JP2008099163A - Noise canceling headphones and noise canceling method for headphones - Google Patents

Abstract

A noise-cancelling headphone that avoids unpleasant noise in the headphones when large environmental noises and sudden high-level noises occur, and does not cause discomfort to the headphone user, and the noises thereof Get a cancellation method.
A cancellation noise generation unit for generating a cancellation noise signal having a phase opposite to that of environmental noise, a mixer for mixing the generated cancellation noise signal and a musical sound signal, and an environmental noise level equal to or higher than a preset threshold value. A noise level detection unit 22 for detecting whether or not, and when the noise level detected by the noise level detection unit 22 is equal to or higher than a threshold, the input level of the environmental noise signal is temporarily limited to the threshold level or lower, When the noise level is equal to or lower than the threshold value, the noise level adjusting unit 24 is configured to release the restriction on the input level of environmental noise.
[Selection] Figure 1

Description

  The present invention relates to a noise canceling headphone and a noise canceling method for the headphone, and particularly, in a case where a noise detecting microphone is arranged outside the headphone, a large noise is generated when a hand touches the microphone part, or It is intended to prevent unpleasant noise from being output when a large environmental noise that cannot be canceled is input, such as when a large wind noise is generated, or when sudden noise is input.

  For example, portable music players such as a tape player, a CD player, and an MD player are widely used. Recently, smaller and larger-capacity portable music players such as a hard disk type and a flash memory type are rapidly spreading. With the spread of portable music players, higher performance headphones are required, and in addition, ambient noise (hereinafter referred to as “environmental noise”) when listening to music in the city or in a vehicle. ) Has been cancelled, and noise-canceling headphones that only allow you to hear music have come to be desired. If environmental noises are mixed with music playback sound, even if the headphones playback sound is high-quality playback sound, the playback sound is drowned out by noise and you cannot enjoy music with high-quality sound. Also, if you try to listen to music in the noise, it will be easy to listen to it by raising the volume, causing the sound to leak from the headphones by raising the volume, and it will be an unpleasant noise source for people around you in the vehicle There is also a problem. With this background, noise-canceling headphones are beginning to become popular.

  Most of the noise canceling headphones on the market at present are analog type noise canceling headphones. This is a method of capturing environmental noise with a microphone incorporated in a headphone, inverting the phase of the captured noise, and adding it to a reproduction signal from a player. The noise that enters the headphones from the outside is canceled by the signal whose phase is inverted, and only the reproduction signal from the player enters the user's ear.

  Recently, digital noise cancellation headphones have also been proposed. An example is shown in FIG. In FIG. 6, reference numeral 50 denotes a digital signal processor (digital signal processing apparatus: hereinafter referred to as “DSP”) which is the main component of a digital noise canceling headphone. The DSP 50 includes a fast Fourier transformer (hereinafter referred to as “FFT”) 54 that performs frequency analysis on a noise signal N captured by a microphone incorporated in a headphone, and a frequency characteristic detection unit 56 that detects frequency characteristics by performing frequency analysis using the FFT 54. And a selection unit 58 that selects a frequency band to be canceled from the detected frequency characteristics, and an inverse Fourier transform that generates a frequency-selected cancellation sound signal -N ″ by performing an inverse Fourier transform on the signal in the selected frequency band. Instrument (hereinafter referred to as “IFFT”) 60. The canceling sound signal -N "is added to the player's reproduction signal S by the adder 64 and output. The adder 64 in this example is an analog type, and the canceling sound signal -N" composed of an analog signal and the reproduction signal. Add S. The noise N that enters and enters the headphones is synthesized with the cancellation sound -N "to become a signal 66 of NN", and most of the noise N is canceled, and the user almost hears only the reproduction sound S. Can do.

  Noise canceling headphones can be divided into those arranged outside the headphones, those arranged inside, and those equipped with both, depending on the arrangement position of the microphone for detecting environmental noise. When the microphone is disposed outside, a large noise is generated when a hand or the like touches the microphone portion. Alternatively, when a sudden change in atmospheric pressure occurs in the vicinity of the noise canceling headphone user due to a gust of wind or the like, a loud wind noise is generated and becomes a large noise. These noises may become environmental noises that cannot be canceled. When such large environmental noises are input, the AD conversion is performed when the AD is converted and taken into the DSP. A so-called overflow occurs that the vessel cannot handle. Since environmental noise is not correctly detected in this overflow state, even if processing by the DSP is performed, the noise canceling effect cannot be obtained accurately, so to speak, the noise canceling operation is performed incorrectly, so that the noise is canceled. I can't. On the contrary, when a loud environmental noise is suddenly input to the microphone, an unpleasant sound such as “buzz” may be generated.

