JP2017129741A - Noise reduction device and noise reduction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise reduction device capable of reducing noises included in output voices of demodulated input signals, and a noise reduction method.SOLUTION: A noise reduction device 10 includes: an analysis section 110; a detection section 130; and a reduction section 150. The analysis section 110 analyzes the frequency spectrum of an input signal. The detection section 130 detects at least one noise component from among frequency components included in the input signal based on the priority of hearing characteristics of the input signals according to the analysis result by the analysis section 110. The reduction section 150 reduces the noise component detected by the detection section 130.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a noise reduction device and a noise reduction method.

  Conventionally, when a system that receives radio broadcast waves is mounted on a vehicle, the system that receives noise due to switching processing performed at the time of power conversion of the battery of the vehicle, for example, may receive the system. Therefore, in the conventional system, noise is reduced by lowering the output intensity of the peak frequency having the highest intensity among the frequency components included in the received signal (see, for example, Patent Document 1).

JP 2013-9066 A

  However, the prior art only reduces the noise of the highest peak frequency. Therefore, for example, when the received signal includes a plurality of noise components, the noise components cannot be reduced, and noise may remain in the output sound obtained by demodulating the received signal.

  The present invention has been made in view of the above, and an object of the present invention is to provide a noise reduction device and a noise reduction method capable of reducing noise included in output sound obtained by demodulating a received signal.

  In order to solve the above problems and achieve the object, the noise reduction device of the present invention includes an analysis unit, a detection unit, and a reduction unit. The analysis unit analyzes the frequency spectrum of the received signal. The detection unit detects at least one noise component from the frequency components included in the reception signal in a priority order corresponding to the auditory characteristic of the reception signal based on the analysis result by the analysis unit. The reduction unit reduces the noise component detected by the detection unit.

  ADVANTAGE OF THE INVENTION According to this invention, the noise reduction apparatus and noise reduction method which can reduce the noise contained in the output sound which demodulated the received signal can be provided.

FIG. 1 is a diagram for explaining a reception method according to the embodiment. FIG. 2 is a diagram illustrating the receiving device according to the embodiment. FIG. 3 is a diagram for explaining high-cut processing performed by the demodulator according to the embodiment. FIG. 4 is a diagram illustrating threshold values set by the setting unit according to the embodiment. FIG. 5 is a flowchart illustrating noise reduction processing according to the embodiment. FIG. 6 is a diagram illustrating a configuration of a receiving apparatus according to the first modification. FIG. 7 is a diagram illustrating an example of spectral intensity correction according to the first modification. FIG. 8 is a diagram illustrating a configuration of a receiving device according to the second modification. FIG. 9 is a diagram illustrating an example of a spectrum distribution of a reception signal according to the second modification. FIG. 10 is a diagram illustrating an example of a spectrum intensity distribution corrected by the intensity correction unit according to the second modification. FIG. 11 is a hardware configuration diagram illustrating an example of a computer that realizes the function of the valve control unit of the receiving device according to the embodiment and the modification.

  Hereinafter, embodiments of a noise reduction device and a noise reduction method disclosed in the present application will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

<1. Reception method>
A reception method according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram for explaining a reception method according to the embodiment. Such a reception method is executed by, for example, a reception device mounted on a vehicle. In the present embodiment, a case will be described in which the receiving apparatus receives a radio broadcast wave including audio data, for example.

  The reception method executed by the reception apparatus according to the present embodiment includes a noise reduction method and a demodulation method. In addition, the reception device includes, for example, a noise reduction device and a demodulation device, and the noise reduction device executes the noise reduction method, and the demodulation device executes the demodulation method.

  The receiving device receives, for example, a radio broadcast wave subjected to amplification processing or A / D conversion processing as a reception signal. In the reception method according to the present embodiment, a noise reduction process and a demodulation process are performed on the received signal, and a demodulated signal is generated.

  Specifically, as shown in FIG. 1A, in the reception method according to the present embodiment, a noise reduction process is performed on the received reception signal as a noise reduction method (step S10). Next, as a demodulation method, the received signal with reduced noise is subjected to demodulation processing to generate a demodulated signal (step S20). The receiving device outputs the generated demodulated signal to, for example, the speaker 30, so that sound corresponding to the sound data included in the radio broadcast wave flows from the speaker 30.

  Next, details of the noise reduction method according to the present embodiment will be described. As shown in FIG. 1A, as noise reduction processing executed by the noise reduction method, the noise reduction device first performs frequency analysis of the received signal (step S11). Specifically, the noise reduction device analyzes the frequency spectrum of the reception signal by generating reception data by performing Fourier transform on the reception signal. That is, the noise reduction device analyzes the frequency distribution of the received signal and calculates the spectrum intensity at each frequency component.

