JP2008060759A - Noise cancel headphone and its noise cancel method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noise cancel headphone preventing large noise from being generated in the headphone when rapid change occurs in atmospheric pressure due to a gust of wind, and preventing a headphone user from having an unpleasant feeling, and to provide a noise cancel method. <P>SOLUTION: The noise cancel headphone includes: a cancel noise generating part 23 for generating a cancel noise signal with a phase opposite to that of environmental noise; a mixer 17 for mixing the generated cancel noise signal with a musical sound signal S; a noise level detecting part 22 for detecting whether or not an environmental noise level is not less than a predetermined level; and a cancel level adjusting part 24 for temporarily attenuating the output level of the cancel noise signal when the noise level detected by the noise level detecting part 22 is not less than the predetermined level, and restoring the output level of the cancel noise signal to the level according to a noise cancel action when the noise level becomes the predetermined level or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a noise that can prevent a large noise from being output when the environmental noise exceeds a certain level due to a sudden change in atmospheric pressure due to a gust of wind or the like and the environmental noise cannot be canceled. The present invention relates to a canceling headphone and a noise canceling method thereof.

  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 when listening to music in the city or in a vehicle, the music should be kept from being heard. Noise-cancelling headphones that can only be heard are also desired. If the ambient noise is mixed with the music playback sound, even if the playback sound from the headphones is high quality playback sound, the playback sound is erased by the noise and the music cannot be enjoyed 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 microphone built into the headphones that captures the ambient sound (because it is noise for the playback sound, henceforth referred to as “noise”), and reverses the phase of the captured noise for playback from the player. This is a method of adding to a signal. 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. Device (hereinafter referred to as “IFFT”) 60. The cancel 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 cancel sound signal -N" composed of an analog signal and the reproduction signal. Add S. The noise N that penetrates into the headphones and intrudes is combined with the canceling sound -N "to become an NN" signal 66, and most of the noise N is canceled, and the user almost hears only the reproduced sound S. Can do.

  Conventional noise-canceling headphones generate a cancellation sound that is different from the correct cancellation sound signal when a sudden change in atmospheric pressure occurs around the noise-canceling headphone user due to a gust of wind, etc., which may cause discomfort to the user. It was. Especially in digital noise cancellation headphones, if the environmental noise signal exceeds the level that can be numerically calculated due to a sudden change in atmospheric pressure, the calculation result will be incorrect, and a cancellation sound different from the correct cancellation sound signal will be generated, On the contrary, it becomes a big noise source, and there is a difficulty in giving the user unpleasant feeling.

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

  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, it is not possible to cancel a high-level “external audio signal” that occurs suddenly when a sudden change in atmospheric pressure occurs around the headphone user. Can not. 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. For example, in the case of digital headphones, if the level of the “external audio signal” is high and exceeds the level at which numerical calculation is possible, the calculation result will be incorrect, and a cancellation sound that is different from the correct cancellation sound signal will be generated. Giving a sense of pleasure cannot be eliminated.

  The present invention has been made in view of the actual situation of such noise-canceling headphones, and when a sudden change in atmospheric pressure occurs due to a gust of wind or the like around a headphone user, a large noise is generated in the headphones. An object of the present invention is to provide a noise canceling headphone and a method for canceling the noise which can be avoided and do not cause discomfort to the headphone user.

  The present invention relates to 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 musical sound signal, and whether or not the environmental noise level is equal to or higher than a preset level. A noise level detection unit for detecting whether the noise level detected by the noise level detection unit is equal to or higher than a preset level, the output level of the cancellation noise signal is temporarily attenuated, and the noise level is preset It has a cancel level adjusting section for returning the output level of the cancel noise signal to a level corresponding to the noise canceling action when the level becomes lower than the level.

  The cancellation noise generation unit, the noise level detection unit, and the cancellation level adjustment unit may be included in the digital signal processing device, and the mixer may be an analog signal mixer.

  The cancel noise generated by the cancel noise generation unit may be converted into an analog signal and input to the mixer.

  When the noise level detected by the noise level detection unit is higher than a preset level, for example, when a sudden change in atmospheric pressure occurs around the noise canceling headphones user due to a gust of wind, etc. Since the cancel level adjustment unit temporarily attenuates the output level of the cancel noise signal, a cancel sound different from the sound signal to be canceled is not output, and it is possible to eliminate discomfort for the headphone user. . When the noise level is equal to or lower than a preset level, the cancel level adjusting unit returns the output level of the cancel noise signal to a level corresponding to the noise canceling action and performs a normal noise canceling operation.

