Noise measuring device and noise measuring method

Abstract

To provide a noise measuring device for measuring noise level requiring no high pass filter for reducing low frequency sounds unwanted for noise level measurement.SOLUTION: The noise measuring device is a noise measuring device for measuring noise level. The noise measuring device includes: a data acquisition unit that acquires sampling data of the noise level sampled during multiple sampling periods, which are shorter than the measurement period to measure one measurement result of the noise level; a central voltage calculation unit that calculates the central voltage value during the sampling period based on the sampling data; and a noise level calculation unit that calculates the noise level from the root mean square of the difference between the voltage value indicated by the sampling data and the central voltage value.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a noise measuring device and a noise measuring method. [Background technology]

[0002] Noise measuring devices that measure noise levels are known.

[0003] Also, in order to reduce the effects of vibrations caused by the user's shaking hands and temporary environmental noise, an acoustic calibrator is known that is equipped with a high-pass filter that attenuates low-frequency components with a cutoff frequency lower than the reference frequency (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-20277 A Summary of the Invention [Problem to be solved by the invention]

[0005] It is desirable for a noise measurement device not to reflect low-frequency sounds that are not the target frequency in the measurement. In this case, it is possible to perform signal processing on sampled data sampled over a sufficiently long period of time to remove data in unnecessary frequency ranges. However, this method requires a large amount of data and data processing capacity, which results in a problem of high power consumption.

[0006] Furthermore, the technology disclosed in Patent Document 1 realizes a relatively small sound calibrator by eliminating unnecessary low-frequency sounds using a high-pass filter with a fixed cutoff frequency that has little effect on the reference frequency. However, in a measurement device, the frequency distribution differs depending on the noise to be measured, so it is not desirable to use a high-pass filter with a fixed cutoff frequency.

[0007] Furthermore, when performing signal processing on sampled data sampled over a short period of time, there is a risk that an inappropriate value for the situation, for example, a momentary sound value in a constantly quiet state, may be used as a representative value.

[0008] One embodiment of the present invention has been made in consideration of the above problems, and in a noise level measuring device for measuring a noise level, a high-pass filter that reduces low-frequency sounds that are not necessary for measuring the noise level is not required, and the influence of sounds that are not appropriate for the situation is suppressed. [Means for solving the problem]

[0009] In order to solve the above problems, a noise measuring device according to one embodiment of the present invention is a noise measuring device that measures a noise level, and includes: a data acquiring unit that acquires sampling data obtained by sampling the noise level during a plurality of sampling periods that are shorter than a measurement period for measuring one measurement result of the noise level; a central voltage calculating unit that calculates a central voltage value during the sampling period based on the sampling data; and a noise level calculating unit that calculates the noise level from the root mean square of the difference between a voltage value indicated by the sampling data and the central voltage value. When the noise measurement device blocks sounds with frequencies lower than frequency F, the sampling period is set to 1 / F. Effect of the Invention

[0010] According to one embodiment of the present invention, in a noise measuring device that measures a noise level, a high-pass filter that reduces low-frequency sounds that are unnecessary for measuring the noise level is not required. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a configuration of a noise measuring device according to an embodiment; [Diagram 2] FIG. 2 is a diagram showing a measurement of the sound pressure level of a sound having a frequency of 300 Hz according to an embodiment. [Diagram 3] FIG. 1 is a diagram showing measurement of the sound pressure level of a sound with a frequency of 40 Hz according to one embodiment; [Figure 4]FIG. 2 shows measurement of the sound pressure level of a sound with a frequency of 40 Hz according to an embodiment. [Diagram 5] FIG. 1 is a diagram showing acquisition of sampling data according to an embodiment; [Figure 6] FIG. 2 illustrates the acquisition of sampling data according to an embodiment; [Figure 7] FIG. 13 is a diagram illustrating frequency characteristics according to the length of a sampling period according to an embodiment. [Figure 8] 1 is a diagram showing a functional configuration of a noise measuring device according to an embodiment; [Figure 9] 4 is a flowchart showing the processing performed by the noise measuring device according to the first embodiment. [Figure 10] 10 is a flowchart showing the processing performed by a noise measuring device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicated description will be omitted.

