JP6953984B2 - Earphones and signal processing methods for earphones - Google Patents

Description

The present invention relates to, for example, earphones and signal processing methods for earphones.

There is a demand for earphones to have a hear-through function. Hear-through is a function that allows the user to listen to ambient sounds as if the earphones were not worn, even if the user was wearing the earphones.
On the other hand, when the earphone is worn so as to obstruct the user's ear canal, the user tends to muffle the target sound (hereinafter referred to as "target sound") supplied from an external terminal such as a music player. Specifically, it is perceived with the low frequency side emphasized.
Therefore, in recent years, a technique for realizing a hear-through function while reducing the above-mentioned muffled state has been proposed (see, for example, Patent Document 1).

Special Table 2015-537465

By the way, although the above technology reduces muffled sound, it has been pointed out that when the user wears earphones, the ambient sound and sometimes the voice of the other person or oneself can be heard unnaturally when talking with the other person. Was done.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique capable of reducing muffled sound and listening to ambient sounds in a natural manner when worn. be.

In order to achieve the above object, the earphone according to one aspect of the present invention has a housing including an earpiece inserted into the user's external auditory canal and a housing provided in the housing to collect ambient sounds outside the external auditory canal. A first microphone, a second microphone provided in the housing and collecting sound in the external auditory canal, a speaker provided in the housing and emitting sound toward the external auditory canal, and a collection of the first microphone. A low-frequency booster that raises the low-frequency volume relative to the high-frequency volume with respect to the first signal based on sound, and a reverse-phase signal that generates a reverse-phase signal of the second signal based on the sound pick-up of the second microphone. It includes a signal generation circuit, an output signal of the low frequency booster, a target signal indicating a target sound, and an adder that adds the reverse phase signal and outputs it to the speaker.
According to the earphone according to this aspect, it is possible to reduce muffled sound and to hear the ambient sound with a natural feeling when worn.

It is a block diagram which shows the structure of the earphone which concerns on 1st Embodiment. It is a figure which shows the structure of an earphone. It is a figure which shows the wearing state of an earphone. It is a figure which shows the sound transmission in the wearing state of an earphone. It is a figure for demonstrating the characteristic of the equalizer (1) in an earphone. It is a figure for demonstrating the characteristic of a low-pass booster in an earphone. It is a block diagram which shows the structure of the earphone which concerns on 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a block diagram showing a configuration of the earphone 10a according to the first embodiment. As shown in this figure, the earphone 10a includes microphone 110, 150, amplifier 112, 134, 152, ADC 114, 154, equalizer 116, 126, low frequency booster 120, AIF 122, adder 128, 130, filter 129, DAC 132. , Speaker 140, subtractor 156, and reverse phase signal generation circuit 158. When the earphone 10a is worn by the user, the sound emitting direction of the speaker 140 is arranged in the direction toward the user's ear canal, and the microphone 150 is the sound emitting direction of the speaker 140 and is acoustically coupled to the ear canal. It is placed in the space.

The microphone 110 (first microphone) picks up the ambient sound of the user who wears the earphone 10a. The amplifier 112 amplifies the signal (first signal) picked up by the microphone 110, and the ADC (Analog to Digital Converter) 114 converts the signal amplified by the amplifier 112 into a digital signal.
The equalizer 116 performs a correction process on the output signal of the ADC 114, for example, a process of raising a high frequency band, and supplies the processed signal to the first input terminal of the low frequency booster 120 and the adder 128, respectively. The equalizer 116 is referred to as "equalizer (1)" in FIG. 1 in order to distinguish it from the equalizer 126.
The low frequency booster 120 applies a process of raising the volume of the low frequency band to the signal corrected by the equalizer 116, and supplies the processed signal to the first input terminal of the adder 130.