  As a related art related to the noise cancellation headphone and the noise cancellation method according to the present invention, an external audio signal is generated by monitoring an external sound portion in a user's ear using a microphone, and a selective noise control circuit of the headphone is provided. A technique has been proposed in which an external audio signal obtained by a microphone is processed and the external audio signal is selectively classified as either noise to be suppressed or audio signal to be reproduced (for example, Patent Document 1). reference).

  The invention described in Patent Document 1 analyzes and evaluates an external audio signal and determines whether a predetermined external audio signal should be suppressed or reproduced. It is conceivable that an “external audio signal” generated when a sudden change in atmospheric pressure occurs is selectively classified as either noise to be suppressed or audio signal to be reproduced.

Special Table 2004-526375

  However, even if the technique described in Patent Document 1 is used, the suddenly generated “external audio signal” cannot be canceled. In the invention described in Patent Document 1, the suddenly generated high-level “external audio signal” is noise to be suppressed. When this signal is to be suppressed, a cancel sound different from the correct cancel sound signal is generated. However, it becomes a big noise source. That is, in the digital headphone, the AD converter overflows as described above due to the sudden input of an “external audio signal” at a high level. Alternatively, if the level of the “external audio signal” is high and exceeds a level at which numerical calculation is possible, an error occurs in the calculation result, and a cancel sound different from the correct cancel sound signal is generated. As a result, abnormal noise may be generated from the speaker, which may cause discomfort to the user.

  The present invention has been made in view of the actual situation of such a noise-canceling headphone. When a large environmental noise occurs or when a sudden high level noise occurs, an unpleasant noise occurs in the headphones. It is an object of the present invention to provide a noise-canceling headphone and a method for canceling the noise that can avoid the above-described problems and prevent the headphone user from feeling uncomfortable.

  The noise cancellation headphone according to the present invention has a cancellation noise generation unit that generates a cancellation noise signal having a phase opposite to that of environmental noise, a mixer that mixes the generated cancellation noise signal and a musical sound signal, and an environmental noise level that is set in advance. A noise level detection unit that detects whether or not the noise level is greater than or equal to the threshold value, and temporarily limits the input level of the environmental noise signal to the threshold level or lower if the noise level detected by the noise level detection unit is greater than or equal to the threshold value. The most important feature is that it has a noise level adjustment unit that removes the restriction on the input level of environmental noise when the noise level falls below a threshold value.

  The headphone noise canceling method according to the present invention includes a step of generating a canceling noise signal having a phase opposite to that of the environmental noise, a step of mixing the generated canceling noise signal and the musical sound signal, and a threshold having a preset environmental noise level. The step of detecting whether or not, and when the noise level detected by the noise level detection unit is equal to or higher than a threshold, the input level of the environmental noise signal is temporarily limited to the threshold level or lower, and the noise level is A step of releasing the restriction of the input level of the environmental noise when it becomes equal to or less than the threshold value is provided.

The characteristic configuration of the present invention described above is applied when the level of the environmental noise signal exceeds a preset threshold value.
However, the environmental noise includes a sudden loud noise that does not exceed the above threshold. In digital noise-canceling headphones, it is necessary to use a high-cost DSP with a high operating speed in order to cancel suddenly loud environmental noise, and there is a problem that power consumption increases. Therefore, another feature of the present invention is that a second threshold is set using a statistical method when environmental noise is suddenly input even if the environmental noise does not exceed a preset threshold. However, the level of the cancellation noise generated by the cancellation noise generation unit is limited to the second threshold value.

According to the present invention, when the environmental noise level is equal to or higher than a preset threshold value, the input level of the environmental noise signal to the cancellation noise generation unit is temporarily limited to the threshold level or lower. Therefore, when a large environmental noise that is equal to or greater than the threshold value is input, such as when the hand touches the environmental noise detection microphone, it is not possible to cancel all the environmental noise. However, the cancellation noise signal for canceling the environmental noise is a correct cancellation noise signal, and the signal level does not reach the environmental noise level. It is possible to avoid problems that cause discomfort to the user.
According to the present invention, in the case of sudden loud environmental noise, the canceling noise level generated by the canceling noise generating unit is limited to the second threshold value set using the statistical method. The level of sudden environmental noise can be reduced without using a fast and costly DSP.

