JP2017518522

Patent Translate
Powered by EPO and Google
Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
financial decisions, should not be based on machine-translation output.
DESCRIPTION JP2017518522
Abstract: The present invention discloses an active noise reduction earphone, and a noise
reduction control method and system applied to the earphone. According to this method, one
feedforward microphone is disposed outside each one of the active noise reduction earphones,
and the magnitude of external noise is detected using the feedforward microphone, and noise
signals are detected. Calculate the energy after weighting, and based on the energy after
weighting, judge whether it is necessary to activate the active noise reduction system, and if
active noise reduction control is required, feed forward noise reduction in the noise signal By
determining the energy reduction values of the feedforward noise reduction system and the
feedback noise reduction system by calculating the energy values of the two subbands
respectively corresponding to the amount and feedback noise reduction amount, the feedforward
noise reduction and accordingly In order to reduce feedback noise To control. The technical
solution of the present invention detects the environment of the active noise reduction earphone
and suppresses the ambient noise by means of dynamically adjustable noise reduction means for
the current noise type and frequency distribution, Compared to the conventional fixed noise
reduction active noise reduction technology, the highest noise reduction effect can be achieved.
[Selected figure] Figure 2
Active noise reduction earphone, noise reduction control method and system applied to the
earphone
[0001]
The present invention relates to the technical field of active noise reduction of smart earphones,
and more particularly, to a noise reduction control method, system and active noise reduction
earphone applied to active noise reduction earphones.
07-05-2019
1
[0002]
Although earphones are widely used in people's daily life and work, they are widely used to
isolate noise and maintain a relatively quiet environment, in addition to the functions of music
appreciation and entertainment. For low frequency noise, the soundproof effect and ability of the
earphone is limited.
[0003]
The method used in the active noise reduction technology is to generate a signal whose
amplitude is the same as the external noise but of which the phase is inverted to offset the noise
in the earphone.
However, the active noise reduction technology currently used in earphones is almost always a
fixed noise reduction technology.
Such fixed noise reduction techniques have the following deficiencies. If the external
environment constantly changes and the external noise is equal to the fixed noise reduction
amount, a relatively good noise reduction effect occurs, but if the external noise exceeds the fixed
noise reduction amount, the noise reduction effect becomes insufficient Also, when the external
noise is less than the fixed noise reduction amount, the active noise reduction module
substantially generates new noise and gets into the human ear.
[0004]
In view of this, the present invention is a noise reduction control method applied to an active
noise reduction earphone in order to solve the problem that a sufficient noise reduction effect
can not be achieved by the active noise reduction technology of fixed noise reduction. It is a main
object to provide a system and active noise reduction earphone.
[0005]
In order to achieve the above object, the solution according to the embodiment of the present
invention is realized as follows.
[0006]
07-05-2019
2
According to one aspect, an embodiment of the present invention provides a noise reduction
control method applied to an active noise reduction earphone, wherein the noise reduction
control method comprises one for each one of the active noise reduction earphones. Two
feedforward microphones are arranged, and the feedforward microphones are arranged outside
each one of the earphones, and frequency domain weighting and time domain weighting are
applied to noise signals collected by the feedforward microphone at the current time, The step of
obtaining later energy, the step of determining whether or not the active noise reduction control
is necessary at the current time based on the energy after weighting, and the feed at the current
time if the active noise reduction control is required Energy value and second of the first
subband of the noise signal collected by the forward microphone Calculating the energy value of
the subband, wherein the first and second subbands are determined by the feedforward noise
reduction curve and the feedback noise reduction curve of the earphone, respectively, and the
first subband Determining the feedforward noise reduction amount and the feedback noise
reduction amount based on the energy value of the second subband and the energy value of the
second sub-band, and performing the feedforward noise reduction according to the feedforward
noise reduction amount And controlling the earphone to perform feedback noise reduction
according to the feedback noise reduction amount.
[0007]
According to another aspect, the embodiments of the present invention further provide a noise
reduction control system applied to the active noise reduction earphones, wherein the noise
reduction control system comprises each one earphone of the active noise reduction earphones.
One feedforward microphone is disposed, and the feedforward microphones are disposed outside
of each one of the earphones, and frequency domain weighting and time domain weighting are
performed on noise signals collected by the feedforward microphone at the current time. Active
noise for determining whether active noise reduction control is required at the current time
based on energy weighting means for obtaining energy after weighting and energy after
weighting obtained by the energy weighting means Active noise reduction control by reduction
determination means and active noise reduction determination means A sub-band energy
calculation means for calculating the energy value of the first sub-band and the energy value of
the second sub-band of the noise signal collected by the feedforward microphone at the current
time, when it is determined that it is necessary, Among them, the first sub-band calculated by the
sub-band energy calculating means and the first sub-band calculated by the first sub-band and
the second sub-band are determined by the feedforward noise reduction curve and the feedback
noise reduction curve of the earphone, respectively. Noise reduction amount determination
means for determining feedforward noise reduction amount and feedback noise reduction
amount based on the energy value of the band and the energy value of the second sub-band, and
feedforward noise according to the feedforward noise reduction amount To do the reduction
Comprising a feed-forward noise reduction control means for controlling the Yahon, and
feedback noise reduction control means for controlling the earphone so as to perform reduction
07-05-2019
3
feedback noise in response to feedback noise reduction amount.