The AIF (Audio InterFace) 122 is an interface that wirelessly receives a signal of a sound (target sound) to be heard by a user from an external terminal 200. The target sound is, for example, a music signal reproduced by the external terminal 200. Further, the AIF 122 may be configured to receive the signal of the target sound by wire instead of wirelessly.
The equalizer 126 performs a process of adjusting the sound quality, such as imparting a frequency characteristic set or selected by the user to the signal of the target sound received by the AIF 122, and transfers the processed signal to the second adder 128. It is supplied to the input end and the second input end of the adder 130, respectively. The equalizer 126 is referred to as "equalizer (2)" in FIG. 1 in order to distinguish it from the equalizer 116.

The adder 130 adds the signals supplied to each of the first input end, the second input end, and the third input end, and supplies the signals to the DAC (Digital to Analog Converter) 132. The DAC 132 converts the signal added by the adder 130 to analog, and the amplifier 134 amplifies the signal converted by the DAC 132. The speaker 140 converts the signal amplified by the amplifier 134 into air vibration, that is, sound, and outputs the signal.

The microphone 150 (second microphone) is provided in the vicinity of the speaker 140, and collects sounds in the user's ear canal, such as the sound output from the speaker 140. Here, the transmission characteristic from the speaker 140 to the microphone 150 is represented by C. The amplifier 152 amplifies the signal (second signal) picked up by the microphone 150, and the ADC 154 converts the signal amplified by the amplifier 152 into a digital signal and supplies it to the subtractor 156.

On the other hand, the adder 128 adds the signals supplied to each of the first input end and the second input end and supplies the added signal to the filter 129, and the filter 129 uses the convolution operation or the like to perform the addition signal. Is given a transfer function C and supplied to the subtractor 156. Therefore, the output signal of the filter 129 is an addition signal between the signals corrected by the equalizers 116 and 126, that is, a sound signal obtained by adding the ambient sound picked up by the microphone 110 and the sound obtained by adjusting the target sound. However, if it is emitted from the speaker 140, it becomes a signal simulating the sound in the external auditory canal that would be picked up by the microphone 150.
The subtractor 156 subtracts the output signal by the filter 129 from the digital signal by the ADC 154 and supplies it to the reverse phase signal generation circuit 158.

The reverse phase signal generation circuit 158 is simply an ANC (Active Noise Control) filter, which has a relationship in which the phase of the subtraction signal by the subtractor 156 is inverted, and the volume (amplitude) is almost the same. To generate. In other words, the reverse phase signal generation circuit 158 generates a reverse phase signal that minimizes the error signal when the subtraction signal by the subtractor 156 is used as an error signal.

FIG. 2 is a diagram showing the structure of the earphone 10a.
As shown in this figure, the earphone 10a is a canal type and includes a housing 160 and an earpiece 180.
The housing 160 has a substantially cylindrical shape. Speakers 140, microphones 110 and 150 are provided in the internal space of the housing 160. Specifically, in the internal space of the housing 160, the speaker 140 is mounted so that the sound emitting surface faces the ear canal, and the microphone 150 is mounted closer to the ear canal (right side in the figure) than the speaker 140. The housing 160 is provided with one or a plurality of ventilation holes 168 for ventilating the internal space closer to the ear canal than the speaker 140 to the outside when worn.
On the other hand, the microphone 110 is provided on the side opposite to the microphone 150 when the speaker 140 is used as a reference in the internal space of the housing 160.

The earpiece 180 is formed into a hollow bullet shape that opens at the opening 186 with an elastic material such as polyvinyl or sponge, and is detachable from the ear canal side of the housing 160. When the earpiece 180 is attached to the housing 160, the opening 186 communicates with the internal space of the housing 160.

Of the elements constituting the earphone 10a shown in FIG. 1, elements other than the microphones 110, 150 and the speaker 140 are provided in the internal space of the housing 160, for example, in the vicinity of the microphone 110, but are omitted in FIG. ing.

FIG. 3 is a diagram showing a wearing state of the earphone 10a, and more specifically, is a diagram showing a state in which the earphone 10a is worn on the right ear of the user W. As shown in this figure, the earpiece 180 of the earphone 10a is inserted into the ear canal 314. Specifically, the earpiece 180 is inserted into the ear canal 314 in the direction of the opening 186 toward the eardrum 312, while a part of the housing 160 is exposed from the ear canal 314.

