JP6890010B2 - Noise detection device and noise detection method - Google Patents

Description

The disclosed embodiments relate to noise detection devices and noise detection methods.

The received signal that receives the broadcast wave may contain noise. Noise is generated, for example, during a switching process for power conversion of a vehicle battery, and is superimposed on a received signal when receiving a broadcast wave. Conventionally, a noise detection device for detecting noise has been known in order to remove noise from a received signal containing noise (see, for example, Patent Document 1).

In the frequency spectrum of the received signal including noise, the broadcast wave is line-symmetrical (hereinafter referred to as "symmetrical") in the upper wave band and the lower wave band centered on the frequency of the carrier wave, and the noise is a specific frequency. It is known to be asymmetric in the upper and lower bands because it appears only in. Therefore, it is conceivable to calculate the asymmetric component from the frequency spectrum and detect the asymmetric component as noise.

Japanese Unexamined Patent Publication No. 2013-9066

However, in a broadcast wave such as a radio, a plurality of broadcast waves may interfere with each other due to SFN (Single Frequency Network) or the like, and the broadcast wave may become asymmetric in the upper wave band and the lower wave band in the frequency spectrum.

In such a case, if the asymmetric component between the upper wave band and the lower wave band is detected as noise, the broadcast wave may be erroneously detected as noise.

One aspect of the embodiment is made in view of the above, and an object thereof is to accurately detect noise.

The noise detection device according to one aspect of the embodiment includes a calculation unit, a symmetry unit, and a detection unit. The calculation unit calculates the asymmetric component between the upper wave band of the frequency spectrum and the lower wave band of the frequency spectrum based on the frequency spectrum of the received signal. The symmetrization section corrects the frequency spectrum based on the asymmetric component to make it symmetric. The detection unit detects noise based on the symmetrized frequency spectrum symmetrized by the symmetry unit.

According to one aspect of the embodiment, noise can be detected accurately.

FIG. 1 is a diagram showing an outline of noise detection according to an embodiment. FIG. 2 is a schematic block diagram showing a configuration of a receiver according to the first embodiment. FIG. 3 is a flowchart illustrating the noise detection process according to the first embodiment. FIG. 4 is a diagram showing an example of the first frequency spectrum. FIG. 5 is a diagram showing a second frequency spectrum in which the first frequency spectrum of FIG. 4 is smoothed in the time direction. FIG. 6 is a diagram showing a first difference in the second frequency spectrum of FIG. FIG. 7 is a diagram showing a smoothed first difference obtained by smoothing the first difference of FIG. 6 in the frequency direction. FIG. 8 is a diagram showing an asymmetric component calculated based on the first difference after smoothing in FIG. 7. FIG. 9 is a diagram showing a third frequency spectrum in which the first frequency spectrum of FIG. 4 is symmetrical. FIG. 10 is a diagram showing a fourth frequency spectrum obtained by smoothing the third frequency spectrum of FIG. 9 in the time direction. FIG. 11 is a second difference in the fourth frequency spectrum of FIG. FIG. 12 is a schematic block diagram showing a configuration of the receiver according to the second embodiment. FIG. 13 is a flowchart illustrating the noise detection process according to the second embodiment. FIG. 14 is a diagram showing an example of the second frequency spectrum. FIG. 15 is a diagram showing the detection result of the peak frequency with respect to the frequency spectrum of FIG. FIG. 16 is a diagram showing the detection result of the symmetrical peak frequency with respect to the detection result of the peak frequency of FIG. FIG. 17 is a diagram showing a second frequency spectrum in which a peak cut is performed with respect to the frequency spectrum of FIG.

Hereinafter, the noise detection device and the noise detection method disclosed in the present application will be described with reference to the accompanying drawings. The present invention is not limited to the embodiments shown below.

Further, in the following embodiment, a case where the receiver is mounted on the vehicle and the noise detection device is mounted on the radio which is the receiver will be described. The receiver shall receive an AM (Amplitude Modulation) modulated radio broadcast wave (hereinafter referred to as a received signal).

