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DESCRIPTION JP2010019876

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DESCRIPTION JP2010019876
An object of the present invention is to provide a noise cancellation apparatus and method that
can be applied to equipment that is required to save power. A noise cancellation headphone 1
according to the present invention generates an external output signal obtained by removing an
external noise detected in advance from an audio signal, and is a frequency band that can be
masked against external noise of a specific frequency band. And a noise cancellation ON / OFF
control unit 13 that determines whether or not to cancel external noise in the specific frequency
band based on the signal level of the audio signal in the above. [Selected figure] Figure 1
Noise cancellation apparatus and method
[0001]
The present invention relates to power saving of a noise cancellation device that generates an
external output signal obtained by removing an external noise detected in advance from an audio
signal, and more particularly to noise cancellation processing in a noise cancellation headphone
or the like.
[0002]
In recent years, with the spread of portable audio devices, noise cancellation headphones have
become widespread.
The noise cancellation headphone is a microphone incorporated in the headphone to detect
10-04-2019
1
ambient noise, and adds the signal of the reverse phase of the detected noise to the music signal
and outputs it from the speaker to cancel the noise in the headphone . By using the noise
cancellation headphones, the user can enjoy music comfortably even in an environment where
the surrounding noise is large.
[0003]
As the technology relating to the noise cancellation headphone, for example, the technologies
disclosed in Patent Documents 1 and 2 are widely performed as a general technology. Patent
Document 1 discloses a technology relating to a noise cancellation headphone in which a filter
characteristic suitable for ambient noise is selected from a plurality of filter characteristics and
set as a band pass filter. Patent Document 2 discloses a technology relating to a noise
cancellation headphone capable of arbitrarily setting and changing the frequency characteristic
of noise to be removed.
[0004]
However, while the above-described noise cancellation function requires a large amount of power
consumption, power saving technology is required for portable audio devices and other devices
having a limited power supply.
[0005]
In order to meet such needs, various techniques related to power saving in noise canceling
headphones have been studied, including the technique described in Patent Document 3.
In Patent Document 3, power saving is achieved by turning off the operation of the noise
cancellation portion when it is not necessary to operate the noise cancellation portion or when
only noise outside the user's audible range is acquired from the external noise detection
microphone. A technology for realizing the technology has been disclosed.
[0006]
Here, FIG. 5 shows a configuration diagram of the noise cancellation headphone 5 for realizing
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the conventional power saving in Patent Document 3. As shown in FIG. The noise cancellation
headphone 5 of FIG. 5 includes the sampling unit 51, the noise level detection unit 52, the
frequency characteristic detection unit 53, the cancellation frequency band selection unit 54, the
noise cancellation signal generation unit 55, and the music signal level detection unit 56. And
[0007]
As parameters for ON / OFF control of the noise cancellation function, the noise level in the noise
level detection unit 52, the music signal level in the music signal level detection unit 56, and the
frequency characteristic in the frequency characteristic detection unit 53 are provided. First,
when the level of the noise N sampled by the sampling unit 51 is detected by the noise level
detection unit 52 and the level exceeds a predetermined threshold, the noise cancellation
function is turned on, while the noise N The noise cancellation function is turned off when the
level of the signal becomes below the threshold. Second, when the level of the music signal is
detected by the music signal level detection unit 56 and the level falls below a predetermined
threshold, the noise cancellation function is turned on, while the music signal exceeds the
threshold. If you do, turn off the noise cancellation function. Third, in the frequency
characteristic of the noise detected by the frequency characteristic detection unit 53, the noise
cancellation function is turned ON only when it is within a predetermined designated band. On
the other hand, if the noise in the designated band is not sampled, the noise cancellation function
is turned off. When the noise cancellation function is ON, the noise cancellation signal generation
unit 55 generates a noise cancellation signal.
