Signal processing device, signal processing method, and signal processing program

Abstract

When an observation signal including noise the pitch of which changes with the passage of time has been received, a comb filter selection unit (21) selects, from a plurality of comb filters having different pitches to be removed, a comb filter having a pitch to be removed, which matches the pitch of noise, as a selected comb filter in response to the change of the pitch of the noise with the passage of time. A comb filter application unit (23) applies the selected comb filter to the observation signal to remove noise from the observation signal.

Description

Technical Field

[0001] The present disclosure relates to a technique for removing noise included in an audio signal.

Background Art

[0002] There is a technique for analyzing an audio signal to detect an abnormality of a device. In such a technique, an acoustic sensor such as a microphone is used to observe the operating sound of the device, and it is determined whether the observation signal, which is the audio signal obtained by the observation, contains abnormal sounds.

[0003] However, such a technique has a problem that the determination accuracy deteriorates due to the influence of noise mixed in the observation signal. Examples of the noise mixed in the observation signal include noise generated from mechanical equipment other than the device to be inspected (for example, noise of an air conditioner), environmental noise (for example, sound of wind and rain), electrical noise associated with measurement, and the like.

[0004] The environments where the above inspection techniques are required are often machine rooms, production lines, etc. In machine rooms, production lines, etc., a large number of mechanical equipment are often arranged around. Therefore, in order to appropriately use the above inspection techniques, it is necessary to establish countermeasures against the noise generated from these mechanical equipment. If such countermeasures cannot be established, it is difficult to accurately detect an abnormality from the operating sound of the device in the actual environment.

[0005] In particular, the noise generated from mechanical equipment includes alarms, chimes, etc. These alarms, chimes, etc. are electronic sounds issued for the purpose of signals and warnings. And these alarms, chimes, etc. often have a melody. Therefore, alarms, chimes, etc. have the characteristic that the pitch frequently changes during reproduction. For this reason, alarms, chimes, etc. do not have stationarity. Many noise removal methods (for example, a simple spectral subtraction method) assuming the stationarity of noise cannot cope with such non-stationary noise.

[0006] The waveform of this melodic noise is periodic within the same pitch interval. Therefore, in the power spectrum domain, the noise waveform appears as several peaks composed of the fundamental frequency component and its harmonic components. Consequently, if we consider only a single pitch, the noise can be removed using a notch filter or comb filter that blocks these peak components. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2006-331567 [Overview of the project] [Problems that the invention aims to solve]

[0008] Patent Document 1 discloses an example of such noise reduction technology. Patent Document 1 discloses a technique for removing periodic waveform noise using a comb filter. However, in the configuration disclosed in Patent Document 1, in order to respond to changes in the pitch of the noise, that is, changes in the period of the noise waveform, it is necessary to separately provide the period by some means. Therefore, in order to respond to noise that is a melody, it is necessary to provide the pitch of the melody at regular intervals by some means. As a result, the technology in Patent Document 1 has the problem that the configuration for removing noise becomes complicated.

[0009] The primary purpose of this disclosure is to solve the problems described above. Specifically, the primary purpose of this disclosure is to enable the removal of noise whose pitch changes over time with a simple configuration. [Means for solving the problem]

[0010] The signal processing device relating to this disclosure is When an audio signal containing noise whose pitch changes over time is received, a comb filter selection unit selects a comb filter from a plurality of comb filters, each with a different target pitch to be removed, that matches the target pitch to be removed to the noise's pitch, in accordance with the change in the noise's pitch over time. The system includes a comb filter application unit that applies the selected comb filter to the audio signal to remove the noise from the audio signal. [Effects of the Invention]

[0011] According to this disclosure, it is possible to remove noise whose pitch changes over time with a simple configuration. [Brief explanation of the drawing]

[0012] [Figure 1] A diagram showing an example of the functional configuration of the alarm removal device according to Embodiment 1. [Figure 2] A diagram showing an example of the hardware configuration of the alarm removal device according to Embodiment 1. [Figure 3] A flowchart showing an example of operation of the alarm removal device according to Embodiment 1. [Figure 4] A flowchart illustrating an example of the operation of the comb filter selection unit when a comb filter is applied in the frequency domain using a fast Fourier transform, according to Embodiment 1. [Figure 5] A flowchart illustrating an example of the operation of the comb filter selection unit when a comb filter is applied in the frequency domain using a fast Fourier transform, according to Embodiment 1. [Modes for carrying out the invention]

[0013] The embodiments will be described below with reference to the drawings. In the following description of the embodiments and in the drawings, the same reference numerals indicate the same part or a corresponding part.