The receiver is not limited to the radio, and may be any communication device capable of receiving the AM-modulated signal. Further, the receiver is not limited to a vehicle, and may be mounted on, for example, a train, a moving body such as an airplane, an electric appliance such as a radio receiver or a personal computer.

The received signal includes a carrier wave and a signal wave which is an audio signal. In addition, the received signal may include, for example, noise generated during a switching process for power conversion of a vehicle battery.

In the frequency spectrum obtained by FFT (Fast Fourier Transform) processing of the received signal containing noise, it is known that the signal wave appears symmetrically in the upper wave band and the lower wave band around the frequency of the carrier wave. ing. It is also known that noise appears only in the characteristic frequency and appears asymmetrically in the upper and lower bands. For example, noise appears only at specific frequencies in the upper wave band.

In addition, "symmetrical in the upper wave band and the lower wave band" means that the frequencies of the upper wave band and the lower wave band are symmetrical with respect to the frequency of the carrier wave, and the level of the upper wave band and the level of the lower wave band. Includes a state in which the absolute value of the difference from and is smaller than the predetermined value. The predetermined value is a preset value, and is a value that can be determined whether or not it is noise. That is, the predetermined value is a value that is determined not to be noise when the absolute value of the difference between the level of the upper wave band and the level of the lower wave band is smaller than the predetermined value.

Since noise appears asymmetrically in the upper wave band and the lower wave band, the noise is detected by comparing the upper wave band and the lower wave band and detecting the asymmetric component between the upper wave band and the lower wave band. Can be detected.

However, when the receiver receives the received signal in a state where the broadcast wave due to SFN, multipath, adjacent interference, or the like interferes, the signal wave may appear asymmetrically in the upper wave band and the lower wave band. Therefore, when noise is detected by comparing the upper wave band and the lower wave band, a signal having a frequency that is not originally determined to be noise is erroneously detected as noise, and the noise cannot be detected accurately. There is a risk.

Therefore, according to the following method, the noise detection device can accurately detect noise even when the broadcast wave interferes with the SFN or the like.

The noise detection device performs FFT processing on the received signal and calculates the frequency spectrum (S1). The noise detection device calculates the asymmetric component between the upper wave band and the lower wave band based on the frequency spectrum (S2).

The noise detection device uses an asymmetric component to correct the frequency spectrum so that the upper wave band and the lower wave band are symmetrical with respect to the carrier wave, and symmetry the frequency spectrum (S3). As a result, it is possible to obtain a frequency spectrum in which the influence of interference of broadcast waves is reduced.

Then, the noise detection device detects noise using a symmetrized frequency spectrum (symmetrized frequency spectrum) (S4). The noise detector compares the upper wave band of the symmetric frequency spectrum with the lower wave band of the symmetric frequency spectrum, and the absolute value of the difference between the level of the upper wave band and the level of the lower wave band is A signal having a frequency equal to or higher than a predetermined value is determined to be noise, and noise is detected.

In this way, the noise detection device detects noise using a frequency spectrum that is corrected and symmetric based on the asymmetric component of the upper wave band and the lower wave band, so that even in a state where the broadcast wave interferes. Noise can be detected accurately.

Next, the receiver 1 according to the first embodiment will be described with reference to FIG. FIG. 2 is a schematic block diagram showing the configuration of the receiver 1 according to the first embodiment.

The receiver 1 includes an RF / IF unit 2, an A / D conversion unit 3, an FFT unit 4, a noise removing device 5, and an output unit 6. Further, the antenna 20 is connected to the receiver 1. The noise removing device 5 is also a noise detecting device that detects noise.

The antenna 20 receives a plurality of signals transmitted from various radio broadcasting stations. The received signal received by the antenna 20 includes a carrier wave of a predetermined frequency (for example, RF (Radio Frequency) band), a signal wave which is an audio signal, noise, and the like.