  Subsequently, the noise reduction device detects a noise component from the received data (step S12). Specifically, the noise reduction device detects at least one noise component from the frequency components of the received signal in the priority order according to the auditory characteristic of the audio data based on the analysis result performed in step S11.

  The noise reduction device reduces the noise by reducing the spectrum intensity of the noise component detected in step S12 among the frequency components included in the received signal (step S13). For example, the noise reduction device uses the notch filter to remove the noise component detected in step S12 from the received signal, thereby reducing the spectral intensity of the noise component. The noise reduction device outputs the received signal with reduced noise to the demodulator at the subsequent stage.

  Note that the processing delay due to the frequency analysis and noise detection in steps S11 and S12 may be considered, and the received signal may be delayed in accordance with the processing delay to reduce noise. In this case, a step of delaying the received signal is added before step S13.

  Here, the details of the method of detecting the noise component in the priority order corresponding to the auditory characteristic in step S12 will be described.

  For example, the case where the frequency distribution of the received signal is the distribution shown in FIG. FIG. 1B is a diagram illustrating an example of the frequency distribution of the received signal. In FIG. 1B, the origin is the carrier frequency f0 of the received signal. As shown in FIG. 1B, it is assumed that the received signal has a frequency distribution with frequency components f1 and f2 having a spectrum intensity greater than that of other frequency components. In the example shown in FIG. 1B, the spectral intensity of the frequency component f2 is larger than the spectral intensity of the frequency component f1.

  Here, if the noise reduction device detects a frequency component having the highest spectrum intensity as a noise component, the frequency component f2 is detected and reduced as a noise component in the example of FIG. 1B. However, since the noise component of the frequency component f1 remains in that case, when the frequency component f1 is output from the speaker 30, the user may recognize it as noise.

  In this case, for example, a method of reducing the noise by detecting the frequency component f1 as a noise component and reducing the spectrum intensity of the frequency component f1 in the subsequent processing can be considered. However, since the number of frequency components that can reduce the spectrum intensity is determined depending on the circuit scale or the like, it is not always possible to perform the process of reducing the spectrum intensity for all frequency components having a large spectrum intensity.

  Therefore, in the present embodiment, attention is paid to the audibility characteristic, and the noise component is detected from the frequency components in the priority order according to the audibility characteristic. Here, the auditory sensation characteristic is a characteristic that a person hears with the same sound pressure, that is, with the same spectral intensity, depending on the frequency.

  In this way, a person has an auditory characteristic that a sound is heard differently depending on a frequency. Therefore, for example, a frequency component that is easy to hear is preferentially detected as a noise component over a frequency component that is difficult for humans to hear. For example, when a frequency component having a low frequency among frequency components included in a received signal is easier to hear than a frequency component having a high frequency, the noise reduction device preferentially detects a component having a low frequency among frequency components having a high spectral intensity as a noise component. .

  Specifically, in the example illustrated in FIG. 1B, the noise reduction device compares, for example, the spectrum intensity of each frequency component with a predetermined threshold Th1. Next, the noise reduction device has a number of frequency components that can reduce the spectrum intensity in order from the component having the lowest frequency among the frequency components (frequency components f1 and f2 in FIG. 1B) whose spectrum intensity is greater than the threshold Th1. Is detected as a noise component. For example, when reducing the spectral intensity of one frequency component in step S13 described above, the noise reduction device detects the frequency component f1 as a noise component and reduces the spectral intensity of the frequency component f1.

  Note that the priority order according to the auditory characteristics is not limited to this. For example, when a demodulating device performs attenuation processing, filtering processing, or the like according to auditory characteristics, the noise reduction device detects noise components with a priority according to the auditory characteristics of the demodulated signal subjected to such filtering processing. It may be.

  Thus, by detecting the noise component from the frequency components in the priority order corresponding to the auditory characteristics, the spectral intensity of the frequency component that the user recognizes as noise when output from the speaker 30 can be preferentially reduced. Like that. Thereby, the noise contained in the output sound at the time of outputting a demodulated signal from the speaker 30 can be reduced, and the noise which a user recognizes can be reduced more.

  Hereinafter, the noise reduction device and the reception device having the noise reduction device will be further described.

<2. Receiver 1>
FIG. 2 is a diagram illustrating the receiving device 1 according to the embodiment of the present invention. The receiving device 1 shown in FIG. 2 is mounted on a vehicle such as an automobile. The receiving apparatus 1 transmits an amplitude-modulated radio broadcast wave (hereinafter, referred to as an AM radio broadcast wave) transmitted using, for example, the intermediate wave band of 526.5 kHz to 1606.5 kHz via an antenna (not shown), for example. Receive. The AM radio broadcast wave includes information related to sound (hereinafter referred to as sound data).

