Noise evaluation device, acoustic characteristic measuring device, noise evaluation method, acoustic characteristic measuring method, and noise evaluation program

Abstract

To provide a noise evaluation device for determining whether or not the frequency spectrum of noise other than measurement target sound included in a sound collection signal can be estimated.SOLUTION: A noise evaluation device includes sound collection signal acquisition means, measurement target sound on / off control means, and determination means. The sound collection signal acquisition means acquires a sound collection signal generated by collecting a measurement target sound output by a measurement target and a sound from a surrounding environment. The measurement target sound on / off control means performs on / off control to repeatedly turn on / off an output of the measurement target sound generated by the measurement target. The determination means takes the sound collection signal when the output of the measurement target sound is on as a first sound collection signal, and takes the sound collection signal when the output of the measurement target sound is off as a second sound collection signal. Then, the intensity of the plurality of second sound collection signals or the time change of the frequency spectrum in a predetermined period is calculated and, based on this time change, it is determined whether or not the frequency spectrum of noise other than the measurement target sound included in the sound collection signal can be estimated.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a noise evaluation device, an acoustic characteristic measuring device, a noise evaluation method, an acoustic characteristic measuring method, and a noise evaluation program. [Background technology]

[0002] Generally, electrical products are composed of multiple modules such as electronic components, mechanical components, housings, etc. In the manufacture of such electrical products, the modules are assembled in order, and then functional and visual inspections are carried out to confirm that there are no problems before the assembly is completed.

[0003] One of the functional tests is a sound test. For example, this is to check whether the device's operation sounds and warning sounds are working properly and whether there are any problems with the audio quality. In such sound tests, noise from the surrounding environment may be mixed in and cause erroneous judgments. For this reason, it is common to carry out tests with soundproofing measures in place, such as storing the product in a highly soundproof box called a soundproof box.

[0004] However, the method using the soundproof box requires the work of removing the inspected product from the soundproof box and storing the next product to be inspected back in the soundproof box every time an inspection is performed, which reduces productivity. Therefore, efforts are being made to collect sound without taking soundproofing measures such as using a soundproof box, and to remove noise by signal processing during inspection. In this case, technology is required to distinguish whether the collected sound is from the target object or from noise from the surrounding environment and to remove the noise.

[0005] For example, Patent Document 1 discloses an invention of a voice recognition device that performs voice recognition by removing noise from the surrounding environment. In this voice recognition device, first, noise without voice (sound to be measured) is sampled, and the distribution of the time components of the noise is converted into a distribution of frequency components by FFT (Fast Fourier Transform). Next, the user's voice including noise is sampled, and the distribution of the time components of the user's voice is converted into a distribution of frequency components by FFT. Then, the frequency components of only the voice can be obtained by subtracting the frequency components of the noise from the frequency components of the voice. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-005788 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the above Patent Document 1, it is assumed that the noise does not change over time. In other words, if the noise is the same when sampling the ambient sound and when sampling the voice, it is possible to accurately extract the frequency components of only the voice. However, if the noise changes between the two sampling periods, there is a problem that the frequency components of the noise that are different from the actual ones are subtracted from the frequency components of the voice. The reason for this is that, even though it is not possible to accurately estimate the noise components when the noise is changing, the noise components sampled under the assumption that they do not change are used.

[0008] The present invention has been made in consideration of the above problems, and aims to provide a noise evaluation device that determines whether or not the frequency spectrum of noise other than the sound to be measured that is included in a collected sound signal can be estimated. [Means for solving the problem]

[0009] In order to solve the above problems, the noise evaluation device of the present invention has a sound collection signal acquisition means, a measurement target sound on / off control means, and a judgment means. The sound collection signal acquisition means acquires a sound collection signal generated by collecting a measurement target sound output by the measurement target and a sound from the surrounding environment. The measurement target sound on / off control means performs on / off control to repeatedly turn on / off the output of the measurement target sound generated by the measurement target. The judgment means sets the sound collection signal when the output of the measurement target sound is on as a first sound collection signal, and sets the sound collection signal when the output of the measurement target sound is off as a second sound collection signal. Then, the judgment means calculates the time change in intensity or frequency spectrum of a plurality of second sound collection signals in a predetermined period, and judges whether or not the frequency spectrum of noise other than the measurement target sound included in the sound collection signal can be estimated based on this time change.