The RF / IF unit 2 extracts and amplifies the broadcast wave signal to be received from the received signal received by the antenna 20, and uses a high frequency signal (RF signal) amplifier circuit, an intermediate frequency signal (IF signal) amplifier circuit, or the like. The IF signal that is configured and the processed signal is output to the A / D conversion unit 3.

The A / D conversion unit 3 converts the IF signal input from the RF / IF unit 2 into a digital signal.

The FFT unit 4 performs FFT processing on the IF signal converted into a digital signal, and calculates the frequency spectrum of the IF signal (hereinafter, referred to as “first frequency spectrum”).

The noise removing device 5 includes a first smoothing unit 50, a first difference calculation unit 51, a second smoothing unit 52, an asymmetric component calculation unit 53, a symmetry unit 54, and a third smoothing unit 55. A second difference calculation unit 56, a noise detection unit 57, and a noise removal unit 58 are provided.

The first smoothing unit 50 smoothes the first frequency spectrum in the time direction, and calculates the frequency spectrum after smoothing in the time direction.

The frequency _{"f j",} the time _{"t i",} and the frequency spectrum after smoothing in the time direction "fft_dB_ave _{(f j, t i)",} the level at time _{t i} "fft_dB _{(f j, t} i) "When" α1 "smoothing time constant, the frequency spectrum fft_dB_ave after smoothing in the time direction _{(f j, t i)} is calculated based on the equation (1) and (2). The equations (1) and (2) are repeatedly calculated for each sampling period, and the smoothed frequency spectrum is updated each time.

Incidentally, "buf_fft_dB _{(f j, t i)"} is a buffer for holding the calculation result. In the formula (1), “f _j ” satisfies the relationship of 1 ≦ f _{j ≦ nfft.} “Nfft” is the FFT order.

The first smoothing unit 50 uses the equations (1) and (2) to obtain a frequency spectrum after smoothing in the time direction based on the first frequency spectrum output from the FFT unit 4 (hereinafter, “second frequency”). "Spectrum") is calculated.

The first difference calculation unit 51 calculates the difference between the upper wave band of the second frequency spectrum and the lower wave band of the second frequency spectrum.

When the difference is "diff_fft_dB _{(f j, t i)",} the difference diff_fft_dB _{(f j, t i)} is calculated based on equation (3).

In addition, "f _j " satisfies the relation of 1 ≦ f _j ≦ nfft / 2.

The first difference calculation unit 51 calculates a difference (hereinafter, referred to as “first difference”) based on the second frequency spectrum using the equation (3).

The second smoothing portion smoothes the first difference in the frequency direction, and calculates the first difference after smoothing in the frequency direction.

The difference after smoothing in the frequency direction to "diff_fft_dB_ave _{(f j, t i)",} the smoothing number to "2m + 1", the difference diff_fft_dB_ave _{(f j, t i)} after smoothing in the frequency direction, wherein Calculated based on (4).

The second smoothing unit 52 calculates the first difference after smoothing in the frequency direction (hereinafter, referred to as “first difference after smoothing”) based on the first difference using the equation (4).

The first difference is calculated based on the second frequency spectrum. Therefore, it can be said that the second smoothing unit 52 smoothes the frequency spectrum in the frequency direction.

The asymmetric component calculation unit 53 calculates the asymmetric component based on the first difference after smoothing. The asymmetric component is calculated in the upper wave band and the lower wave band, respectively.

When the asymmetric component of the upper sideband and "asym_dB _{(f j, t i)",} the asymmetric component of the upper sideband asym_dB _{(f j, t i)} is calculated based on the equation (5). The asymmetric component of the lower sideband _{"asym_dB (nfft-f j, t} i) " When, asymmetric component _{asym_dB (nfft-f j, t} i) of the lower sideband, on the basis of the equation (6) is calculated Will be done.

The asymmetric component calculation unit 53 calculates the asymmetric component based on the first difference after smoothing using the equations (5) and (6).