[0014] Embodiment 1. ***overview*** In the present embodiment, a configuration for removing noise whose pitch changes over time and is mixed in an observation signal, which is an audio signal obtained from an acoustic sensor, will be described. The noise to be removed in the present embodiment is composed of a plurality of discrete pitches such as an alarm or a chime, and different pitches are reproduced at each time. Further, the noise to be removed may be such that a plurality of pitches are reproduced simultaneously to form a harmony.

[0015] In the present embodiment, a comb filter is used to remove such noise. A comb filter is a filter that selectively removes noise of a certain pitch. A comb filter has a characteristic of blocking only the fundamental frequency of the pitch to be removed and its harmonic components. A simple comb filter blocks only a single pitch, but a comb filter that blocks a plurality of pitches can also be obtained by combining a plurality of simple comb filters. Since such a comb filter blocks a plurality of pitches simultaneously, it is also possible to remove a harmony. In order to remove the noise that forms a melody, an appropriate comb filter may be selected and applied for each time according to the pitch of the melody.

[0016] In the present embodiment, an alarm removal device 2 described later holds a plurality of comb filters having different blocking characteristics. Then, the alarm removal device 2 selects an optimal comb filter from the plurality of comb filters based on the observation signal. Further, the alarm removal device 2 applies the selected comb filter to the observation signal and outputs a signal from which the noise has been removed. By selecting an optimal comb filter according to the pitch of the noise from the observation signal, it becomes possible to remove noise whose pitch frequently changes with a simple configuration.

[0017] ***Description of Configuration*** FIG. 1 shows a functional configuration example of an alarm removal device 2 according to the present embodiment. FIG. 2 shows a hardware configuration example of an alarm removal device 2 according to the present embodiment. The alarm removal device 2 corresponds to a signal processing device. The operation procedure of the alarm removal device 2 corresponds to a signal processing method. Also, the program for realizing the operation of the alarm removal device 2 corresponds to a signal processing program.

[0018] First, referring to FIG. 2, a hardware configuration example of the alarm removal device 2 will be outlined.

[0019] The alarm removal device 2 according to the present embodiment is a computer. As hardware, the alarm removal device 2 includes a processor 901, a main storage device 902, an auxiliary storage device 903, and an input / output device 904. Also, as shown in FIG. 1, the alarm removal device 2 includes, as a functional configuration, a comb filter selection unit 21, a comb filter storage unit 22, and a comb filter application unit 23. The functions of the comb filter selection unit 21 and the comb filter application unit 23 are realized by, for example, a program. The auxiliary storage device 903 stores a program for realizing the functions of the comb filter selection unit 21 and the comb filter application unit 23. These programs are loaded from the auxiliary storage device 903 to the main storage device 902. Then, the processor 901 executes these programs to perform the operations of the comb filter selection unit 21 and the comb filter application unit 23, which will be described later. FIG. 2 schematically shows a state in which the processor 901 is executing a program for realizing the functions of the comb filter selection unit 21 and the comb filter application unit 23. The comb filter storage unit 22 is realized by, for example, the auxiliary storage device 903. The input / output device 904 is used to input an observation signal from a signal input device 1, which is an external device. Also, the input / output device 904 is used to output a noise-removed signal, which is a signal with noise removed.

[0020] Next, referring to FIG. 1, a functional configuration example of the alarm removal device 2 will be described.

[0021] Alarm removal device 2 receives observation signals from signal input device 1. As mentioned earlier, the observed signal is an audio signal containing noise whose pitch changes over time. Alarm removal device 2 removes noise from the observed signal and outputs the noise-removed signal.