Embodiments of a noise canceling headphone and a noise canceling method for the headphone according to the present invention will be described below with reference to the drawings.
FIG. 1 shows an embodiment of a digital noise canceling headphone. In FIG. 1, reference numeral 16 denotes a digital signal processor (digital signal processing device: hereinafter referred to as “DSP”) which is a main component of a digital noise canceling headphone. A noise signal N indicated by reference numeral 11 is input to the DSP 16 from a microphone 14 that is incorporated in headphones and converts ambient noise into an electrical signal. The DSP 16 includes a sampling circuit 21 that samples the noise signal N with a predetermined number of bits and converts it into digital data, and also includes a noise level detection unit 22, a cancellation noise generation unit 23, and a noise level adjustment unit 24. . The noise signal N input from the microphone 14 is input to the sampling circuit 21 via the noise level adjustment unit 24. The noise level detection unit 22 detects whether or not the level (amplitude) of the noise signal N input from the microphone 14 is equal to or higher than a preset threshold value, and controls the operation of the noise level adjustment unit 24 based on the result. It is configured. The cancellation noise generation unit 23 is configured to generate a cancellation noise signal -N ″ having a phase opposite to that of the noise signal N by numerically calculating the noise signal N sampled by the sampling circuit 21.

  When the noise level detection unit 22 detects that the level of the environmental noise signal N is equal to or higher than a preset threshold, the noise level adjustment unit 24 is sampled by the sampling circuit 21 and input to the cancellation noise generation unit 23. The level of the noise signal to be generated is temporarily limited to the threshold level or lower. Further, when the noise level detection unit 22 detects that the level of the environmental noise signal N is equal to or lower than a preset threshold, the noise level adjustment unit 24 uses the detection output of the noise level detection unit 22 to detect the sampling circuit 21. Is configured to release the restriction on the noise signal level input to the. Therefore, in this case, the environmental noise signal N detected and converted by the microphone 14 is input to the sampling circuit 21 as it is, and further input to the cancellation noise generation unit 23.

  The threshold value preset by the noise level detection unit 22 is set in light of the overflow level of the sampling circuit 21 that converts environmental noise into a digital signal. That is, the specification of the sampling circuit 21 functioning as an AD converter is determined in consideration of various conditions such as the purpose of use and the cost corresponding to the equipment used, and the processing capability is limited. For this reason, there is a limit to the environmental noise level at which AD conversion can be performed correctly. When environmental noise exceeding this limit is input, the sampling circuit 21 overflows and converts it into a digital signal faithful to environmental noise. I can't. Therefore, as described above, in light of the overflow level of the sampling circuit 21, the threshold set in advance by the noise level detection unit 22 is set to be equal to or lower than the overflow level. When the environmental noise N exceeding the threshold value is input, the noise level detection unit 22 detects this, and the noise level adjustment unit 24 temporarily sets the input level of the environmental noise N to the sampling circuit 21 at the threshold level or higher. It is configured to limit to the following. Further, when the noise level detection unit 22 detects that the environmental noise level is equal to or lower than the threshold value, the noise level adjustment unit 24 is configured to release the restriction on the input level of the environmental noise signal N based on this detection output. ing.

  The cancellation noise signal −N ″ generated by the cancellation noise generation unit 23 is adjusted in output level by the cancellation level adjustment unit 24 and converted into an analog signal by a D / A converter (not shown). The mixer 17 has the same function as the adder, and mixes the cancellation noise signal −N ″ generated by the cancellation noise generation unit 23 and the reproduction signal, that is, the musical sound signal (audio signal) S by the player 10. It is supposed to be.