  In the following description, it is assumed that a reception signal that has been subjected to amplification processing or A / D conversion processing is input to the receiving apparatus 1 for AM radio broadcast waves received via an antenna, but is not limited thereto. Absent. For example, the receiving device 1 may include an antenna, an amplification unit, and an A / D conversion unit (not shown). In this case, the AM radio broadcast wave received via the antenna of the receiving device 1 performs amplification processing and A / D conversion processing on the AM radio broadcast wave, respectively, and generates a reception signal.

  The receiving apparatus 1 shown in FIG. 2 includes a noise reducing apparatus 10 and a demodulating apparatus 20, and performs noise reduction processing and demodulation processing on the received signal.

<2.1. Noise Reduction Device 10>
The noise reduction device 10 includes a noise detection unit 100 and a reduction unit 150. The noise detection unit 100 detects a noise component from the frequency distribution of the received signal. The reduction unit 150 reduces the noise component detected by the noise detection unit 100.

<2.1.1. Noise Detection Unit 100>
First, details of the noise detection unit 100 will be described. The noise detection unit 100 includes an analysis unit 110, a comparison unit 120, a detection unit 130, and a storage unit 140.

<2.1.1.1. Analysis unit 110>
The analysis unit 110 analyzes the frequency spectrum of the received signal. The analysis unit 110 performs FFT (Fast Fourier Transform) processing on the reception signal, thereby calculating the spectrum intensity at each frequency component and generating reception data. The analysis unit 110 outputs received data including the calculated spectrum intensity at each frequency component to the comparison unit 120.

<2.1.1.2. Comparison unit 120>
The comparison unit 120 compares the threshold Th2 corresponding to the auditory characteristic for each frequency component with the spectrum intensity based on the received data. The comparison unit 120 includes a setting unit 121.

<2.1.1.2.1. Setting unit 121>
The setting unit 121 sets a threshold Th2 corresponding to the auditory sensation characteristic. The threshold value Th2 set by the setting unit 121 will be described with reference to FIGS. FIG. 3 is a diagram for explaining a high cut process that is one of the filter processes performed by the demodulator 20, and FIG. 4 is a diagram for explaining a threshold value Th <b> 2 set by the setting unit 121.

  First, the high cut processing performed in the demodulator 20 will be described with reference to FIG. The AM radio broadcast wave received by the receiving apparatus 1 mainly includes audio data related to human voice. Human speech does not include relatively high frequencies in the human audible range. Therefore, high frequency components included in AM radio broadcast waves are often noise components.

  Therefore, the demodulator 20 that demodulates AM radio broadcast waves often performs high cut processing (attenuation processing) for attenuating the spectrum intensity of high frequency components. Thus, the high frequency noise component can be reduced by performing high cut processing on the demodulated signal obtained by demodulating the received signal by the demodulator 20. For this reason, the audible characteristic of the demodulated signal subjected to the high cut processing in this way is a characteristic in which the sound pressure at a low frequency is large and the sound pressure at a high frequency is small. In the demodulator 20 according to the present embodiment, as shown in FIG. 3, it is assumed that high cut processing for increasing the attenuation amount as the frequency increases is performed.

  As described above, when the high-cut process is performed in the demodulator 20 in the subsequent stage and the noise component of the harmonic is reduced, the setting unit 121 has the frequency according to the auditory characteristic of the reception signal subjected to the high-cut process. A threshold value Th2 that increases as the value increases is set.

  In the example of FIG. 4, the set value 121 sets a threshold value Th <b> 2 that reverses the attenuation amount of the high cut processing performed in the demodulator 20. The threshold value Th2 set by the setting unit 121 is not limited to the example shown in FIG. The threshold value may be a threshold value that increases as the frequency increases according to the high cut processing. For example, the threshold value may be represented by a linear function, or may be a threshold value that increases stepwise. Further, it is assumed that the threshold Th2 set by the setting unit 121 is stored in advance in the storage unit 140, for example.

  The comparison unit 120 calculates a difference between the threshold Th2 set by the setting unit 121 and the spectrum intensity for each frequency component, and outputs the calculated difference and each frequency component in association with each other to the detection unit 130.

<2.1.1.3. Detection unit 130>
Based on the comparison result of the comparison unit 120, the detection unit 130 detects, for example, a frequency component having a spectral intensity greater than the threshold Th2 as a noise component, thereby detecting the noise component with a priority according to the auditory characteristics. The detection unit 130 outputs the detected noise component to the reduction unit 150.

  As described above, the setting unit 121 sets the threshold value Th <b> 2 that increases as the frequency increases in accordance with the auditory characteristics of the received signal that has been subjected to the high cut processing. For this reason, the detection unit 130 detects, for example, a frequency component having a spectrum intensity greater than the threshold Th2 as a noise component, so that the detection unit 130 preferentially detects the noise component as the frequency is lower.