[0022] The signal input device 1 consists of, for example, a microphone and an A / D (Analog / Digital) converter. In the signal input device 1, the A / D converter converts the analog signal observed by the microphone into a digital signal and outputs it to the alarm rejection device 2. In addition to the microphone, other observation means such as an acceleration pickup, ultrasonic sensor, or laser Doppler accelerometer may also be used in the signal input device 1.

[0023] The comb filter selection unit 21 receives the observation signal from the signal input device 1. The comb filter selection unit 21 then selects a comb filter suitable for noise removal for each unit of time, in accordance with the change in the pitch of the noise over time. More specifically, the comb filter selection unit 21 selects a comb filter for each unit of time whose target pitch for removal matches the pitch of the noise. The unit time is significantly shorter than the change in the noise's pitch. For example, the unit time is 1 millisecond or less. The unit time can be appropriately changed depending on the degree of change in the noise's pitch and the processing capacity of the processor or processing circuit that operates the alarm suppression device 2. For example, if the change in the noise's pitch is gradual, increasing the unit time reduces the number of processing cycles (frequency) required to select the comb filter. Therefore, the processing load on the processor or processing circuit that operates the alarm suppression device 2 can be reduced. The comb filter selection unit 21 refers to the target pitch information, which indicates the target pitches for removal for each of the multiple comb filters stored in the comb filter storage unit 22. The target pitch information is held, for example, in the auxiliary storage device 903. The target pitch information is loaded into the main storage device 902, and the comb filter selection unit 21 can then refer to the target pitch information. The comb filter selection unit 21 identifies the pitch of the noise contained in the observed signal at each unit time interval and selects a comb filter whose target pitch for removal, as indicated in the target pitch information, matches the pitch of the noise. The comb filter selection unit 21 notifies the comb filter storage unit 22 of the selection result. In other words, the comb filter selection unit 21 notifies the comb filter storage unit 22 of the selected comb filter (hereinafter referred to as the selected comb filter). The processing performed by the comb filter selection unit 21 corresponds to the comb filter selection process.

[0024] The comb filter storage unit 22 houses multiple comb filters. Multiple comb filters have different target pitches that are removed. The comb filter storage unit 22 outputs the selected comb filter notified as the selection result from the comb filter selection unit 21 to the comb filter application unit 23.

[0025] The comb filter application unit 23 applies a selected comb filter to the observed signal to remove noise from the observed signal. The comb filter application unit 23 then outputs the denoised signal, which is the observed signal from which noise has been removed, to a predetermined output destination. The processing performed by the comb filter application unit 23 corresponds to the comb filter application process.

[0026] In this way, the comb filter selection unit 21 selects a comb filter suitable for noise removal on a per-unit time basis, according to the change in the pitch of the noise over time. With this configuration, an appropriate comb filter is applied to noise whose pitch changes over time on a per-unit time basis. Therefore, non-stationary noises such as alarms and chimes can be effectively removed. Furthermore, this configuration selects the appropriate comb filter based solely on the observed signal, eliminating the need to provide external information about the noise's pitch. This avoids increasing the complexity of the device.

[0027] ***Explanation of operation*** Figure 3 shows an example of the operation of the alarm removal device 2 according to this embodiment. The flow shown in Figure 3 is repeated every unit of time.

[0028] In step S1, the comb filter selection unit 21 receives the observation signal from the signal input device 1.

[0029] Next, in step S2, the comb filter selection unit 21 selects a comb filter suitable for noise reduction. Details of how the comb filter is selected by the comb filter selection unit 21 will be described later.

[0030] Next, in step S3, the comb filter selection unit 21 notifies the comb filter storage unit 22 of the selected comb filter.

[0031] Next, in step S4, the comb filter storage unit 22 outputs the selected comb filter to the comb filter application unit 23.

[0032] Next, in step S5, the comb filter application unit 23 applies the selected comb filter to the observed signal to remove noise from the observed signal.

[0033] Finally, in step S6, the comb filter application unit 23 outputs the noise-removed signal.

[0034] Next, we will explain the specific method of selecting a comb filter by the comb filter selection unit 21.

