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DESCRIPTION JP2010050739

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DESCRIPTION JP2010050739
PROBLEM TO BE SOLVED: To provide a noise cancellation system and a noise cancellation
method capable of correcting displacement of a phase caused due to the characteristics of a
noise cancellation system capable of canceling ambient noise. SOLUTION: A microphone unit for
collecting ambient noise through an electroacoustic transducer and outputting a noise signal, a
filter circuit for outputting a signal of a predetermined frequency range included in the noise
signal, and inverting the output of the filter circuit And an addition circuit for adding an output of
the inversion amplifier circuit to the noise signal and outputting the generated signal and
generating a cancellation signal for eliminating the noise. According to a noise cancellation
system including cancellation signal generation means, and a speaker unit for outputting an
audio signal and a cancellation signal. [Selected figure] Figure 2
ノイズキャンセルシステム
[0001]
The present invention relates to a noise cancellation system capable of canceling a surrounding
noise, capable of correcting phase displacement caused due to characteristics, and outputting a
cancellation signal with higher accuracy. It is.
[0002]
A noise cancellation system capable of canceling out ambient noise by cancellation sound can be
used as a noise cancellation headphone capable of listening to reproduced music while canceling
out noise by using it for headphones or the like.
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1
The noise cancellation headphones convert ambient noise collected by a microphone unit
attached to the headphone casing etc. into a noise signal which is an electrical signal, and use
this noise signal to pass through the headphone casing to the ear A signal (cancel signal) that
cancels audible noise is generated, and it is configured so that the user can listen to music in a
state where surrounding noise is canceled by the cancellation sound output from the headphone
speaker unit together with the music to be reproduced ing.
[0003]
It would be ideal if the canceling sound could completely cancel out the noise heard in the ear.
However, the microphone unit and the speaker unit that constitute the noise cancellation system
have a characteristic (phase characteristic) in which the phase is displaced by the frequency. The
phase characteristic is such that as the frequency is lower, the phase relatively advances and the
gain is attenuated, and as the frequency is higher, the phase is relatively delayed. Since the
cancellation signal output from the speaker unit of the noise cancellation system is affected by
this phase characteristic, it is difficult to generate a cancellation signal that completely cancels
out the noise heard in the ear. When a cancellation sound whose phase relative to the noise is
displaced under the influence of such phase characteristics is output from the speaker unit, the
effect (cancellation effect) to cancel the noise that is supposed to be exhibited is only lowered.
Instead, the cancellation signal may intensify a specific frequency included in the noise to make
the noise louder.
[0004]
In addition, there are other causes that the phase of the cancellation sound is displaced. Since the
ambient noise to be canceled contains various sounds, it is difficult to generate a cancellation
note for all frequencies included in the noise. Therefore, the noise cancellation system uses a
filter circuit to narrow the frequency band for generating the cancellation signal to some extent.
[0005]
The filter circuit used for the audio signal includes a low pass filter for blocking a signal below a
predetermined frequency, a high pass filter for blocking a signal above a predetermined
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2
frequency, a band pass filter for blocking signals other than a predetermined frequency band,
and a predetermined frequency There is a notch filter that blocks signals in the band. The noise
cancellation headphone is configured to determine a frequency band for exhibiting a cancellation
effect by using these filter circuits in combination, and generate a predetermined cancellation
signal. In other words, the signal used for generating the cancellation signal by the filter circuit is
extracted from the noise signal, and the frequency band is limited. According to such a
configuration, although the cancellation effect is exhibited in a specific frequency band, the
cancellation effect can not be exhibited in other frequency bands. Therefore, a noise cancellation
system that can increase the types of noise that can be canceled by mounting a plurality of filter
circuits and selectively switching the filter circuit with a switch or the like so as to cancel more
various noises. Are known (see, for example, "Patent Document 1").
[0006]
Japanese Patent Application Laid-Open No. 4-8099
[0007]
The filter circuit is of passive type using passive elements, active type using operational amplifier,
etc. In any filter circuit, the phase advances relatively to the lower frequency component of the
input original signal and the higher frequency The component has a characteristic that the phase
is relatively delayed and displaced.
[0008]
As described above, in the noise cancellation system, the phase of the noise heard by the ear and
the phase of the cancellation sound are relatively displaced due to the phase characteristic by the
configuration and the phase characteristic of the filter circuit.
Therefore, in order to output a more accurate cancellation signal to enhance the noise
cancellation effect, a noise cancellation system capable of generating and outputting a
cancellation signal with the above phase characteristics corrected is required.