  For example, in the example shown in FIG. 4, the frequency component f1 and the frequency component f3 have substantially the same spectral intensity, but the frequency component f3 higher than the frequency component f1 has a spectral intensity smaller than the threshold Th2. Therefore, the detection unit 130 detects the frequency component f1 as a noise component, but does not detect the frequency component f3 as a noise component.

  Note that the frequency component f3 that is not detected by the detection unit 130 is not recognized as noise by the user because the spectrum intensity is reduced in the high-cut processing of the demodulator 20 at the subsequent stage. Thus, by not detecting the frequency component f3 that is difficult for the user to recognize as noise, the frequency component f1 that the user can easily recognize as noise can be detected as the noise component, and the user can detect the noise as the noise. It is possible to improve the detection accuracy of easily recognized noise components.

  Further, when the number of frequency components that can reduce the spectrum intensity is limited in the reduction unit 150 described later, the detection unit 130 may detect the noise component according to the number. In this case, the detection unit 130 detects at least one or more noise components according to, for example, the difference between the spectrum intensity calculated by the comparison unit 120 and the threshold Th2.

  Specifically, the detection unit 130 detects noise components in order from the higher frequency component calculated by the comparison unit 120 among the frequency components having a spectral intensity greater than the threshold Th2. For example, a case will be described where the number of frequency components whose spectral intensity can be reduced by the reduction unit 150 is “1” and the received signal has the frequency distribution shown in FIG. In this case, the detection unit 130 detects, as a noise component, the frequency component f1 having a large difference calculated by the comparison unit 120 among the frequency components f1 and f2 having a spectral intensity greater than the threshold Th2.

  Here, it is assumed that the threshold Th1 having a constant value is compared with the spectrum intensity. That is, if noise components are simply detected in order of increasing spectrum intensity, the frequency component f2 having the highest spectrum intensity is detected as a noise component, and the frequency component f1 remains in the received signal. The frequency component f1 is less likely to be attenuated by the subsequent high-cut processing than the frequency component f2, and may be recognized as noise by the user.

  However, the detection unit 130 according to the present embodiment detects a noise component according to the difference between the spectrum intensity and the threshold value Th2. As a result, it is possible to preferentially detect a frequency component that is not easily attenuated by the subsequent high-cut processing, that is, is likely to be recognized as noise by the user.

<2.1.1.4. Storage unit 140>
The storage unit 140 in FIG. 2 stores information necessary for processing performed by each unit of the noise detection unit 100, such as the threshold Th2. In addition, the storage unit 140 stores processing results performed by each unit of the noise detection unit 100.

  In addition, although the noise detection part 100 shall be provided with the memory | storage part 140 here, it is not restricted to this. For example, the noise reduction device 10 may include the storage unit 140 or the reception device 1.

  The storage unit 140 is a semiconductor memory device such as a RAM (Random Access Memory) or a flash memory, or a storage device such as a hard disk or an optical disk.

<2.1.2. Reduction unit 150>
The reduction unit 150 illustrated in FIG. 2 reduces the spectral intensity of the noise component detected by the detection unit 130. The reduction unit 150 includes, for example, at least one notch filter. The reduction unit 150 uses the frequency of the noise component detected by the detection unit 130 as a stop band, attenuates the spectral intensity of the stop band from the received signal, and removes the noise component, thereby reducing the noise of the received signal. The reduction unit 150 outputs the received signal from which the noise component has been removed (reduced) to the demodulator 20 by reducing the spectral intensity of the noise component.

  Note that the number of noise components detected by the detection unit 130 is determined by the number of noise components whose spectral intensity is reduced by the reduction unit 150. That is, the number of notch filters included in the reduction unit 150 is the number of noise components detected by the detection unit 130.

<2.2. Demodulator 20>
The demodulator 20 includes a demodulator and an attenuator (not shown), for example. The demodulator 20 performs amplitude demodulation processing on the received signal whose noise has been reduced by the noise reduction device 10 to generate a demodulated signal, and performs high-cut processing or the like on the demodulated signal. Generate. Such an audio signal is a signal corresponding to the audio data included in the received signal.

  Demodulator 20 outputs the generated demodulated signal to, for example, speaker 30. Thereby, the user listens to the AM radio broadcast by the sound signal flowing from the speaker. Since such an audio signal is generated from a received signal with reduced noise, the user can listen to an audio signal with less noise.

<3. Noise reduction processing>
The noise reduction process performed by the noise reduction apparatus 10 will be described with reference to FIG. FIG. 5 is a flowchart showing noise reduction processing according to the present embodiment. In the noise reduction process, for example, the noise reduction process is executed in response to the reception device 1 receiving a reception signal. The noise reduction process is repeatedly executed at predetermined time intervals while the reception device 1 is receiving a reception signal.