[0035] A state in which an appropriate comb filter is selected is one in which the pitch of the noise to be removed matches the pitch that the selected comb filter blocks. Therefore, the comb filter selection unit 21 can, for example, use analytical methods such as autocorrelation or linear prediction to identify the pitch of the noise and select a corresponding comb filter based on the identified noise pitch. However, in situations where a desired signal is superimposed on the observed signal in addition to noise, the desired signal will act as a disturbance to these analysis methods. The desired signal, in the case of inspecting machine operating sounds, would be the operating sound of the machine being inspected. In such cases, it is difficult to ensure that analytical methods such as autocorrelation and linear prediction function robustly.

[0036] Therefore, one possible method for selecting a comb filter in the comb filter selection unit 21 is to select a comb filter that maximizes the total amount of energy blocked. In other words, the comb filter selection unit 21 calculates, for each unit of time, the amount of energy removed from the observed signal when each comb filter removes signal components of a pitch that matches the pitch to be removed from the observed signal, and this amount of energy removed is calculated as the removal energy amount of each comb filter. The comb filter selection unit 21 then selects the comb filter with the largest calculated removal energy amount for each comb filter. The frequency components blocked by the selected comb filter coincide with the fundamental frequency and its harmonics of the noise. As a result, the noise is effectively removed. Furthermore, the comb filter allows signals to pass through most frequency bands. Therefore, external disturbances have little effect on the calculation of the amount of energy that is blocked. As a result, compared to the aforementioned analysis methods that estimate pitch using autocorrelation, linear prediction, etc., it is more robust and can be expected to have high noise reduction accuracy.

[0037] Furthermore, when applying a comb filter in the frequency domain using the Fast Fourier Transform, the comb filter selection unit 21 prepares in advance an array a of frequency bin index numbers corresponding to the frequencies to be blocked. Then, as shown in Figure 4, the comb filter selection unit 21 refers only to the frequency bins of each index number stored in array a and blocks those frequency components. In other words, each comb filter is assigned a frequency bin corresponding to the frequency components of the pitch to be removed. The comb filter selection unit 21 calculates the amount of energy of the frequency bins assigned to each comb filter as the amount of energy removed by each comb filter for each unit of time. The comb filter selection unit 21 then selects the comb filter for which the maximum amount of energy removed has been calculated. When applying a comb filter in the frequency domain using the Fast Fourier Transform, the observed signal is processed block by block. Therefore, it is preferable to set the unit time in the range of approximately 10 to 30 ms, linked to the block length. The unit time can be appropriately changed depending on the analysis window length or block length of the Fast Fourier Transform.

[0038] Figure 4 shows an example of the operation of the comb filter selection unit 21 when the comb filter is applied in the frequency domain by fast Fourier transform according to this embodiment. The flow shown in Figure 4 is repeated every unit of time.

[0039] In step S21, the comb filter selection unit 21 initializes the loop counter i to 1.

[0040] Next, in step S22, the comb filter selection unit 21 determines whether the loop counter i is less than or equal to the length (size) of array a. If the loop counter i is less than or equal to the length of array a (YES in step S22), the process proceeds to step S23. If the loop counter i exceeds the length of array a (NO in step S22), the flow ends.

[0041] Next, in step S23, the comb filter selection unit 21 assigns the i-th index number of array a to the variable w.

[0042] Next, in step S24, the comb filter selection unit 21 blocks the component of the w-th frequency bin.

[0043] Next, in step S25, the comb filter selection unit 21 adds 1 to the loop counter i. Then, the comb filter selection unit 21 returns to the determination process in step S22.

[0044] The comb filter application unit 23 applies a selective comb filter to the frequency components obtained by performing a fast Fourier transform on the observed signal at each unit time interval. The comb filter selection unit 21 performs the process of blocking frequency components by replacing the value stored in that frequency bin with 0. Alternatively, the comb filter selection unit 21 may perform the process of blocking frequency components by flooring (multiplying by a small real number such as 0.001). In this case, the total amount of energy blocked by the comb filter can be quantified as the sum of the amplitude or power that those frequency bins possessed. This quantification process can be performed in the same way as the comb filter application process. Specifically, as shown in Figure 5, the comb filter selection unit 21 refers only to the frequency bins of each index number stored in array a and quantifies by calculating the sum of the absolute values ​​(or squares of the absolute values) of those frequency components.