[0008]
According to a further aspect, an embodiment of the present invention provides an active noise
reduction earphone, wherein one feedforward microphone and one feedback microphone are
arranged on each one of the active noise reduction earphones, The feedforward microphone is
located outside the earphones, the feedback microphones are located in the combined cavity of
the earphones and the human ear, and noise reduction with the above technical solution in each
one of the active noise reduction earphones A control system is in place.
[0009]
Compared to the prior art, the beneficial effects of the embodiments of the present invention are
as follows.
[0010]
The technical solution according to the embodiment of the present invention is an active means
of calculating the energy after signal weighting from two viewpoints of the frequency domain
and the time domain, in consideration of the auditory characteristics of the human ear, the user's
It is possible to detect the environmental condition in which the noise reduction earphone is
mounted, and comprehensively determine whether active noise reduction control is necessary
based on the current noise type and frequency distribution.
In addition, it is possible to dynamically calculate the amount of adjustment of the noise
reduction amount by the technical means of calculating the sub-band energy value of the noise
signal collected in real time by the microphone.
Furthermore, different noise reduction means are intelligently used for different noise reduction
systems by means of technology that performs feedforward noise reduction according to
feedforward noise reduction and feedback noise reduction according to feedback noise reduction.
The solution can control noise reduction accurately, perform intelligent noise reduction
adjustment dynamically, and achieve the highest noise reduction effect compared to the
07-05-2019
4
conventional fixed noise reduction based active noise reduction technology. be able to.
[0011]
In one preferred solution, the present invention places a feedback microphone in each one of the
active noise reduction earphones and utilizes the feedback microphones located in the combined
cavity of the earphone and the human ear The feedback noise reduction amount of the feedback
noise reduction system may be fine-tuned to ensure that the maximum effect of noise
suppression is achieved.
In another preferred solution, the present invention uses dynamic dual thresholding to make the
dynamic adjustment process a gradual process, avoiding noise due to frequent adjustment of the
noise reduction level Do.
In a further preferred solution, the present invention determines whether current wind noise is
present or not by the correlation of noise signals collected by the two feedforward microphones,
and if wind noise is present, special ones. Noise reduction control may be performed.
[0012]
The drawings form a part of the specification and, while providing a further understanding of the
invention, are used to interpret the invention with the embodiments of the invention and do not
limit the invention. .
FIG. 5 is a schematic view of an active noise reduction earphone in which two microphones are
arranged according to an embodiment of the present invention. 5 is a flowchart of a noise
reduction control method applied to an active noise reduction earphone according to an
embodiment of the present invention. FIG. 5 is a schematic view of a level jump of the noise
reduction system according to an embodiment of the present invention. FIG. 5 is a structural
diagram of a noise reduction control system applied to an active noise reduction earphone
according to an embodiment of the present invention. FIG. 2 is a structural diagram of an active
noise reduction earphone according to an embodiment of the present invention.
07-05-2019
5
[0013]
The main technical idea of the present invention is to detect the environment in which the user's
active noise reduction earphone is worn by the multi microphone, and based on the hearing
effect of the human ear, against the current noise type and frequency distribution, Determine
whether to use active noise reduction and use the dynamically adjustable noise reduction means
to intelligently combine the two noise reduction systems with feed forward and feedback in the
earphone to ensure noise suppression Try to achieve the best effect.
[0014]
BRIEF DESCRIPTION OF THE DRAWINGS In order that the objects, technical solutions and
advantages of the present invention will be more apparent, the embodiments of the present
invention will be described in more detail below with reference to the drawings.
[0015]
Although the conventional active noise reduction earphone performed uniform processing on all
noise without considering the type of external noise, this solution uses a multi-microphone to
improve its defects. Detect the external environment.
FIG. 1 shows a schematic view of an active noise reduction earphone in which two microphones
are arranged according to an embodiment of the present invention.