In order to correct the phase characteristic, it is only necessary to realize a circuit having such a
characteristic that the low frequency phase contained in the noise signal is relatively delayed and
the high frequency phase is relatively advanced. In order to realize such a phase characteristic
with a filter circuit, it is necessary to use, as a component of the filter circuit, an element in which
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the impedance is low and the phase advances in the high region, or an element in which the
impedance is high and the phase is delayed in the high region . However, such components are
not electronic circuits and therefore impossible to implement.
[0009]
In the conventional noise cancellation system, in order to reduce the influence of the phase
characteristic received by the cancellation signal as much as possible, various filters are
appropriately combined to artificially match the phases and prevent displacement. By this, it
becomes difficult to come out of the fault by the influence of phase characteristics. However, in
any of the filter circuits, the phase characteristic advances at a relatively low frequency, and the
phase is delayed at a high frequency. Therefore, the phase characteristic should be corrected at a
frequency that is a joint of a plurality of filter circuits. It is difficult, and at this joint frequency,
the cancellation effect becomes extremely bad, and in order to prevent this, it is necessary to
suppress and balance the overall cancellation amount. For this reason, the noise cancellation
system has an insufficient canceling effect and an aurally unnatural output.
[0010]
The present invention has been made in view of the above problems, and in a noise cancellation
system capable of canceling ambient noise, it has a filter circuit having phase characteristics
capable of correcting the conventional phase characteristics, An object of the present invention is
to provide a noise cancellation system capable of outputting a cancellation signal whose
displacement has been corrected.
[0011]
The present invention comprises a microphone unit for collecting ambient noise through an
electroacoustic transducer and outputting a noise signal, a cancellation signal generation means
for generating and outputting a cancellation signal for canceling the noise, and an audio signal
such as music. A noise cancellation system comprising: a speaker unit for outputting the
cancellation signal; wherein the cancellation signal generation means outputs a signal of a
predetermined frequency range included in the noise signal; an output of the filter circuit The
present invention is mainly characterized in that it has an inverting amplifier circuit that
amplifies the amplitude of the signal by more than 0 and less than 1 and an adding circuit that
adds the output of the inverting amplifier circuit to the noise signal and outputs it.
[0012]
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The present invention also relates to a microphone unit that collects ambient noise through an
electroacoustic transducer and outputs a noise signal, a cancellation signal generation unit that
generates and outputs a cancellation signal that cancels the noise, and an audio signal such as
music. And a speaker unit for outputting the cancellation signal, wherein the cancellation signal
generation means outputs a signal of a predetermined frequency range included in the noise
signal, the filter circuit The present invention is mainly characterized in that it has a noninverting amplification circuit that amplifies the output and is greater than 0 and less than 1 and
a subtraction circuit that subtracts the output of the non-rotation amplification circuit from the
noise signal and outputs it.
[0013]
In the noise cancellation system according to the present invention, the filter circuit is a low pass
filter, or the filter circuit is a high pass filter, or the filter circuit is a band pass filter, or The filter
circuit is a notch filter.
[0014]
The present invention also relates to a microphone unit that collects ambient noise through an
electroacoustic transducer and outputs a noise signal, a cancellation signal generation unit that
generates and outputs a cancellation signal that cancels the noise, and music, etc. A filter circuit
including a speaker unit for outputting an audio signal and the cancel signal, wherein the cancel
signal generation means outputs a signal of a predetermined frequency range included in the
noise signal; and inverting the output of the filter circuit A noise cancellation method using a
noise cancellation system, comprising: an inverting amplification circuit whose amplification
degree to be amplified is greater than 0 and less than 1; and an addition circuit which adds the
output of the inverting amplification circuit to the noise signal and outputs the result. A filter
circuit extracting a signal of a predetermined frequency band from the noise signal; And
amplifying the signal with an amplification factor of more than 0 and less than 1 and adding the
signal obtained by inverting and amplifying the noise signal, and outputting the signal. The noise
can be canceled by outputting the signal from the speaker unit.
[0015]
In the noise cancellation method according to the present invention, the filter circuit is a low pass
filter, or the filter circuit is a high pass filter, or the filter circuit is a band pass filter, or The filter
circuit is characterized by being a notch filter
[0016]
According to the present invention, it is possible to obtain a noise cancellation system and a noise
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cancellation method which can cancel out noise over a wide band without difficulty and can
exhibit a natural noise cancellation effect without the user feeling uncomfortable.