  In the mixer 17, the musical sound signal S reproduced by the appropriate player 10 and the cancel noise signal −N ″ are mixed, and the amplifier 18 drives the speaker 19 in the headphones by the mixed signal S−N ″. The sound corresponding to -N "is emitted from the speaker 19. Ambient noise wraps around the headphones and enters the user's ear. This noise N corresponds to the cancellation noise -N" whose phase is inverted. The sound is synthesized in the headphones and becomes N−N ″ to cancel the noise N. In other words, the sound entering the user's ear is S + N−N ″. Since the portions NN "are canceled with each other as described above, only the musical sound signal S enters the user's ear. The player 10 is an analog system such as a cassette type tape recorder. Alternatively, it may be a digital signal processing system such as a CD player, an MD player, or an MP3 system player, and any one of these can be selected and used.

  In the example shown in FIG. 1, the mixer 17 is assumed to be an analog system, and the output signal of the player 10, that is, the musical tone signal S and the cancellation noise signal -N ″ input to the mixer 17, are assumed to be analog signals. If the musical tone signal S and the cancel noise signal -N ″ are digital signals, the adder 17 may be a digital system. In this case, the function of the adder 17 can be provided as a part of the function of the DSP 16. When the output of the adder 17 is a digital signal, it is converted into an analog signal and input to the amplifier 18.

  FIG. 2 schematically shows the embodiment of the noise canceling headphone according to the present invention described above. In FIG. 2, the code | symbol 12 has shown the headphone unit. The headphone unit 12 includes a casing that covers the user's ear, a microphone 14 that is incorporated in the casing and converts ambient noise N into an electrical signal, and a musical sound signal S that is reproduced by an external player 10 as an acoustic signal. The above-mentioned speaker as a signal acoustic conversion element for converting to the above and the DSP 16 described above are provided. The microphone 14 is disposed outwardly in the housing and converts the environmental noise N outside the headphone unit 12 into an electrical signal. The noise signal is input to the DSP 16 and processed as described above. The DSP 16 outputs a cancel noise signal −N ″ obtained by inverting the noise signal N ″ generated based on the noise signal N. The cancel noise signal -N "and the musical tone signal S are added by the adder 17 to output a signal S-N", and the speaker in the headphones is driven by the signal S-N ". The noise N around the headphone unit 12 reaches the user's ear by going around the headphone unit 12. The noise N changes the sound pressure level for each frequency band by going around the headphone unit 12, and the noise N ' Therefore, the sound that enters the user's ear is S−N ″ + N ′. Since the cancellation noise -N "is in the opposite phase to the noise N 'entering the user's ear, and the cancellation noise -N" and the noise N' are noise N sources, the noise N ' Canceled by the cancellation noise -N ", almost only the musical sound signal S enters the user's ear.

  FIG. 3 shows an operation example of the digital noise canceling headphones according to the embodiment described above. S1, S2,... Indicate operation steps. While the noise canceling headphones are operating, the sampling circuit 18 samples the environmental noise signal converted by the microphone 14 at a constant time interval, as in step S1. Next, in step S2, it is determined whether or not the level of the sampled noise signal is equal to or higher than a predetermined threshold value. This determination is made by the noise level detector 22. If it is equal to or lower than the threshold value, the process proceeds to step S3 to perform a normal operation of outputting a mute signal, that is, a canceling noise signal -N ", and returns to step S1. For example, the AD converter that converts the noise signal N into a digital signal (corresponding to the sampling circuit 21 in the embodiment shown in FIG. 1) overflows, and correct AD conversion cannot be performed. Since there is a possibility that a cancel noise signal different from −N ″ may be output, the process proceeds to step S4, the environmental noise signal level is limited, and the process returns to step S1.

  The mute signal is a cancel noise signal −N ″ output from the cancel noise generator 23. If the mute signal, that is, the cancel noise signal −N ″ is a signal different from the correct cancel noise signal. For example, when this signal is mixed with the musical sound signal S, a strange sound is output from the headphone speaker in addition to the reproduced sound of the musical sound signal S, which makes the headphone user uncomfortable. Therefore, in such a case, the level of the environmental noise signal N is limited in step S4. That is, as described above, when the noise level detection unit 22 detects that the level of the environmental noise N input from the microphone 14 exceeds the threshold, the noise level adjustment unit 24 detects the environmental noise input to the sampling circuit 21. Limit the level to be equal to or less than the above threshold. As a result, the noise canceling function is limited, but it is possible to avoid the output of strange sounds and to prevent the user from feeling uncomfortable. After the level of the environmental noise signal N is limited in step S4, the process returns to step S1 and the above operation is repeated. Therefore, when the level of the environmental noise signal N is equal to or lower than the threshold value, the operation is performed in the order of steps S1, S2, and S3, the restriction of the environmental noise level by the noise level adjusting unit 24 is released, and the environment input from the microphone 14 The noise signal N is input to the sampling circuit 21 at the level as it is.