Next, the outline of the operation of the earphone 10a will be described without considering the equalizer 116 and the low frequency booster 120.
When the earphone 10a is worn by the user W as shown in FIG. 3, the peripheral sound signal picked up by the microphone 110 and the target sound signal supplied from the external terminal 200 are added by the adder 130. And sounded by the speaker 140. The sound emitted from the speaker 140 reaches the eardrum 312 via the ear canal 314 and is perceived by the user W.

On the other hand, when the earphone 10a is worn, the ear canal 314 is blocked by the earpiece 180. Therefore, the microphone 150 collects the sound generated in the closed ear canal 314 through the opening 186 of the earpiece 180.
The sound generated in the ear canal 314 includes not only the sound component emitted from the speaker 140 but also the sound component other than the sound emitted from the speaker 140 (sometimes simply referred to as "noise"). Is included. Of these, the sound components emitted from the speaker 140 are, specifically, the peripheral sound picked up by the microphone 110 and the target sound supplied from the external terminal 200. The noise is a component of sound that is picked up by the microphone 150 but is caused by a sound other than the sound emitted by the speaker 140.

In the subtractor 156, the transmission function C is applied to the addition signal from the signal picked up by the microphone 150 to the signal based on the ambient sound picked up by the microphone 110 and the signal based on the target sound supplied from the external terminal 200. The components of the applied signal are subtracted. Therefore, the error signal input to the reverse phase signal generation circuit 158 indicates a noise component other than the sound emitted by the speaker 140.
When the ambient sound signal, the target sound signal, and the reverse phase signal by the reverse phase signal generation circuit 158 are added by the adder 130 and emitted from the speaker 140, the noise in the external auditory canal 314 is the reverse phase signal. It is canceled (cancelled) by the sound component based on. Therefore, the user W can perceive the ambient sound and the target sound while the noise is suppressed.

The above is the outline of the operation of the earphone 10a, but in reality, when the equalizer 116 and the low frequency booster 120 are not taken into consideration, the ambient sound, specifically, the voice of the other person or oneself is not heard when talking with the other person. It may sound natural. In particular, when the airtightness is low due to the air volume of the earpiece 180 or the ventilation hole 168, the sound tends to be unnatural.

When the canal type earphone 10a is worn by the user W, it is blocked by the earpiece 180, so that the ear canal 314 becomes a kind of closed space. Therefore, in the ear canal, the low frequency range of several hundred Hz or less is amplified, and the volume of the low frequency band becomes loud, and the user perceives it as muffled. When the user perceives muffled voice, it becomes difficult to utter because the voice generated by himself / herself is heard unnaturally (because the self-voice heard by feedback is modulated).
The higher the airtightness of the ear canal 314, the more the muffler tends to be emphasized. Therefore, in the earphone 10a according to the present embodiment, the muffler is caused by adjusting the hole diameter and number of the ventilation holes 168 and selecting the material of the earpiece 180. Is kept low.

The sound transmission in the earphone 10a will be examined. When the earphone 10a is worn as shown in FIG. 3, the microphones 110 and 150 pick up the sound transmitted by the following paths, respectively.

FIG. 4 is a diagram for explaining a sound transmission path in the wearing state of the earphone 10a.
The path (a) is a path in which the microphone 110 directly collects the peripheral sound from the sound source X. The sound source X includes a component that propagates air and a voice uttered by a person other than the user W among the voices uttered by the user W wearing the earphone 10a. The microphone 150 mainly collects the sound transmitted through the paths (b) and (c). Specifically, the path (b) is a path (b) of the ambient sound from the sound source X that reaches the microphone 150 located in the ear canal 314 through the ventilation hole 168, the gap between the earpiece 180 and the skin of the user W, and the like. Is. The path (b') is a path that reaches the microphone 150 through the skin and bones of the user W among the ambient sounds from the sound source X. Since it is not necessary to strictly distinguish between the route (b) and the route (b'), the route (b) will be described below assuming that the route (b') is included. The path (c) is a path in which the microphone 150 collects the sound emitted from the speaker 140 in the ear canal 314.
Since the microphone 150 is located in the closed ear canal 314 when the earphone 10a is worn, the sound picked up by the microphone 150 is substantially equal to the sound perceived by the user W due to the vibration of the eardrum 312.