The symmetry unit 54 corrects the first frequency spectrum based on the asymmetric component to make it symmetric, and calculates the symmetric frequency spectrum (hereinafter, referred to as “third frequency spectrum”).

If the third frequency spectrum to the "comp_asym_dB _{(f j, t i)",} the third frequency spectrum comp_asym_dB _{(f j, t i)} is calculated based on equation (7).

The "asym_dB (fj, ti)" is _{"asym_dB (nfft-f j, t} i) " of the formula (6) contains, based on the asymmetric component, the first frequency spectrum, the upper sideband And symmetry is done in the lower wave band.

By making the first frequency spectrum symmetric by the asymmetric component, in the third frequency spectrum, the upper wave band and the lower wave band are more symmetric than the first frequency spectrum around the frequency of the carrier wave.

The third smoothing unit 55 smoothes the third frequency spectrum in the time direction, and calculates the smoothed third frequency spectrum (hereinafter, referred to as “fourth frequency spectrum”) in the time direction. The third smoothing unit 55 calculates the fourth frequency spectrum based on the third frequency spectrum using the above equations (1) and (2).

The second difference calculation unit 56 calculates the difference between the upper wave band of the fourth frequency spectrum and the lower wave band of the fourth frequency spectrum (hereinafter, referred to as “second difference”). The second difference calculation unit 56 calculates the second difference based on the fourth frequency spectrum using the above formula (3).

The noise detection unit 57 detects noise based on the second difference. Specifically, the noise detection unit 57 has a predetermined value of the absolute value of the second difference, that is, the absolute value of the difference between the level of the upper wave band of the fourth frequency spectrum and the level of the lower wave band of the fourth frequency spectrum. A frequency larger than is detected as a noise frequency.

The noise removing unit 58 removes noise based on the second difference. For example, the noise removing unit 58 calculates a coefficient based on the second difference so as to reduce the noise, and removes the noise based on the magnitude of the first difference using the coefficient. The larger the second difference, the larger the amount of decrease in the level at the noise frequency.

The output unit 6 converts the signal output from the noise removing device 5 into an analog signal and outputs the signal to an external device such as a speaker.

Next, the noise detection process will be described with reference to FIG. FIG. 3 is a flowchart illustrating the noise detection process.

The first smoothing unit 50 smoothes the first frequency spectrum in the time direction and calculates the second frequency spectrum (S10).

By smoothing the first frequency spectrum in the time direction by the first smoothing unit 50, for example, the second frequency spectrum shown in FIG. 5 is calculated from the first frequency spectrum shown in FIG. 4. FIG. 4 is a diagram showing an example of the first frequency spectrum. FIG. 5 is a diagram showing a second frequency spectrum in which the first frequency spectrum of FIG. 4 is smoothed in the time direction.

In the first frequency spectrum shown in FIG. 4, the upper wave band and the lower wave band are not symmetrical with respect to the frequency fc of the carrier wave due to the interference of a plurality of broadcast waves by SFN or the like. In the first frequency spectrum shown in FIG. 4, it is assumed that the received signal does not include noise. The second frequency spectrum is a gentle frequency spectrum in which level fluctuations are suppressed with respect to the first frequency spectrum.

The first difference calculation unit 51 calculates the first difference, which is the difference between the upper wave band and the lower wave band, based on the second frequency spectrum (S11).

FIG. 6 shows an example of the first difference calculated by the first difference calculation unit 51. FIG. 6 is a diagram showing a first difference in the second frequency spectrum of FIG. The first difference becomes large due to the interference of a plurality of broadcast waves due to SFN or the like.

The second smoothing unit 52 smoothes the first difference in the frequency direction, and calculates the first difference after smoothing (S12).

FIG. 7 shows an example of the first difference after smoothing smoothed in the frequency direction by the second smoothing unit 52. FIG. 7 is a diagram showing a smoothed first difference obtained by smoothing the first difference of FIG. 6 in the frequency direction. The first difference after smoothing is a gentle difference in which level fluctuation is suppressed with respect to the first difference.