  According to the embodiment described above, a noise signal that is so large that the sampling circuit 21 having the AD conversion function overflows when the hand touches the environmental noise detection microphone 14 disposed outwardly on the housing of the headphones. Is input by the noise level adjustment unit 24 according to a command from the noise level detection unit 22, and the input level of the environmental noise signal N to the sampling circuit 21 is set to a threshold of the detection level set in advance in the noise level detection unit 22. To a level equal to or lower than

If a large noise signal that overflows the sampling circuit 21 is input to the sampling circuit 21, the sampling circuit 21 cannot faithfully convert the environmental noise signal N into a digital signal. Since it is converted into a different digital signal and the cancel noise generating unit 23 generates cancel noise based on the wrong digital signal, the environmental noise cannot be canceled. In some cases, an unpleasant noise may be generated by generating erroneous cancellation noise.
According to the above embodiment of the present invention, all environmental noises cannot be canceled, but environmental noises can be correctly canceled up to the detection level by the noise level detection unit 22, so that a noise canceling effect can be obtained. No unpleasant noise is generated.

  Even if the level of environmental noise input from the microphone 14 is lower than the detection level threshold set in advance in the noise level detection unit 22, environmental noise that suddenly and rapidly changes may be input. In this case, even if the environmental noise level is not such that the AD converter overflows, the environmental noise signal N may change instantaneously, so that the conversion speed of the AD converter cannot catch up with the change in the environmental noise signal N. . Therefore, even if cancel noise is generated by the cancel noise signal generation unit 23 based on the digital signal converted by the AD conversion unit, a cancel noise signal faithful to the environmental noise signal N cannot be generated. Cannot cancel correctly. Also, unpleasant noise may occur.

  Therefore, if the threshold value of the noise level detection unit 22 for detecting a noise signal that is so large that the sampling circuit 21 overflows is set to “threshold value 1”, the noise level detection unit 22 against a relatively large environmental noise that occurs unexpectedly. The threshold value is “threshold value 2”. The threshold value 2 is set and corrected by obtaining an average value and a standard deviation from past environmental noise data sampled by the digital signal processor (DSP 16), taking the average value as a center and adding the standard deviation to the center. Therefore, the threshold value 1 is fixed, and the threshold value 2 has an upper limit and a lower limit, and varies with each sampling. FIG. 5 shows the relationship between threshold 1 and threshold 2. The threshold 2 is obtained from, for example, 100 environmental noise data sampled in the past by the DSP 16 and an average value and a standard deviation σ thereof are obtained. It is calculated by adding to the side and the minus side. Therefore, the threshold 2 has an upper limit and a lower limit, and the upper limit and the lower limit of the threshold 2 are set as the limit value of the cancel noise level generated by the cancel noise generation unit 23. Further, every time sampling is performed, the DSP 16 performs an operation for obtaining the threshold value 2 from, for example, 100 environmental noise data, and corrects the limit value of the cancel noise level generated by the cancel noise generation unit 23. In FIG. 5, the horizontal axis indicates time, and the vertical axis indicates the value (level) of environmental noise. As shown in FIG. 5, the threshold value 2 varies with each sampling. The threshold 1 is higher than the threshold 2, and the sampling circuit 21 is set to a level close to the overflow level. The noise level detection unit 22 applies the threshold value 2 to a relatively large environmental noise that occurs suddenly. When the threshold value 2 is exceeded, the noise level detection unit 22 performs a cancel noise generation unit 23 according to a command from the noise level detection unit 22. The limit value of the cancellation noise level to be generated is limited to be equal to or lower than the level of threshold value 2. By obtaining the threshold value 2 as described above, the threshold value 2 is not disturbed by the sudden environmental noise when the sudden environmental noise is input. As a result, the threshold value 2 is suddenly changed. Since noise cancellation operation is not disturbed by the input of various environmental noises, unpleasant noises are not generated.