[0013] <Configuration of noise measurement device> 1 is a diagram showing the configuration of a noise measuring device 100 according to one embodiment. The noise measuring device 100 is a device that measures noise levels and transmits the measurement results to an external device such as an information terminal or a gateway via wireless communication such as Bluetooth (registered trademark) Low Energy (hereinafter referred to as BLE).

[0014] Noise measurement device 100 includes a battery 101 , a DC (Direct Current) / DC converter 102 , an LDO (Low Drop Out) 103 , a communication unit 110 , and a microphone unit 120 .

[0015] The battery 101 is a battery that supplies power to the noise measuring device 100. Since it is not always possible to secure a power source at the installation location of the noise measuring device 100, it is desirable for the noise measuring device 100 to operate on a small, low-capacity battery such as a coin battery.

[0016] The DC / DC converter 102 is a circuit that boosts or lowers the output voltage of the battery 101, and supplies a predetermined power supply voltage to the communication unit 110. The LDO 103 is a constant voltage circuit that operates even with a low potential difference between input and output, and supplies power of a predetermined voltage to the communication unit 110, microphone unit 120, etc. The battery 101, DC / DC converter 102, and LDO 103 are examples of a power supply circuit provided in the noise measuring device 100. The power supply circuit provided in the noise measuring device 100 may have another configuration as long as it supplies power to the communication unit 110 and microphone unit 120.

[0017] The communication unit 110 is a circuit, module, board, IC (Integrated Circuit), etc. that transmits the measurement result of the noise level by wireless communication such as BLE communication. The communication unit 110 includes, for example, a microcomputer (hereinafter referred to as a microcomputer) 111, an AD (Analog to Digital) converter 112, a wireless circuit 113, an antenna 114, and crystal oscillators 116 and 117.

[0018] Microcomputer 111 is a processor that includes, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), flash ROM (Read Only Memory), etc., and realizes the various functions of noise measuring device 100 by executing predetermined programs.

[0019] The AD converter 112 is an electronic circuit that converts an analog signal into a digital signal.

[0020] The wireless circuit 113 is a circuit that communicates with an external device using a wireless communication method such as BLE communication, and includes a high-frequency circuit that transmits and receives wireless signals, a signal processing circuit that processes baseband signals, a matching circuit that performs impedance matching with the antenna 114, and the like.

[0021] The microcomputer 111, the AD converter 112, and the wireless circuit 113 may be integrated into an IC 115 for communication.

[0022] Noise measuring device 100 may communicate with an external device using a wireless communication method other than BLE, such as Zigbee (registered trademark) or Wirepas Mesh. Noise measuring device 100 may also communicate using wired communication such as PLC (Power Line Communication). Here, as an example, the following description will be given assuming that noise measuring device 100 is capable of communicating using wireless communication according to BLE.

[0023] The microphone unit 120 includes a microphone 121 that picks up sounds around the noise measuring device 100, and an operational amplifier 122 that amplifies the sound wave signal output from the microphone.

[0024] The microphone unit 120 acquires noise around the noise measuring device 100, converts it into a sound wave signal (analog signal), and outputs it to the communication unit 110. The communication unit 110 samples the sound wave signal output from the microphone unit 120 and calculates the noise level based on the acquired sampling data, and transmits the noise level to the destination as the measurement result.

[0025] As an example, noise measuring device 100 transmits the measurement results by BLE communication to an information device such as a PC (Personal Computer), tablet terminal, or smartphone, or a receiving device such as a gateway. The receiving device may transmit the data to a server, cloud, or the like via a communication network such as the Internet, a wireless / wired LAN (Local Area Network), or a wireless WAN (Wide Area Network). This allows data analysis to be performed by the receiving device that receives the measurement results, or by the server or cloud.