[0045] Figure 5 shows an example of the operation of the comb filter selection unit 21 when the comb filter is applied in the frequency domain by fast Fourier transform according to this embodiment. The flow shown in Figure 5 is repeated every unit of time.

[0046] In step S31, the comb filter selection unit 21 initializes the loop counter i to 1 and the total energy s to 0.

[0047] Next, in step S32, the comb filter selection unit 21 determines whether the loop counter i is less than or equal to the length (size) of array a. If the loop counter i is less than or equal to the length of array a (YES in step S32), the process proceeds to step S33. If the loop counter i exceeds the length of array a (NO in step S32), the process proceeds to step S36.

[0048] Next, in step S33, the comb filter selection unit 21 assigns the i-th index number of array a to the variable w.

[0049] Next, in step S34, the comb filter selection unit 21 adds the energy of the w-th frequency bin to the variable s.

[0050] Next, in step S35, the comb filter selection unit 21 adds 1 to the loop counter i. Then, the comb filter selection unit 21 returns to the determination process in step S32.

[0051] In step S36, the comb filter selection unit 21 outputs the value of variable s as the sum of the energies. Then the flow ends.

[0052] A comb filter blocks only a small number of frequency bins. Therefore, by implementing the comb filter selection and application processes as described above, highly accurate noise reduction can be achieved with extremely low computational cost. Alternatively, the Discrete Fourier Transform may be used in the comb filter instead of the Fast Fourier Transform.

[0053] The comb filter storage unit 22 stores multiple comb filters as selection targets for the comb filter selection unit 21. For example, the comb filter storage unit 22 stores comb filters in advance that block all pitches that may occur as noise. This allows for the removal of noise at various pitches. The following are possible methods for generating such a comb filter: Method 1 Determine the fundamental frequency of the possible pitches. Then, design a comb filter that blocks all frequencies of the fundamental frequency and its harmonics. Method 2 Samples of potential noise are recorded individually for each pitch. Then, a comb filter is designed to block the peaks of each pitch in the power spectrum. Method 3 A series of noise samples forming a melody are recorded. The spectrogram is then decomposed into a basis for each pitch using non-negative matrix factorization. Based on these, a comb filter corresponding to each pitch is designed.

[0054] If the noise that forms the melody contains chords, a comb filter is provided that removes all the intervals that make up that chord. This allows the system to handle chords as well.

[0055] As described above, the comb filter application unit 23 applies the selected comb filter to the observed signal from the signal input device 1. The comb filter application unit 23 then outputs the noise-removed signal. In addition to the frequency domain method described above, the following method can be considered as an example of a time domain method by which the comb filter application unit 23 applies the comb filter to the observed signal. For example, the comb filter application unit 23 can be configured to create an IIR (Infinite Impulse Response) filter by connecting BiQuad type notch filters in series to block the fundamental frequency and harmonic frequencies. In this case, the energy blocked by the comb filter can be quantified, for example, by the following method. The energy of the signal before and after applying the comb filter is compared. The amount of energy attenuation is then considered to be the amount of energy blocked by the comb filter.

[0056] It is also possible to configure the system such that the comb filter selection unit 21 selects multiple comb filters, and the comb filter application unit 23 applies those comb filters simultaneously. For example, consider a case where the noise that constitutes the melody includes chords, and the number of intervals that make up the chord is at most three. In this case, the comb filter storage unit 22 prepares a corresponding comb filter for all the single notes included in the melody. The comb filter selection unit 21 then selects the top three comb filters with the highest effectiveness. In other words, for each unit of time, the comb filter selection unit 21 selects three comb filters whose target intervals correspond to the three intervals that make up the noise. The comb filter application unit 23 then applies the three selected comb filters to the observed signal for each unit of time to remove the noise from the observed signal. This configuration eliminates the need to prepare a corresponding comb filter for each chord, thus reducing implementation costs. Furthermore, it can remove noise including reverberation. Specifically, when the reverberation of a previously uttered note is superimposed on the next note, creating a chord-like effect, the noise, including the reverberation, can be removed. This results in a higher level of noise reduction.