Among them, one is a feed-forward microphone and is disposed outside the earphone as in
MIC̲1 in FIG. 1, and the other is a feedback microphone, and as in MIC 2 in FIG. It is located
inside. When the earpiece is turned on and energized, the active noise reduction earpiece begins
to operate (it can be forced off). The entire noise reduction system consists of a feed forward
noise reduction system and a feedback noise reduction system. These two systems have different
noise reduction frequency bands to be focused, so it is necessary to intelligently detect the
external environment and to intelligently combine the two noise reduction systems, thereby
achieving an optimal noise reduction amount.
[0016]
As the principle of the active noise reduction earphone, the purpose of noise reduction is realized
07-05-2019
6
by generating a signal whose phase is reversed from the external noise and canceling out the
noise. As shown in FIG. 1, in order to detect external noise, MIC̲1 is attached to the outside of
the earphone (e.g., the top outside corner) and this detected external noise is a speaker so as to
generate a signal whose phase is inverted. Is controlled. This is a feed forward noise reduction
system. The MIC̲2 is mounted in the coupling cavity between the earphone and the human ear,
detects the magnitude of noise remaining in the coupling cavity, and generates a signal whose
phase is opposite to that of the coupled cavity noise, thereby Further reduce the noise that has
come into your ears and maximize the noise reduction effect.
[0017]
According to one aspect, embodiments of the present invention provide a noise reduction control
method applied to active noise reduction earphones. FIG. 2 shows a flowchart of a noise
reduction control method applied to an active noise reduction earphone according to an
embodiment of the present invention. As shown in FIG. 2, the method includes the following
steps S210 to S250, in which frequency domain weighting and time domain weighting are
performed on the noise signal collected by the feedforward microphone at the current time, Get
the energy after weighting.
[0018]
Due to the characteristics of the human ear, the sensitivity of the human ear to low frequency
and high frequency signals is lower than that of the medium frequency signal. In order to
calculate the sense of human noise more objectively, this embodiment dynamically adjusts the
present noise type and frequency distribution by performing weighted measurement on the input
signal. Use possible noise reduction solutions.
[0019]
The weighting measurements include both frequency domain weighting and time domain
weighting.
[0020]
The first stage is frequency domain weighting.
07-05-2019
7
The frequency filter R (f) is designed by the following frequency weighting equation. Here, f is
the frequency of the signal, and R A (f) is a frequency weighting coefficient, <img class = "EMIRef"
id = "453473672-000003" />
When the sound signal is s1, if y (n) is obtained through frequency weighting, then y (n) = RA (f)
* s1. [0021] The second stage is time domain weighting. The data after frequency weighting is
closer to hearing in the frequency domain of the human ear, but in the time domain, if the noise
suddenly disappears, its sound level does not disappear immediately but falls at a certain speed,
but Time-domain weighting is performed by smoothing the signal using time constants. [0022] It
is possible to perform time domain weighting according to the following time weighting scheme:
<img class = "EMIRef" id = "453473672-000004" /> Here, SPL (n) is an acoustic level, that is,
energy after weighting obtained finally, α is a time weighting coefficient, and Energy (n) is the
energy value of the current frame, and Energy (n) is the square of y (n) after the above frequency
weighting. In step S220, based on the energy after weighting, it is determined whether active
noise reduction control is required at the current time. Comparing the weighted energy SPL (n)
obtained in step S210 with one threshold value. When SPL (n) is larger than the threshold, active
noise reduction is performed, and when SPL (n) is smaller than the threshold, active noise
reduction does not need to be performed. The size of the threshold needs to be selected in
accordance with the actually designed earphone. In step S230, if active noise reduction control is
required, the energy value of the first subband and the energy value of the second subband of
the noise signal collected by the feedforward microphone at the current time are calculated . In
the present embodiment, the influence of external environmental noise is suppressed for each
frequency band, and the effect of noise reduction is different for different frequencies. This is
mainly due to the following reasons. Active noise reduction mainly concentrates on the low
frequency part, but when the noise that entered the human ear is mainly high frequency noise, it
is actually in practice if still using the same active noise reduction method in different frequency
bands Not only does it help to reduce noise, it also draws more noise and causes discomfort in
the human ear. Therefore, in the present embodiment, the noise reduction effect is improved by
performing different noise reduction processing in different frequency bands.
