Noise detection device, noise detection method, and program

Abstract

A noise detection device (1) for detecting cyclic noise included in an input signal is provided with: a cycle detection unit (10) that detects a cycle of noise; a timing estimation unit (20) that estimates a cyclic occurrence timing of noise in the future on the basis of the detected cycle; a threshold calculation unit (30) that lowers, for each estimated occurrence timing, a first threshold for use in detecting noise to a second threshold; and a noise detection unit (40) that detects noise by comparing, for each estimated occurrence timing, the magnitude of the input signal and the second threshold.

Description

Noise detection device, noise detection method and program

[0001] The present disclosure relates to a noise detection device for detecting periodic noise contained in an input signal.

[0002] Japanese Patent Application Laid-Open No. 2003-124222 discloses a technique for detecting periodic noise contained in an input signal.

[0003] Special Publication No. 2000-507054

[0004] However, Patent Document 1 only describes detecting noise whose period can be detected (i.e., large noise), and does not describe detecting small noise whose period cannot be detected.

[0005] Therefore, the present disclosure provides a noise detection device and the like that can detect small noise whose period cannot be detected.

[0006] The noise detection device according to the present disclosure is a noise detection device for detecting periodic noise contained in an input signal, and includes a period detection unit that detects the period of the noise, a timing estimation unit that estimates future periodic occurrence timings of the noise based on the detected period, a threshold calculation unit that lowers a first threshold for detecting the noise to a second threshold for each estimated occurrence timing, and a noise detection unit that detects the noise by comparing the magnitude of the input signal with the second threshold for each estimated occurrence timing.

[0007] The noise detection method according to the present disclosure is a noise detection method executed by a noise detection device for detecting periodic noise contained in an input signal, and includes a period detection step of detecting the period of the noise, a timing estimation step of estimating future periodic occurrence timings of the noise based on the detected period, a threshold calculation step of lowering a first threshold for detecting the noise to a second threshold for each estimated occurrence timing, and a noise detection step of detecting the noise by comparing the magnitude of the input signal with the second threshold for each estimated occurrence timing.

[0008] A program according to the present disclosure is a program for causing a computer to execute the above-described noise detection method.

[0009] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0010] According to a noise detection device and the like according to an aspect of the present disclosure, it is possible to detect small noise whose period cannot be detected.

[0011] Fig. 1 is a diagram for explaining that it is difficult to detect small noise whose period cannot be detected. Fig. 2 is a block diagram showing an example of a noise detection device according to an embodiment. Fig. 3 is a diagram for explaining the operation of a period detection unit according to an embodiment. Fig. 4 is a diagram for explaining the operation of a timing estimation unit, a threshold calculation unit, and a noise detection unit according to an embodiment. Fig. 5 is a flowchart showing an example of a noise detection method according to another embodiment.

[0012] (Background to the Invention of One Aspect of the Present Disclosure) Conventionally, a fixed threshold value has been used as a detection threshold value for detecting noise contained in an input signal input to a noise detection device. This allows periodic noise to be detected by detecting noise when the magnitude of the input signal exceeds the detection threshold value. However, a fixed detection threshold value makes it difficult to detect small noise whose period cannot be detected.

[0013] Fig. 1 illustrates the difficulty of detecting noise so small that its period cannot be detected. Fig. 1 shows the time variation of an input signal containing noise, and also shows a fixed detection threshold value in bold.

[0014] For example, the input signal may contain periodic noise, but the magnitude of the noise may be small, as shown by "NG" in Figure 1, and there may be times when the magnitude of the input signal does not exceed the detection threshold and the period of the noise cannot be detected. In such cases, it is difficult to detect the periodic noise.

[0015] Therefore, a noise detection device and a noise detection method that can detect small noises whose period cannot be detected will be described below.

[0016] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0017] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, materials, components, arrangement and connection of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0018] (Embodiment) A noise detection device according to an embodiment will be described below.

[0019] FIG. 2 is a block diagram showing an example of a noise detection device 1 according to an embodiment.

[0020] The noise detection device 1 is a device for detecting periodic noise contained in an input signal input to the noise detection device 1. For example, the periodic noise is pulse noise. Note that the periodic noise is not limited to pulse noise, and is not particularly limited as long as it is noise that occurs periodically. For example, the noise detection device 1 may be used in combination with a noise removal device, and the noise detected by the noise detection device 1 may be removed by the noise removal device.

[0021] The noise detection device 1 includes a period detection unit 10, a timing estimation unit 20, a threshold calculation unit 30, and a noise detection unit 40. The noise detection device 1 is a computer including a processor (microprocessor) and a memory. The memory may be a read-only memory (ROM) or a random access memory (RAM), and can store programs executed by the processor. The period detection unit 10, the timing estimation unit 20, the threshold calculation unit 30, and the noise detection unit 40 are realized by the processor executing programs stored in the memory.