  In the case of digital noise-canceling headphones, the cancellation level adjustment unit temporarily sets the output level of the cancellation noise signal when the noise level due to a sudden change in atmospheric pressure around the headphone user exceeds a level that allows numerical calculations. Attenuate. By doing this, it is possible to prevent problems such as the output of a cancellation sound that is different from the sound signal to be canceled due to an error in the calculation result, and output of sound that makes the headphone user uncomfortable. Can prevent

Embodiments of a noise canceling 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 cancellation level adjustment unit 24. . The noise level detector 22 detects the level (amplitude) of the noise signal N sampled by the sampling circuit 21 by numerical calculation, and detects whether the level of the noise signal N is equal to or higher than a preset level. The result is output. 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. The level adjustment unit 24 temporarily attenuates the output level of the cancellation noise signal from the cancellation noise generation unit 23 when the level of the noise signal N detected by the noise level detection unit 22 is equal to or higher than a preset level. When the level of the noise signal N becomes equal to or lower than a preset level, the output level of the cancel noise signal by the cancel noise generator 23 is returned to a level corresponding to the noise canceling action.

  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. A noise around the headphone circulates 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 converts the environmental noise N around the headphone unit 12 into an electrical signal, and this noise signal is input to the DSP 16 and processed as described above. The DSP 16 adds a cancel noise signal −N ″ obtained by inverting the noise signal N ″ generated based on the noise signal N and the musical tone signal S to output a signal S−N ″. The speaker in the headphone is driven by the -N "signal. On the other hand, the noise N around the headphone unit 12 goes around the headphone unit 12 and reaches the user's ear. As the noise N wraps around the headphone unit 12, the sound pressure level changes for each frequency band, and enters the user's ear as N 'noise. Therefore, the sound that enters the user's ear is SN− + N ′. The cancellation noise −N ″ is in the opposite phase to the noise N ′ that enters the user's ear, and the cancellation noise −N ″ is also Since the noise N ′ is also a source of the noise N, the noise N ′ is substantially canceled by the cancel noise −N ″, and 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 regular time intervals 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 cancellation noise signal -N ″, and returns to step S1. For example, the numerical calculation of the noise signal N becomes impossible, and the cancellation noise generation unit 23 may output a cancellation noise signal different from the correct cancellation noise signal −N ″. Is attenuated. 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. 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 output level of the cancel noise signal is attenuated in step S4. As a result, although the noise canceling function is eliminated, it is possible to avoid outputting an unusual sound and to prevent the user from feeling uncomfortable.

  Returning from step S4 to step S1, the environmental noise signal converted by the microphone 14 is sampled in step S1. If the sampling value of the environmental noise signal is equal to or less than a predetermined threshold value in step S2, the process proceeds to step S3, where the output level of the cancellation noise signal is restored to a level corresponding to the noise cancellation action, and normal noise is Return to cancel operation.

The noise canceling processing operation described above can be realized by the software configuration of the DSP 16.
The same idea as the operation example shown in FIG. 3 can be applied to the analog noise canceling headphones.

It is a block diagram which shows the Example of the noise cancellation headphones concerning this invention. It is a model figure which shows the outline | summary of the said Example. It is a flowchart which shows the operation example of the said Example. It is a block diagram which shows the example of the conventional digital system noise cancellation headphones.

Explanation of symbols

10 players 14 microphones 16 DSP
17 Mixer 21 Sampling Circuit 22 Noise Level Detection Unit 23 Cancel Noise Generation Unit 24 Cancel Level Adjustment Unit

Claims (4)

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 level;
When the noise level detected by the noise level detector is equal to or higher than the preset level, the output level of the cancel noise signal is temporarily attenuated, and when the noise level falls below the preset level, the cancel noise signal A noise-canceling headphone having a cancellation level adjustment unit that restores the output level of the signal to a level corresponding to the noise-canceling action.   2. The noise canceling headphone according to claim 1, wherein the cancel noise generating unit, the noise level detecting unit, and the cancel level adjusting unit are included in the digital signal processing device, and the mixer is an analog signal mixer.   The noise cancellation headphones according to claim 2, wherein the cancellation noise generated by the cancellation noise generation unit is converted into an analog signal and input to the mixer. A noise canceling method for a noise canceling headphone having a function of canceling noise by generating a canceling noise signal having an opposite phase to environmental noise and mixing the generated canceling noise signal and a musical sound signal,
Detects whether the environmental noise level is higher than a preset level,
When the detected noise level is equal to or higher than the preset level, the output level of the cancellation noise signal is temporarily attenuated, and when the noise level falls below the preset level, the output level of the cancellation noise signal is reduced to noise. Noise canceling method for noise canceling headphones that returns to a level corresponding to the canceling action.

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