  FIG. 4 shows an example of setting operation of the threshold value 1 and the threshold value 2 of the noise level detection unit 22. First, the threshold value S of the noise level detection unit 22 is set to an appropriate value in advance (S11). The threshold value S is the threshold value 1 described above. Next, the input is repeated until the number of inputs of the environmental noise signal N reaches a certain number n (for example, n = 100), and the average value and the standard deviation σ are obtained (S12). This standard deviation value is set as the threshold value 2 of the noise level detection unit 22. Next, the real-time input value (level) of the environmental noise signal N is sampled (S13), and it is determined whether or not this sampling value is equal to or less than the preset threshold value S (threshold value 1) of the noise level detection unit 22 (S14). ). If the sampling value is equal to or greater than the threshold value S (NO in S14), the sampling value is set as the threshold value S (S16). That is, the sampling value is limited to the threshold value S, and the process proceeds to the next step S17. If the sampling value is equal to or smaller than the threshold value S in step S14, the sampling value is input to the sampling circuit 21 as it is without restricting the sampling value, that is, without adjusting the level, and the process proceeds to the next step S17. Steps S13 to S16 are a comparison between the threshold value 1 and the sampling signal, and are substantially the same in operation and technical idea level described with reference to FIG.

  After the comparison between the threshold value 1 and the sampling signal, the threshold value 2 and the sampling signal are compared and the threshold value 2 is reset in step S17 and subsequent steps. Here, first, it is determined whether the sampling value of the noise signal N is equal to or less than the average value + mσ (S17). m is an arbitrary coefficient to be multiplied by the standard deviation σ, and is “3” in the example shown in FIG. In step S17, it is determined whether or not the sampling value of the noise signal N is equal to or less than the upper limit of the threshold value 2 described in FIG. If the sampling value of the noise signal N is equal to or greater than the upper limit of the threshold value 2 (NO in step S17), the process proceeds to step S21, and the sampling value is set to the average value + mσ. That is, the sampling value is limited to the average value + mσ which is the upper limit value. Thereafter, the process proceeds to step S22.

  If the sampling value of the noise signal N is equal to or lower than the average value + mσ in step S17 (YES in step S17), it is subsequently determined in step S18 whether the sampling value is equal to or higher than the average value−mσ. That is, it is determined whether the sampling value of the noise signal N is equal to or higher than the lower limit of the threshold 2 described with reference to FIG. When the sampling value of the noise signal N is equal to or lower than the lower limit of the threshold value 2 (NO in step S18), the process proceeds to step S20, and the sampling value is set to the average value −mσ. That is, the lower limit of the sampling value is set to the lower limit value of the threshold value 2, the lower limit of the sampling value is limited to be equal to or lower than the lower limit value of the threshold value 2, and the process proceeds to step S22.

  If the sampling value of the noise signal N is greater than or equal to the average value −mσ in step S18 (YES in step S18), the process proceeds to step S22 without correcting the sampling value.

  In step S22, the average value and standard deviation of the sampling values of the noise signal N are obtained, and the threshold value 2 is reset. Based on the reset threshold 2, the noise level detection unit 22 detects the noise level, and the noise level adjustment unit 24 adjusts the noise level according to the detection result and inputs it to the sampling circuit 21. Corresponding to the noise signal sampled by the sampling circuit 21, the cancel noise generator 23 performs a cancel noise generation process having a phase opposite to that of the noise signal (S23), and outputs a cancel signal (S24).

  In this way, the input value is statistically processed to obtain a new average value and standard deviation σ of the environmental noise signal N (S22), cancel noise generation processing is performed (S23), and a cancel signal is output. (S24). In step 22 for obtaining the new average value and standard deviation σ, the threshold value 2 is reset. In the cancel noise generation process, if suddenly loud environmental noise is input, the cancel noise level to be generated is limited by the reset threshold 2. When the cancel signal is output, the process returns to step S13 to repeat the operation.

  The cancel noise generated in this manner is mixed with the musical tone signal reproduced by the player 10 in the mixer 17, so that the environmental noise reaching the headphones is canceled by the cancel noise reproduced by the speaker 19. . However, when the input value of the environmental noise is larger than the threshold value S (threshold value 1) of the noise level detection unit 22, the noise is canceled with the threshold value S of the noise level detection unit 22 as an upper limit, and uncancelled noise remains. However, most of the noise can be canceled, and the function as a noise canceling headphone is sufficiently provided. In addition, if the input value of the environmental noise is larger than the threshold value S of the noise level detection unit 22, if an attempt is made to cancel the input value without restricting the input value, an accurate canceling noise cannot be generated and an unpleasant noise is generated. However, according to the above embodiment of the present invention, such abnormal noise is not generated.