The asymmetric component calculation unit 53 calculates the asymmetric component based on the first difference after smoothing (S13).

FIG. 8 shows an example of the asymmetric component calculated by the asymmetric component calculation unit 53. FIG. 8 is a diagram showing an asymmetric component calculated based on the first difference after smoothing in FIG. 7. In FIG. 8, the asymmetric component of the upper wave band and the asymmetric component of the lower wave band are shown centering on the frequency fc of the carrier wave.

The symmetry unit 54 symmetry the first frequency spectrum using the asymmetric component and calculates the third frequency spectrum (S14).

FIG. 9 shows an example of a third frequency spectrum in which the first frequency spectrum is symmetric by the symmetry unit 54. FIG. 9 is a diagram showing a third frequency spectrum in which the first frequency spectrum of FIG. 4 is symmetrical. Although it is not completely symmetric due to being symmetric by the symmetry unit 54, in the third frequency spectrum, the upper wave band and the lower wave band are on the carrier wave rather than the first frequency spectrum shown in FIG. It becomes symmetric with respect to the frequency fc.

The third smoothing unit 55 smoothes the third frequency spectrum in the time direction and calculates the fourth frequency spectrum (S15).

FIG. 10 shows an example of the fourth frequency spectrum calculated by the third smoothing unit 55. FIG. 10 is a diagram showing a fourth frequency spectrum obtained by smoothing the third frequency spectrum of FIG. 9 in the time direction. In the fourth frequency spectrum, the upper wave band and the lower wave band are more symmetrical about the frequency fc of the carrier wave than the second frequency spectrum shown in FIG.

The second difference calculation unit 56 calculates the second difference, which is the difference between the upper wave band and the lower wave band, based on the fourth frequency spectrum (S16).

FIG. 11 shows an example of the second difference calculated by the second difference calculation unit 56. FIG. 11 is a diagram showing a second difference in the fourth frequency spectrum of FIG. In the second difference, the difference is smaller than the first difference shown in FIG.

The noise detection unit 57 detects noise based on the second difference (S17).

In the second difference shown in FIG. 11, noise is not detected because the absolute value of the second difference is smaller than the predetermined value at each frequency.

The processing of S10 to S12 is not limited to the above order. For example, the second smoothing unit 52 may smooth the second frequency spectrum smoothed in the time direction in the frequency direction, and the first difference calculation unit 51 may smooth the second frequency spectrum smoothed in the frequency direction. The difference between the upper wave band and the lower wave band (first difference) may be calculated based on the above.

Here, a comparative example in which the noise detection process of the present embodiment is not used and the first frequency spectrum is not symmetric due to the asymmetric component will be described. In the comparative example, for example, noise detection is performed based on the first difference shown in FIG.

In the first difference shown in FIG. 6, the absolute value of the difference at the frequency level included in the regions "A1" to "A3" is equal to or higher than a predetermined value. Such a difference is a difference caused by interference of broadcast waves due to SFN or the like, and is not caused by noise. However, since the absolute value of the difference is equal to or greater than a predetermined value, the frequencies included in the regions "A1" to "A3" may be erroneously detected as noise frequencies in the comparative example. If it is erroneously detected, the levels of these frequencies are lowered, so that the level of the audio signal of the broadcast wave may be lowered.

On the other hand, in the present embodiment, the noise frequency is detected based on the second difference calculated using the third frequency spectrum in which the first frequency spectrum is symmetricalized by the asymmetric component. Therefore, even when the broadcast wave interferes with SFN or the like, it is possible to suppress erroneous detection of the noise frequency as compared with the comparative example. In this way, noise can be detected accurately. In addition, it is possible to prevent the level of the audio signal from dropping.