[0026] <Processing Overview> When measuring indoor noise levels with noise measuring device 100, indoor noise levels are constantly changing, so measurement data at one point alone is insufficient to measure accurate noise levels, and measurement data must be obtained multiple times. In this case, the more samples of measurement data there are, the more accurate the measurement results will be, but the longer the sampling period for sampling the measurement data, the higher the power consumption will be, and if the battery is a small, low-capacity coin battery or other such battery, the sooner it will need to be replaced.

[0027] On the other hand, if the sampling period is shortened to reduce power consumption, there is a risk that a measurement value that does not match the situation, such as a momentary noise that occurs in a constantly quiet environment, will be taken as the representative value, and accurate noise level measurements may not be possible.

[0028] Therefore, the noise measuring device 100 according to this embodiment obtains sampling data by sampling the noise level during a plurality of sampling periods that are shorter than the measurement period for measuring one measurement result of the noise level. Here, the sampling period is the period for obtaining the sampling data. As an example, when the measurement period is one second, the noise measuring device 100 performs sampling four times with a sampling frequency of 40 kHz (sampling period of 25 μs), resulting in 1024 samples, with a sampling period of 25.6 milliseconds.

[0029] Furthermore, the noise measuring device 100 calculates a central voltage value for each sampling period based on the acquired sampling data. For example, the noise measuring device 100 calculates a representative value (e.g., an average voltage value) for each sampling period and sets it as the central voltage value. Note that the representative value is not limited to the average voltage value, and may be other representative values ​​such as a median value or a mode value. Furthermore, the noise measuring device 100 may calculate the central voltage value by performing moving average processing on the sampling data.

[0030] Furthermore, sound level measuring device 100 calculates the sound level using the calculated central voltage value as a reference voltage. For example, sound level measuring device 100 calculates the sound level during a sampling period from the root mean square (RMS) of the difference between the sampling data acquired during the sampling period and the calculated central voltage value. In this way, when an abnormal value is sampled due to the influence of noise or the like, sound level measuring device 100 also fluctuates the central voltage value, making it possible to suppress the influence of noise or the like.

[0031] Noise measuring device 100 performs the above-mentioned calculation process of the center voltage value and the calculation process of the noise level for each of a plurality of sampling periods within the measurement period, and outputs the average value of the noise levels calculated for the plurality of sampling periods as the noise level for the measurement period.

[0032] <Reducing unnecessary frequencies> Since the purpose of the noise measuring device 100 is to measure noise levels, it is desirable not to reflect low-frequency sounds that are not in the human audible range in the measurement results. In this case, it is conceivable to perform signal processing on sampled data sampled over a sufficiently long period of time and cut out data in unnecessary frequency ranges. However, this method requires a large amount of data and data processing capacity, which results in a problem of high power consumption.

[0033] Furthermore, when the frequency distribution varies depending on the noise to be measured, it is not desirable to use a high-pass filter with a fixed cutoff frequency.

[0034] Therefore, the noise measuring device 100 according to this embodiment has a function of reducing low frequency sounds that are not required for measuring the noise level, without using a high-pass filter, by setting the sampling period for sampling the noise level. In this embodiment, when sounds with frequencies lower than frequency F are to be blocked, the sampling period is set to 1 / F. For example, when the sampling period is set to 4 milliseconds, the noise measuring device 100 can reduce sounds with frequencies lower than 250 Hz.

[0035] Fig. 2 is a diagram showing measurement of the sound pressure level of a sound with a frequency of 300 Hz according to one embodiment. Fig. 2 shows an example in which the noise measuring device 100 measures the sound pressure level by sampling a sound wave signal 201 with a frequency of 300 Hz at a sampling frequency of 40 kHz for sampling periods of 4 ms and 62.5 ms.

[0036] In FIG. 2, sound level measuring device 100 samples a 300 Hz sound wave signal 201 at a sampling frequency of 40 kHz within a sampling period of 4 ms to obtain sampling data.