[0010] An acoustic characteristic measurement device of the present invention includes the above-mentioned noise evaluation device and an acoustic characteristic calculation unit that calculates the acoustic characteristics of the measurement target sound by using the first and second collected sound signals during a period in which the noise evaluation device has determined that the frequency spectrum of noise other than the measurement target sound contained in the collected sound signals can be estimated.

[0011] In addition, the noise evaluation method of the present invention performs control to repeatedly turn on and off the measurement target sound output by the measurement target, and obtains a collected sound signal generated by collecting the measurement target sound. Furthermore, based on this control, the collected sound signal when the output of the measurement target sound is on is taken as a first collected sound signal, and the collected sound signal when the output of the measurement target sound is off is taken as a second collected sound signal, and a time change in the intensity or frequency spectrum of the second collected sound signal is calculated. Then, based on this time change, it is determined whether or not the frequency spectrum of noise other than the measurement target sound contained in the collected sound signal can be estimated.

[0012] The noise evaluation program of the present invention causes a computer to execute a process of acquiring a sound collection signal generated by collecting a measurement target sound output by a measurement target, and a process of controlling the output of the measurement target sound of the measurement target to be repeatedly turned on and off. Based on this control, the computer further executes a process of setting the sound collection signal when the output of the measurement target sound is on as a first sound collection signal, and a process of setting the sound collection signal when the output of the measurement target sound is off as a second sound collection signal. The computer then executes a process of calculating a time change in intensity or frequency spectrum of the second sound collection spectrum, and determining whether or not the frequency spectrum of noise other than the measurement target sound contained in the sound collection signal can be estimated based on this time change. Effect of the Invention

[0013] An effect of the present invention is to provide a noise evaluation device that determines whether or not the frequency spectrum of noise other than a measurement target sound that is included in a collected sound signal can be estimated. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a noise evaluation device according to a first embodiment. [Diagram 2] 4 is a flowchart showing the operation of the noise evaluation device of the first embodiment. [Diagram 3] FIG. 11 is a block diagram showing an acoustic characteristic measuring device according to a second embodiment. [Figure 4] FIG. 11 is a block diagram showing an acoustic characteristic measuring device according to a third embodiment. [Diagram 5] 13 is a timing chart showing the relationship between a measurement target sound on / off control signal and a collected sound signal in the third embodiment. [Figure 6] 13 is a graph showing an example of a difference calculation of a second sound collection signal in the third embodiment. [Figure 7] 13 is a graph showing another example of the difference calculation of the second sound collection signal in the third embodiment. [Figure 8] 10 is a flowchart showing the operation of an acoustic characteristic measuring apparatus according to a third embodiment. [Figure 9] 9 is a flowchart showing details of S104 in the flowchart of FIG. 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. However, the embodiments described below are limited in a technically preferable manner for carrying out the present invention, but the scope of the invention is not limited to the following. Note that the same components in each drawing are given the same numbers, and the description may be omitted.

[0016] (First embodiment) 1 is a block diagram showing a noise evaluation device 10 of the first embodiment. The noise evaluation device 10 has a collected sound signal acquisition means 1, a measurement target sound on / off control means 2, and a determination means 3.

[0017] The sound collection signal acquisition means 1 acquires a sound collection signal generated by collecting a measurement target sound outputted from a measurement target and a sound from the surrounding environment. Here, the sound from the surrounding environment is noise.

[0018] The measurement object sound on / off control means 2 performs on / off control for repeatedly turning on / off the output of the measurement object sound generated by the measurement object.

[0019] The determination means 3 determines the collected sound signal when the output of the sound to be measured is on as the first collected sound signal, and determines the collected sound signal when the output of the sound to be measured is off as the second collected sound signal. Then, the determination means 3 calculates the time change in intensity or frequency spectrum of the second collected sound signals in a predetermined period, and determines whether or not the frequency spectrum of the noise contained in the first collected sound signal can be estimated based on the time change. Details of this process will be described later.