In FIG. 4, the peripheral sound from the sound source X includes the eardrum 312 and the microphone of the user W in the two paths (path via the microphone 110 and the speaker 140) of the path (a) and the path (c) and the path (b). Reach 150 respectively.
When the frequency characteristic of the ambient sound picked up by the microphone 110, that is, the frequency characteristic of the sound picked up by the path (a) is flat at a volume of 0 dB normalized as shown by the solid line in FIG. 5, the path The frequency characteristic of the ambient sound reaching the tympanic membrane 312 in (b) is attenuated on the high frequency side as shown by the dotted line in FIG.

When the user W wears the earphone 10a, the peripheral sound from the sound source X is perceived by the sum of the sounds passing through both the path (a, c) and the path (b). Peripheral sounds from the sound source X will be heard unnaturally due to the attenuation of the high frequencies on the a and c) sides.
Therefore, the equalizer 116 performs a process in which the microphone 110 lifts the high frequency side of the signal that picks up the peripheral sound in the path (a). By this processing, the high frequency side of the sound reaching the eardrum 312 from the speaker 140 is lifted by the path (c), and when combined with the sound passing through the path (b), the result is almost flat at a volume of 0 dB. Therefore, the user W can perceive the ambient sound X in a natural way.
Regarding the processing of the equalizer 116 described here, it is assumed that the low frequency booster 120 does not exist and the noise cancellation by the reverse phase signal generation circuit 158 does not operate.

Therefore, next, a case where noise cancellation by the reverse phase signal generation circuit 158 is operating will be examined.
In the present embodiment, the anti-phase signal generation circuit 158 generates an anti-phase signal so that the input error signal is minimized. The sound pick-up signal of the microphone 150 includes not only the sound emitted from the speaker 140, that is, the sound component transmitted by the path (c), but also the sound component transmitted by the path (b). Since the error signal input to the reverse phase signal generation circuit 158 has the sound component transmitted in the path (c) removed in advance by the subtractor 156, it substantially represents the sound component transmitted in the path (b). Will be there.

Since the frequency characteristic of the sound when it reaches the microphone 150 from the sound source X on the path (b) is attenuated on the high frequency side as described above, relatively speaking, the low frequency side is emphasized. When such a signal in which the low frequency side is emphasized is input to the negative phase signal generation circuit 158 as an error signal, the negative phase signal becomes a signal that suppresses the low frequency band on the contrary. That is, when the reverse phase signal is added to the signal obtained by collecting the peripheral sound from the same sound source X by the microphone 110, the low frequency side of the added signal is attenuated.

Therefore, when noise cancellation is operating, ambient sounds such as voices uttered by the user W himself or others are emitted from the speaker 140 in a state where the low frequency side is attenuated, and are therefore perceived by the user W. The ambient sound becomes unnatural.

If the low frequency side is attenuated when the sound pick-up signal of the microphone 110 is added to the reverse phase signal, the low frequency side of the sound pick-up signal of the microphone 110 is preliminarily set before the addition with the reverse phase signal. If it is lifted, the attenuation on the low frequency side due to the addition will be compensated. Therefore, in the present embodiment, the low-frequency booster 120 executes a process of raising the low-frequency side of the sound pick-up signal of the microphone 110 when the low-frequency noise cancellation is operating.