[0057] In the above configuration, the comb filter selection unit 21 is always assumed to select one of the comb filters. Therefore, even if the observed signal does not contain noise, one of the comb filters will be applied. Since comb filters block only a small number of frequency components, the impact on the output signal is usually considered to be small even in such a configuration.

[0058] However, if the distortion of the output signal is to be reduced, it is also possible to introduce a state in which the comb filter selection unit 21 does not select any comb filters. When the comb filter selection unit 21 does not select a comb filter, the comb filter application unit 23 outputs the observed signal from the signal input device 1 as is. The following are possible conditions under which the comb filter selection unit 21 does not select a comb filter. For example, if the comb filter that blocks the maximum total amount of energy is known, the comb filter selection unit 21 determines that the observed signal is not mixed with noise if the total amount of energy blocked by that comb filter is below a predetermined threshold. In other words, the comb filter selection unit 21 determines that the observed signal is not mixed with noise if the maximum total amount of energy (maximum amount of energy removed) is below a predetermined threshold in any unit of time. In this case, the comb filter selection unit 21 does not select any comb filters. In this configuration, when there is no noise mixed into the observed signal, the signal output from the comb filter application unit 23 does not experience distortion, resulting in good sound quality.

[0059] In the above configuration, there are no particular constraints on the operation of switching the applied comb filter over time. Therefore, if there is a large disturbance in the observed signal, it is possible that an appropriate comb filter will not be selected per unit time. In this case, the comb filter may switch more frequently than necessary, potentially causing distortion in the output signal. To avoid this, a configuration can be considered that prevents the comb filter from switching more than necessary. Specifically, a configuration can be considered that imposes a penalty on the comb filter selection unit 21 for switching the comb filter. For example, a score function is introduced in which the sum of the energy blocked by the selected comb filter in each unit of time is included as a reward term, and the number of times the selected comb filter switches is included as a penalty term. The comb filter selection unit 21 then selects the comb filter that maximizes this score function in each unit of time. The comb filter selection unit 21 can efficiently determine the method for switching comb filters that maximizes this score function, for example, by using dynamic programming. This ensures that the comb filter selection remains stable even when large disturbances occur. As a result, better sound quality can be achieved.

[0060] ***Explanation of the effects of the embodiment*** As described above, according to this embodiment, it is possible to eliminate noise whose pitch changes over time with a simple configuration. Furthermore, according to this embodiment, by using the array a of frequency bin index numbers, high-precision noise reduction can be achieved with extremely low computational cost. Furthermore, according to this embodiment, even if the noise contains chords, the chords in the noise can be effectively removed. Furthermore, according to this embodiment, even if the noise contains reverberation, the noise, including the reverberation, can be removed. Furthermore, according to this embodiment, the comb filter is not selected if there is no noise in the observed signal. Therefore, no distortion occurs in the output signal, and good sound quality can be obtained. Furthermore, according to this embodiment, even when large disturbances occur, the selection result of the comb filter is stabilized by using the score function. As a result, better sound quality can be obtained.

[0061] Note that the procedure described in this embodiment is just one example. Therefore, it is acceptable to perform only a portion of the procedure described in this embodiment. Furthermore, at least some of the procedures described in this embodiment may be combined with procedures not described in this embodiment. Furthermore, the configuration and procedures described in this embodiment may be modified as necessary.

[0062] ***Supplementary explanation of hardware configuration*** Finally, we will provide supplementary information on the hardware configuration of alarm removal device 2. The processor 901 shown in Figure 2 is an integrated circuit (IC) that performs processing. Processor 901 includes components such as a CPU (Central Processing Unit) and a DSP (Digital Signal Processor). The main memory 902 shown in Figure 2 is RAM (Random Access Memory). The auxiliary storage device 903 shown in Figure 2 includes ROM (Read Only Memory), flash memory, HDD (Hard Disk Drive), etc.