[0008]
Patent Document 3 discloses that any of the above-described criteria for turning on / off the
noise cancellation function is combined arbitrarily. In particular, when all the above three
conditions are combined, the music signal level detected by the music signal level detection unit
56 is predetermined according to the noise level detected by the noise level detection unit 52
being equal to or lower than the predetermined threshold. If the frequency band detected by the
frequency characteristic detection unit 53 is out of the designated band, the noise cancellation
function is turned off. On the other hand, if the detected noise level is above the threshold, the
detected frequency band is within the designated band, and the music signal level is below the
threshold, the noise cancellation function is turned on. JP, 2007-110536, A JP, 2008-028937, A
JP, 2008-005269, A
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[0009]
In Patent Document 3, in anticipation of canceling noise by the auditory masking effect, the noise
cancellation function is stopped when the level of the music signal is equal to or higher than the
threshold. However, even if the level of the music signal is above the threshold, if the frequency
characteristics of the music signal and the noise are different, not only can the noise be canceled
out by the auditory masking effect, but rather the noise will stand out There is a problem that the
user feels unpleasant.
[0010]
Further, Patent Documents 1 and 2 are general techniques of the noise cancellation function, and
no consideration is given to power saving.
[0011]
The noise cancellation device according to the present invention is a noise cancellation device
that generates an external output signal obtained by removing an external noise detected in
advance from an audio signal, and the audio in the frequency band that can be masked against
external noise in a specific frequency band. A determination unit is provided that determines
whether to cancel external noise in the specific frequency band based on the signal level of the
signal.
[0012]
A noise cancellation method according to the present invention is a noise cancellation method for
generating an external output signal obtained by removing an external noise detected in advance
from an audio signal, and the audio in the frequency band that can be masked against external
noise in a specific frequency band. Based on the signal level of the signal, it is determined
whether to cancel external noise in the specific frequency band.
[0013]
According to the noise cancellation apparatus and method of the present invention described
above, for example, even when the audio signal includes a high signal level, the signal level of the
audio signal in the specific frequency band including the external noise to be detected is If the
auditory masking effect can not be expected, such as low, it can be determined to perform the
noise cancellation process.
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Therefore, it is possible to avoid a state in which the user feels unpleasant, and further, power
saving can be realized without performing processing when noise cancellation processing is
unnecessary.
[0014]
According to the present invention, it is possible to provide a noise cancellation apparatus and
method that can also be applied to devices that require power saving.
[0015]
Hereinafter, specific embodiments to which the present invention is applied will be described in
detail with reference to the drawings.
In the drawings, the same components are denoted by the same reference symbols, and
redundant description will be omitted as appropriate for the sake of clarity.
[0016]
First Embodiment of the Invention
FIG. 1 is a block diagram showing the configuration of the noise cancellation headphone 1
according to the first embodiment of the present invention.
The noise cancellation headphone 1 is connected to a portable audio device or the like, and
receives an input of an audio signal output from the portable audio device. Here, the audio signal
may be, for example, a digital signal obtained by digitizing audio data such as music and lectures.
[0017]
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In addition, the noise cancellation headphone 1 detects external noise including ambient noise
and the like, and generates an external output signal in which a cancellation signal for the
external noise is added to an audio signal to be output in advance. To remove In particular, the
noise cancellation headphone 1 performs noise cancellation processing on external noise in a
specific frequency band, which will be described later, based on the signal level of the audio
signal in the frequency band that can be masked against external noise in the specific frequency
band. To determine the The noise cancellation headphone 1 is not limited to the headphone. For
example, it may be an audio device including the determination process of the noise cancellation
process.
[0018]
The noise cancellation headphone 1 includes an external noise sampling unit 11, a noise
frequency characteristic detection unit 12, a noise cancellation ON / OFF control unit 13, an
audio frequency characteristic detection unit 14, a noise cancellation signal generation unit 15,
and an adder 16. And
[0019]
The external noise sampling unit 11 receives external noise as an input, samples a part of the
external noise from the external noise, outputs the sampled signal to the noise frequency
characteristic detection unit 12, and generates the noise cancellation signal generation unit for
the entire external noise. Output to 15.
[0020]
The noise frequency characteristic detection unit 12 receives external noise sampled from the
external noise sampling unit 11 as an input, analyzes the frequency characteristic of the external
noise, detects a signal level corresponding to a specific frequency band, and turns on noise
cancellation. Output to the / OFF control unit 13.
[0021]
Here, the specific frequency band is a frequency band that occupies a part of the frequency band
of the sampled external noise, and is a narrow frequency band with respect to the entire
frequency band of the external noise.
