-frequency limit; determining whether a first acoustic pressure difference corresponding to the target frequency and the upper-frequency limit and a second acoustic pressure difference corresponding to the target frequency and the lower-frequency limit are greater than an acoustic pressure difference threshold value or not; recording the target frequency as an abnormal frequency when determining the first acoustic pressure difference and the second acoustic pressure difference are greater than the acoustic pressure difference threshold value; filtering the acoustic wave according to the abnormal frequency and a preset bandwidth.

Description

Sound processing method and sound processing device

The present invention relates to the technical field of sound processing, in particular to a sound processing method and sound processing device for determining abnormal peak frequencies in sound waveforms.

Recently, the performance of electronic products has gradually improved, and the heat energy generated by electronic products has also increased accordingly. Fans are required to dissipate heat when electronic products generate heat. Therefore, the quality of the fans determines the smooth operation of electronic products. However, the fan will produce noise when running at high speed, causing discomfort to the user. Operators (such as engineers) need to conduct noise tests on the fans to confirm the performance of the fans before shipping electronic products (such as notebook computers, all-in-one computers, etc.) Noise conditions.

Currently, fan noise testing includes objective fan noise listening tests and subjective fan noise listening tests. The objective listening test and analysis of fan noise are all done in a soundless room, while the subjective listening test and analysis of fan noise are done in a conference room or other places, resulting in different analysis results of objective listening of fan noise and subjective listening analysis of fan noise. For example, the analysis result of objective listening of fan noise is that there is no noise, and the analysis result of subjective listening of fan noise is that there is uncomfortable noise.

According to the foregoing, the present invention provides a sound processing method and a sound processing device that analyze the sound spectrum of the sound waveform to find and filter out noise, which can assist operators to clarify noise problems.

A sound processing method according to an embodiment of the present invention includes: obtaining a sound spectrum of a sound waveform; determining a target frequency in the sound spectrum corresponding to a target sound pressure value higher than a sound pressure critical value; obtaining a frequency corresponding to the target frequency Range, the frequency range includes the upper limit frequency and the lower limit frequency; determine whether the first sound pressure value difference corresponding to the target frequency and the upper limit frequency and the second sound pressure value difference corresponding to the target frequency and the lower limit frequency are greater than the sound pressure difference critical value; when When it is determined that both the first sound pressure value and the second sound pressure value are greater than the sound pressure difference critical value, the target frequency is recorded as the abnormal peak frequency; the sound waveform is filtered according to the abnormal peak frequency and the preset bandwidth.

A sound processing device according to an embodiment of the present invention includes a recorder and a processor. The recorder records sound waveforms. The processor is connected to the recorder and generates a sound spectrum according to the sound waveform. The processor performs the following steps: determine the target frequency in the sound spectrum that corresponds to the target sound pressure value higher than the sound pressure critical value; obtain the frequency range corresponding to the target frequency, The frequency range includes the upper limit frequency and the lower limit frequency; determine whether the first sound pressure value difference corresponding to the target frequency and the upper limit frequency and the second sound pressure value difference corresponding to the target frequency and the lower limit frequency are greater than the sound pressure difference critical value; when judging whether the first sound pressure value difference corresponding to the target frequency and the lower limit frequency is greater than the sound pressure difference critical value; When the sound pressure value and the second sound pressure value are both greater than the sound pressure difference critical value, the target frequency is recorded as the abnormal peak frequency; the sound waveform is filtered according to the abnormal peak frequency and the preset bandwidth.

To sum up, the sound processing method and sound processing device of the present invention use the sound pressure critical value and the sound pressure difference critical value to determine the abnormal peak frequency and filter the sound waveform according to the abnormal peak frequency and the preset bandwidth. This improves the accuracy of abnormal peak frequency judgment, thereby improving the filtering effect and helping operators clarify noise problems. Furthermore, the sound processing device of the present invention uses a recorder to record the subjective listening sound, and uses the processor to analyze the abnormal peak frequency of the recorded sound, thereby achieving the effect of real-time recording and analysis of sound quality.