[0017]
An example of an embodiment of a noise cancellation system according to the present invention
will be described.
Here, it uses for the example of the noise cancellation headphone which is an example of a noise
cancellation system.
FIG. 1 is a schematic view showing only one casing of noise canceling headphones configured as
a pair of left and right.
In FIG. 1, a noise cancellation unit 100 (hereinafter referred to as an “NC unit 100”), which is
the core of the noise cancellation system, and an ambient noise N of the noise cancellation
headphones are collected inside the headphone case 1 A microphone unit 60 for producing
sound and converting it into an electric signal and outputting it is incorporated toward the
outside of the headphone case 1.
A through hole 201 is provided in a part of the outer wall of the headphone casing 1 for the
microphone unit 60 to easily collect noise N.
A sound signal such as a portable music player is connected to the NC unit 100, and a music
signal input thereto and a cancellation sound that cancels noise N 'which is heard by the ear 200
through the headphone housing 1 are output to the ear 200. Speaker unit is provided.
Further, a battery (not shown) which is a drive power source of the NC unit 100 is
accommodated in the headphone case 1.
[0018]
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The noise cancellation headphones which are an example of the noise cancellation system which
concerns on this invention are implement | achieved by combining a pair of headphone housing |
casings 1 on either side by a headband, for example.
The left and right headphone casings 1 may both have the configuration as shown in FIG. 1 and
cords may be connected to the respective casings 1 for inputting musical tone signals from the
sound source 300, In the case of headphones of a type in which the left and right headphone
casings 1 are coupled by a headband, a wire through which a musical tone signal is transmitted
from one headphone casing 1 to the other headphone casing 1 may be embedded in the
headband. Further, the drive battery may be configured to be loaded into only one headphone
casing 1.
[0019]
Next, the details of the NC unit 100 will be described with reference to the block diagram of FIG.
In FIG. 2, the NC unit 100 includes a microphone amplifier 20 that adjusts and outputs a noise
signal collected by the microphone unit 60 and converted into an electrical signal to a
predetermined level, and included in the noise signal output from the microphone amplifier 20.
Filter circuit 11 for extracting and outputting the predetermined frequency band, inverting
amplifier circuit 12 for inverting and amplifying the output of the filter circuit 11 and amplifying
it by M times, noise signal output from the microphone amplifier 20 and inverting amplifier
circuit 12 The phase inversion filter circuit 10 including the addition circuit 13 which adds the
outputs of the first and second lines to output the cancellation signal, the amplifier 30 which
amplifies the cancellation signal output from the phase inversion filter circuit 10, and the
speaker unit 50 by the output of the amplifier 30. Drive by headphone amplifier 40 and
headphone amplifier 40 Comprising a speaker unit 50 that. A musical tone signal from the sound
source 300 is input to the headphone amplifier 40 together with a cancel signal which is an
output signal of the amplifier 30. This tone signal may be added to the cancel signal by the
addition circuit by adding another addition circuit between the amplifier 30 and the headphone
amplifier 40. The speaker unit 50 outputs a musical tone and a cancellation sound to the user's
ear 200. The noise that passes through the headphone case 1 and is heard by the ear 200 is
canceled by the cancellation sound, and the user can hear only the musical tone.
[0020]
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The feature of the noise cancellation system according to the present invention resides in the
phase inverting filter circuit 10 described above. Also, the feature of the noise cancellation
method according to the present invention lies in the flow of the operation of the phase inversion
filter circuit 10 described above. Therefore, the details of the phase inverting filter circuit 10 will
be described as an embodiment of the present invention. The phase inversion filter circuit 10
exhibits the same function as the filter circuit used in the conventional noise cancellation system,
and extracts a specific frequency component for generating a cancellation signal from the noise
signal collected by the microphone unit 60. Also has the function of Since the phase inverting
filter circuit 10 inverts the output of the conventional filter circuit by the inverting amplifier
circuit 12, a high pass filter is used for the filter circuit 11 in order to make the phase inverting
filter circuit 10 function as a low pass filter. Similarly, to make the phase inverting filter circuit
10 function as a high pass filter, the filter circuit 11 uses a low pass filter, to function as a band
pass filter, and the filter circuit 11 to function as a notch filter or as a notch filter A band pass
filter will be used for the circuit 11.
[0021]
Here, when the filter circuit 11 is a high pass filter, that is, an example in which the phase
inversion filter 10 functions as a low pass filter to output a cancellation signal will be described.