[0022] The period detector 10 detects the period of noise contained in the input signal. The operation of the period detector 10 will be described with reference to FIG.

[0023] 3 is a diagram for explaining the operation of the period detector 10 according to the embodiment, which shows the time variation of an input signal containing noise.

[0024] For example, the period detector 10 detects the period of noise when the noise is relatively large and can be detected. Specifically, as shown in FIG. 3 , the period detector 10 detects the period of noise (period T shown in FIG. 3 ) when the magnitude of the input signal periodically exceeds a first threshold for detecting noise. For example, the first threshold is a predetermined threshold or a threshold determined according to the magnitude of the input signal. That is, the first threshold may be a fixed value or a value that varies according to the magnitude of the input signal. For example, if the first threshold is a value that varies according to the magnitude of the input signal, the first threshold is set to a value that is a predetermined value (e.g., 12 dB) greater than the average magnitude of the input signal.

[0025] Although there are no particular limitations on the method for detecting the noise period, the noise period can be detected by autocorrelation, for example, which results in the noise period being detected as shown in FIG.

[0026] The timing estimation unit 20 estimates future periodic noise occurrence timings based on the detected period. The operation of the timing estimation unit 20 will be described with reference to Fig. 4. Fig. 4 is also used to explain the operation of the threshold calculation unit 30 and the noise detection unit 40, which will be described later.

[0027] 4 is a diagram illustrating the operations of the timing estimation unit 20, the threshold calculation unit 30, and the noise detection unit 40 according to the embodiment. Fig. 4 shows the time change of an input signal including noise. Note that the input signal shown in Fig. 4 is a signal that was input to the noise detection device 1 after the input signal shown in Fig. 3 , and the magnitude of the noise included in the input signal shown in Fig. 4 is generally smaller than the noise included in the input signal shown in Fig. 3 .

[0028] For example, the timing estimation unit 20 estimates future periodic noise occurrence timings starting from the timing at which the magnitude of the input signal exceeds a first threshold for detecting noise. The "starting point" timing shown in FIG. 4 is the timing at which the magnitude of the input signal exceeds the first threshold, and the timing estimation unit 20 estimates future periodic noise occurrence timings for each estimated period (period T) starting from this timing, as shown in FIG. 4. Since it can be determined that periodic noise occurs when the magnitude of the input signal exceeds the first threshold, this timing can be used as the starting point for future periodic noise occurrence timings. In FIG. 4, vertical dashed lines are drawn for each period T to represent the periodic noise occurrence timings.

[0029] The threshold calculation unit 30 reduces the first threshold for detecting noise to the second threshold for each estimated occurrence timing. The operation of the threshold calculation unit 30 will be described with reference to FIG.

[0030] As shown in FIG. 4 , the detection threshold for detecting noise at the estimated occurrence timing is lowered from the first threshold to the second threshold. For example, the second threshold may be a predetermined threshold, a threshold determined according to the magnitude of the input signal, or a threshold determined according to the first threshold. That is, the second threshold may be a fixed value or a value that varies according to the magnitude of the input signal. For example, if the second threshold is a value that varies according to the magnitude of the input signal, the second threshold is set to a value that is a predetermined value (e.g., 6 dB) higher than the average magnitude of the input signal. For example, if the second threshold is a threshold determined according to the first threshold, the second threshold is set to a value that is a predetermined value (e.g., 6 dB) lower than the first threshold.

[0031] The period during which the first threshold is lowered to the second threshold is not particularly limited, but may be, for example, half the period. Specifically, when the detected period is T, the period during which the first threshold is lowered to the second threshold may be ±T / 2 of the estimated occurrence timing.

[0032] As described above, for example, the first threshold is a predetermined threshold or a threshold determined according to the magnitude of the input signal. In other words, the threshold calculation unit 30 sets the first threshold to a predetermined threshold or a threshold determined according to the magnitude of the input signal. Also, as described above, for example, the second threshold is a predetermined threshold, a threshold determined according to the magnitude of the input signal, or a threshold determined according to the first threshold. In other words, the threshold calculation unit 30 sets the second threshold to a predetermined threshold, a threshold determined according to the magnitude of the input signal, or a threshold determined according to the first threshold.

[0033] The noise detection unit 40 detects noise by comparing the magnitude of the input signal with the second threshold for each estimated occurrence timing. The operation of the noise detection unit 40 will be described with reference to FIG.

[0034] As shown in Fig. 4, the noise detection unit 40 detects noise by comparing the magnitude of the input signal with the lowered second threshold at the estimated occurrence timing. Therefore, even if the noise is small, the detection threshold for detecting the noise is small at the occurrence timing, so the noise detection unit 40 can detect the small noise by comparing the magnitude of the input signal with the first threshold at times other than the estimated occurrence timing.