[0020] FIG. 2 is a flowchart showing the operation of the noise evaluation device 10. The noise evaluation device 10 controls the measurement target to repeatedly turn on / off the measurement target sound emitted by the measurement target (S1). The judgment means 3 regards the collected sound signal acquired by the collected sound signal acquisition means 1 when the measurement target sound is on as the first collected sound signal, and the collected sound signal acquired by the collected sound signal acquisition means 1 when the measurement target sound is off as the second collected sound signal. Then, a number corresponding to the number of times of on / off switching is given (S2). For example, the second off can be called the second collected sound signal (2), the fifth off can be called the first collected sound signal (5), and so on. Next, the difference between the second collected sound signal in a certain off time of on / off switching of the measurement target sound output and the second collected sound signal in a certain off time after the on / off time is calculated (S3). The calculation of the difference can be performed, for example, by using the time change of the signal strength within the same time width. This signal strength can be calculated, for example, by the root mean square (effective value). If the difference in the root mean square is equal to or less than a predetermined threshold, it can be determined that the noise level has not changed. Alternatively, in calculating the difference, the time change in the second collected signal strength may be Fourier transformed for each time, converted into a frequency spectrum, and calculated as the difference in sound pressure at each frequency. In this case, for example, first, the frequency spectrum of the second collected signal at a certain time is calculated, and similarly, the frequency spectrum of the second collected signal a predetermined number of times after the certain time is calculated. Next, subtraction is performed for each component to calculate the difference spectrum. Then, for example, the absolute value of each frequency component of the difference spectrum is calculated, and if this absolute value does not have a component equal to or greater than a predetermined threshold, it can be determined that the second collected signal (noise) has not changed, and if there is a component equal to or greater than the threshold, it can be determined that the second collected signal (noise) has changed. In addition, in calculating the difference spectrum, for example, a threshold may be set in the frequency spectrum of the second collected signal, and the difference may be calculated only for frequency components equal to or greater than the threshold. Next, it is determined whether the difference calculated as above, for example the maximum value of the components of the difference spectrum, is less than a predetermined threshold (S4). If the difference is less than the threshold (S4_Yes), it is determined that the frequency spectrum of the noise during the period in which the difference was calculated can be estimated (S5).This is because it can be determined that the noise has not changed during the above period. If the noise has not changed, it is considered that the noise components contained in the first collected signal are the same as those in the second collected signal of the time adjacent to the first collected signal of interest. Therefore, the collected spectrum of the noise contained in the first collected signal can be estimated by calculating the frequency spectrum of the second collected signal of the time. On the other hand, if the difference is equal to or greater than the threshold (S4_No), it is determined that it is impossible to estimate the frequency spectrum of the noise during the period in which the difference was calculated (S6). This is because it is determined that the noise has changed during the period, and the frequency spectrum of the noise contained in the first collected signal cannot be accurately estimated.

[0021] By performing the above operations, the noise evaluation device of this embodiment can determine whether or not the frequency spectrum of noise other than the measurement target sound, which is included in the collected sound signal, can be estimated.

[0022] Second embodiment 3 is a block diagram showing an acoustic characteristic measurement device 20 that uses the noise evaluation device 10 of the first embodiment. The acoustic characteristic measurement device 20 includes an acoustic characteristic calculation means 4 in addition to the noise evaluation device 10. The acoustic characteristic calculation means 4 receives the first and second sound collection signals and a determination result from the determination means 3. This determination result indicates a period during which the frequency spectrum of the noise can be estimated and a period during which the frequency spectrum of the noise cannot be estimated.

[0023] In the above configuration, the acoustic characteristic calculation means 4 performs Fourier transform on the first sound collection signal and the second sound collection signal, respectively, to calculate the first sound collection spectrum and the second sound collection spectrum. Then, during a period in which the determination means 3 determines that the frequency spectrum of the noise can be estimated, the noise is removed by subtracting the second sound collection spectrum of an adjacent time from the first sound collection spectrum of a certain time, and the spectrum of the measurement target sound is extracted. In this way, the acoustic characteristic of the measurement target sound can be obtained as the spectrum of the measurement target sound.

[0024] As described above, according to the acoustic characteristic measuring device of this embodiment, the acoustic characteristic is calculated only during the period during which the frequency spectrum of the noise can be estimated, and therefore it is possible to perform accurate acoustic characteristic measurement.

[0025] (Third embodiment) In this embodiment, a specific configuration example of the acoustic characteristic measurement device of the second embodiment will be described. Fig. 4 is a block diagram showing an acoustic characteristic measurement device 100 of the third embodiment. The acoustic characteristic measurement device 100 has a measurement target sound on / off control unit 110, a collected sound signal acquisition unit 120, a collected sound signal division unit 130, an FFT processing unit 140, a noise spectrum estimation feasibility determination unit 150, and an acoustic characteristic calculation unit 160. Here, FFT is an abbreviation for Fast Fourier Transform. For example, a computer equipped with a processor, memory, and storage can be used as the hardware of the acoustic characteristic measurement device 100.