First, the phase characteristics of the high pass filter will be described with reference to the
drawings. FIG. 3 is a graph showing an example of the phase characteristic of the high pass filter.
In FIG. 3, the horizontal axis indicates the frequency (Hz) of the input signal as a logarithm, and
the vertical axis indicates the phase shift (°) of the input signal and the output signal by a
constant. The cutoff frequency f0 is 200 Hz.
[0022]
Assuming that the phase displacement at the cutoff frequency f0 is θf0, θf0 is expressed by
“tan <−1> (1 / (2πf0CR)), 2πf0 = 1 / CR”, so that the phase displacement θf0 is tan <−1>
(1 And the phase advances 45 ° at the cutoff frequency f0. That is, when the frequency of the
input signal of the filter circuit 11 is low, the phase of the output signal leads as close to 90 ° as
possible from the phase of the input signal, and the phase advance at the cutoff frequency f0 is
45 °. Also, as the frequency becomes higher, the phase lead becomes dull, and at a frequency
sufficiently higher than the cutoff frequency f0, the phase becomes substantially in phase (phase
shift is 0 °). Here, the above C and R are the resistance value (R) of the resistor used for the
filter circuit 11 which is a high pass filter and the capacitance value (C) of the capacitor.
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[0023]
The output of the filter circuit 11 is inverted (a phase is shifted by 180 °) by the inverting
amplifier circuit 12 at the subsequent stage, amplified by M times, and output. Therefore,
focusing on the phase characteristics, the phase displacement characteristics of the output signal
of the filter circuit 11 (the input signal of the inverting amplifier circuit 12) and the output signal
of the inverting amplifier circuit 12 are the phase characteristics of the filter circuit 11 as shown
by graph H2 in FIG. It is displaced 180 ° from.
[0024]
The cutoff frequency f0 of the filter circuit 11 is also the cutoff frequency f0 of the phase
inversion filter circuit 10. Therefore, the phase θf0r at the cut-off frequency f0 of the phase
inversion type filter circuit 10 is represented by “−tan <−1> (1 / (2πf0CR)), 2πf0 = 1 / CR”
by the function of the inversion circuit 12. The phase displacement θf0r is −tan <−1> (1), and
the phase is delayed by 45 °. That is, the displacement of the phase at the cutoff frequency f0 of
the phase inversion filter circuit 10 is relatively delayed by 45 °. This is when the amplification
degree M of the inverting amplification circuit 12 is 1.
[0025]
When the amplification degree M is 0 or more and less than 1, the above-mentioned formula is
expressed by “−tan <−1> (1 / (M2πf0CR)), 2πf0 = 1 / CR”. Therefore, the phase
characteristic of the phase inverting filter circuit 10 is such that the phase displacement θf0r is
expressed by tan <−1> (M) when the amplification factor M of the inverting amplifier circuit 12
is 0 or more and less than 1. The value changes the phase displacement in the range of 0 ° to 45 °. When the amplification factor M of the inverting amplification circuit 12 is larger than 1,
the phase displacement θr of the phase inversion filter circuit 10 is in phase with the phase θ
of the input signal at a frequency sufficiently higher than the cutoff frequency f0. It is unsuitable
for obtaining the effect of the present invention. The phase characteristic θrM at this time is
approximately expressed by “tan <−1> (M / ((M−1) 2πfCR), M> 1, f >> f0”).
[0026]
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Therefore, the phase characteristic θrM of the signal (cancel signal) obtained by adding the
output of the inverting amplifier circuit 12 output from the adding circuit 13 and the output
(noise signal) of the microphone amplifier 20 is “−tan <−1> (M2πfCR / It is represented by
(1+ (1-M) (2πfCR) <2>)). An example of the phase characteristic when the value of amplification
degree M is changed based on this equation is shown in FIG. In FIG. 4, the horizontal axis
indicates the frequency (f) in logarithm, and the vertical axis indicates the phase displacement
θrM (°) of the output signal of the microphone amplifier 20 and the output signal of the phase
inversion filter circuit 10 by a constant.
[0027]
A graph P1 linearly changing at a phase shift of 0 ° is a case where the amplification factor M is
zero. When the amplification factor M is 0, the output of the microphone amplifier 20 becomes
the output of the phase inverting filter circuit 10, and there is no phase displacement. A graph P3
represented by an alternate long and short dash line indicates the case where the amplification
factor M is 1.5. As already described above, when the amplification factor M of the inverting
amplification circuit 12 is larger than 1 and approaches the phase of the noise signal input from
the microphone unit 20 if it exceeds the cutoff frequency f0 (200 Hz in this embodiment), phase
inversion The relative phase of the output of filter circuit 10 will be advanced. Therefore, in the
graph P3, the phase shift turns to lead at a frequency higher than the cutoff frequency f0.