[0037] Thereafter, sound level measuring device 100 calculates an average voltage value 202 of the sampling data acquired within the sampling period. Furthermore, sound level measuring device 100 calculates the sound pressure level during the sampling period from the RMS of the difference between the acquired sampling data and the calculated average voltage value 202. In the example shown in Figure 2, the sound pressure level measurement result when the sampling period was 4 ms was 75.613 dB SPL.

[0038] Similarly, sound level measuring device 100 samples 300 Hz sound wave signal 201 at a sampling frequency of 40 kHz over a sampling period of 62.5 ms, and calculates average voltage value 203 of the sampling data acquired during the sampling period. Sound level measuring device 100 then calculates the sound pressure level during the sampling period from the RMS of the difference between the acquired sampling data and the calculated average voltage value 203. In the example of Fig. 2, the measurement result of the sound pressure level when the sampling period was 62.5 ms was 75.867 dB SPL.

[0039] In this way, when one or more periods of the waveform of the sound wave signal 201 of the measurement target frequency are included within a sampling period of 4 ms, the same measurement results are obtained as when the sampling period is 62.6 ms, which is a sufficiently long period.

[0040] Fig. 3 is a diagram (1) showing a measurement of the sound pressure level of a sound with a frequency of 40 Hz according to an embodiment. Fig. 3 shows an example in which a sound wave signal 301 with a frequency of 40 Hz is sampled at a sampling frequency of 40 kHz for sampling periods of 4 ms and 62.5 ms, respectively, to measure the sound pressure level.

[0041] In FIG. 3, sound level measuring device 100 samples a 40 Hz sound wave signal 301 at a sampling frequency of 40 kHz over a sampling period of 4 ms to obtain sampling data, and calculates an average voltage value 302 within the sampling period.

[0042] Thereafter, sound pressure measuring device 100 calculates the sound pressure level during the sampling period from the RMS of the difference between the acquired sampling data and calculated average voltage value 302. In the example of Fig. 3, the measurement result of the sound pressure level when the sampling period is 4 ms is 65.284 dB SPL.

[0043] Similarly, sound level measuring device 100 samples 40 Hz sound wave signal 301 at a sampling frequency of 40 kHz for a sampling period of 62.5 ms to obtain sampling data, and calculates average voltage value 303 within the sampling period. Sound level measuring device 100 then obtains the sound pressure level during the sampling period from the RMS of the difference between the obtained sampling data and the calculated average voltage value 303. In the example of Fig. 3, the measurement result of the sound pressure level when the sampling period was 62.5 ms was 75.774 dB SPL.

[0044] In this way, when the sampling period does not include one or more periods of the waveform of the sound wave signal 301 at the frequency to be measured, the measured sound pressure level is measured to be lower by the amount of low-frequency noise compared to when the sampling period includes one or more periods of the waveform of the sound wave signal 301, such as when the sampling period is 62.5 ms.

[0045] Fig. 4 is a diagram (2) showing a sound pressure level measurement of a sound with a frequency of 40 Hz according to an embodiment. Fig. 4 shows another example of a case where a sound wave signal 301 with a frequency of 40 Hz is sampled at a sampling frequency of 40 kHz for sampling periods of 4 ms and 62.5 ms to measure the sound pressure level, similar to Fig. 3. In Fig. 4, the sampling period of 4 ms is set at a different timing from Fig. 3. When the sound pressure level is calculated in Fig. 4 as in Fig. 3, the measurement result of the sound pressure level when the sampling period is 4 ms is 55.108 dB SPL.

[0046] As described above, when the sampling period is set to 4 ms, although there is some variation in the sound pressure level measurement results depending on the sampling timing, it is clear that the sound pressure level at a frequency of 40 Hz can be reduced more than when the sampling period is set to 62.5 ms.