[0027] wherein the first and second sub-bands are determined by the feed forward noise
reduction curve and the feedback noise reduction curve of the active noise reduction earphone,
respectively. Specifically, a feedforward noise reduction curve is obtained by detecting the
feedforward noise reduction performance of the active noise reduction earphone, and a feedback
noise reduction curve is obtained by detecting the feedback noise reduction performance of the
active noise reduction earphone. Furthermore, a constant frequency band range around the
maximum amplitude value point of the feedforward noise reduction curve (in the constant
07-05-2019
8
frequency band range, the frequency point of the maximum amplitude value and the frequency
point of the maximum amplitude value point of the entire feedforward noise reduction curve The
first sub-band is selected within the difference between the two) and the constant frequency
band range near the maximum amplitude value point of the feedback noise reduction curve (in
the constant frequency band range, the maximum amplitude value of The second sub-band may
be selected within the difference between the frequency point and the frequency point of the
maximum amplitude value point of the entire feedback noise reduction curve being smaller than
the set value. If the noise has reached the threshold requirement and it is necessary to carry out
active noise reduction control, it is necessary to determine the energy value of the first subband
and the energy value of the second subband respectively. [0029] There are two calculation
methods. First, the noise signal s1 collected at the current time by the feedforward microphone
MIC̲1 is applied to the band pass filter h A (n) of the first subband A and the band pass filter h B
(n) of the second subband B You may pass it. The other is that s1 may be transformed to the
frequency domain by FFT (Fast Fourier Transformation, Fast Fourier Transform), and then the
magnitudes of the energy values of the first subband A and the second subband B may be
statistically processed. . Here, the first subband A will be described as an example. [0030]
Method 1 calculates the energy value Energy A of the first subband A by the subband filter
method, and uses the following equation. <img class = "EMIRef" id = "453473672-000005" />
Here, y (n) represents a sub-band signal obtained through the sound signal s1 through h A (n),
and n is a time Represent.
Method 2 is a method of calculating the subband energy Energy A of the first subband A by FFT,
using the following equation. <img class = "EMIRef" id = "453473672-000006" /> Here, α is a
weighting coefficient, the value of α can be determined by the frequency response curve, and
(subband1, subband2) is the sub-band A It is a frequency domain range. In step S240, the
feedforward noise reduction amount and the feedback noise reduction amount are respectively
determined based on the energy value of the first subband and the energy value of the second
subband. After obtaining the energy of the first subband and the second subband, the energy
values of the two subbands are compared with a preset threshold. Specifically, in the present
embodiment, the energy value of the first subband and the energy value of the second subband
are respectively compared with the threshold values corresponding to different noise reduction
levels, and the feedforward noise reduction amount initial value and feedback are compared. The
noise reduction amount initial value is determined respectively. [0034] What I would like to
explain is that as soon as the earphone is turned on, it is set by default not to require active noise
reduction now. When it is determined that it is necessary to activate active noise reduction, initial
values of two sub-band energies are calculated, and then feedforward noise reduction at the
initial time according to the noise reduction level corresponding to the initial values. Determine
the amount and feedback noise reduction amount. [0035] Since the noise in the environment in
which the earphones are located is constantly changing, in order to track the change, in the
present embodiment, the subband energy values are tracked once at regular intervals (for
07-05-2019
9
example, per second). Calculate. The change in noise causes the feedforward active noise
reduction module and the feedback active noise reduction module to adjust their noise reduction
amount again. However, the adjustment process is a progressive process that prevents the noise
reduction level from jumping up and down due to noise changing near the threshold, causing
discomfort in the human ear's hearing In order to solve the problem, this solution uses a dual
threshold scheme. Specifically, the rising threshold and the falling threshold are respectively set
for two adjacent noise reduction levels, and the rising threshold is made larger than the falling
threshold, and collection is performed by the feedforward microphone at each time. Record the
energy values of the subbands of the received noise signal.
It is necessary to explain that the energy value of the first subband and the energy value of the
second subband need to be recorded respectively, and the method of determining the
feedforward noise reduction amount based on the energy value of the first subband Is the same
as the method of determining the feedback noise reduction amount based on the energy value of
the second sub-band, and therefore, the following description is collectively referred to as subband and the first sub-band and the second sub-band are divided. do not do. [0037] When it is
determined that the energy value of the sub-band is in the process of changing from small to
large at the current time (a change trend of the energy value can be obtained by the magnitude
of the energy value of the recorded sub-band) ), The feedforward noise reduction amount
(corresponding to the first subband) or the feedback noise reduction amount (corresponding to
the second subband) to the original noise reduction level even if the energy value of the subband
is greater than its falling threshold value Is determined to be kept as it is, and when the energy
value of the sub-band becomes larger than the rising threshold, the amount of feed forward noise
reduction or the amount of feedback noise reduction is determined such that the noise reduction
level is increased by one. [0038] If it is determined that the energy value of the sub-band is in the
process of changing from large to small at the current time, the feedforward noise reduction
amount or the feedback noise even if the energy value of the sub-band becomes smaller than the
rising threshold. The amount of reduction is determined so that the original noise reduction level
is maintained as it is, and when the energy value of the sub-band becomes smaller than the
falling threshold, the amount of feed forward noise reduction or feedback noise reduction is
reduced by one. Decide to go down. FIG. 3 shows a schematic view of a level jump of a noise
reduction system according to an embodiment of the present invention. As shown in FIG. 3, at
two adjacent noise reduction levels (for example, noise reduction level A and noise reduction
level B), the rising threshold Threshold0̲up and the falling threshold Threshold0̲down are used,
and the relationship of Threshold0̲up> Threshold0̲down always holds. . 1; In the first kind of
change situation, when the system is at the noise reduction level A in the process of changing the
sub-band energy of external environment noise from small to large, the sub-band energy
becomes larger than Threshold0̲down Also, the noise reduction level of the active noise
reduction system does not jump, but when the energy is further increased and the sub-band
energy becomes larger than Threshold0̲up, the feedforward noise reduction amount or feedback
07-05-2019
10
noise reduction amount of the active noise reduction system is one level higher. Jump to the
noise reduction level B.