[0028]
A graph P4 represented by a long dotted line is a case where the amplification degree M is 1.
When the amplification factor M is 1, the phase characteristic of the filter circuit 11 is reflected
as it is, so the higher the frequency, the later the phase is delayed. Since the output of the
microphone unit 20 input to the adding circuit 13 and the output of the inverting amplification
circuit 12 are substantially in phase at a low frequency, the phase displacement is approximately
0 °, but a filter that the phase is delayed as the frequency becomes higher The characteristics of
the circuit appear as they are, and the low frequency phase displacement becomes approximately
0 ° as shown by the graph P4, and the phase displacement tends to be greatly delayed as the
frequency becomes higher.
[0029]
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A graph P2 represented by a short dotted line shows the case where the amplification degree M
is 0.75. In this case, the level of the output of the inverting amplification circuit 12 is lower (by
0.75) than the original signal (the output of the microphone unit 20). Therefore, the adder circuit
13 adds the inverted signal multiplied by 0.75 to the output signal of the microphone unit 20. At
frequencies lower than the cutoff frequency f0, the amount of phase displacement of the output
signal of the microphone amplifier 20 and the output signal of the inverting amplification circuit
12 is small and close to the same phase, but as the frequency increases, the phase displacement
becomes "delayed" gradually. Become. When the cutoff frequency f0 is exceeded, the phase
displacement gradually approaches the same phase, so that the characteristic is such that the
phase displacement "leads" when the frequency becomes high, as shown by graph P2. By this, it
becomes possible to obtain a phase characteristic in which the phase advances relatively as the
frequency increases.
[0030]
Next, the gain characteristic of the phase inverting filter 10 will be described with reference to
FIG. In FIG. 5, the vertical axis represents the gain (dB) of the phase inversion filter 10, and the
horizontal axis represents the frequency (Hz) of the input signal of the phase inversion filter in
logarithm. When the amplification degree of the inverting amplification circuit 12 is 0, the output
of the filter circuit 11 is not amplified at all, so the gain becomes 0 dB, as shown by the graph G1.
The gain characteristic when the amplification degree M is 1.5 is as shown by a graph G3
represented by a two-dot chain line. As in the characteristic of the phase shift described above,
the phase shift turns to the lead when the cutoff frequency f0 is exceeded, so a signal larger than
the signal input from the microphone amplifier 20 (because the amplification factor M is 1.5
times) The output level of the phase inversion filter circuit 10 is suppressed. Therefore, the gain
is characterized by being attenuated as the frequency becomes higher.
[0031]
A graph G4 represented by a long dotted line shows the gain characteristic when the
amplification degree M is one. Since the phase characteristic of the filter circuit 11 is reflected as
it is, the phase shift when the amplification degree M is 1 will be delayed in phase as the
frequency becomes higher. Since this is the same as the phase characteristic of the output signal
of the microphone amplifier 20, the output of the adding circuit 13 becomes the same as the gain
characteristic at the output of the inverting amplifier circuit 12, and the gain attenuates as the
frequency increases.
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[0032]
A graph G2 represented by a short dotted line shows the gain characteristic when the
amplification factor M is 0.75. At this time, as described above, the phase shift is relatively
delayed at a low frequency, and becomes smaller as the frequency becomes higher (relatively
advanced) as the phase shifts. Accordingly, as the frequency also increases in the gain
characteristic, the attenuation of the gain is blunted by the output signal of the inverting
amplification circuit 12, and the gain characteristic as shown in FIG. 5 can be obtained.
[0033]
In the above example, when the amplification factor M is 0.75, it is possible to obtain the
characteristic of the phase shift in which the phase is relatively delayed at low frequencies and
the phase is relatively advanced at high frequencies. Can be obtained as the gain becomes higher.
The optimum value of the amplification degree M depends on the characteristics of the
microphone unit 60, the speaker unit 50, and the like in the range of 0 to 1.