[0047] It should be noted that the variation in the measurement results can be suppressed, for example, by performing sampling multiple times with a sampling period of 4 ms and averaging the measurement results.

[0048] Based on the above results, in this embodiment, for example, sampling data is acquired as follows.

[0049] Fig. 5 is a diagram (1) showing acquisition of sampling data according to one embodiment. As shown in Fig. 5, the noise measuring device 100 according to this embodiment sets multiple sampling periods shorter than the measurement period T for measuring the noise level, and acquires sampling data by sampling during each sampling period. In the example of Fig. 5, four sampling periods of 4 ms are set within one measurement period T.

[0050] Here, noise measuring device 100 transmits the measurement results every measurement period T, but the transmission interval for transmitting the measurement results may be different from the measurement period T.

[0051] 5, noise measuring device 100 performs a first sampling in sampling period 501 from time t0 to t1, and a second sampling in sampling period 502 from time t2 to t3. Noise measuring device 100 also performs a third sampling in sampling period 503 from time t4 to t5, and a fourth sampling in sampling period 504 from time t6 to t7. Furthermore, measurement intervals 511-513 are provided between each sampling period.

[0052] When setting multiple sampling periods and performing sampling, the noise measuring device 100 of this embodiment does not perform measurements over successive sampling periods, but instead performs measurements at predetermined measurement intervals 511-513 between the sampling periods. This prevents continuous measurement of sounds that are inappropriate for a certain situation, such as a momentary sound that occurs in a quiet environment. Furthermore, the noise measuring device 100 may randomly change the measurement intervals 511-513 so that the sampling periods are not synchronized with sounds of a specific frequency.

[0053] The measurement interval is determined by the sampling period and the number of sampling periods in the measurement period. By reducing the number of sampling periods in the measurement period, the measurement interval becomes longer and power consumption can be reduced, but the averaging effect is reduced, which may increase the variability of the measurement results.

[0054] Noise measuring device 100 calculates the noise level (sound pressure level) for each of a plurality of sampling periods 501-504, and takes the average value of the noise levels calculated for each of sampling periods 501-504 as the noise level measurement result for measurement period T. In the example of Fig. 5, the noise level measurement result is 63.782 dB SPL.

[0055] 6 is a diagram (2) showing acquisition of sampling data according to an embodiment of the present invention. This diagram shows an example in which the same process as in FIG. 5 is executed by changing the timing for setting the sampling period.

[0056] 5, noise measuring device 100 calculates the noise level for each of a plurality of sampling periods 501-504, and takes the average value of the noise levels calculated for each sampling period 501-504 as the noise level measurement result for measurement period T. In the example of Fig. 6, the noise level measurement result is 66.675 dB SPL.

[0057] In this way, by taking the average value of the noise levels over multiple sampling periods 501 to 504 as the noise level measurement result for one measurement period, it is possible to average out the variation in the sound pressure level measurement results due to the sampling timing described with reference to Figures 3 and 4.

[0058] FIG. 7 is a diagram showing frequency characteristics according to the length of the sampling period. In the graph of FIG. 7, the horizontal axis indicates frequency and the vertical axis indicates sound pressure. Curve 701 indicates the frequency characteristics of a sound wave signal sampled when the sampling period is set to 62.5 ms as in FIGS. 2 to 4. Curve 702 indicates the frequency characteristics of a sound wave signal sampled when a 4 ms sampling period is set once as in FIGS. 2 to 4. Curve 703 indicates the frequency characteristics of a sound wave signal sampled when a 4 ms sampling period is set multiple times in one measurement period as in FIGS. 5 and 6. 7, the sound pressure of frequency components below 250 Hz is also high in curve 701, but the sound pressure of audio frequencies below 250 Hz is reduced in curves 702 and 703. Curve 703 also shows frequency characteristics similar to those of curve 702, but by averaging the measurement results obtained over four sampling periods, there is less variation in the degree of reduction in sound pressure at low frequencies compared to curve 702.