  First, the noise reduction device 10 analyzes the frequency of the received signal (step S101). Next, the noise reduction apparatus 10 compares the spectrum intensity of the analyzed frequency component of the received signal with the threshold value Th2 (step S102). As a result of comparison, when the spectrum intensity is equal to or less than the threshold Th2 (step S102; No), the noise reduction apparatus 10 determines that the frequency component of the spectrum intensity is not a noise component, and proceeds to step S104.

  On the other hand, if the comparison result shows that the spectrum intensity is greater than the threshold Th2 (step S102; Yes), the noise reduction apparatus 10 determines the frequency component of the spectrum intensity as a noise component candidate (step S103).

  Next, the noise reduction apparatus 10 determines whether or not the spectral intensity and the threshold value Th2 have been compared for all frequency components of the received signal (step S104). If there is a frequency component for which threshold comparison has not been performed (step S104; No), the process returns to step S102.

  When threshold comparison is performed for all frequency components included in the received signal (step S104; Yes), the noise reduction apparatus 10 starts from a noise component candidate in a predetermined number in descending order of the difference between the spectrum intensity and the threshold Th2. The noise component is detected by selecting the noise component (step S105). The noise reduction apparatus 10 reduces the noise of the received signal by attenuating and reducing the spectral intensity of the noise component detected in step S105 (step S106).

  As described above, the noise reduction device 10 according to the present embodiment can detect and reduce the noise component according to the auditory characteristics by setting the threshold Th2 according to the high cut processing performed by the demodulation device 20. . The receiving device 1 can reduce the noise included in the output sound by demodulating the received signal whose noise has been reduced by the noise reducing device 10 using the demodulating device 20.

<4. Modification>
As mentioned above, although embodiment of this invention has been described, this invention is not limited to the said embodiment, A various deformation | transformation is possible. Below, such a modification is demonstrated. All the forms including the above embodiment and the forms described below can be appropriately combined.

<4.1. Modification 1>
A first modification of the present embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 is a diagram illustrating a configuration of the receiving device 2 according to the first modification, and FIG. 7 is a diagram illustrating an example of spectrum intensity correction according to the first modification.

  The noise reduction device 11 of the reception device 2 according to this modification is different from the noise reduction device 10 illustrated in FIG. 2 in that a correction unit 160 is provided instead of the setting unit 121. In addition, the same code | symbol is attached | subjected to the same structure as the receiver 1 shown in FIG. 2, and description is abbreviate | omitted.

  The correction unit 160 of the noise reduction device 11 corrects the spectrum intensity of each frequency component according to the auditory characteristic based on the analysis result by the analysis unit 110. For example, as described above, when the high-cut process is performed in the demodulator 20, the correction unit 160 corrects the spectrum intensity of each frequency component according to the attenuation amount of the high-cut process.

  An example of correction performed by the correction unit 160 will be described with reference to FIG. For example, when the demodulator 20 performs the high cut processing shown in FIG. 3 on the received signal, the correction unit 160 attenuates, for example, the spectrum intensity of each frequency component by an attenuation amount that is attenuated by the high cut processing. The correction unit 160 outputs the spectrum intensity attenuated for each frequency component to the comparison unit 122.

  The comparison unit 122 compares the spectrum intensity corrected by the correction unit 160 with a predetermined threshold Th1, and outputs the comparison result to the detection unit 130. Specifically, the comparison unit 122 calculates a difference between the spectral intensity and a predetermined threshold Th1, and outputs the frequency component having a spectral intensity greater than the threshold Th1 to the detected difference in association with the calculated difference.

  In this way, by correcting the spectrum intensity according to the auditory characteristic by the correction unit 160, it is possible to detect and reduce the noise component according to the auditory characteristic. The receiving device 2 can reduce the noise contained in the output sound by demodulating the received signal whose noise has been reduced by the noise reducing device 11 with the demodulating device 20.

<4.2. Modification 2>
FIG. 8 is a diagram illustrating a configuration of the receiving device 3 according to the second modification. The noise reduction device 12 of the reception device 3 according to this modification is different from the noise reduction device 10 shown in FIG. 2 in that an intensity correction unit 170 is provided. In addition, the same code | symbol is attached | subjected to the same structure as the receiver 1 shown in FIG. 2, and description is abbreviate | omitted.

  The noise reduction device 12 according to the second modification improves the detection accuracy of the noise component by the detection unit 130 by reducing the spectral intensity of the frequency component related to the audio data included in the received signal by the intensity correction unit 170. is there.

  The receiving device 3 receives an AM radio broadcast wave as a received signal. As shown in FIG. 9, in AM radio broadcasting, a signal is transmitted with a predetermined bandwidth around the carrier frequency f0. FIG. 9 shows a case where the predetermined bandwidth is 14 kHz (f0 ± 7 kHz). FIG. 9 is a diagram illustrating an example of the spectrum distribution of the received signal.