  Further, the environmental noise signal N is set using a statistical method to set a threshold value 2 and each time the environmental noise signal N is sampled, the sampling signal and the threshold value 2 are compared to correct the threshold value 2 to cancel the noise. Since the level of the cancellation noise generated by the generation unit 23 is limited by the modified threshold value 2, the threshold value 2 is not disturbed by the sudden input of loud environmental noise, and the sudden high level Even if volume environmental noise is input, the noise canceling operation is not disturbed, and the generation of unpleasant noise can be eliminated.

It is a block diagram which shows the Example of the noise cancellation headphones concerning this invention. It is a conceptual diagram which shows the example of the noise cancellation operation | movement by the noise cancellation headphones concerning this invention. It is a flowchart figure which shows the operation example of the noise cancellation headphones concerning this invention. It is a flowchart figure which shows the threshold value setting operation example by the noise cancellation headphones concerning this invention. It is explanatory drawing of the concept of the threshold value in the noise cancellation headphones concerning this invention. It is a block diagram which shows the example of the conventional noise cancellation headphones.

Explanation of symbols

10 player 14 microphone 16 digital signal processor (DSP)
17 Mixer 19 Speaker 21 Sampling Circuit 22 Noise Level Detection Unit 23 Cancel Noise Generation Unit 24 Noise Level Adjustment Unit

Claims (10)

A cancellation noise generation unit that generates a cancellation noise signal having a phase opposite to that of the environmental noise;
A mixer for mixing the generated cancellation noise signal and the musical sound signal;
A noise level detector that detects whether the environmental noise level is equal to or higher than a preset threshold;
When the noise level detected by the noise level detector is above the threshold, the input level of the environmental noise signal is temporarily limited to the above threshold level or lower, and when the noise level falls below the threshold, the environmental noise signal A noise-canceling headphone having a noise level adjustment unit that releases the restriction on the input level.   The noise-canceling headphone according to claim 1, wherein a microphone for detecting environmental noise is disposed outside the headphone.   The noise cancellation headphone according to claim 1, wherein the cancellation noise generation unit, the noise level detection unit, and the noise level adjustment unit are included in the digital signal processing unit.   4. The noise canceling headphone according to claim 3, wherein the threshold value of the noise level detection unit for large environmental noise is set in light of an overflow level of a sampling circuit that converts environmental noise into a digital signal.   The threshold value of the noise level detection unit for sudden and large environmental noise is obtained by calculating an average value and a standard deviation from past data sampled by the digital signal processing unit, and taking the average value as a center and adding the standard deviation to the second value. The noise-canceling headphone according to claim 3, wherein the level of the cancellation noise generated by the cancellation noise generation unit is limited to the second threshold. Generating a cancellation noise signal that is opposite in phase to the environmental noise;
Mixing the generated cancellation noise signal and musical sound signal;
Detecting whether the environmental noise level is equal to or higher than a preset threshold;
When the noise level detected by the noise level detection unit is above the threshold, the input level of the environmental noise signal is temporarily limited to the threshold level or below, and when the noise level falls below the threshold, A headphone noise canceling method comprising a step of releasing an input level restriction.   7. The headphone noise canceling method according to claim 6, wherein the environmental noise is obtained from an environmental noise detection microphone disposed outside the headphone.   Cancel noise signal generation, mixing, detection of whether or not the threshold is exceeded, and the environmental noise input level is temporarily limited to the threshold level or lower, and the environmental noise input level restriction is removed. The headphone noise canceling method according to claim 6, wherein the step of performing is performed by digital signal processing.   9. The headphone noise canceling method according to claim 8, wherein a threshold for detecting a noise level for a large environmental noise is set in light of an overflow level of a sampling circuit that converts the environmental noise into a digital signal.   The threshold of noise level detection for sudden and large environmental noise is set and corrected by calculating the average value and standard deviation from the past data sampled in the digital signal processing unit, taking the standard deviation into account, centering on the average value 9. The headphone noise canceling method according to claim 8, wherein the headphone noise canceling method is a second threshold value.

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