The detailed features and advantages of the present invention are described in detail below in the implementation mode. The content is sufficient to enable anyone skilled in the relevant art to understand the technical content of the present invention and implement it according to the content disclosed in this specification, the patent scope and the drawings. , anyone familiar with the relevant art can easily understand the relevant objectives and advantages of the present invention. The following examples further illustrate the aspects of the present invention in detail, but do not limit the scope of the present invention in any way.

It will be understood that, although the terms "first," "second," etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections These terms should not be limited. These terms are only used to distinguish one element, component, region, layer and/or section from another element, component, region, layer and/or section.

Additionally, the terms "comprises" and/or "comprises" refer to the presence of stated features, regions, integers, steps, operations, elements and/or parts, but do not exclude the presence of one or more other features, regions, integers, steps, operations , elements, parts and/or combinations thereof.

Please refer to FIG. 1 , which is a functional block diagram of a sound processing device according to an embodiment of the present invention. As shown in FIG. 1 , the sound processing device 1 includes a recorder 10 and a processor 20 . The recorder 10 records a sound waveform, which may be a sound waveform recorded by a device under test (such as a notebook computer, an all-in-one computer, and other electronic devices with a fan). The processor 20 can be connected to the recorder 10 in a wired or wireless manner, generate a sound spectrum according to the sound waveform, and analyze the sound spectrum to find and filter out noise. The detailed operation mechanism for finding and filtering out noise will be described later. The processor 20 may be a central processing unit, a graphics processor, or other types of processors. The foregoing are only examples and do not limit the scope of the present invention. Furthermore, the processor 20 may provide a band-stop filtering function. In addition, the sound processing device 1 may further include a display. The display is connected to the processor 20 through a wired or wireless method, and is used to display the measurement interface and the sound filter playback program interface. The format of the interface will be described with examples below.

Please refer to FIG. 1 and FIG. 2 . FIG. 2 is a flow chart of a sound processing method according to an embodiment of the present invention. As shown in Figure 2, the sound processing method includes steps S11 to S17. The sound processing method shown in Fig. 2 can be applied to the sound processing device 1 shown in Fig. 1, but is not limited thereto. Steps S11 to S17 will be described below by taking the operation of the sound processing device 1 shown in FIG. 1 as an example.

Step S11: Obtain the sound spectrum of the sound waveform. Specifically, the processor 20 obtains the sound waveform from the recorder 10 and generates a sound spectrum based on the sound waveform.

Step S12: Determine the target frequency in the sound spectrum corresponding to the target sound pressure value higher than the sound pressure threshold value. Specifically, the sound spectrum includes multiple correspondences between frequencies and sound pressure values (especially a one-to-one relationship), for example, multiple sounds corresponding to multiple frequencies in the range of 100 to 20,000 Hertz (Hz). Pressure value, the sound spectrum can be a Fourier transform spectrum or a prominence ratio spectrum. The sound pressure threshold value is pre-stored in the memory of the processor 20 . The processor 20 compares each sound pressure value with a sound pressure threshold value. If the sound pressure value is greater than the sound pressure critical value, the processor 20 determines that the sound pressure value is the target sound pressure value and uses its corresponding frequency as the target frequency; if the sound pressure value is not greater than the sound pressure critical value, the processor 20 No action is taken or the frequency corresponding to the recorded sound pressure value is not the target frequency. In particular, the frequency points included in the protrusion rate spectrum and the frequency points included in the Fourier spectrum are different from each other, and the sound pressure critical value set by the protrusion rate spectrum and the sound pressure critical value set by the Fourier spectrum are also different from each other. . For example, the sound pressure threshold applicable to the prominence spectrum can be set to 6 dB, and the sound pressure threshold applicable to the Fourier spectrum can be set to 50 dB, but the present invention is not limited to the above.

Step S13: Obtain the frequency range corresponding to the target frequency. The frequency range includes an upper limit frequency and a lower limit frequency. Specifically, the processor 20 sets the upper limit frequency and the lower limit frequency according to the target frequency, and sets the frequency range according to the upper limit frequency, the target frequency and the lower limit frequency. In an implementation where the sound spectrum is a Fourier transformed spectrum, the frequency range includes the target frequency. Furthermore, the processor 20 may set the target frequency as the center frequency, and take frequencies plus or minus N Hz of the center frequency as the upper and lower limit frequencies, where N ranges from 10 to 20, for example.