[0026] The measurement target sound on / off control unit 110 outputs a command to the measurement target 300 to output (on) sound or stop (off) sound, and controls the output of the measurement target sound of the measurement target 300 to be turned on / off at a predetermined cycle. The measurement target sound on / off control unit 110 also outputs a control signal to the collected sound signal division unit 130 and the FFT processing unit 140.

[0027] The collected sound signal acquisition unit 120 acquires the collected sound signal generated by the sound collection microphone 200 by collecting the sound generated from the measurement target and the surrounding environmental sound and converting the sound into an electrical signal. The sound collection microphone 200 collects noise coming from the surrounding environment in addition to the measurement target sound output from the measurement target, so the collected sound signal also contains noise.

[0028] The sound collection signal division unit 130 divides the received sound collection signal into a first sound collection signal when the output of the sound to be measured is on, and a second sound collection signal when the output is off. The sound collection signal division unit 130 also counts the number of times the sound to be measured is switched on / off, and adds numbers to the first sound collection signal and the second sound collection signal according to the number of times the sound is switched on / off. Then, the first sound collection signal and the second sound collection signal are output to the FFT processing unit 140.

[0029] The FFT processing unit 140 performs FFT processing on the first collected sound signal and the second collected sound signal for each on period and off period.

[0030] The noise spectrum estimation feasibility determination unit 150 obtains a difference between a second sound collection signal at a certain time and a second sound collection signal at a time a predetermined number of times after the time, and determines whether or not the frequency spectrum of the noise can be estimated in the period for which the difference was obtained based on the difference. Details will be described later.

[0031] The acoustic characteristic calculation unit 160 calculates acoustic characteristics using the first sound collection signal and the second sound collection signal during the period in which the noise spectrum estimation feasibility determination unit 150 has determined that the frequency spectrum of the noise can be estimated. The calculation of the acoustic characteristics will also be described later.

[0032] Next, a concrete example will be used to explain the estimation possibility judgment of the frequency spectrum of noise and the calculation of acoustic characteristics. First, the collected sound signal will be explained. FIG. 5 is a timing chart showing the signal strength of the collected sound signal acquired by the collected sound signal acquisition unit 120 and an output example of the on / off control signal output by the measurement target sound on / off control unit 110. When the on / off control signal is transmitted from the measurement target sound on / off control unit 110 to the measurement target 300, the measurement target 300 turns on / off the measurement target sound output accordingly. Note that the number of on / off switching is counted by the collected sound signal division unit 130, for example, and as shown in FIG. 5, numbers are assigned to each on period and off period, such as the i-th on, the i-th off, the i+1-th on, ....

[0033] Next, we will explain the estimation of the frequency spectrum of noise. First, FFT processing is performed for each on-period and off-period, and the time change of the collected sound signal is converted into a frequency spectrum. Here, the sound pressure of frequency f1 in the second collected sound spectrum obtained by FFT processing the second collected sound signal when the measurement target sound is off is P OFF (in the order of sound collection). The sound pressure of frequency f1 in the first sound collection spectrum obtained by FFT processing the first sound collection signal when the measurement target sound is on is P ON (in the order of sound collection). For example, if it is off, the (i-1)th sound collection is P OFF (i-1), if it is the i-th collection, P OFF (i). Whether it is possible to estimate the frequency spectrum of noise depends on the P OFF And P after a certain number of times OFF The absolute value of the difference between th It is judged whether it is less than or not.

[0034] FIG. 6 is a graph showing the sound pressure at frequency f1 for the (i-1)th off and the i-th off. In the case of FIG. 6, the difference ΔP OFF (i)=P OFF (i)-P OFF (i-1) <P th Therefore, the change in noise between the i-1th off and the ith off is small and can be considered constant. Therefore, the sound pressure P ON From (i), P OFF (i) or P OFF (i-1), or by subtracting the average value of these, the component of the frequency f1 of the sound to be measured can be obtained. By performing this component acquisition in a specified frequency range, the sound pressure spectrum of the sound to be measured, i.e., the acoustic characteristics, can be obtained.