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Further, the specific frequency band is a frequency band in which the noise cancellation effect
can be sufficiently obtained or a frequency band in which the auditory masking effect is difficult
to be obtained that is not included so much in the audio signal among all frequency bands of the
sampled external noise.
For example, the noise frequency characteristic detection unit 12 may set in advance a frequency
band that has been empirically known that noise cancellation processing is necessary, in other
words, a frequency band to be detected as external noise as a specific frequency band. Just do it.
Alternatively, the noise frequency characteristic detection unit 12 may analyze the frequency
characteristic of the external noise and set a frequency band having a high signal level as a
specific frequency band.
[0022]
The noise frequency characteristic detection unit 12 may be one that analyzes the frequency
spectrum to detect the frequency and the signal level.
[0023]
The audio frequency characteristic detection unit 14 receives an input of an audio signal,
analyzes the frequency characteristic of the audio signal, detects a masking frequency band
where a masking effect can be expected with respect to external noise, and performs noise
cancellation ON / OFF control unit 13 Output to
[0024]
Here, the masking frequency band indicates a frequency band in which the external noise
detected by the noise frequency characteristic detection unit 12 can obtain an auditory masking
effect by an audio signal output at the same timing.
That is, in order to obtain a high auditory masking effect, the audio frequency characteristic
detection unit 14 specifically detects an audio signal in a frequency band close to the external
noise.
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For example, it may be a specific frequency band in the noise frequency characteristic detection
unit 12. Alternatively, it may be a band including a band around the specific frequency band.
[0025]
The noise cancellation ON / OFF control unit 13 receives external noise from the noise frequency
characteristic detection unit 12 and an audio signal from the audio frequency characteristic
detection unit 14 as input, and based on them, noise is transmitted to the noise cancellation
signal generation unit 15 It outputs a control signal for instructing generation of a cancellation
signal. That is, the noise cancellation ON / OFF control unit 13 also plays a role as a
determination unit that determines to execute the noise cancellation process when the
predetermined condition is satisfied.
[0026]
Here, the predetermined condition is the case where the external noise is equal to or higher than
the threshold and the audio signal is equal to or lower than the threshold. That is, the noise
cancellation ON / OFF control unit 13 determines that the noise cancellation process is to be
performed when the predetermined condition is satisfied. Note that the threshold value of the
external noise and the threshold value of the audio signal described above may be set in the
noise cancellation ON / OFF control unit 13 in advance.
[0027]
The noise cancellation signal generation unit 15 receives external noise from the external noise
sampling unit 11 as an input, and the control signal from the noise cancellation ON / OFF control
unit 13 indicates execution of noise cancellation processing, A noise cancellation signal, which is
a signal in reverse phase to the external noise, is generated and output to the adder 16.
[0028]
The adder 16 receives the audio signal and the noise cancellation signal from the noise
cancellation signal generation unit 15 as an input, and outputs an external output signal obtained
by adding the noise cancellation signal to the audio signal to the outside of a speaker or the like.
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Here, the external output signal is a signal obtained by adding a noise cancellation signal to an
audio signal, in other words, a signal obtained by removing external noise from the audio signal.
[0029]
In the noise cancellation headphone 1 according to the first embodiment of the present
invention, it may be determined at least whether the signal level of the audio signal is less than or
equal to the threshold, and whether the signal level of external noise is greater than or equal to
the threshold The determination of whether or not it does not matter.
[0030]
FIG. 2 is a flowchart for determining the noise cancellation process according to the first
embodiment of the present invention.
First, the noise frequency characteristic detection unit 12 acquires external noise (S201). Next,
the noise frequency characteristic detection unit 12 detects the signal level present in the
specific frequency band, and outputs the signal level to the noise cancellation ON / OFF control
unit 13 (S202).
[0031]
Further, the audio frequency characteristic detection unit 14 acquires an audio signal (S203).
Then, the audio frequency characteristic detection unit 14 detects a signal level corresponding to
the specific frequency band, and outputs the signal level to the noise cancellation ON / OFF
control unit 13 (S204). In the audio frequency characteristic detection unit 14, the signal level to
be detected may be at least at least based on the specific frequency band used for detection by
the noise frequency characteristic detection unit 12 in step S202. It may be included. Steps S201
and S202 and steps S203 and S204 are performed in parallel, but may be performed in order.