Further, the asymmetric component is calculated based on the second frequency spectrum smoothed in the time direction. Therefore, the asymmetric component due to the interference of the broadcast wave can be accurately calculated by SFN or the like, and the third frequency spectrum that is accurately symmetrical can be calculated. Therefore, noise can be detected more accurately. In addition, it is possible to prevent the level of the audio signal from dropping.

Further, the asymmetric component is calculated based on the second frequency spectrum smoothed in the frequency direction. Therefore, the asymmetric component due to the interference of the broadcast wave can be accurately calculated by SFN or the like, and the third frequency spectrum that is accurately symmetrical can be calculated. Therefore, noise can be detected more accurately. In addition, it is possible to prevent the level of the audio signal from dropping.

Next, the receiver 1 according to the second embodiment will be described with reference to FIG. FIG. 12 is a schematic block diagram showing the configuration of the receiver 1 according to the second embodiment. Here, the parts different from those of the first embodiment will be mainly described, and the same configurations as those of the first embodiment are designated by the same reference numerals as those of the first embodiment, and detailed description thereof will be omitted.

The noise removing device 5 is symmetrical with the first smoothing unit 50, the peak detection unit 59, the peak cut unit 60, the first difference calculation unit 51, the second smoothing unit 52, and the asymmetric component calculation unit 53. It includes a conversion unit 54, a third smoothing unit 55, a second difference calculation unit 56, a noise detection unit 57, and a noise removal unit 58.

The peak detection unit 59 detects the peak frequency at which the level peaks in the second frequency spectrum.

Specifically, the peak detection unit 59 compares the level of a certain frequency with the level of frequencies before and after the certain frequency. Then, when the level of a certain frequency is larger than the level of the frequencies before and after, it is determined that the level of a certain frequency is the peak. Then, the peak detection unit 59 detects as a peak frequency a frequency having a level equal to or higher than a preset predetermined level among the peak frequencies. The carrier frequency is not detected as the peak frequency.

Further, the peak detection unit 59 detects a peak frequency that appears at a position symmetrical in the upper wave band and the lower wave band with respect to the frequency of the carrier wave as a symmetrical peak frequency. The symmetric peak frequency is a peak frequency that appears at a position that is completely symmetrical in the upper wave band and the lower wave band with the frequency of the carrier wave as the center.

The peak cut unit 60 performs peak cut for lowering the level of the peak frequency detected by the peak detection unit 59 with respect to the second frequency spectrum. For example, the peak cut unit 60 sets the peak frequency level to the average value of the frequency levels before and after the peak frequency, or to a preset level.

The peak cut unit 60 cuts peaks at all peak frequencies, that is, symmetric peak frequencies and asymmetric peak frequencies other than symmetric peak frequencies.

The first difference calculation unit 51 calculates the first difference based on the second frequency spectrum in which the peak cut is performed by the peak cut unit 60. The asymmetric component calculated by the asymmetric component calculation unit 53 based on the first difference has a smaller influence of the peak level than the asymmetric component of the first embodiment.

The second difference calculation unit 56 calculates the second difference using the fourth frequency spectrum in which the third frequency spectrum is smoothed in the time direction. This second difference has a larger difference at the peak frequency than the second difference of the first embodiment.

The noise detection unit 57 detects noise based on the second difference. Specifically, the noise detection unit 57 detects as a noise frequency a frequency excluding the symmetric peak frequency among frequencies in which the absolute value of the second difference is larger than a predetermined value. Noise appears at positions that are asymmetrical in the upper and lower bands around the carrier frequency. Therefore, the noise detection unit 57 determines that the symmetric peak frequency is not the noise frequency, and detects the peak frequency excluding the symmetric peak frequency as the noise frequency. Further, the noise detection unit 57 does not detect the symmetric peak frequency as the noise frequency among the frequencies in which the absolute value of the second difference is larger than the predetermined value.

The noise detection unit 57 may detect all frequencies in which the absolute value of the second difference is larger than a predetermined value as noise frequencies. In this case, when the noise is removed by the noise removing unit 58, the signal having the symmetric peak frequency is not processed as noise. In this case, the noise removing unit 58 has a function as a noise detecting unit 57.