[0063] Furthermore, the auxiliary storage device 903 also stores the OS (Operating System). Then, at least a portion of the OS is executed by processor 901. The processor 901 executes a program that implements the functions of the comb filter selection unit 21 and the comb filter application unit 23 while executing at least a part of the OS. Processor 901 executes the OS, handling task management, memory management, file management, communication control, and other functions. Furthermore, at least one of the information, data, signal values, and variable values ​​indicating the processing results of the comb filter selection unit 21 and the comb filter application unit 23 is stored in at least one of the main memory 902, auxiliary memory 903, registers in the processor 901, and cache memory. Furthermore, the programs that implement the functions of the comb filter selection unit 21 and the comb filter application unit 23 may be stored on portable recording media such as magnetic disks, flexible disks, optical disks, compact disks, Blu-ray® discs, and DVDs. Portable recording media containing the programs that implement the functions of the comb filter selection unit 21 and the comb filter application unit 23 may also be distributed.

[0064] Furthermore, at least one of the "parts" in the comb filter selection unit 21 and the comb filter application unit 23 may be read as "circuit," "process," "procedure," "processing," or "circuitry." Furthermore, the alarm removal device 2 may be implemented by a processing circuit. Examples of processing circuits include logic ICs (Integrated Circuits), GAs (Gate Arrays), ASICs (Application Specific Integrated Circuits), and FPGAs (Field-Programmable Gate Arrays). In this case, the comb filter selection unit 21 and the comb filter application unit 23 are each implemented as part of the processing circuit. In this specification, the higher-level concept encompassing both the processor and the processing circuit is referred to as "processing circuitry." In other words, a processor and a processing circuit are specific examples of "processing circuits," respectively. [Explanation of Symbols]

[0065] 1 Signal input device, 2 Alarm removal device, 21 Comb filter selection unit, 22 Comb filter storage unit, 23 Comb filter application unit, 901 Processor, 902 Main memory, 903 Auxiliary memory, 904 Input / output device.

Claims

1. When an audio signal containing noise whose pitch changes over time is received, a comb filter selection unit selects a comb filter from a plurality of comb filters, each with a different target pitch to be removed, that matches the target pitch to be removed to the noise's pitch, in accordance with the change in the noise's pitch over time. The system includes a comb filter application unit that applies the selected comb filter to the audio signal to remove the noise from the audio signal, The comb filter selection unit is, For each unit of time, the amount of energy removed from the audio signal when each comb filter removes signal components with pitches matching the target pitch to be removed is calculated as the removal energy amount of each comb filter, and the selected comb filter is selected based on the calculated removal energy amount of each comb filter. Each comb filter is assigned a frequency bin corresponding to the frequency components of the pitch to be removed. The comb filter selection unit is, For each unit time, the amount of energy in the frequency bin assigned to each comb filter is calculated as the amount of energy removed by each comb filter. The comb filter application unit is, A signal processing device that applies the selection comb filter to the frequency components obtained by performing a Fourier transform on the audio signal at each unit time.

2. The comb filter selection unit is, The signal processing apparatus according to claim 1, wherein the comb filter from which the maximum removal energy amount is calculated is selected as the selected comb filter.

3. When an audio signal containing noise whose pitch changes over time is received, a comb filter selection unit selects a comb filter from a plurality of comb filters, each with a different target pitch to be removed, that matches the target pitch to be removed to the noise's pitch, in accordance with the change in the noise's pitch over time. The system includes a comb filter application unit that applies the selected comb filter to the audio signal to remove the noise from the audio signal, The aforementioned noise consists of two or more pitches, The comb filter selection unit is, For each unit of time, two or more comb filters are selected as the selected comb filters, each corresponding to one of the two or more pitches that constitute the noise, and each comb filter corresponds to a pitch to be removed. The comb filter application unit is, A signal processing device that applies two or more of the selected comb filters to the audio signal at each unit time interval to remove the noise from the audio signal.