In an implementation where the sound spectrum is a prominence spectrum, the processor 20 first converts the target frequency to obtain the conversion frequency, and then obtains the frequency range based on the conversion frequency. Please further refer to FIG. 3 , which is a flow chart of the steps of obtaining a frequency range in a sound processing method according to an embodiment of the present invention. As shown in Figure 3, the step of obtaining the frequency range may include steps S131 and S132. Steps S131 and S132 are described below by taking the operation of the sound processing device 1 shown in FIG. 1 as an example.

Step S131: Convert the conversion frequency corresponding to the target frequency in the Fourier spectrum of the sound waveform. Specifically, the processor 20 converts the target frequency in the prominence spectrum into a frequency in the Fourier spectrum as the conversion frequency. The psychoacoustic salience rate is based on 1/12 octave band as the bandwidth analysis. Therefore, the corresponding frequency in the Fourier spectrum can be deduced from the frequency in the salience rate spectrum within the bandwidth, and the sound pressure can be automatically captured. value.

Step S132: Obtain the frequency range according to the conversion frequency. Specifically, the processor 20 sets the upper limit frequency and the lower limit frequency according to the conversion frequency. The conversion frequency is between the upper limit frequency and the lower limit frequency. The processor 20 sets the frequency range according to the upper limit frequency, the conversion frequency and the lower limit frequency. Furthermore, the processor 20 can convert the frequency to a center frequency, and take the frequency plus or minus N Hz of the center frequency as the upper and lower limit frequencies, where N ranges from 10 to 20, for example.

In particular, the sound pressure level of some noises is not high, and the Fourier transform spectrum will not show a peak exceeding the sound pressure critical value, but it will give users an uncomfortable feeling. This is because these noises contain There are many prominent pure tone components, and the prominence rate is a parameter used to evaluate whether these components are prominent. Therefore, through the above-mentioned implementation of searching the target frequency from the prominence spectrum, the effect of subsequent noise elimination can be improved. In yet another implementation aspect, the processor 20 can simultaneously search for the target frequency from the Fourier transform spectrum and the prominence sound spectrum, and perform subsequent steps on each target frequency value.

Step S14: Determine whether the first sound pressure value difference corresponding to the target frequency and the upper limit frequency and the second sound pressure value difference corresponding to the target frequency and the lower limit frequency are greater than the sound pressure difference critical value. Specifically, in an implementation where the sound spectrum is a Fourier transform spectrum, the processor 20 calculates the difference between the target sound pressure value corresponding to the target frequency and the sound pressure value corresponding to the upper limit frequency as the first sound pressure value. difference, and calculate the difference between the target sound pressure value corresponding to the target frequency and the sound pressure value corresponding to the lower limit frequency as the second sound pressure value difference, and then determine the first sound pressure value difference and the second sound pressure value difference Whether they are all greater than the sound pressure difference critical value. The sound pressure values corresponding to each of the above frequencies are the sound pressure values corresponding to the Fourier transform spectrum of each frequency.

In an implementation where the sound spectrum is a prominence spectrum, the processor 20 calculates the difference between the sound pressure value corresponding to the conversion frequency converted from the target frequency and the sound pressure value corresponding to the upper limit frequency as the first sound pressure value. difference, and calculate the difference between the sound pressure value corresponding to the conversion frequency and the sound pressure value corresponding to the lower limit frequency as the second sound pressure value difference, and then determine whether the first sound pressure value difference and the second sound pressure value difference All are greater than the critical value of sound pressure difference. The sound pressure values corresponding to each of the above frequencies are the sound pressure values corresponding to the Fourier transform spectrum of each frequency.

When the processor 20 determines that both the first sound pressure value difference and the second sound pressure value difference are greater than the sound pressure difference threshold, step S15 is continued; when the processor 20 determines that the first sound pressure value difference or the second sound pressure value difference is not When it is greater than the sound pressure difference critical value, continue to step S17.

Step S15: Record the target frequency as the abnormal peak frequency. Specifically, when the processor 20 determines that the first sound pressure value difference and the second sound pressure value difference are both greater than the sound pressure difference critical value, the processor 20 determines that the target frequency corresponds to the abnormal peak, and records that the target frequency is abnormal. peak frequency.