Next, the noise detection process according to the second embodiment will be described with reference to FIG. FIG. 13 is a flowchart illustrating the noise detection process according to the second embodiment.

The first smoothing unit 50 smoothes the first frequency spectrum in the time direction and calculates the second frequency spectrum (S20).

The peak detection unit 59 detects the peak frequency based on the second frequency spectrum (S21) and detects the symmetric peak frequency (S22).

For example, in the second frequency spectrum shown in FIG. 14, the level peaks at the frequencies “B1”, “B2” and “B3”, and the level is equal to or higher than a predetermined level. In this case, as shown in FIG. 15, the peak detection unit 59 detects frequencies “B1”, “B2” and “B3” as peak frequencies. FIG. 14 is a diagram showing an example of the second frequency spectrum. FIG. 15 is a diagram showing the detection result of the peak frequency with respect to the frequency spectrum of FIG. In FIG. 15, when it is the peak frequency, it is “1”. In FIG. 15, for the sake of explanation, a part of frequencies other than the peak frequency is omitted.

In the peak frequency detection result shown in FIG. 15, the peak frequencies “B2” and “B3” are located symmetrically with respect to the carrier frequency fc, and are symmetrical peak frequencies as shown in FIG. FIG. 16 is a diagram showing the detection result of the symmetrical peak frequency with respect to the detection result of the peak frequency of FIG. In FIG. 15, for the sake of explanation, a part of frequencies other than the symmetrical peak frequencies is omitted.

The peak cut unit 60 performs peak cut to lower the level of the peak frequency (S23).

FIG. 17 shows an example of the second frequency spectrum in which the peak cut is performed by the peak cut unit 60. FIG. 17 is a diagram showing a second frequency spectrum in which a peak cut is performed with respect to the frequency spectrum of FIG. In the second frequency spectrum of FIG. 17, the levels at the peak frequencies “B1”, “B2” and “B3” are smaller than the frequency spectrum shown in FIG.

The first difference calculation unit 51 calculates the first difference based on the second frequency spectrum in which the peak is cut (S24).

The second smoothing unit 52 smoothes the first difference in the frequency direction, and calculates the first difference after smoothing (S25).

The asymmetric component calculation unit 53 calculates the asymmetric component based on the first difference after smoothing (S26).

The symmetry unit 54 symmetry the first frequency spectrum using the asymmetric component and calculates the third frequency spectrum (S27).

The third smoothing unit 55 smoothes the third frequency spectrum in the time direction and calculates the fourth frequency spectrum (S28).

The second difference calculation unit 56 calculates the second difference, which is the difference between the upper wave band and the lower wave band, based on the fourth frequency spectrum (S29).

The noise detection unit 57 detects noise based on the second difference (S30).

The peak detection unit 59 may detect the peak frequency based on the first frequency spectrum.

In the second embodiment, the peak frequency is detected by the peak detection unit 59, and the peak cut unit 60 performs peak cut that lowers the level of the peak frequency from the second frequency spectrum. Then, the asymmetric component is calculated by the asymmetric component calculation unit 53 based on the first difference calculated using the second frequency spectrum in which the peak is cut.

Thereby, an asymmetric component having a small influence of the peak frequency level can be calculated, and in the third frequency spectrum in which the first frequency spectrum is symmetric using the asymmetric component, the peak frequency level is the first embodiment. Will be greater than the level of.

Therefore, when the received signal contains noise, the second difference becomes large in the noise frequency, so that the noise can be detected accurately. Further, when the noise reduction amount is calculated according to the second difference when removing the noise, it is possible to suppress the noise reduction amount from becoming small. Therefore, noise can be appropriately removed.

Further, since the symmetric peak frequency is not detected as a noise frequency, a signal having a symmetric peak frequency with a low possibility of noise is not processed as noise. Therefore, it is possible to suppress a decrease in the level of the audio signal.