  As shown in FIG. 9, the signals transmitted in the AM radio broadcast are the same in the bandwidth Wfu (upper sideband) on the high frequency side and the bandwidth Wfd (lower sideband) on the low frequency side from the carrier frequency f0. It becomes frequency distribution.

  In this modification, paying attention to this point, by comparing the spectral intensities of the upper sideband Wfu and the lower sideband Wfd of the received signal, the component corresponding to the audio data of the received signal is reduced, and the noise component is detected. Improve accuracy.

  Specifically, the intensity correction unit 170 corrects the spectral intensity of the frequency component in accordance with the spectral intensity of the upper sideband Wfu and the lower sideband Wfd of the received signal, so that the component corresponding to the audio data of the received signal Reduce. Note that the spectral intensity of the carrier frequency f0 is not used for correcting spectral intensity, detecting noise, or the like by removing it with a notch filter, for example.

  An example of correction performed by the intensity correction unit 170 will be described with reference to FIG. FIG. 10 is a diagram illustrating an example of the spectrum intensity distribution corrected by the intensity correction unit 170.

  For example, the intensity correction unit 170 subtracts the spectrum intensity of the corresponding lower sideband Wfd from the spectrum intensity of the upper sideband Wfu of the received signal. Specifically, the intensity correction unit 170 subtracts the spectrum intensity of the lower sideband Wfd from the spectrum intensity of the upper sideband Wfu located at an equal distance from the carrier frequency f0, for example.

  As described above, a signal transmitted by AM radio broadcasting has an axisymmetric frequency distribution centering on the carrier frequency f0 in the upper sideband Wfu and the lower sideband Wfd. Therefore, for example, when the spectral intensity of the lower sideband Wfd is subtracted from the upper sideband Wfu of the received signal, the frequency distribution after the subtraction has a spectral intensity of the signal component transmitted by AM radio broadcasting substantially zero as shown in FIG. Thus, a distribution in which noise components remain is obtained. Note that although the spectral intensity after subtraction may be a negative value, FIG. 10 shows the absolute value of the corrected spectral intensity in order to simplify the illustration.

  In this way, by calculating the difference between the upper sideband Wfu and the lower sideband Wfd of the received signal by the intensity correction unit 170, the noise component of the received signal can be extracted. The intensity correction unit 170 outputs the subtracted spectrum intensity to the comparison unit 120.

  If the spectrum intensity is corrected by the intensity correction unit 170, the corrected spectrum intensity value may be negative. In this case, the setting unit 121 of the comparison unit 120 may set a positive threshold value Th2 and a negative threshold value (not shown) obtained by inverting the signs of the positive threshold value Th2, or an intensity correction unit. 170 may output the absolute value of the subtraction result to the comparison unit 120.

  Thus, the noise component of the received signal can be emphasized by correcting the spectral intensity of the frequency component according to the spectral intensity of the upper sideband Wfu and the lower sideband Wfd of the received signal by the intensity correcting unit 170. And the noise component detection accuracy can be improved.

<4.3. Other variations>
In the embodiment and the modification described above, noise detection is performed according to the audibility characteristic by detecting the noise component in the priority order according to the high cut processing performed by the demodulator 20, but according to the audibility characteristic. Noise detection is not limited to this. For example, noise detection may be performed according to auditory characteristics by detecting a noise component according to whether the electric field strength of the received signal is strong or sudden, or whether an interference wave from an adjacent base station is received.

  Here, for example, a description will be given of an example in which noise components are detected in priority order according to the magnitude of the electric field strength of the received signal. If the electric field strength of the received signal is low, noise components are likely to be included in the received signal. Therefore, as the electric field strength of the received signal is lower, the setting unit 121 of the noise reduction apparatus 10 illustrated in FIG. 2 sets the threshold value so that the threshold value on the high frequency side becomes a lower value, for example.

  As described above, when the electric field strength of the received signal is low, the detection accuracy of the noise component included in the received signal can be improved by facilitating detection of a high frequency component as a noise component.

  Alternatively, the setting unit 121 of the noise reduction device 10 illustrated in FIG. 2 may set a threshold value having a lower value as compared with the case where the electric field strength of the received signal is lower. Thereby, even when the electric field strength of the received signal is low, the detection accuracy of the noise component included in the received signal can be improved.

  In addition, when the demodulator 20 changes the attenuation amount according to the electric field strength of the received signal in the high cut processing, the setting unit 121 of the noise reduction device 10 may set a threshold value according to the changed attenuation amount. Good. Thereby, the noise component contained in the received signal can be detected according to the electric field strength of the received signal and the high cut processing.

  In the above-described example, the case where the noise component is detected according to the electric field strength of the received signal has been described, but the present invention is not limited to this. For example, the noise component may be detected according to the measurement result of the auditory sensation characteristic by experiments or the like. In this case, the threshold value Th2 set by the setting unit 121 in FIG. 2 may be determined based on the measurement result. Alternatively, based on the measurement result, the correction unit 160 in FIG. 6 may determine a correction amount for correcting the spectrum intensity.