Step S16: Filter the sound waveform according to the abnormal peak frequency and preset bandwidth. Specifically, after obtaining the abnormal peak frequency, the processor 20 sets the upper boundary frequency and the lower boundary frequency of the filter according to the preset bandwidth, and filters the sound waveform using the frequency range composed of the upper boundary frequency and the lower boundary frequency as the filtering range. . The filtering performed by the processor 20 on the sound waveform may be band-stop filtering, high-pass filtering or low-pass filtering, especially band-stop filtering. The preset bandwidth may be pre-stored in the processor 20 and may be set to plus or minus N Hz of the abnormal peak frequency, where N is, for example, between 10 and 20. In one implementation, the processor 20 automatically filters the sound waveform after obtaining the filtering range. In another implementation, the processor 20 presents the filtering range to the operator through the display,

Step S17: No action or record the target frequency as the normal peak frequency. Specifically, when the processor 20 determines that the first sound pressure value difference or the second sound pressure value difference is not greater than the sound pressure difference critical value, the processor 20 determines that the target frequency is a normal frequency, and may not act or record the target frequency. is the normal frequency.

In addition, in addition to the above steps, the sound processing method may further include: when it is determined that the target frequency is a multiple of the rotation frequency of the fan, determining that the fan is the source of the abnormal sound. This step can be performed after step S15. Specifically, the processor 20 calculates and determines whether the abnormal peak frequency is a multiple of the rotation frequency of the fan. When it is determined that the abnormal peak frequency is a multiple of the rotation frequency of the fan, the processor 20 determines that the abnormal peak frequency is related to the rotation frequency of the fan. The fan is determined to be the source of abnormal sound; when it is determined that the abnormal peak frequency is not a multiple of the rotation frequency of the fan, the processor 20 determines that the abnormal peak frequency has nothing to do with the rotation frequency of the fan and the abnormal peak frequency may be caused by other abnormal sound sources (such as motor vibration) . This step can help operators (such as engineers) clarify the source of abnormal sounds.

In another embodiment, in addition to the steps described in the foregoing embodiments, the sound processing method may further include the step of defining a sound pressure difference critical value. Please refer to FIG. 1 and FIG. 4 . FIG. 4 is a flow chart for defining a sound pressure difference critical value in a sound processing method according to another embodiment of the present invention. As shown in Figure 4, the step of defining the sound pressure difference critical value may include steps S21 to S23. Steps S21 to S23 can be performed at any time point before step S14 as shown in Figure 2, and steps S21 and S22 The execution order of the two steps can be reversed as shown in Figure 4 or executed simultaneously. The step of defining the sound pressure difference critical value shown in FIG. 4 can be applied to the sound processing device shown in FIG. 1 , but is not limited thereto. Steps S21 to S23 are described below by taking the operation of the sound processing device 1 shown in FIG. 1 as an example.

Step S21: Obtain a plurality of first sound pressure values corresponding to a plurality of first frequency points greater than the upper limit frequency. Specifically, the processor 20 calculates the estimated upper limit frequency according to the upper limit frequency and the frequency resolution, and then obtains a plurality of first frequency points between the upper limit frequency and the estimated upper limit frequency and a plurality of corresponding first sound pressure values. For example, the upper limit frequency is 538Hz, the frequency resolution is 3.125Hz, the number of first frequency points is set to 10, the estimated upper limit frequency is 600.5Hz, and the processor 20 obtains 10 first frequencies between 538Hz and 600.5Hz. The 10 first sound pressure values corresponding to the points.

Step S22: Obtain a plurality of second sound pressure values corresponding to a plurality of second frequency points less than the lower limit frequency. Specifically, the processor 20 calculates the estimated lower limit frequency based on the lower limit frequency and the frequency resolution, and then obtains multiple second frequency points between the lower limit frequency and the estimated lower limit frequency and their corresponding multiple second sound pressures. value. For example, the lower limit frequency is 518Hz, the frequency resolution is 3.125Hz, the number of second frequency points is set to 10, the estimated lower limit frequency is 455.5Hz, and the processor 20 obtains 10 second frequencies between 455.5Hz and 518Hz. The 10 second sound pressure values corresponding to the points.