[0032]
Thereafter, the noise cancellation ON / OFF control unit 13 determines whether the signal level
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in the specific frequency band of the external noise detected by the noise frequency
characteristic detection unit 12 is equal to or higher than the threshold (S205). If it is determined
in step S205 that the signal level in the specific frequency band of the external noise is not
higher than the threshold, that is, if the signal level of the external noise in the specific frequency
band is less than the threshold, noise cancellation processing is not performed. It returns to step
S201 and S203. At this time, the noise cancellation ON / OFF control unit 13 does not output the
control signal to the noise cancellation signal generation unit 15. Alternatively, the noise
cancellation ON / OFF control unit 13 may output a control signal for turning off the noise
cancellation process to the noise cancellation signal generation unit 15.
[0033]
When it is determined in step S205 that the signal level in the specific frequency band of the
external noise is equal to or higher than the threshold, the noise cancellation ON / OFF control
unit 13 detects the audio signal detected by the audio frequency characteristic detection unit 14
It is determined whether the signal level in the specific frequency band is less than or equal to
the threshold (S206). If it is determined in step S206 that the signal level in the specific
frequency band of the audio signal is not below the threshold, that is, if the signal level of the
audio signal in the specific frequency band exceeds the threshold, noise cancellation processing
is not performed. Return to the top of the flowchart. The order of the processes in steps S205
and S206 may be reversed.
[0034]
When it is determined in step S206 that the signal level in the specific frequency band of the
audio signal is less than or equal to the threshold, the noise cancellation ON / OFF control unit
13 turns on the noise cancellation processing to the noise cancellation signal generation unit 15.
Output control signal. Then, noise cancellation processing is executed by the noise cancellation
signal generation unit 15 and the adder 16 (S207). That is, the noise cancellation signal
generation unit 15 generates a noise cancellation signal from external noise based on the control
signal, and the adder 16 generates and outputs an external output signal obtained by adding the
noise cancellation signal to the audio signal.
[0035]
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As a result, when the auditory masking effect can not be expected, the external noise and the
noise cancellation signal included in the external output signal cancel each other out, so that the
user who wears the noise cancellation headphone 1 has the voice from which the external noise
has been removed. Only the signal part will be heard. Conversely, if the auditory masking effect
can be expected, that is, if the signal level of the external noise is low or if the signal level of the
audio signal corresponding to the specific frequency band of the external noise is high, the noise
cancellation process is not performed. Therefore, it is possible to avoid consuming power
unnecessarily.
[0036]
In other words, in the first embodiment of the present invention, the noise cancellation function
is turned ON only when the masking effect by the audio signal can not be expected due to the
external noise, and when the masking effect can be expected, the user performs the external
noise by the masking effect. The power consumption of the noise cancellation headphone 1 can
be suppressed by making it not feel unpleasant.
[0037]
Further, in the first embodiment of the present invention, when the signal level of the audio
signal is detected by the audio frequency characteristic detection unit 14, the noise frequency
characteristic detection unit 12 uses the band applied to the external noise to use the frequency
characteristic. Analysis and signal level detection may be performed.
[0038]
In the first embodiment of the present invention, when the auditory masking effect can not be
expected by associating the specific frequency band used as the determination reference of the
execution of the noise cancellation processing in the noise cancellation ON / OFF control unit 13
with the external noise and the audio signal. Only by removing an external noise signal from the
audio signal in advance, it is possible to generate a signal, and it is possible to control an optimal
noise cancellation process.
[0039]
Second Embodiment of the Invention
In the second embodiment of the present invention, the noise cancellation according to the first
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embodiment of the present invention is realized by replacing the noise frequency characteristic
detection unit 12 and the audio frequency characteristic detection unit 14 in the first
embodiment of the present invention with band pass filters. A noise cancellation headphone 2
that can be realized at low cost compared to the headphone 1 will be described.
[0040]
FIG. 3 is a block diagram showing the configuration of the noise cancellation headphone 2
according to the second embodiment of the present invention.
In addition, in FIG. 3, about the structure similar to FIG. 1, the same code | symbol is attached
and description is abbreviate | omitted.