[0041] 2, conversely, in the second kind of change situation, when the system is at noise
reduction level B in the process of changing the sub-band energy of external environment noise
from high to low, the sub-band energy is from Threshold 0̲up Even if it becomes smaller, the
noise reduction level of the active noise reduction system does not jump, but if the energy
becomes smaller and the subband energy becomes smaller than Threshold0̲down, the
feedforward noise reduction amount or feedback noise reduction amount of the active noise
reduction system Jump down one level to reach noise reduction level A. The number of noise
reduction levels can be selected and divided according to the needs of the active noise reduction
earphones. That is, the noise reduction level may jump between the noise reduction level B, the
noise reduction level C, and the like. For example, ten noise reduction levels may be selected, and
if the noise reduction amplitude range that can be achieved by the active noise reduction
earphone is 25 dB, the number of dB corresponding to each noise reduction level changes
stepwise, The first level is a noise reduction of 2.5 dB, the second level is a noise reduction of 5
dB, and the third level is a noise reduction of 7.5 dB. [0043] In step S250, the earphone is
controlled to perform feedforward noise reduction according to the determined feedforward
noise reduction amount, and the earphone is controlled to perform feedback noise reduction
according to the determined feedback noise reduction amount. Control. For example, the
earphone is controlled to control the feedforward noise reduction module in the earphone to
perform feedforward noise reduction according to the determined feedforward noise reduction
amount, and to perform feedback noise reduction according to the determined feedback noise
reduction amount Control the feedback noise reduction module in At this point, the noise
reduction control method applied to the active noise reduction earphone shown in FIG. 2 is
completed. The operations in steps S210 to S250 may be performed by the control chip in the
earphone. [0045] The technical solution according to the embodiment of the present invention
takes account of the auditory characteristics of the human ear using a technical means for
calculating the energy after weighting of the signal from two viewpoints of the frequency domain
and the time domain. Then, it is possible to detect an environmental condition in which the user's
active noise reduction earphone is worn and comprehensively judge whether active noise
reduction control is necessary based on the current noise type and frequency distribution.
Also, the magnitude of adjusting the noise reduction amount can be dynamically calculated using
a technical means for calculating the sub-band energy value of the noise signal collected in real
time by the microphone. Furthermore, using technical means to perform feedforward noise
reduction according to feedforward noise reduction amount and feedback noise reduction
according to feedback noise reduction amount, different noise reduction means are intelligently
made to different noise reduction systems. Use. This solution can control noise reduction
07-05-2019
11
accurately, perform intelligent noise reduction adjustment dynamically, and achieve superior
noise reduction effect compared to the conventional fixed noise reduction active noise reduction
technology. Can. According to the present invention, the active noise reduction amount of the
earphone is properly adjusted according to the environment in which the user's earphone is
used, and it is ensured that the earphone obtains the noise reduction effect against external
environment noise at maximum. At the same time, it is possible to judge the use state of the user
and completely prevent the adverse effect on the music signal. [0047] Based on the above
embodiment, the noise reduction control method in another preferred embodiment is a solution
that appropriately fine-tunes the noise reduction amount of the feedback microphone in order to
improve the accuracy of the feedback noise reduction control. Provide a means. This method
makes use of feedback microphones located in the combined cavity of the earphone and the
human ear in each one of the active noise reduction earphones when it is determined that there
is no sound to be reproduced from the speakers of the earphones And calculating the energy of
the signal collected by the feedback microphone at the current time. In this case, controlling the
earphone to perform feedback noise reduction in accordance with the determined feedback noise
reduction amount in step S250 may be performed on the signal collected by the feedback
microphone at the calculated current time. The method further includes adjusting the feedback
noise reduction amount based on energy, and controlling the earphone to perform feedback
noise reduction according to the adjusted feedback noise reduction amount. Thereby, based on
the noise reduction result of the feedback microphone, appropriate adaptive correction is
performed on the feedback noise reduction amount. [0049] The process of performing
appropriate adaptive correction on the feedback noise reduction amount is as follows. After
controlling the earphone to perform feedback noise reduction according to the feedback noise
reduction amount after adjustment, the signal after noise reduction collected by the feedback
microphone is acquired, and the energy of the signal after noise reduction is Calculate and
compare whether the energy of the signal collected by the feedback microphone at this
calculated current time is smaller than the energy of the signal after the noise reduction, and if
smaller, the adjusted feedback The earphone is controlled to perform feedback noise reduction
according to the noise reduction amount, and otherwise, the earphone is controlled to perform
feedback noise reduction according to the feedback noise reduction amount before adjustment.