[0059] In this way, sound pressure measuring device 100 can cut off sounds with frequencies lower than 250 Hz by setting the sampling period to 4 ms. If it is desired to cut off sounds with frequencies lower than frequency F, the sampling period can be set to 1 / F seconds, and the cutoff frequency can be changed by changing the length of the sampling period.

[0060] As described above, according to this embodiment, a high-pass filter is not necessary in noise measuring device 100. Furthermore, in this embodiment, the cutoff frequency can be changed by changing the sampling period, so that an appropriate cutoff frequency can be set in accordance with the noise to be measured.

[0061] <Functional configuration> 8 is a diagram showing the functional configuration of a noise measuring device according to one embodiment. Noise measuring device 100 realizes the functions of data acquisition section 801, center voltage calculation section 802, noise level calculation section 803, output section 804, wireless communication section 805, setting acceptance section 806, and storage section 807 by executing a program in microcomputer 111.

[0062] At least a part of the above-described functional configurations may be realized by hardware.

[0063] The data acquiring unit 801 uses the AD converter 112 to sample the sound wave signal sent from the microphone unit 120 during a sampling period shorter than the measurement period T for measuring the noise level, and acquires sampling data. For example, as shown in Fig. 5, the data acquiring unit 801 samples the sound wave signal during each of a plurality of sampling periods 501 to 504 shorter than the measurement period T. This allows a signal indicating the noise level around the noise measuring device 100 to be obtained.

[0064] When the data acquisition unit 801 blocks frequencies lower than frequency F, it sets the sampling period to 1 / F seconds and samples the sound wave signal.

[0065] The center voltage calculation unit 802 calculates a center voltage value for each sampling period based on the sampling data acquired by the data acquisition unit 801. In the example of Fig. 6, the center voltage calculation unit 802 calculates center voltage values ​​505-508 for each sampling period 501-504 by averaging the sampling data obtained by sampling the voltage values ​​in each of the sampling periods 501-504.

[0066] The noise level calculation unit 803 obtains the RMS of the difference between the measured voltage value indicated by the sampling data acquired by the data acquisition unit 801 and the central voltage value calculated by the central voltage calculation unit 802, and calculates the noise level for each sampling period.

[0067] For example, the noise level calculation unit 803 calculates the RMS of the difference between the measured voltage value and the central voltage value indicated by the sampling data by using the following formula (1).

[0068]

number

[0069] Furthermore, the noise level calculation unit 803 calculates the noise level L from the calculated RMS and the following equation (2).

[0070]

number

[0071] The output unit 804 averages the noise levels for multiple sampling periods calculated by the noise level calculation unit 803, and outputs the average value as the noise level for the measurement period T. For example, the output unit 804 wirelessly transmits the noise level for the measurement period T calculated by averaging the noise levels for each of the sampling periods 501 to 504 to an external device using the wireless communication unit 805.

[0072] If noise measuring device 100 has a display unit, output unit 804 may output the noise level measurement results (noise level during measurement period T, maximum noise level, average noise level, etc.) to the display unit. Also, output unit 804 may output the noise level measurement results to storage unit 807 or the like.

[0073] The wireless communication unit 805 communicates with an external device through wireless communication such as BLE communication using the wireless circuit 113, etc. For example, the wireless communication unit 805 intermittently transmits a beacon (advertisement packet, etc.) including the measurement result of the noise level in accordance with the control of the output unit 804. Note that the wireless communication unit 805 may communicate with an external device through wireless communication other than BLE communication.

[0074] The wireless communication unit 805 can establish a communication link in response to a request from an external device, and receive request information such as a request to change the sampling period from the external device.

[0075] The setting reception unit 806 receives request information received from an external device by the wireless communication unit 805. For example, when the wireless communication unit 805 receives a request to change the sampling period from the external device, the setting reception unit 806 changes the setting of the sampling period of the noise measuring device 100 in accordance with the change request.

