JP2008124564A - Noise cancellation headphones - Google Patents

Abstract

A noise canceling headphone capable of arbitrarily setting and changing a canceling noise frequency band, arbitrarily setting and changing a canceling effect amount, and arbitrarily setting and changing a noise level to be canceled.
A microphone 10 for collecting environmental noise, a cancel signal generating unit that generates a cancel signal having a phase opposite to that of the environmental noise detected by the microphone 10, and a mixer that mixes the generated cancel signal and a musical sound signal. The speaker 30 is driven by the mixed signal. A frequency band change switch SW1 capable of setting and changing a cancel frequency band is provided. A cancel noise level change switch SW2 that can set and change the output volume level of the cancel signal is provided. A cancel noise level change switch SW3 that can set and change the level of noise to be canceled is provided.
[Selection] Figure 1

Description

  The present invention generates a cancellation signal having a phase opposite to that of the noise collected by the microphone, mixes it with the musical sound signal, and outputs the mixed signal from the speaker, thereby canceling the noise with the cancellation signal sound and only the musical sound signal sound. It relates to noise-canceling headphones that can be heard.

  For example, portable music players such as a tape player, a CD player, and an MD player are widely used. Recently, smaller and large-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 sound of the signal whose phase is inverted, and only the reproduction signal from the player enters the user's ear (for example, Patent Document 1, Patent Document 2, (See Patent Document 3).

JP 2006-14307 A JP 2005-287018 A JP-A-9-54592

Although most of the conventional noise canceling headphones including the techniques described in Patent Document 1, Patent Document 2 and Patent Document 3 are analog systems, a digital system which converts an audio signal into a digital signal and processes the digital signal Technology development is underway for noise-canceling headphones.
In a conventional noise canceling headphone, whether it is an analog method or a digital method, the cancel frequency band, the canceling effect amount, and the noise canceling level are fixedly set and cannot be changed once set.

The environmental conditions under which headphones are used are constantly changing. Even when used in a train, for example, noise when traveling in the suburbs and when traveling in a tunnel or underground have different frequency bands and different noise levels. It is desirable to set a cancel frequency band according to each frequency band and cancel only noise in the frequency band to be canceled.
It is also desirable to be able to change to the minimum canceling effect amount as required according to the noise level. This is because it is desirable to reduce the noise canceling effect amount as much as possible in order to obtain a higher quality reproduced sound. However, whether the user wants to listen to the musical tone with little noise or whether he wants to hear the musical tone with a higher sound quality even if the noise is heard to some extent depends on the user's preference. Therefore, it is desirable that the noise canceling effect amount can be changed according to the user's preference.
When the noise level is below a certain level, it is desirable to stop the noise canceling operation in order to obtain a higher quality reproduced sound. However, how to set the noise level for stopping the cancel operation depends on the preference of the user. Therefore, it is desirable to change or switch the level of noise to be canceled according to the user's preference.

  The present invention has been made in view of the above-described conventional technology, and can arbitrarily set and change the frequency band of cancellation noise, or can arbitrarily set and change the cancellation effect amount, or An object of the present invention is to provide a noise canceling headphone capable of arbitrarily setting and changing a noise level to be canceled.

  The present invention has a microphone for collecting environmental noise, a cancel signal generating unit for generating a cancel signal having a phase opposite to that of the environmental noise detected by the microphone, and a mixer for mixing the generated cancel signal and music signal. The noise canceling headphone that drives the speaker with the signal mixed by the mixer has a frequency band change switch that can set and change the canceling frequency band.

The present invention is also characterized by including a cancel noise level change switch that can set and change the output volume level of the cancel signal.
The present invention is also characterized in that a cancel noise level change switch that can set and change the level of noise to be canceled is provided.

  Since the frequency band of the environmental noise varies depending on the environmental conditions in which the headphones are used, the cancel frequency band is switched by the frequency band change switch according to the frequency band of the environmental noise. By canceling noise by limiting the frequency band, it is possible to reduce the deterioration in sound quality due to noise cancellation and to reproduce high sound quality.

  The level of environmental noise varies depending on the environmental conditions in which the headphones are used. On the other hand, in order to reproduce with higher sound quality, the amount of noise cancellation effect should be as small as possible. If the cancel output volume level change switch is provided as in the present invention, the cancel output volume level change switch can be operated to arbitrarily change the noise cancellation effect amount according to the user's preference. Therefore, if the user places importance on sound quality, the noise canceling effect amount is set to be moderate, and if the user is concerned about noise, the noise canceling effect amount may be set to a large amount.

  The noise level to be canceled can be arbitrarily set and changed with the cancel level change switch. If the noise level to be canceled is set low, the noise canceling operation is performed from the low noise level. If the noise level to be canceled is set high, the noise cancel operation is not performed at a low noise level, and the musical sound signal can be reproduced with high sound quality. A user who dislikes environmental noise may set a low noise level to be canceled, and a user who likes high sound quality may set a high noise level to cancel.