That is, first, the noise reduction control is performed by applying the solution shown in FIG. 2,
the energy of the signal s2 collected by the feedback microphone is determined, and the
feedback noise reduction amount is exceeded when a certain threshold is exceeded. Adjust the
feedback noise reduction amount by increasing the new noise reduction level. Then compare the
signal energy before adjustment and the signal energy after adjustment, and if the energy of s2
can be reduced by increasing the feedback noise reduction amount, continue to use the new
noise reduction level after adjustment If the energy of s2 can not be reduced by increasing the
feedback noise reduction amount, return to the original noise reduction level before adjustment.
[0052] This preferred embodiment of the present invention utilizes the feedback microphone
07-05-2019
12
disposed within the earphone and human ear coupling cavity to properly fine-tune the feedback
noise reduction amount of the feedback noise reduction system To ensure that noise suppression
achieves the best effect. In another preferred embodiment, the noise reduction control method of
the present invention provides a wind noise solution. This method calculates the correlation of
the noise signal collected by the feedforward microphone of each of the two earphones of the
active noise reduction earphone at the current time, and based on the calculation result of the
correlation, is wind noise present at the current time? If it is determined that wind noise is
present at the current time, the earphone is controlled to stop performing feedforward noise
reduction according to the feedforward noise reduction amount, and the feedforward noise
reduction amount Controlling the earphone to increase feedback noise reduction accordingly and
to provide feedback noise reduction according to the increased feedback noise reduction. [0054]
The feedforward active noise reduction system not only can not reduce noise from wind noise,
but also has the problem of amplifying noise, so when wind noise appears, the present
implementation In the example, the solution is to turn off feed forward active noise reduction and
increase feedback noise reduction. The wind noise detection used in the present embodiment is
realized by examining the correlation of the signals. The inventor analyzed the principle of wind
noise generation and found that pressure is generated in the microphone when the wind passes
through the microphone.
The wind noises collected by each microphone are all random, ie, the wind noises collected by
either of the two microphones are uncorrelated. On the other hand, for any active noise and
signal, there is a correlation between the signal collected by the microphone and the signal
source. Because the earphones are stereo, it is possible to make a correlation decision with the
inputs of the two feedforward microphones, ie if the signals arriving at the two feedforward
microphones are uncorrelated, then wind noise is now generated It can be determined that Also,
since all other noises have a very strong correlation with speech, the determination of wind noise
can be made by calculating the correlation of the signals of the two feed-forward microphones.
The specific calculation process is as follows. [0056] Assume that the signals collected by the two
feedforward microphones are x1 (n) and x2 (n), respectively. First, the FFT of both signals is
calculated to obtain frequency domain signals X1 (k) and X2 (k) of both signals. [0057] 2.
Calculate the autocorrelation function R (k) in the frequency domain of both signals according to
the following autocorrelation equation, <img class = "EMIRef" id = "453473672-000007" />
where Represents a complex conjugate operation. 3) Normalize the calculation result R (k) to
smooth the calculation result. The correlation of the smoothed calculation results obtained in this
step makes it possible to confirm whether or not wind noise is present. That is, when the
smoothed calculation result shows low correlation, it is confirmed that wind noise is present.
Alternatively, in step 4, the smoothed calculation result obtained in this step is extracted and
then judged. [0059] 4; Make a judgment by extracting the correlation of signals in a set
frequency band (for example, 93.75 Hz to 781.25 Hz). [0060] In this preferred embodiment of
the present invention, it is possible to determine whether or not wind noise is currently present,
07-05-2019
13
and to perform noise reduction control to remove wind noise if wind noise is present. [0061]
According to another aspect, embodiments of the present invention further provide a noise
reduction control system for application to active noise reduction earphones. FIG. 4 is a
structural schematic diagram of a noise reduction control system applied to an active noise
reduction earphone according to an embodiment of the present invention, wherein the noise
reduction control system comprises an energy weighting means 41, an active noise reduction
judging means 42, a subband energy It includes calculation means 43, noise reduction amount
determination means 44, feed forward noise reduction control means 45, and feedback noise
reduction control means 46.