Step S23: Use the average value of the above-mentioned first sound pressure value and the above-mentioned second sound pressure value as the sound pressure difference critical value. Specifically, the processor 20 averages the first sound pressure value and the second sound pressure value to obtain an average value, and uses the average value as the sound pressure difference threshold value. For example, the processor 20 averages 10 first sound pressure values and 10 second sound pressure values to obtain an average value as the sound pressure difference critical value.

As mentioned above, in one embodiment, the sound processing device can provide a measurement interface and a sound filter playback program interface. Please refer to FIGS. 5 to 7 . FIG. 5 is a measurement interface of a sound processing device according to an embodiment of the present invention, and FIG. 6 and FIG. 7 are respectively illustrating the measurement interface before performing filtering according to an embodiment of the present invention. and filtered sound filter playback program interface.

As shown in Figure 5, the measurement interface includes multiple sound-related parameter setting fields, a storage path (file path) setting field, a recording time field, a start recording button, and a stop recording button. The operator can first set various sound-related parameters, then enter the storage path and recording seconds, press the start recording button to start recording, and stop recording at any time by pressing the stop recording button.

Figures 6 and 7 exemplarily present spectrograms before and after processing by the sound processing method described in the previous embodiments. As shown in Figure 6, the Fourier transform spectrum shows the wave peaks P1 and P2 with sound pressure values 50dB higher than the sound pressure critical value, corresponding to the target frequencies of 528Hz and 1056Hz respectively. The prominence rate spectrum shows the wave peaks with the sound pressure value 6dB higher than the sound pressure critical value. P3 and P4 correspond to the target frequencies of 485.766Hz and 1029Hz respectively. Among them, 528Hz of the Fourier transform spectrum corresponds to 485.766Hz of the protrusion rate spectrum, and 1056Hz of the Fourier transform spectrum corresponds to 1029Hz of the protrusion rate spectrum. Through the aforementioned sound processing method that uses the Fourier transform spectrum as the sound spectrum, the sound processing device can determine that the sound pressure differences before and after the target frequencies of 528 Hz and 1056 Hz are greater than the sound pressure difference critical value, and determine that it is an abnormal peak frequency. Through the aforementioned sound processing method that uses the prominence frequency spectrum as the sound spectrum, the sound processing device can convert the target frequencies 485.766Hz and 1029Hz into 528Hz and 1056Hz respectively, and then determine them as abnormal peak frequencies.

As shown in Figure 7, the sound processing device can automatically fill in the abnormal peak frequency plus or minus 10Hz in the lower boundary frequency (Low Freq.) and upper boundary frequency (Up Freq.) of the filter as the filter bandwidth. Filter settings For band resistance. From the Fourier transform spectrogram in Figure 7, we can see that the peak waves at 528Hz and 1056Hz have disappeared, and the sound pressure values corresponding to 485.766Hz and 1029Hz on the prominence rate spectrogram have also dropped to values close to zero, indicating that they are uncomfortable. The sound has disappeared.

To sum up, the sound processing method and sound processing device of the present invention use the sound pressure critical value and the sound pressure difference critical value to determine the abnormal peak frequency and filter the sound waveform according to the abnormal peak frequency and the preset bandwidth. This improves the accuracy of abnormal peak frequency judgment, thereby improving the filtering effect and helping operators clarify noise problems. Furthermore, the sound processing device of the present invention uses a recorder to record the subjective listening sound, and uses the processor to analyze the abnormal peak frequency of the recorded sound, thereby achieving the effect of real-time recording and analysis of sound quality.

Although the present invention is disclosed in the foregoing embodiments, they are not intended to limit the present invention. All changes and modifications made without departing from the spirit and scope of the present invention shall fall within the scope of patent protection of the present invention. Regarding the protection scope defined by the present invention, please refer to the attached patent application scope.

1: Sound processing device 10:recorder 20: Processor P1~P4: peak point S11~S17, S131~S132, S21~S23: steps

FIG. 1 is a functional block diagram of a sound processing device according to an embodiment of the present invention. FIG. 2 is a flow chart of a sound processing method according to an embodiment of the present invention. FIG. 3 is a flow chart of the steps of obtaining a frequency range in a sound processing method according to an embodiment of the present invention. FIG. 4 is a flow chart for defining a sound pressure difference critical value in a sound processing method according to another embodiment of the present invention. FIG. 5 is a measurement interface of a sound processing device according to an embodiment of the present invention. FIG. 6 illustrates a sound filter playback program interface before performing filtering according to an embodiment of the present invention. FIG. 7 illustrates a sound filter playback program interface after filtering according to an embodiment of the present invention.