[0035] FIG. 7 is a graph showing the sound pressure at frequency f1 during the i-1th off and the ith off when the difference in sound pressure during the off state is large. In this case, ΔP OFF (i)=P OFF (i)-P OFF (i-1) ≧ P thIn such a case, since the noise component changes significantly between the two off periods, it is difficult to accurately estimate the noise component in the on period between the two. OFF (i) and P OFF If the average value of (i-1) is subtracted as a noise component to calculate the measurement target sound component, it is considered that the error will be large. Therefore, in this embodiment, the sound collection spectrum during the period when the absolute value of the difference is equal to or greater than the threshold value is discarded without being used for acoustic characteristic measurement.

[0036] As described above, acoustic measurement is performed after removing noise using only the collected sound signal from a period in which the noise components can be accurately estimated. Therefore, according to this embodiment, erroneous noise removal can be avoided and accurate acoustic measurement can be performed.

[0037] In the above explanation of Figs. 6 and 7, the noise removal possibility judgment was performed using the sound collection signal when the i-th time and the previous (i-1)th time when the sound collection signal was off, but the judgment may be performed by calculating the difference in another predetermined period, for example, two times before, three times before, etc. Also, the judgment may be performed for all frequencies, but a certain threshold value C1 may be set and the judgment may be performed only for frequencies where the sound pressure is C1 or higher. Also, the sound pressure change may be calculated not as a difference but as a ratio P OFF (i) / P OFF It may be judged by (i-1).

[0038] 8 is a flowchart showing the operation of the acoustic characteristic measuring device 100 described above. First, the collected sound signal is divided into a first collected sound signal when the output of the sound to be measured is on, and a second collected sound signal when it is off (S101). Next, FFT processing is performed for each on period and off period to convert into a frequency distribution (S102).

[0039] Next, a loop process L from S103 to S106 is performed. In the loop process, P ONIt is determined whether it is possible to estimate the frequency spectrum of the noise from (i) (S104). If it is determined that it is possible to estimate the frequency spectrum of the noise, the sound pressure P(i) at the frequency f of the sound to be measured is calculated as P(i)=P ON (i)-P OFF The noise frequency spectrum is calculated by (i) (S105). On the other hand, if it is determined that it is impossible to estimate the frequency spectrum of the noise, the collected signal for that period is discarded. In this loop process, the processes of S104 and S105 are performed N times, which is determined as a predetermined range, and are repeated until they are completed for a predetermined frequency range (L). In this way, the influence of noise fluctuations is reduced and the acoustic characteristics can be calculated.

[0040] Fig. 9 is a flowchart showing details of the noise removal determination step S104 in the flowchart of Fig. 8. First, the difference ΔP OFF (i) is expressed as the formula, ΔP OFF (i)=P OFF (i)-P OFF (ia) (S1041). Next, the difference ΔP OFF It is determined whether the absolute value of (i) is less than a threshold value (S1042). OFF If the absolute value of (i) is less than the threshold (S1042_Yes), it is determined that it is possible to estimate the frequency spectrum of the noise in the i-th first sound collection signal (S1043), and P ON (i) is stored for calculating acoustic characteristics (S1044).

[0041] On the other hand, the difference ΔP in S1042 OFF The absolute value of (i) is the threshold P th If it is equal to or greater than this (S1042_No), it is determined that it is impossible to estimate the frequency spectrum of the noise in the i-th first collected sound signal (S1045), and P ON (i) is excluded from the calculation of acoustic characteristics (S1046).

[0042] As described above, according to this embodiment, it is possible to avoid erroneous noise removal, and therefore it is possible to perform acoustic characteristic measurement that is less susceptible to the effects of noise fluctuations.

[0043] The scope of the present invention also includes a program for causing a computer to execute the processes of the first to third embodiments described above, and a recording medium storing the program. As the recording medium, for example, a magnetic disk, a magnetic tape, an optical disk, a magneto-optical disk, a semiconductor memory, etc. can be used.