[0076] Storage unit 807 is realized, for example, by a program executed by microcomputer 111 and a memory (RAM, flash ROM, etc.) included in microcomputer 111, and stores various information and data such as setting values ​​of noise measuring device 100, sampling data, etc.

[0077] <Processing flow> Next, the process of the noise measurement method according to this embodiment will be described.

[0078] [First embodiment] Fig. 9 is a flowchart showing the processing of the noise measuring device according to the first embodiment. The noise measuring device 100 measures the noise level and transmits the measurement result to an external device by, for example, executing the processing of Fig. 9.

[0079] In S901, sound level measuring apparatus 100 determines based on the timer value, the current time, etc. whether it is time to start measurement, and if so, executes the processes in S902 and onwards.

[0080] In S902, the data acquiring unit 801 samples the voltage value during a sampling period of a predetermined length (e.g., 4 ms) to acquire sampling data. For example, the data acquiring unit 801 acquires sampling data indicating the voltage value from the AD converter 112 for a preset number of samplings (e.g., 160 times) during one sampling period, and stores the data in the storage unit 807 or the like.

[0081] In S903, the central voltage calculation unit 802 calculates a central voltage value in a sampling period during which the sampling data was acquired, based on the sampling data acquired by the data acquisition unit 801. For example, the central voltage calculation unit 802 calculates an average voltage value by averaging the voltages indicated by the sampling data within the sampling period, and stores the average voltage value in the storage unit 807.

[0082] In S904, the noise level calculation unit 803 calculates the noise level from the sampling data using the calculated central voltage value as a reference voltage value. For example, the noise level calculation unit 803 calculates the noise level in the sampling period from the RMS (root mean square) of the voltage value and the central voltage value indicated by the sampling data. In this case, the noise level calculation unit 803 calculates the RMS in the sampling period using equation (1), and calculates the noise level L using equation (2) and the calculated RMS.

[0083] In S905, the noise measuring device 100 judges whether the number of measurements, which is the number of sampling periods within the measurement period, has reached a predetermined number (e.g., 4 times). If the number of measurements has not reached the predetermined number, in S906, the noise measuring device 100 waits for the measurement interval and then executes the processes from S902 onwards again.

[0084] On the other hand, when the predetermined number of measurements has been reached, the output unit 804 transmits the measurement result, which is the average of the noise levels for each sampling period calculated by the noise level calculation unit 803, to an external device via the wireless communication unit 805.

[0085] By the above processing, noise measuring device 100 can measure noise levels by reducing low frequencies unnecessary for noise level measurement, as shown by curve 703 in FIG. 7, even if it does not have a high-pass filter with a fixed cutoff frequency.

[0086] [Second embodiment] Fig. 10 is a flowchart showing the processing of the noise measuring device according to the second embodiment. The processing of Fig. 10 shows another example of the noise level measurement processing executed by the noise measuring device 100. Fig. 10 illustrates an example of processing when the transmission interval for transmitting the measurement results is set longer than the measurement period T. Note that steps S901 to S906 are the same as those in Fig. 9, and therefore their explanation will be omitted.

[0087] In S1001, the output unit 804 stores in the storage unit 807 the measurement result obtained by averaging the noise levels for each sampling period calculated by the noise level calculation unit 803.

[0088] In S1002, the output unit 804 judges whether it is time to transmit the measurement results based on the timer value, the current time, etc. If it is not time to transmit the measurement results, the output unit 804 returns the process to S901. On the other hand, if it is time to transmit the measurement results, the output unit 804 shifts the process to S1003.

[0089] When the process proceeds to S1003, the output unit 804 transmits the measurement results stored in the memory unit 307 to an external device via the wireless communication unit 805.

[0090] As in the process of FIG. 10, the measurement period T for measuring the noise level and the transmission interval for transmitting the measurement results may be different.