[0035] For example, before the first threshold is lowered to the second threshold for each estimated occurrence timing, the noise detection unit 40 detects noise by comparing the magnitude of the input signal with the first threshold and outputs this detection result to the period detection unit 10 and the timing estimation unit 20. By using the detection result, the period detection unit 10 can detect the period of the noise when the magnitude of the input signal periodically exceeds the first threshold. Furthermore, by using the detection result, the timing estimation unit 20 can estimate future periodic occurrence timings of the noise, starting from the timing at which the magnitude of the input signal exceeds the first threshold.

[0036] The threshold calculation unit 30 may lower the first threshold to a third threshold different from the second threshold at the estimated occurrence time. The third threshold may be greater than or less than the second threshold. In this case, the noise detection unit 40 detects noise by comparing the magnitude of the input signal with the second or third threshold for each estimated occurrence time. For example, the third threshold may be a predetermined threshold, a threshold determined according to the magnitude of the input signal, or a threshold determined according to the first threshold, like the second threshold.

[0037] Furthermore, the timing estimation unit 20 may estimate occurrence timings at intervals of n (n is a natural number) times or 1 / n times the detected period. Because noise often includes second or third harmonics, the timing estimation unit 20 may estimate occurrence timings that are twice, three times, ..., or half, one-third, ... of the detected period. This makes it possible to detect noise such as second or third harmonics.

[0038] Furthermore, the noise detection unit 40 may stop noise detection if the number of noise detections in a predetermined period corresponding to the detected period does not fall within a predetermined numerical range. For example, the predetermined period is an integer multiple of the detected period. For example, if the predetermined period is 10 times the detected period, the expected number of times periodic noise will be detected will be approximately 10. However, if noise is erroneously detected, the number of noise detections will be significantly different from 10. In this way, if the number of noise detections is more or less than the expected number, it is possible that noise has been erroneously detected. Therefore, in such cases, stopping noise detection can reduce the adverse effects of erroneous noise detection.

[0039] As described above, when the noise is large enough to allow its period to be detected, the period of the noise is detected, and the first threshold for detecting the noise at each future periodic occurrence timing of the noise estimated based on the detected period is lowered to the second threshold. Therefore, the lowered second threshold makes it possible to detect small noise whose period cannot be detected.

[0040] If the detection threshold for detecting noise is always lowered, there is a risk that the noise floor may be erroneously detected as noise. In contrast, in the noise detection device 1, the detection threshold is lowered at least at the estimated occurrence timing, and is not always lowered, thereby making it possible to prevent the noise floor from being erroneously detected as noise.

[0041] (Other Embodiments) As described above, the embodiments have been described as examples of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present disclosure.

[0042] For example, the present disclosure can be realized not only as the noise detection device 1 but also as a noise detection method including steps (processing) performed by the components that make up the noise detection device 1.

[0043] FIG. 5 is a flowchart showing an example of a noise detection method according to another embodiment.

[0044] The noise detection method is executed by the noise detection device 1 to detect periodic noise contained in an input signal, and as shown in FIG. 5 , includes a period detection step (step S11) of detecting the period of the noise, a timing estimation step (step S12) of estimating future periodic occurrence timings of the noise based on the detected period, a threshold calculation step (step S13) of lowering a first threshold for detecting noise to a second threshold for each estimated occurrence timing, and a noise detection step (step S14) of detecting noise by comparing the magnitude of the input signal with the second threshold for each estimated occurrence timing.

[0045] For example, the present disclosure can be realized as a program for causing a computer (processor) to execute steps included in the noise detection method. Furthermore, the present disclosure can be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0046] For example, when the present disclosure is realized as a program (software), each step is performed by running the program using hardware resources such as a computer's CPU, memory, input / output circuits, etc. In other words, each step is performed by the CPU acquiring data from memory or input / output circuits, etc., performing calculations, and outputting the calculation results to memory or input / output circuits, etc.

[0047] In the above embodiment, each component included in the noise detection device 1 may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0048] Some or all of the functions of the noise detection device 1 according to the above embodiment are typically realized as an LSI, which is an integrated circuit. These may be individually integrated into single chips, or some or all of them may be integrated into a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. It is also possible to use an FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells within the LSI.

[0049] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, it is natural that each component included in the noise detection device 1 can be integrated using that technology.

[0050] In addition, this disclosure also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope of the present disclosure.

[0051] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0052] (Technology 1) A noise detection device for detecting periodic noise contained in an input signal, comprising: a period detection unit that detects the period of the noise; a timing estimation unit that estimates future periodic occurrence timings of the noise based on the detected period; a threshold calculation unit that lowers a first threshold for detecting the noise to a second threshold for each estimated occurrence timing; and a noise detection unit that detects the noise by comparing the magnitude of the input signal with the second threshold for each estimated occurrence timing.