  As described above, by determining the threshold Th2 and the correction amount according to the measurement result of the auditory characteristic, the noise component can be detected in the priority order according to the actual auditory characteristic, and the noise component that is easy for humans to hear is more enhanced. It can be detected with high accuracy.

<5. Hardware configuration>
The noise reduction apparatuses 10 to 12 according to the present embodiment and the modifications can be realized by a computer 600 having a configuration illustrated as an example in FIG. FIG. 11 is a hardware configuration diagram illustrating an example of a computer that implements the functions of the noise reduction apparatuses 10 to 12.

  The computer 600 includes a CPU (Central Processing Unit) 610, a ROM (Read Only Memory) 620, a RAM (Random Access Memory) 630, and an HDD (Hard Disk Drive) 640. The computer 600 also includes a media interface (I / F) 650, a communication interface (I / F) 660, and an input / output interface (I / F) 670.

  The computer 600 may include an SSD (Solid State Drive), and the SSD may execute a part or all of the functions of the HDD 640. Further, an SSD may be provided instead of the HDD 640.

  The CPU 610 operates based on a program stored in at least one of the ROM 620 and the HDD 640 and controls each unit. The ROM 620 stores a boot program executed by the CPU 610 when the computer 600 starts up, a program depending on the hardware of the computer 600, and the like. The HDD 640 stores a program executed by the CPU 610, data used by the program, and the like.

  The media I / F 650 reads programs and data stored in the storage medium 680 and provides them to the CPU 610 via the RAM 630. The CPU 610 loads such a program from the storage medium 680 onto the RAM 630 via the media I / F 650, and executes the loaded program. Alternatively, the CPU 610 executes a program using such data. The storage medium 680 is, for example, a magneto-optical recording medium such as a DVD (Digital Versatile Disc), an SD card, or a USB memory.

  The communication I / F 660 receives data from other devices via the network 690 and sends the data to the CPU 610, and transmits the data generated by the CPU 610 to other devices via the network 690. Alternatively, the communication I / F 660 receives a program from another device via the network 690, sends the program to the CPU 610, and the CPU 610 executes the program.

  The CPU 610 controls a display device such as a display, an output unit such as a speaker 30, and an input unit such as a keyboard, a mouse, and a button via the input / output I / F 670. The CPU 610 acquires data from the input unit via the input / output I / F 670. In addition, the CPU 610 outputs the generated data to the display unit or the output unit via the input / output I / F 670.

  For example, when the computer 600 functions as the noise reduction devices 10 to 12, the CPU 610 of the computer 600 executes a program loaded on the RAM 630, thereby analyzing the analysis unit 110, the comparison unit 120, the detection unit 130, and the reduction unit 150. The functions of the correction unit 160 and the intensity correction unit 170 are realized.

  For example, the CPU 610 of the computer 600 reads these programs from the storage medium 680 and executes them, but as another example, these programs may be acquired from other devices via the network 690. Further, the HDD 640 can store information stored in the storage unit 140.

  As described above, the noise reduction apparatuses 10 to 12 according to the present embodiment and the modification include the analysis unit 110, the detection unit 130, and the reduction unit 150. The analysis unit 110 analyzes the frequency spectrum of the received signal. Based on the analysis result of the analysis unit 110, the detection unit 130 detects at least one noise component from the frequency components included in the reception signal in a priority order corresponding to the audibility characteristics of the reception signal. The reduction unit 150 reduces the noise component detected by the detection unit 130.

  As a result, the noise reduction devices 10 to 12 according to the present embodiment and the modified example output the output sound flowing from the speaker 30 when the demodulated signal obtained by demodulating the received signal by the demodulator 20 at the subsequent stage is output from the speaker 30 or the like. The included noise can be reduced.

  In addition, the detection units 130 of the noise reduction apparatuses 10 to 12 according to the present embodiment and the modified example perform noises in the order according to the high-frequency component attenuation process (high cut process) performed according to the auditory characteristic in the demodulation process of the received signal. Detect ingredients.

  As a result, the noise reduction devices 10 to 12 can detect a noise component from frequency components having a small attenuation amount by the attenuation processing in the demodulator 20 at the subsequent stage, and detect a noise component that is easy for the user to recognize as noise. Accuracy can be improved.

  The noise reduction apparatus 10 according to the present embodiment further includes a comparison unit 120 that compares the threshold Th2 corresponding to the auditory characteristic with the spectrum intensity of the frequency component based on the analysis result by the analysis unit 110, and the detection unit 130 includes Based on the comparison result by the comparison unit 120, a frequency component having a spectral intensity equal to or higher than the threshold Th2 is detected as a noise component.