[0091] In the second embodiment, sound level measuring device 100 can also measure the sound level by reducing low frequencies unnecessary for sound level measurement, as shown by curve 703 in Fig. 7, even if it does not have a high-pass filter with a fixed cutoff frequency. Furthermore, according to the second embodiment, sound level measuring device 100 can transmit the measurement results to an external device at any transmission timing.

[0092] As described above, according to each embodiment of the present invention, noise measuring device 100 does not require a high-pass filter for reducing low-frequency sounds that are not required for noise level measurement.

[0093] Furthermore, noise measuring device 100 makes it possible to change the cutoff frequency, which reduces low-frequency sounds that are not necessary for noise level measurement, according to the noise to be measured by changing the sampling period setting.

[0094] Furthermore, because noise measuring device 100 uses the central voltage value calculated based on multiple sampling data as the reference voltage value, unlike when the noise level is calculated from the difference between the analog signal sent from the microphone unit and a reference voltage value set up on the circuit, it is possible to ignore offset fluctuations due to aging of the operational amplifiers and peripheral circuit components, and there is no need to correct the reference voltage values ​​of the operational amplifiers, etc.

[0095] Furthermore, by performing moving average processing on the central voltage value, even if the sampling data contains abnormal values ​​due to the influence of noise or the like, the influence of this can be suppressed.

[0096] Furthermore, by providing a predetermined measurement interval between multiple sampling periods, noise measuring device 100 can prevent continuous measurement of sounds that occur in quiet conditions that are not appropriate for the situation. This makes it possible to reduce the effect that a momentary sound generation has on the overall measurement values, for example.

[0097] The configurations shown in the above embodiments are examples of the contents of the present invention, and may be combined with other known technologies. Parts of the configurations may be omitted or modified without departing from the gist of the present invention. [Explanation of symbols]

[0098] 100 noise measurement device, 801 data acquisition unit, 802 center voltage calculation unit, 803 noise level calculation unit, 804 output unit, 805 wireless communication unit, 806 setting reception unit

Claims

1. A noise measuring device for measuring a noise level, comprising: a data acquisition unit that acquires sampling data obtained by sampling the noise level during a plurality of sampling periods that are shorter than a measurement period for measuring one of the noise level measurement results; a central voltage calculation unit that calculates a central voltage value during the sampling period based on the sampling data; a noise level calculation unit that calculates the noise level from the root mean square of the difference between a voltage value indicated by the sampling data and the central voltage value; having The noise measuring device, when blocking sounds of frequencies lower than frequency F, sets the sampling period to 1 / F.

2. The noise level calculation unit calculates the noise level for each of the plurality of sampling periods, 2. The noise measuring device according to claim 1, further comprising an output section that outputs an average value of the noise level for each of the plurality of sampling periods.

3. 2. The noise measuring device according to claim 1, wherein the central voltage calculation section calculates the central voltage value by performing a moving average process on the sampling data.

4. 4. The noise measuring device according to claim 1, wherein the data acquiring section samples the noise level at a predetermined measurement interval during the sampling period, and changes the measurement interval randomly.

5. A noise measurement method for measuring a noise level, comprising: a data acquisition unit acquires sampling data obtained by sampling the noise level during a plurality of sampling periods that are shorter than a measurement period for measuring one of the noise level measurement results; a central voltage calculation unit calculates a central voltage value during the sampling period based on the sampling data; a noise level calculation unit calculates the noise level from the root mean square of the difference between the sampling data and the central voltage value; A noise measurement method, wherein the data acquisition unit sets the sampling period to 1 / F when blocking sounds of frequencies lower than a frequency F.

6. A noise measuring device for measuring a noise level, comprising: a data acquisition unit that acquires sampling data obtained by sampling the noise level during a sampling period for measuring the noise level; a central voltage calculation unit that calculates a central voltage value during the sampling period based on the sampling data; a noise level calculation unit that calculates the noise level from the root mean square of the difference between a voltage value indicated by the sampling data and the central voltage value; having The noise measuring device, when blocking sounds of frequencies lower than frequency F, sets the sampling period to 1 / F.

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