[0062] Among them, the energy weighting means 41 is used to perform frequency domain
weighting and time domain weighting on the noise signal collected by the feedforward
microphone at the current time, and obtain energy after weighting. [0063] Due to the peculiarity
of the human ear, the sensitivity of the human ear to low frequency and high frequency signals is
both lower than the medium frequency signal, and is input to calculate the sense of human noise
more objectively By performing weighted measurement on the received signal, noise reduction
means capable of dynamically adjusting the current noise type and frequency distribution is
used. Specifically, the energy weighting means 41 is used to sequentially calculate the energy
after weighting of the frequency domain weighting and the time domain weighting. [0065] The
first step is frequency domain weighting. The frequency filter R (f) is designed by the following
frequency weighting equation. Here, f is the frequency of the signal and R A (f) is the frequency
weighting factor. <img class = "EMIRef" id = "453473672-000008" /> When the sound signal is
s1, if y (n) is obtained after frequency weighting, then y (n) = RA (f) * s1 .
[0066] The second stage is time domain weighting. The data after frequency weighting is closer
to hearing in the frequency domain of the human ear, but in the time domain, if the noise
suddenly disappears, its sound level does not disappear immediately, but falls at a certain speed,
At this time, time domain weighting processing is performed by smoothing the signal using a
time constant.
[0067] It is possible to perform time domain weighting by the following time weighting scheme.
<img class = "EMIRef" id = "453473672-000009" /> Here, SPL (n) is the sound level, that is, the
finally obtained energy after weighting, α is a time weighting coefficient, and Energy (n) is the
energy value of the current frame, and Energy (n) is the square of y (n) after the above frequency
weighting.
[0068] The active noise reduction determining means 42 is used to determine whether active
07-05-2019
14
noise reduction control is required at the current time based on the energy after weighting
obtained by the energy weighting means 41.
[0069] When the sub-band energy calculating means 43 determines that the active noise
reduction control is necessary by the active noise reduction determining means 42, the energy
value of the first sub-band of the noise signal collected by the feedforward microphone at the
current time and It is used to calculate the energy values of the two subbands, of which the first
and second subbands are determined by the earphone feedforward noise reduction curve and the
feedback noise reduction curve, respectively.
[0070] In the present embodiment, the influence of external environmental noise is suppressed
for each frequency band, and the effect of noise reduction is different for different frequencies.
This is mainly due to the following reasons. Active noise reduction mainly concentrates on low
frequency parts, but when the noise that entered the human ear is mainly high frequency noise,
if the same active noise reduction method is still used in different frequency bands, it is actually
for noise reduction It is not only useless, but also conversely attracts more noise, causing
discomfort in the human ear. Therefore, in the present embodiment, the noise reduction effect is
improved by performing different noise reduction processing in different frequency bands.
[0071] Specifically, a feedforward noise reduction curve is obtained by detecting the feedforward
noise reduction performance of the active noise reduction earphone, and a feedback noise
reduction curve is obtained by detecting the feedback noise reduction performance of the active
noise reduction earphone. In addition, a constant frequency band range around the maximum
amplitude value point of the feedforward noise reduction curve (in the constant frequency band
range, the frequency point of the maximum amplitude value and the maximum amplitude value
point of the entire feedforward noise reduction curve While selecting the first sub-band within
the difference between the frequency point and the set value, the constant frequency band range
around the maximum amplitude point of the feedback noise reduction curve (in the constant
frequency band range, the maximum amplitude) The second sub-band may be selected within the
difference between the frequency point of the value and the frequency point of the maximum
amplitude point of the entire feedback noise reduction curve.
[0072] If the noise reaches the threshold requirement and it is necessary to carry out active
noise reduction control, it is necessary to determine the energy value of the first subband and the
energy value of the second subband respectively.
07-05-2019
15
[0073] There are two calculation methods. First, the noise signal s1 collected at the current time
by the feedforward microphone MIC̲1 is applied to the band pass filter h A (n) of the first
subband A and the band pass filter h B (n) of the second subband B You may pass it. The other is
that s1 may be transformed to the frequency domain by FFT (Fast Fourier Transformation, Fast
Fourier Transform), and then the magnitudes of the energy values of the first subband A and the
second subband B may be statistically processed. . Here, the first subband A will be described as
an example.
[0074] In method 1, the energy value Energy A of the first subband A is calculated by the
subband filter method, and the following equation is used. <img class = "EMIRef" id =
"453473672-000010" /> Here, y (n) represents a sub-band signal obtained through the sound
signal s1 through h A (n), and n is a time Represent.
[0075] Calculation method 2 is a method of calculating subband energy by FFT, using the
following equation. <img class = "EMIRef" id = "453473672-000011" /> where α is a weighting
coefficient, the value of α can be determined by the frequency response curve, and (subband1,
subband2) is the sub-band A It is a frequency domain range.