Embodiments of a noise canceling headphone according to the present invention will be described below with reference to the drawings.
FIG. 1 schematically shows an embodiment of a digital noise canceling headphone. In FIG. 1, a digital noise canceling headphone includes a digital signal processor (digital signal processing device: hereinafter referred to as “DSP”) 20, and signal processing is mainly performed by the DSP 20.

  An outline of an example of a digital noise canceling headphone mainly composed of the DSP 20 will be described. The DSP 20 includes a fast Fourier transformer (hereinafter referred to as “FFT”) that performs frequency analysis on the noise signal N captured by the microphone 10 incorporated in the headphones, and a frequency characteristic detection unit that detects frequency characteristics by performing frequency analysis using FFT. A selection unit that selects a frequency band to be canceled from the detected frequency characteristics; and an inverse Fourier transformer that generates a frequency-selected canceling sound signal -N ″ by performing an inverse Fourier transform on the signal in the selected frequency band. The canceling sound signal -N ″ is added to the reproduction signal S by the player by an analog adder different from the DSP 20 and output. The noise N that enters the headphone and enters it is combined with the cancel sound -N "to become a signal NN", and most of the noise N is canceled and only the reproduction signal S remains. The speaker 30 is driven by the reproduction signal S, and the user can hear the reproduction sound S.

  The embodiment shown in FIG. 1 is characterized in that the DSP 20 includes a filter coefficient setting unit 21, a cancel effect amount setting unit 22, and a cancel level setting unit 23. The DSP 20 includes an FIR (Finite Impulse Response) filter that can set a filter coefficient for each frequency band, and the filter coefficient set for each frequency band is registered in the filter coefficient setting unit 21. The filter coefficient registered in the filter coefficient setting unit 21 can be arbitrarily selected by the switch SW1 operated from the outside, whereby the filter coefficient can be arbitrarily set and changed. . Since the cancel frequency band can be set and changed by selecting the filter coefficient with the switch SW1, the switch SW1 is a cancel frequency band change switch.

  In the case of analog noise-canceling headphones that do not use the DSP 20, in place of the FIR filter, one of a band pass filter, a low pass filter, a high pass filter, a low cut filter, a high cut filter, or some combination of these filters. Have a thing. An arbitrary filter is selected from these filters with a cancel frequency band change switch.

  The cancel effect amount setting unit 22 sets the output volume level of the cancel signal step by step when outputting the cancel signal sound having the opposite phase of the environmental noise collected by the microphone 10 from the speaker 30. The level is registered in the DSP 20. Each setting level of the output volume can be arbitrarily selected by the switch SW2 operated from the outside, whereby the output volume level of the cancel signal can be arbitrarily set and changed. Therefore, the switch SW2 is a cancel output volume level change switch.

  The cancel level setting unit 23 sets the level of noise to be canceled in a stepwise manner according to the environmental noise signal level collected by the microphone 10 and converted into an electrical signal. It is registered. Each setting level of the noise signal to be canceled can be arbitrarily selected by the switch SW3 operated from the outside, whereby the noise level to be canceled can be arbitrarily set and changed. ing. Therefore, the switch SW3 is a cancel level change switch.

  Next, the operation of the above embodiment will be described with reference to FIGS. In FIG. 2 and FIG. 3, “S1,” “S2,” “S3”,. In FIG. 2, a ROM (Read Only Memory) 24 is included in the DSP 20, and a power switch 25 and an I / O port 26 are provided at arbitrary positions of the headphones. Each of the three switches SW 1, SW 2, SW 3 shown in FIG. 1 is included in the I / O port 26. That is, the I / O port 26 includes a cancel frequency band I / O port as a first I / O port, a cancel effect amount I / O port as a second I / O port, and a third I / O port. An I / O port having a cancellation noise level is provided as the I / O port. Each of these I / O ports can set a cancel frequency band, a cancel effect amount, and a cancel noise level in a plurality of stages, and the cancel frequency band, cancel effect amount, and cancel noise level can be set by operating the corresponding switches. You can select, set, and change.

  The ROM 24 stores, in a predetermined storage area, the filter coefficient group of the cancel frequency band from the coefficient 1 to the coefficient N1, the cancel effect amount value group from the value 1 to the value N2, and the cancel noise level value group from the value 1 to the value. Up to N3 is registered. These coefficient groups and value groups are registered in the same number of stages as the number of stages that can be set by the first, second, and third I / O ports.

  The operation described below is performed according to a program installed in the control unit in the DSP 20. When the power switch 25 is turned on, first, the switch number of the cancel frequency band is acquired from the I / O port of the cancel frequency band, and the filter coefficient corresponding to the switch number is designated from the filter coefficient group in the ROM 24 (S1). ). Subsequently, the cancel effect amount switch number is obtained from the cancel effect amount I / O port, and the cancel effect amount value corresponding to the switch number is designated from the cancel effect amount value group in the ROM 24 (S2). ). Further, the switch number of the cancel noise level is acquired from the I / O port of the cancel noise level, and the cancel noise level value corresponding to the switch number is designated from the cancel noise level value group in the ROM 24 (S3). .