Specifically, when the low frequency booster 120 does not exist and the output signal of the equalizer 116 is attenuated on the low frequency side by addition with the reverse phase signal as shown by the dotted line in FIG. 6, the low frequency booster 120 Is processed so that the low frequency side is raised relative to the high frequency side, and when it is added to the reverse phase signal, the result is a flat characteristic as shown by the solid line in the figure.
According to the earphone 10a having such a low frequency booster 120, when noise cancellation is operating, even if the sound pick-up signal of the microphone 110 is added to the reverse phase signal, the low frequency side is not attenuated and is flat. It is possible to make the user W perceive a natural ambient sound because it approaches a characteristic characteristic.

In the earphone 10a according to the first embodiment, the signal corrected by the equalizer 116 is supplied to the first input terminal of the adder 128, but the output signal from the low frequency booster 120 is supplied. May be. In addition, the earphone 10a can be changed as long as the linearity is maintained.

<Second Embodiment>
In the first embodiment, noise is canceled by subtracting the signal to which the transmission characteristic C is added to the signal of the sound obtained by adding the ambient sound and the target sound to be heard by the user W from the error signal supplied to the reverse phase signal generation circuit 158. The configuration is such that the ambient sound and the additional sound of the target sound are excluded from the target of.
In this configuration, the filter 129 requires not only complicated processing such as a convolution operation, but also an adder 128 and a subtractor 156. Therefore, a second embodiment that does not require such complicated processing will be described.

FIG. 7 is a block diagram showing a configuration of the earphone 10b according to the second embodiment. As shown in this figure, the earphone 10b does not have an adder 128, a filter 129 and a subtractor 156 as compared with the earphone 10a, and the digital signal by the ADC 154 is directly supplied to the reverse phase signal generation circuit 158. It is composed.

In the earphone 10b, the sound obtained by adding the peripheral sound and the target sound is also subject to noise cancellation, so that the quality of the peripheral sound and the target sound perceived by the user W is lower than that in the first embodiment.
However, since the earphone 10b also has the equalizer 116 and the low frequency booster 120, it is possible for the user W to perceive a natural ambient sound. Further, since the processing of the earphone 10b is simplified as compared with the earphone 10a, it is advantageous in terms of circuit space, battery consumption, and the like.

<Application example / Modification example>
In the first embodiment (second embodiment), the earphones 10a (10b) worn on the right ear have been described as an example, but they may be worn on the left ear.
In addition, two earphones 10a (10b) having the same configuration are prepared so that one is worn on the right ear and the other is worn on the left ear, and the earphone 10a (10b) worn for the left ear has a stereo left signal. However, a stereo right signal may be supplied from the external terminal 200 to the earphones 10a (10b) worn for the right ear.

The external terminal 200 may have a function different from the function of supplying the signal indicating the target sound to the earphone 10a. For example, the external terminal 200 may be provided with a function of adjusting and setting the frequency characteristics of the equalizer 126, or when a plurality of frequency characteristics are preset and one of the characteristics is selected by the user W, The selected characteristics may be set in the equalizer 126.

<Additional notes>
From the first embodiment and the second embodiment described above, for example, the following aspects can be grasped.

<Aspect 1>
The earphone according to a preferred embodiment 1 of the present invention includes a housing including an earpiece inserted into the user's external auditory canal, a first microphone provided in the housing and collecting peripheral sounds outside the external auditory canal, and the above. A second microphone provided in the housing and picking up the sound in the external auditory canal, a speaker provided in the housing and emitting sound toward the external auditory canal, and a first signal based on the sound picked up by the first microphone. A low-frequency booster that raises the volume of the low-frequency range relatively higher than the volume of the high-frequency band, a reverse-phase signal generation circuit that generates a negative-phase signal of the second signal based on the sound picked up by the second microphone, and the above-mentioned It includes an output signal of a low frequency booster, a target signal indicating a target sound, and an adder that adds the reverse phase signal and outputs the output signal to the speaker.
According to the earphone according to the first aspect, it is possible to reduce muffled sound and allow the user to hear the ambient sound with a natural feeling when wearing the earphone.