[0041]
The band pass filters 22 and 24 in the noise cancellation headphone 2 are obtained by replacing
the noise frequency characteristic detection unit 12 and the audio frequency characteristic
detection unit 14 in the noise cancellation headphone 1 of FIG. 1.
The noise cancellation headphone 2 passes the external noise to the band pass filter 22 to detect
the signal level of the external noise in a predetermined specific frequency band. Then, the signal
level of the detected external noise is input to the noise cancellation ON / OFF control unit 13.
[0042]
Similarly, the noise cancellation headphone 2 passes the audio signal to the band pass filter 24
so that the signal of the audio signal for the specific frequency band used for the band pass filter
22 or the frequency band including the periphery of the specific frequency band. Detect the level.
Then, the signal level of the detected audio signal is input to the noise cancellation ON / OFF
control unit 13.
[0043]
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Moreover, since the determination processing of the noise cancellation processing in
Embodiment 2 of this invention is the same as that of FIG. 2, description and illustration are
abbreviate | omitted.
[0044]
In the noise cancellation headphone 2, at least the band pass filter 24 may be used, and the band
pass filter 22 may be the noise frequency characteristic detection unit 12.
[0045]
From the above, in the second embodiment of the present invention, mounting can be easily
performed at low cost by using a band pass filter simpler than frequency characteristic detection.
Further, when the present invention is implemented by an analog circuit, the band pass filter can
be implemented more easily than frequency characteristic detection by not requiring digital
operation.
[0046]
Embodiment 3 of the Invention
In the first embodiment of the present invention, in step S205 of FIG. 2, it is determined whether
the noise cancellation process is ON or OFF depending on whether the signal level of the external
noise is equal to or higher than a threshold. Therefore, even if the signal level of the audio signal
is lower than the threshold, switching the noise cancellation processing ON or OFF when the
signal level of the external noise changes frequently frequently before and after the threshold
due to the influence of the external environment or the like. Is frequently performed, the control
of the noise cancellation signal generation unit 15 is not stable, and whether or not the noise
cancellation processing is performed is switched depending on the difference of minute external
noises, which may also be unpleasant for the user. .
[0047]
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Therefore, in the third embodiment of the present invention, an improvement is added to the first
embodiment of the present invention, and in the noise cancellation ON / OFF control unit 13, a
threshold when noise cancellation processing is switched from ON to OFF and noise cancellation
processing. The control of the noise cancellation signal generation unit 15 can be stably executed
by setting the threshold value to be different from the threshold value at the time of switching
from OFF to ON. Therefore, it is possible to prevent repetitive processing of switching of
unnecessary noise cancellation processing. In addition, since the noise cancellation headphone
concerning Embodiment 3 of this invention is the structure similar to the noise cancellation
headphone 1 of FIG. 1, illustration and description are abbreviate | omitted.
[0048]
In the noise cancellation headphone according to the third embodiment of the present invention,
when it is determined in step S205 of FIG. 2 that the signal level in the specific frequency band of
the external noise is equal to or higher than the threshold, that is, it is determined to execute the
noise cancellation process. In this case, the noise cancellation ON / OFF control unit 13 lowers
the threshold. In addition, when it is determined that the value is less than the threshold value,
that is, when it is determined that the noise cancellation process is not performed, the noise
cancellation ON / OFF control unit 13 raises the threshold value.
[0049]
Thus, once noise cancellation processing is executed, noise cancellation is performed while the
signal level of external noise makes a slight change, for example, until the signal level is reduced
to a certain extent, even if it falls below the initial threshold. Processing continues. In addition,
once noise cancellation processing is not performed, noise cancellation processing is performed
until the signal level increases to some extent even if the initial threshold is exceeded while the
signal level of external noise changes slightly. Will not run.