Next, a modified example of the above embodiment will be described.

In the second embodiment, the peak cut unit 60 performs peak cut at all peak frequencies, but is not limited to this. The peak cut portion 60 may reduce only the level of the peak frequency that appears at asymmetric positions in the upper wave band and the lower wave band, that is, the peak frequency excluding the symmetric peak frequency.

As a result, an asymmetric component that reflects only the peak frequency with a high possibility of noise is calculated. Therefore, in the second difference, the difference becomes large only at the frequency where the possibility of noise is high, and the noise can be detected more accurately by the noise detecting unit 57.

Further, in the above embodiment, the processes in each part and the device may be integrated or separated. For example, the first difference calculation unit 51 and the second difference calculation unit 56 may be integrated into one calculation unit.

Further effects and variations can be easily derived by those skilled in the art. For this reason, the broader aspects of the invention are not limited to the particular details and representative embodiments expressed and described as described above. Therefore, various modifications can be made without departing from the spirit or scope of the general concept of the invention as defined by the appended claims and their equivalents.

1: Receiver 5: Noise removal device 50: First smoothing unit (time-direction smoothing unit)
51: First difference calculation unit 52: Second smoothing unit (frequency direction smoothing unit)
53: Asymmetric component calculation unit (calculation unit)
54: Symmetrization unit 55: Third smoothing unit 56: Second difference calculation unit 57: Noise detection unit (detection unit)
58: Noise removal unit 59: Peak detection unit (peak frequency detection unit)
60: Peak cut part

Claims (8)

A calculation unit that calculates the asymmetric component between the upper wave band of the frequency spectrum and the lower wave band of the frequency spectrum based on the frequency spectrum of the received signal.
A symmetry unit that corrects the frequency spectrum based on the asymmetric component to symmetry the upper wave band of the frequency spectrum and the lower wave band of the frequency spectrum.
A noise detection device including a detection unit that detects noise based on the difference between the upper and lower sidebands of the symmetry frequency spectrum symmetric by the symmetry unit. A time-direction smoothing unit for smoothing the frequency spectrum in the time direction is provided.
The calculation unit
The noise detection device according to claim 1, wherein the asymmetric component is calculated based on the frequency spectrum smoothed in the time direction. A frequency direction smoothing unit for smoothing the frequency spectrum in the frequency direction is provided.
The calculation unit
The noise detection apparatus according to claim 1 or 2, wherein the asymmetric component is calculated based on the frequency spectrum smoothed in the frequency direction. A peak frequency detection unit that detects the peak frequency at which the level peaks in the frequency spectrum, and
It is provided with a peak cut portion that performs a peak cut that lowers the level of the peak frequency.
The calculation unit
The noise detection device according to any one of claims 1 to 3, wherein the asymmetric component is calculated based on the peak-cut frequency spectrum. The peak cut portion is
The noise detection device according to claim 4, wherein the peak cut is performed only at the peak frequency at which the peak appears at an asymmetric position between the upper wave band and the lower wave band. The detection unit
The noise detection device according to claim 4 or 5, wherein the signal having the peak frequency at which the peak appears at symmetrical positions in the upper wave band and the lower wave band is not detected as the noise. The detection unit
Noise is detected based on the difference between the upper and lower sidebands of the smoothed frequency spectrum whose symmetric frequency spectrum is smoothed in the time direction.
The noise detection device according to any one of claims 1 to 6. A calculation step of calculating the asymmetric component between the upper wave band of the frequency spectrum and the lower wave band of the frequency spectrum based on the frequency spectrum of the received signal, and the calculation step.
A symmetry step of correcting the frequency spectrum based on the asymmetric component to symmetry the upper wave band of the frequency spectrum and the lower wave band of the frequency spectrum.
A noise detection method including a detection step of detecting noise based on the difference between the upper and lower sidebands of a symmetric frequency spectrum.

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