  Following the operation shown in FIG. 2 described above, the operation shown in FIG. 3 is performed. The environmental noise signal collected by the environmental noise collecting microphone 10 and converted into an electric signal is converted into a digital signal by an AD converter 27 included in the DSP 20. This environmental noise digital signal is captured (S4), and this environmental noise is compared with the cancellation noise level designated in step S3 to determine whether or not to cancel (S5). If the environmental noise level is higher than the designated cancellation noise level, it is determined in step S6 that “cancel” and the process proceeds to step S7. If the environmental noise level is lower than the designated cancellation noise level, it is determined in step S6 that “cancel is not performed”, and the process returns to step S1.

  In step S7, a canceling sound in the designated frequency band is created using the filter coefficient designated in step S1. Further, the canceling sound effect amount is set or changed using the value of the canceling effect amount specified in step S2. In this way, a canceling sound signal corresponding to the designated canceling effect amount is output in the designated frequency band (S9). The output cancellation sound signal is converted into an analog signal by the DA converter 28 included in the DSP 20. The musical sound signal reproduced by the player and the canceling sound signal converted into an analog signal are mixed by a mixer (not shown), and a driver (power amplifier) drives the speaker according to the mixed signal, and sound is output from the speaker. The This sound is a mixture of a musical sound and a canceling sound. The canceling sound cancels environmental noises that enter the headphones, and only the musical sound signal reaches the user's ear.

  While the power switch 25 is on, the above noise canceling operation is repeated. Whether the power switch 25 is turned on and the noise canceling operation is being performed or the operation is being stopped, the filter coefficient, the cancel effect amount, and the cancel level can be changed by the switches SW1, SW2, and SW3 shown in FIG. After the change, noise canceling operation is performed according to each set value.

According to the embodiment described above, it is possible to select and cancel only the frequency band to be canceled, and to set the cancel frequency band according to the user's desire so as not to cancel the frequency band that is not desired to be canceled. it can.
Since the output volume level of the cancel signal can be arbitrarily changed, it is possible to prevent noise cancellation more than the user needs.
At the level of noise that you do not want to cancel, you can stop the noise canceling operation and not cancel the noise.

It is a block diagram which shows the Example of the noise cancellation headphones which concern on this invention. It is a flowchart which shows operation | movement of the said Example. It is a flowchart which shows operation | movement of the said Example following FIG.

Explanation of symbols

10 Microphone for collecting environmental noise 20 DSP
30 Speaker 24 ROM

Claims (8)

A microphone for collecting environmental noise, a cancel signal generating unit for generating a cancel signal having a phase opposite to that of the environmental noise detected by the microphone, and a mixer for mixing the generated cancel signal and musical sound signal. In the noise-canceling headphones that drive the speaker with the signal mixed by
Noise canceling headphones equipped with a frequency band change switch that can set and change the cancellation frequency band.   The noise canceling headphone according to claim 1, further comprising a filter for setting a canceling frequency band, wherein the canceling frequency band is set and changed by switching the filter by a frequency band changing switch.   3. The noise canceling headphone according to claim 2, wherein the filter is an FIR filter, the filter coefficient of which is registered in a digital signal processing device (or “DSP”), and the frequency band change switch switches the filter coefficient.   The noise-canceling headphone according to claim 2, wherein the filter includes a plurality of filters that pass or block a signal of a specific frequency band, and the frequency band change switch selects any one or a plurality of the plurality of filters. A microphone for collecting environmental noise, a cancel signal generating unit for generating a cancel signal having a phase opposite to that of the environmental noise detected by the microphone, and a mixer for mixing the generated cancel signal and musical sound signal. In the noise-canceling headphones that drive the speaker with the signal mixed by
Noise canceling headphones equipped with a cancel output volume level change switch that can set and change the output volume level of the cancel signal. A microphone for collecting environmental noise, a cancel signal generating unit for generating a cancel signal having a phase opposite to that of the environmental noise detected by the microphone, and a mixer for mixing the generated cancel signal and musical sound signal. In the noise-canceling headphones that drive the speaker with the signal mixed by
Noise canceling headphones equipped with a cancel level change switch that can set and change the noise level to be canceled.   7. The noise canceling headphone according to claim 6, wherein a cancel level is registered in the DSP, and a cancel level change switch switches the cancel level. A microphone for collecting environmental noise, a cancel signal generating unit for generating a cancel signal having a phase opposite to that of the environmental noise detected by the microphone, and a mixer for mixing the generated cancel signal and musical sound signal. In the noise-canceling headphones that drive the speaker with the signal mixed by
A frequency band change switch that can set and change the cancellation frequency band; and
Cancel output volume level change switch that can set and change the output volume level of the cancel signal,
Noise canceling headphones equipped with a cancel level change switch that can set and change the cancel signal level.

Images