  Thereby, the noise reduction apparatus 10 can detect the noise component according to the auditory sensation characteristic by threshold value comparison, and can improve the detection accuracy of the noise component that the user can easily recognize as noise.

  In addition, the comparison unit 120 of the noise reduction device 10 according to the present embodiment includes a setting unit 121 that sets a threshold Th2 according to the attenuation amount of the high-frequency component attenuation process performed according to the auditory characteristic in the demodulation process of the received signal. Prepare.

  Thereby, the noise reduction apparatus 10 can detect a noise component from the frequency components with a small attenuation amount by the attenuation process performed by the demodulator 20 in the subsequent stage by the threshold comparison, and the noise component that the user can easily recognize as noise is detected. Detection accuracy can be improved.

  The noise reduction device 11 according to the present modification further includes a correction unit 160 that corrects the spectral intensity of the frequency component according to the auditory characteristic based on the analysis result by the analysis unit 110, and the detection unit 130 includes the correction unit 160. A noise component is detected based on the corrected spectrum intensity.

  Thereby, the noise reduction apparatus 11 can detect the noise component according to the auditory characteristic, and can improve the detection accuracy of the noise component that the user can easily recognize as noise.

  Further, the correction unit 160 of the noise reduction device 11 according to the present modification corrects the spectrum intensity according to the attenuation amount of the high-frequency component attenuation process performed according to the auditory characteristic in the demodulation process of the received signal.

  As a result, the noise reduction device 11 can detect a noise component from frequency components having a small attenuation amount by the attenuation processing in the demodulator 20 at the subsequent stage, and the noise component detection accuracy that the user can easily recognize as noise is improved. Can be improved.

  Further, the noise reduction device 12 according to the present modification corrects the spectrum intensity of the frequency component according to the spectrum intensity of the upper sideband Wfu and the lower sideband Wfd of the received signal based on the analysis result by the analysis unit 110. An intensity correction unit 170 is further provided. The detection unit 130 of the noise reduction device 12 detects a noise component based on the spectrum intensity corrected by the intensity correction unit 170.

  Thereby, the noise reduction apparatus 12 can emphasize the noise component of a received signal, and can improve the detection accuracy of a noise component.

  In addition, the noise reduction method according to the present embodiment and the modified example is applied to the received signal in the priority order according to the auditory characteristic of the received signal based on the analysis step of analyzing the frequency spectrum of the received signal and the analysis result of the analyzing step. A detection step of detecting at least one noise component from the included frequency components, and a reduction step of reducing the noise component detected in the detection step.

  Thus, when the demodulated signal obtained by demodulating the received signal by the demodulator 20 at the subsequent stage is output from the speaker 30 or the like by the noise reduction method according to the present embodiment and the modification, the noise included in the output sound flowing from the speaker 30 Can be reduced.

  Further effects and modifications can be easily derived by those skilled in the art. Thus, the broader aspects of the present invention are not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications can be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

1-3 Receiving devices 10-12 Noise reduction device 20 Demodulation device 110 Analysis unit 120, 122 Comparison unit 121 Setting unit 130 Detection unit 140 Storage unit 150 Reduction unit 160 Correction unit 170 Strength correction unit

Claims (6)

An analysis unit for analyzing the frequency spectrum of the received signal;
Based on the analysis result by the analysis unit, a detection unit that detects at least one noise component from among the frequency components included in the reception signal in a priority order according to the auditory characteristics of the reception signal;
A reduction unit for reducing the noise component detected by the detection unit;
A noise reduction device comprising: The detector is
The noise reduction device according to claim 1, wherein the noise components are detected in an order according to processing performed according to the auditory characteristic in demodulation processing of the received signal. Based on the analysis result by the analysis unit, further comprising a comparison unit that compares the threshold according to the auditory characteristics and the spectral intensity of the frequency component,
The detector is
The noise reduction device according to claim 1, wherein the frequency component having the spectral intensity equal to or greater than the threshold is detected as the noise component based on a comparison result by the comparison unit. Based on the analysis result by the analysis unit, further comprising a correction unit for correcting the spectral intensity of the frequency component according to the auditory characteristics,
The detector is
The noise reduction device according to any one of claims 1 to 3, wherein the noise component is detected based on the spectrum intensity corrected by the correction unit. Based on the analysis result by the analysis unit, further comprising an intensity correction unit that corrects the spectrum intensity of the frequency component according to the spectrum intensity of the upper sideband and the lower sideband of the received signal,
The detector is
The noise reduction device according to any one of claims 1 to 4, wherein the noise component is detected based on the spectrum intensity corrected by the intensity correction unit. An analysis process for analyzing the frequency spectrum of the received signal;
A detection step of detecting at least one noise component from frequency components included in the reception signal in a priority order according to the auditory characteristic of the reception signal based on the analysis result of the analysis step;
A reduction step of reducing the noise component detected in the detection step;
A noise reduction method comprising:

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