[0050]
FIG. 4 is a diagram showing an example of the noise level and the threshold value for performing
the noise cancellation process determination according to the third embodiment of the present
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invention. As shown in FIG. 4, when the signal level of the external noise exceeds the "OFF to ON
switching threshold", the noise cancellation process switches from OFF to ON, and from "OFF to
ON switching threshold" to "ON to OFF switching threshold" Go down to. As a result, as long as
there is no rapid decrease in external noise, noise cancellation processing will be continued for a
while. Also, after the external noise is sufficiently reduced and the signal level of the external
noise falls below the "ON → OFF switching threshold", the noise cancellation process switches
from ON to OFF, and from "ON → OFF switching threshold" to "OFF → The ON switching
threshold is raised. As a result, as long as there is no rapid increase in external noise, noise
cancellation processing will not be performed for a while.
[0051]
Therefore, it is possible to appropriately suppress the switching between ON and OFF of the
noise cancellation processing that is unnecessarily frequent, and it is possible to reduce the
unpleasant feeling for the user. Furthermore, power saving can be realized by preventing
unnecessary switching of noise cancellation processing. In particular, it is possible to improve the
robustness to a minute change of the acquired signal when implemented by an analog circuit.
[0052]
Embodiment 4 of the Invention In the fourth embodiment of the present invention, an
improvement is added to the first embodiment of the present invention, and the specific
frequency band of the noise frequency characteristic detection unit 12 and the audio frequency
characteristic detection unit 14 or the threshold of the noise cancellation ON / OFF control unit
13 External input means for changing the specific frequency band or the threshold value. This
enables the user to control the power saving process. In addition, since the noise cancellation
headphones concerning Embodiment 4 of this invention are the structures similar to the noise
cancellation headphones 1 of FIG. 1 except the input means mentioned above, illustration and
description are abbreviate | omitted.
[0053]
For example, the noise cancellation headphone according to the fourth embodiment of the
present invention further includes an input unit for receiving an input of designation of a specific
frequency band, and the noise frequency characteristic detection unit 12 and the audio
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frequency characteristic detection unit 14 use the input unit. The signal level may be detected
based on the input specific frequency band. Alternatively, the noise cancellation headphone
according to the fourth embodiment of the present invention further includes an input unit that
receives an input of specification of a threshold of the signal level, and the noise cancellation ON
/ OFF control unit 13 determines the threshold input by the input unit. It may be determined
based on whether or not to execute the noise cancellation process.
[0054]
Thus, the user can switch the mode in which noise cancellation processing is prioritized by
setting the threshold low in the noise cancellation ON / OFF control unit 13 and the mode in
which power saving is prioritized by setting the threshold high. It becomes possible to control the
noise cancellation processing appropriately according to the situation.
[0055]
In addition, a low pass filter with a narrow passband is prepared as the band pass filter, and the
user is provided with a mode that achieves power saving by applying noise cancellation only to a
band where the effect of noise cancellation can be sufficiently obtained. It can also be done.
[0056]
From the above, it is possible to provide the power saving processing method of the noise
canceling headphone which is most suitable for the situation of the user.
[0057]
Other Embodiments of the Invention
As described above, according to the present invention, it is possible to improve the user's music
appreciation environment while the noise cancellation function is OFF by the power saving of the
noise cancellation function.
[0058]
Furthermore, the present invention is not limited to the above-described embodiment, and it goes
without saying that various modifications can be made without departing from the scope of the
present invention already described.
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[0059]
It is a block diagram which shows the structure of the noise cancellation apparatus concerning
Embodiment 1 of this invention.
FIG. 6 is a flowchart for determining the noise cancellation process according to the first
embodiment of the present invention.
It is a block diagram which shows the structure of the noise cancellation apparatus concerning
Embodiment 2 of this invention.
It is a figure which shows the example of the threshold value for determining the noise level
concerning Embodiment 3 of this invention, and a noise cancellation process. It is a block
diagram showing the composition of the noise cancellation headphone of related art.
Explanation of sign
[0060]
DESCRIPTION OF SYMBOLS 1 noise cancellation headphone 11 external noise sampling part 12
noise frequency characteristic detection part 13 noise cancellation ON / OFF control part 14
audio frequency characteristic detection part 15 noise cancellation signal generation part 16
adder 2 noise cancellation headphone 22 band pass filter 24 band pass filter DESCRIPTION OF
SYMBOLS 5 noise cancellation headphone 51 sampling part 52 noise level detection part 53
frequency characteristic detection part 54 cancellation frequency band selection part 55 noise
cancellation signal generation part 56 music signal level detection part
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