S11~S17: Steps

Claims (10)

A sound processing method includes executing with a processor: Obtain a sound spectrum of a sound waveform; Determine a target frequency in the sound spectrum corresponding to a target sound pressure value higher than the sound pressure critical value; Obtain a frequency range corresponding to the target frequency, the frequency range includes an upper limit frequency and a lower limit frequency; Determine whether a first sound pressure value difference corresponding to the target frequency and the upper limit frequency and a second sound pressure value difference corresponding to the target frequency and the lower limit frequency are greater than a sound pressure difference critical value; When it is determined that both the first sound pressure value and the second sound pressure value are greater than the sound pressure difference threshold, the target frequency is recorded as an abnormal peak frequency; and The sound waveform is filtered according to the abnormal peak frequency and a preset bandwidth. The sound processing method as described in claim 1, wherein the sound spectrum is a prominence spectrum, and obtaining the frequency range corresponding to the target frequency includes: Convert the target frequency to a conversion frequency corresponding to a Fourier spectrum of the sound waveform; and Obtain the frequency range based on the conversion frequency; The first sound pressure value difference is the difference between the sound pressure value corresponding to the conversion frequency and the sound pressure value corresponding to the upper limit frequency, and the second sound pressure value difference is the sound pressure value corresponding to the conversion frequency. The difference between the sound pressure value and the sound pressure value at the lower limit frequency. The sound processing method as described in claim 1 further includes: when determining that the target frequency is a multiple of a rotation frequency of a fan, determining that the fan is an abnormal sound source. The sound processing method as claimed in claim 1, wherein the filtering performed on the sound waveform is band-stop filtering. The sound processing method as described in request item 1 further includes: Obtain multiple first sound pressure values corresponding to multiple first frequency points greater than the upper limit frequency; Obtain multiple second sound pressure values corresponding to multiple second frequency points that are less than the lower limit frequency; and An average value of the first sound pressure values and the second sound pressure values is used as the sound pressure difference critical value. A sound processing device including: a recorder to record a sound waveform; and A processor is connected to the recorder and generates a sound spectrum according to the sound waveform. The processor performs the following steps: Determine a target frequency in the sound spectrum corresponding to a target sound pressure value higher than the sound pressure critical value; Obtain a frequency range corresponding to the target frequency, the frequency range includes an upper limit frequency and a lower limit frequency; Determine whether a first sound pressure value difference corresponding to the target frequency and the upper limit frequency and a second sound pressure value difference corresponding to the target frequency and the lower limit frequency are greater than a sound pressure difference critical value; When it is determined that both the first sound pressure value and the second sound pressure value are greater than the sound pressure difference threshold, the target frequency is recorded as an abnormal peak frequency; and The sound waveform is filtered according to the abnormal peak frequency and a preset bandwidth. The sound processing device of claim 6, wherein the sound spectrum is a prominence spectrum, and the processor converts a conversion frequency corresponding to the target frequency in a Fourier spectrum of the sound waveform and obtains the conversion frequency based on the conversion frequency. frequency range, the first sound pressure value difference is the difference between the sound pressure value corresponding to the conversion frequency and the sound pressure value corresponding to the upper limit frequency, and the second sound pressure value difference is the difference between the sound pressure value corresponding to the conversion frequency The difference between the sound pressure value and the sound pressure value corresponding to the lower limit frequency. The sound processing device of claim 6, wherein the processor further determines that the target frequency is a multiple of a rotational frequency of a fan, and determines that the fan is an abnormal sound source. The sound processing device as claimed in claim 6, wherein the filtering performed by the processor on the sound waveform is band-stop filtering. The sound processing device of claim 6, wherein the processor further obtains a plurality of first sound pressure values corresponding to a plurality of first frequency points greater than the upper limit frequency, and obtains a plurality of second sound pressure values less than the lower limit frequency. A plurality of second sound pressure values corresponding to the frequency points, and an average value of the first sound pressure values and the second sound pressure values is used as the sound pressure difference critical value.

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