<Aspect 2>
The earphone according to the second aspect includes an equalizer that raises a high frequency range of a predetermined frequency or higher in the first signal in the earphone according to the first aspect, and an output signal of the equalizer is input to the low frequency booster.
According to the earphone according to the second aspect, the peripheral sound can be heard by the user with a more natural feeling.

<Aspect 3>
The earphone according to the third aspect is the earphone according to the first or second aspect, from the speaker to the signal obtained by adding the signal input to the low frequency booster or the signal output from the low frequency booster and the target signal. A filter that imparts characteristics that imitate the sound transmission path to the second microphone, and a subtraction that subtracts the output signal of the filter from the sound pick-up signal of the second microphone and supplies it to the reverse-phase signal generation circuit as the second signal. It has a vessel and.
According to the earphone according to the third aspect, the quality of the ambient sound and the target sound perceived by the user can be improved.

<Aspect 4>
The signal processing method of the earphone according to the fourth aspect includes a housing including an earpiece inserted into the user's external auditory canal, a first microphone provided in the housing and collecting peripheral sounds outside the external auditory canal, and the housing. A signal processing method for an earphone having a second microphone provided on a body and collecting sound in the external auditory canal and a speaker provided on the housing and emitting sound toward the external auditory canal. The volume of the low frequency band is made relatively higher than the volume of the high frequency band with respect to the first signal based on the sound picked up by the first microphone, and a reverse phase signal of the second signal based on the sound picked up by the second microphone is generated. The signal with the enhanced low frequency, the target signal indicating the target sound, and the reverse phase signal are added and output to the speaker.
According to the signal processing method of the earphone according to the fourth aspect, it is possible to reduce muffled sound and allow the user to hear the ambient sound with a natural feeling when wearing the earphone.

10a, 10b ... Earphones, 110 ... Microphone (1st microphone), 116 ... Equalizer, 120 ... Low frequency booster, 128, 130 ... Adder, 129 ... Filter, 140 ... Speaker, 150 ... Microphone (2nd microphone), 156 ... subtractor, 158 ... reverse phase signal generation circuit, 200 ... external terminal.

Claims (4)

A housing containing earpieces that are inserted into the user's ear canal,
A first microphone provided in the housing and collecting peripheral sounds outside the ear canal,
A second microphone provided in the housing and collecting sound in the ear canal,
A speaker provided in the housing and emitting sound toward the ear canal,
A low-frequency booster that raises the low-frequency volume relative to the high-frequency volume with respect to the first signal based on the sound picked up by the first microphone.
An anti-phase signal generation circuit that generates an anti-phase signal of the second signal based on the sound picked up by the second microphone, and
An adder that adds the output signal of the low frequency booster, the target signal indicating the target sound, and the reverse phase signal and outputs the signal to the speaker.
Including earphones. The first signal is provided with an equalizer that raises high frequencies above a predetermined frequency.
The earphone according to claim 1, wherein the output signal of the equalizer is input to the low-frequency booster. A characteristic that imitates the sound transmission path from the speaker to the second microphone is added to the signal input to the low-frequency booster or the signal output from the low-frequency booster and the target signal. With a filter
A subtractor that subtracts the output signal of the filter from the sound pick-up signal of the second microphone and supplies it to the reverse phase signal generation circuit as the second signal.
The earphone according to claim 1 or 2. A housing containing earpieces that are inserted into the user's ear canal,
A first microphone provided in the housing and collecting peripheral sounds outside the ear canal,
A second microphone provided in the housing and collecting sound in the ear canal,
A speaker provided in the housing and emitting sound toward the ear canal,
It is a signal processing method of earphones having
The volume of the low frequency band is made relatively higher than the volume of the high frequency band with respect to the first signal based on the sound picked up by the first microphone.
A reverse phase signal of the second signal based on the sound pick-up of the second microphone is generated.
A signal processing method for an earphone that adds a signal having an enhanced low range, a target signal indicating a target sound, and the reverse phase signal and outputs the signal to the speaker.

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