[0053] According to this method, when the noise is large enough to detect its period, the period of the noise is detected, and the first threshold for detecting the noise at each future periodic occurrence timing of the noise estimated based on the detected period is lowered to the second threshold, thereby making it possible to detect small noise whose period cannot be detected by the lowered second threshold.

[0054] (Technology 2) The noise detection device according to Technology 1, wherein the timing estimation unit estimates the occurrence timing based on the timing at which the magnitude of the input signal exceeds the first threshold.

[0055] According to this, when the magnitude of the input signal exceeds the first threshold, it can be determined that periodic noise is occurring, and this timing can be used as the starting point for future periodic noise occurrences.

[0056] (Technology 3) The noise detection device according to Technology 1 or 2, wherein the first threshold is a predetermined threshold or a threshold determined according to the magnitude of the input signal.

[0057] In this way, the first threshold value can be set.

[0058] (Technology 4) A noise detection device according to any one of techniques 1 to 3, wherein the second threshold is a predetermined threshold, a threshold determined according to the magnitude of the input signal, or a threshold determined according to the first threshold.

[0059] In this way, the second threshold value can be set.

[0060] (Technology 5) The noise detection device according to any one of Technologies 1 to 4, wherein the timing estimation unit estimates the occurrence timing at intervals of n (n is a natural number) times or 1 / n times the detected period.

[0061] This makes it possible to detect noise such as second or third harmonics.

[0062] (Technology 6) A noise detection device according to any one of Techniques 1 to 5, wherein the noise detection unit stops detecting the noise if the number of detected noises in a predetermined period corresponding to the detected cycle is not within a predetermined numerical range.

[0063] According to this, if the number of noise detections is more or less than the expected number, there is a possibility that the noise has been mistakenly detected. In such cases, noise detection can be stopped to reduce the adverse effects caused by mistaken noise detection.

[0064] (Technology 7) A noise detection method executed by a noise detection device for detecting periodic noise contained in an input signal, the noise detection method including: a period detection step of detecting the period of the noise; a timing estimation step of estimating future periodic occurrence timings of the noise based on the detected period; a threshold calculation step of lowering a first threshold for detecting the noise to a second threshold for each estimated occurrence timing; and a noise detection step of detecting the noise by comparing the magnitude of the input signal with the second threshold for each estimated occurrence timing.

[0065] This provides a noise detection method that can detect small noise whose period cannot be detected.

[0066] (Technology 8) A program for causing a computer to execute the noise detection method according to Technology 7.

[0067] This makes it possible to provide a program that can detect small noises whose period cannot be detected.

[0068] The present disclosure is applicable to devices that detect and remove periodic noise contained in an input signal.

[0069] REFERENCE SIGNS LIST 1 noise detection device 10 period detection unit 20 timing estimation unit 30 threshold calculation unit 40 noise detection unit

Claims

1. A noise detection device for detecting periodic noise contained in an input signal, comprising: a period detection unit for detecting a period of the noise; a timing estimation unit that estimates future periodic occurrence timing of the noise based on the detected period; a threshold calculation unit that reduces a first threshold for detecting the noise to a second threshold for each of the estimated occurrence times; a noise detection unit that detects the noise by comparing a magnitude of the input signal with the second threshold for each of the estimated occurrence times. Noise detection device.

2. the timing estimation unit estimates the occurrence timing from a timing at which the magnitude of the input signal exceeds the first threshold.

2. The noise detection device according to claim 1.

3. The first threshold is a predetermined threshold or a threshold determined according to the magnitude of the input signal.

3. The noise detection device according to claim 1.

4. The second threshold is a predetermined threshold, a threshold determined according to the magnitude of the input signal, or a threshold determined according to the first threshold.

3. The noise detection device according to claim 1.

5. the timing estimation unit estimates the occurrence timing at intervals that are n (n is a natural number) times or 1 / n times the detected period; 3. The noise detection device according to claim 1.

6. the noise detection unit stops detecting the noise when the number of times the noise is detected during a predetermined period corresponding to the detected cycle is not within a predetermined numerical range.

3. The noise detection device according to claim 1.

7. 1. A noise detection method executed by a noise detection device for detecting periodic noise included in an input signal, comprising: a period detection step of detecting a period of the noise; a timing estimation step of estimating future periodic occurrence timings of the noise based on the detected period; a threshold calculation step of lowering a first threshold for detecting the noise to a second threshold for each of the estimated occurrence times; a noise detection step of detecting the noise by comparing a magnitude of the input signal with the second threshold for each of the estimated occurrence times. Noise detection methods.

8. A program for causing a computer to execute the noise detection method according to claim 7.