[0034]
Next, an embodiment of the noise cancellation method according to the present invention will be
described. In the noise cancellation unit 100 shown in FIG. 2, first, the noise signal converted into
the electric signal by the microphone unit 60 is amplified to a predetermined level in the
microphone amplifier 20. Next, the filter circuit 11 extracts a signal of a predetermined
frequency region included in the noise signal at a predetermined cutoff frequency. Next, in the
inverting amplifier circuit 12, the above extracted noise signal is inverted, amplified by the
amplification factor M as described above, and output. Next, the addition circuit 13 adds the
noise signal output from the microphone amplifier 20 and the output signal of the inverting
amplification circuit 12 and outputs the result. Since the output signal of the addition circuit 13
becomes a cancellation signal, the signal is amplified by the amplifier 30 and output from the
speaker unit 50 through the headphone amplifier 40 to cancel the ambient noise.
[0035]
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Next, another configuration example of the headphone unit included in the noise cancellation
system according to the present invention will be described using FIG. In FIG. 6, the NC unit 100a
includes a phase inverting filter circuit 10a having a configuration different from that of the
phase inverting filter circuit 10 included in the NC unit 100 described above. Therefore, the
phase inverting filter circuit 10a will be described. The phase inverting filter circuit 10a extracts
the predetermined frequency band included in the noise signal output from the microphone
amplifier 20 and outputs the filter circuit 11, and the output of the filter circuit 11 amplified by
N times and output in the forward direction The circuit 14 is composed of a subtraction circuit
13 that subtracts the output of the non-inversion amplification circuit 14 from the noise signal
output from the microphone amplifier 20 and outputs a cancellation signal.
[0036]
In the embodiment of the noise cancellation system described above, the phase inversion filter
circuit 10 inverts and amplifies the output signal of the filter circuit 11 and adds it to the original
signal (the output signal of the microphone amplifier 20) to obtain a cancellation signal. . On the
other hand, the phase inversion filter circuit 10a of the embodiment shown in FIG. 6 amplifies
the output signal of the filter circuit 11 without inverting it and subtracts it from the original
signal (the output signal of the microphone amplifier 20) to obtain a cancel signal. It is a thing.
The characteristics of the phase shift and the gain characteristics are the same as the
characteristics of the phase inverting filter circuit 10 in the above embodiment. That is, by
providing the phase inversion filter circuit 10a, the noise cancellation system according to the
present invention can also be obtained.
[0037]
The same applies to the embodiment of the noise cancellation method, and the same applies to
the non-inverting circuit in which the output signal of the microphone amplifier 20 is amplified
with a predetermined amplification factor M without inverting the output signal of the filter
circuit 11 in the subtraction circuit 13. Since the signal output by subtracting the output signal of
the amplification circuit 14 becomes a cancellation signal, by outputting this from the speaker
unit 50 via the amplifier 30 and the headphone amplifier 40, it is possible to cancel the ambient
noise. become.
[0038]
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As described above, by providing the phase inversion filter 10 or the phase inversion filter 10a, it
is possible to generate a cancellation signal having a phase characteristic in which the phase is
delayed at a low frequency and the phase is advanced at a high frequency.
The filter circuit characteristics of the phase inversion filter 10 or 10 a depend on the selection
of the filter circuit 11. That is, if the filter circuit 11 is a low pass filter, the phase inversion filters
10 and 10a operate as a high pass filter. When the phase inversion filters 10 and 10a operate as
band pass filters, a notch filter may be used for the filter circuit 11, and when operating as a
notch filter, a band pass filter may be used for the filter circuit 11.
[0039]
The noise cancellation system according to the present invention can be used not only for noise
cancellation headphones as described above, but also for noise cancellation speakers and the like.
[0040]
It is a sectional view showing typically the embodiment of the noise cancellation headphone
which is an example of the noise cancellation system concerning the present invention.
It is a block diagram showing an example of a signal processing system of a noise cancellation
unit with which the above-mentioned noise cancellation system is provided. It is a graph which
shows the example of the phase characteristic of the high pass filter circuit with which the said
noise cancellation unit is provided. It is a graph which shows the example of the phase
characteristic of the phase inversion filter circuit with which the said noise cancellation unit is
equipped. It is a graph which shows the example of the gain characteristic of the said phase
inversion filter circuit. It is a block diagram which shows the example of another signal
processing system | strain of the noise cancellation unit with which the said noise cancellation
system is equipped.
Explanation of sign
[0041]
DESCRIPTION OF SYMBOLS 10 phase inversion filter circuit 11 filter circuit 12 inverting
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amplifier circuit 13 addition circuit 14 amplifier circuit 15 subtraction circuit 20 microphone
amplifier 30 amplifier 40 headphone amplifier 50 speaker unit 60 microphone unit 100 noise
cancellation unit
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