[0044] The present invention has been described above by taking the above-mentioned embodiment as an exemplary example. However, the present invention is not limited to the above-mentioned embodiment. That is, the present invention can be applied in various aspects that can be understood by a person skilled in the art within the scope of the present invention. [Explanation of symbols]

[0045] 1 Sound signal acquisition means 2. Measurement target sound on / off control means 3 Judgment means 4. Acoustic characteristic calculation method 10 Noise evaluation device 20, 100 Acoustic characteristic measuring device 110 Measurement target sound on / off control section 120 Sound signal acquisition section 130 Sound collection signal division section 140 FFT processing section 150 Noise spectrum estimation feasibility determination unit 160 Acoustic characteristic calculation unit 200 Sound collection microphone 300 Measurement targets

Claims

1. A sound collection signal acquisition means for acquiring a sound collection signal generated by collecting a measurement target sound outputted from a measurement target; a measurement target sound on / off control means for repeatedly turning on / off the output of the measurement target sound of the measurement target; a determination means for determining, based on the control, a sound collection signal when the output of the sound to be measured is on as a first sound collection signal, a sound collection signal when the output of the sound to be measured is off as a second sound collection signal, calculating a time change in intensity or frequency spectrum of the second sound collection signal during a certain period, determining that the frequency spectrum of the noise contained in the first sound collection signal during that period can be estimated if the time change is less than a preset threshold value, and determining that the frequency spectrum of the noise contained in the first sound collection signal during that period cannot be estimated if the time change is equal to or greater than the threshold value; A noise evaluation device comprising:

2. The determination means: An FFT processing unit that performs FFT processing on the second collected sound signal during each off period, Calculating the time change of the second sound collection signal using a second sound collection spectrum obtained by FFT processing of the second sound collection signal.

2. The noise evaluation device according to claim 1.

3. The noise evaluation device according to claim 1 or 2; an acoustic characteristic calculation unit that calculates acoustic characteristics of the measurement target sound by using the first sound collection signal and the second sound collection signal during a period during which the noise evaluation device has determined that the frequency spectrum of the noise can be estimated; 1. An acoustic characteristic measuring device comprising:

4. The acoustic characteristic calculation unit, A first sound collection spectrum obtained by FFT processing the first sound collection signal for a certain period of time; A second sound collection spectrum obtained by FFT processing of a second sound collection signal in a period adjacent to the certain period, Calculate the frequency components of the acoustic characteristics 4. The acoustic characteristic measuring device according to claim 3.

5. Acquire a collected sound signal generated by collecting the measurement target sound output by the measurement target, performing control to repeatedly turn on / off the output of the measurement target sound of the measurement target; Based on the control, the sound collection signal when the output of the sound to be measured is on is set as a first sound collection signal, and the sound collection signal when the output of the sound to be measured is off is set as a second sound collection signal, a time change in the intensity or frequency spectrum of the second sound collection signal during a certain period is calculated, and if the time change is less than a preset threshold value, it is determined that the frequency spectrum of the noise contained in the first sound collection signal during that period can be estimated, and if the time change is equal to or greater than the threshold value, it is determined that the frequency spectrum of the noise contained in the first sound collection signal during that period cannot be estimated; A noise evaluation method comprising:

6. The second collected sound signal is subjected to FFT processing during each off period; Calculating the time change of the second sound collection signal using a second sound collection spectrum obtained by subjecting the second sound collection signal to the FFT processing.

6. The noise evaluation method according to claim 5.

7. The noise is evaluated by the noise evaluation method according to claim 5 or 6, Calculating acoustic characteristics of the measurement target sound using the first sound collection signal and the second sound collection signal during a period in which it is determined that the frequency spectrum of the noise can be estimated.

13. An acoustic characteristic measuring method comprising:

8. The first sound collection signal for a certain period is subjected to FFT processing to calculate a first sound collection spectrum; A second sound collection spectrum is calculated by performing FFT processing on a second sound collection signal in a period adjacent to the certain period; Calculating a frequency component of the acoustic characteristic based on the first sound collection spectrum and the second sound collection spectrum.

8. The acoustic characteristic measuring method according to claim 7.

9. A process of acquiring a collected sound signal generated by collecting a measurement target sound output from a measurement target; A process of periodically turning on / off the output of the measurement target sound of the measurement target; A process of setting the sound collection signal when the output of the sound to be measured is on as a first sound collection signal and setting the sound collection signal when the output of the sound to be measured is off as a second sound collection signal based on the control; A process of calculating a time change in the intensity or frequency spectrum of the second sound collection signal during a certain period, determining that the frequency spectrum of the noise contained in the first sound collection signal during the period can be estimated if the time change is less than a preset threshold value, and determining that the frequency spectrum of the noise contained in the first sound collection signal during the period cannot be estimated if the time change is equal to or greater than the threshold value; A noise evaluation program that causes a computer to execute the above steps.

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