4. When an audio signal containing noise whose pitch changes over time is received, a comb filter selection unit selects a comb filter from a plurality of comb filters, each with a different target pitch to be removed, that matches the target pitch to be removed to the noise's pitch, in accordance with the change in the noise's pitch over time. The system includes a comb filter application unit that applies the selected comb filter to the audio signal to remove the noise from the audio signal, The comb filter selection unit is, For each unit of time, the amount of energy removed from the audio signal when each comb filter removes signal components with pitches matching the target pitch to be removed is calculated as the removal energy amount of each comb filter, and the selected comb filter is selected based on the calculated removal energy amount of each comb filter. The comb filter selection unit is, If the maximum amount of removed energy in any unit of time is less than or equal to a predetermined threshold, none of the comb filters are selected as the selected comb filters. The comb filter application unit is, A signal processing device that outputs the audio signal to a default output destination without processing the audio signal if the selection comb filter is not selected.

5. When an audio signal containing noise whose pitch changes over time is received, a comb filter selection unit selects a comb filter from a plurality of comb filters, each with a different target pitch to be removed, that matches the target pitch to be removed to the noise's pitch, in accordance with the change in the noise's pitch over time. The system includes a comb filter application unit that applies the selected comb filter to the audio signal to remove the noise from the audio signal, The comb filter selection unit is, A signal processing device that selects a comb filter as the selected comb filter that maximizes a score function in which the amount of removal energy of each comb filter is included as a reward term, and the number of times the selected comb filter switches is included as a penalty term.

6. When an audio signal containing noise whose pitch changes over time is received, the computer selects a comb filter from among several comb filters, each with a different target pitch to be removed, that matches the target pitch of the noise, as the selected comb filter, in accordance with the change in the noise's pitch over time. The computer applies the selected comb filter to the audio signal to remove the noise from the audio signal. The aforementioned noise consists of two or more pitches, In the selection of the aforementioned comb filter, the computer, For each unit of time, two or more comb filters are selected as the selected comb filters, each corresponding to one of the two or more pitches that constitute the noise, and each comb filter corresponds to a pitch to be removed. In the noise reduction described above, the computer, A signal processing method that applies two or more of the selected comb filters to the audio signal at each unit time interval to remove the noise from the audio signal.

7. When an audio signal containing noise whose pitch changes over time is received, the computer selects a comb filter from among several comb filters, each with a different target pitch to be removed, that matches the target pitch of the noise, as the selected comb filter, in accordance with the change in the noise's pitch over time. The computer applies the selected comb filter to the audio signal to remove the noise from the audio signal. In the selection of the aforementioned comb filter, the computer, A signal processing method for selecting a comb filter as the selected comb filter that maximizes a score function in which the amount of energy removed by each comb filter is included as a reward term, and the number of times the selected comb filter switches is included as a penalty term.

8. When an audio signal containing noise whose pitch changes over time is received, a comb filter selection process is performed to select a comb filter from a plurality of comb filters, each with a different target pitch to be removed, in accordance with the change in the pitch of the noise over time, the comb filter whose target pitch matches the pitch of the noise. A signal processing program that causes a computer to perform a comb filter application process, which involves applying the selected comb filter to the audio signal to remove the noise from the audio signal, The aforementioned noise consists of two or more pitches, In the aforementioned comb filter selection process, the computer is instructed to: For each unit of time, two or more comb filters are selected as the selected comb filters, each corresponding to one of the two or more pitches that constitute the noise and the pitch to be removed. In the comb filter application process, the computer will A signal processing program that applies two or more of the selected comb filters to the audio signal at each unit of time to remove the noise from the audio signal.

9. When an audio signal containing noise whose pitch changes over time is received, a comb filter selection process is performed to select a comb filter from a plurality of comb filters, each with a different target pitch to be removed, in accordance with the change in the pitch of the noise over time, the comb filter whose target pitch matches the pitch of the noise. A signal processing program that causes a computer to perform a comb filter application process, which involves applying the selected comb filter to the audio signal to remove the noise from the audio signal, In the aforementioned comb filter selection process, the computer is instructed to: A signal processing program that causes a comb filter to be selected as the selected comb filter, which maximizes a score function in which the amount of energy removed by each comb filter is included as a reward term, and the number of times the comb filter selected as the selected comb filter switches is included as a penalty term.

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