[0076] The noise reduction amount determination unit 44 determines the feedforward noise
reduction amount and the feedback noise reduction amount based on the energy value of the
first subband and the energy value of the second subband calculated by the subband energy
calculation unit 43. Used to
[0077] Preferably, the noise reduction amount determination means 44 includes an initial value
determination module, a dual threshold setting module, an energy value recording module, a
noise reduction level increase module and a noise reduction level decrease module, and the initial
value determination module includes the first subband Are used to determine the feedforward
noise reduction initial value and the feedback noise reduction initial value, respectively, by
comparing the energy value of the second subband and the energy value of the second sub-band
with thresholds corresponding to different noise reduction levels, The dual threshold setting
module is used to set rising and falling thresholds respectively for two adjacent noise reduction
levels, and to increase the rising threshold above the falling threshold, and the energy value
recording module is used at each time Picked up by the feedforward microphone The noise
reduction level raising module is used to record the energy value of the first sub-band and the
energy value of the second sub-band of the identified noise signal, the energy reduction value of
the first sub-band at the current time or the second sub-band Feedforward noise reduction
amount or feedback noise even if the energy value of the first subband or the energy value of the
07-05-2019
16
second subband becomes larger than the falling threshold when it is determined that the energy
value of is in the process of changing from small to large. The amount of reduction is determined
such that the original noise reduction level is maintained as it is, and when the energy value of
the first subband or the energy value of the second subband becomes larger than the rising
threshold, the feedforward noise reduction amount or feedback noise reduction Used to
determine the amount to increase the noise reduction level by If it is determined that the energy
level of the first subband or the energy value of the second subband changes from high to low at
the current time, the decrease level falling module determines the energy value of the first
subband or the second sub-band. If the energy value of the band becomes smaller than the rising
threshold, the feedforward noise reduction amount or feedback noise reduction amount is
determined so that the original noise reduction level is maintained as it is, and the energy value
of the first subband or the second When the energy value of the sub-band is less than the falling
threshold, the feedforward noise reduction amount or the feedback noise reduction amount is
used to determine the noise reduction level to drop by one.
[0078] The feedforward noise reduction control means 45 is used to control the earphone to
perform feedforward noise reduction according to the feedforward noise reduction amount.
[0079] The feedback noise reduction control means 46 is used to control the earphone to
perform feedback noise reduction in accordance with the feedback noise reduction amount.
[0080] In one preferred embodiment, the noise reduction control system comprises a feedback
microphone disposed in each one of the active noise reduction earphones, the feedback
microphone being disposed within the combined earphone and human ear cavity. There is. The
noise reduction control system further includes feedback energy calculating means for
calculating the energy of the signal collected by the feedback microphone at the current time
when it is determined that there is no sound reproduced from the speaker of the earphone.
[0081] Preferably, the feedback noise reduction control means 46 in the embodiment shown in
FIG. 4 is based on the energy of the signal collected by the feedback microphone at the current
time calculated by the feedback energy calculation means, for the feedback noise reduction
amount. The system further includes a feedback noise reduction adjustment module for
controlling the earphone to make adjustments and to perform feedback noise reduction
according to the adjusted feedback noise reduction.
[0082] More preferably, the feedback noise reduction adjustment module specifically controls
07-05-2019
17
the earphone to perform feedback noise reduction according to the feedback noise reduction
after adjustment, and then reduces noise collected by the feedback microphone. Acquire the
signal, calculate the energy of the signal after noise reduction, and compare whether the energy
of the signal collected by the feedback microphone at this calculated current time is smaller than
the energy of the signal after noise reduction If smaller, control the earphone to perform
feedback noise reduction according to the feedback noise reduction amount after adjustment,
otherwise, perform feedback noise reduction according to the feedback noise reduction amount
before adjustment It is also used to control the earphones.
[0083] This preferred embodiment of the present invention utilizes the feedback microphones
located in the earpiece to ear cavity coupling to fine tune the feedback noise reduction of the
feedback noise reduction system to reduce noise. Is guaranteed to achieve the best effect.
[0084] In another preferred embodiment, the noise reduction control system calculates the
correlation of noise signals collected by the feedforward microphones of both of the active noise
reduction earphones at the current time, based on the calculation result of the correlation. When
it is determined that the wind noise is present at the current time by the wind noise judging
means for judging whether the wind noise is present at the current time and the wind noise
judging means, the feed according to the feed forward noise reduction amount The earphone is
controlled to stop performing the forward noise reduction, and the feedback noise reduction
amount is increased according to the feed forward noise reduction amount, and the feedback
noise reduction is performed according to the increased feedback noise reduction amount. And
wind noise processing means for controlling the earphone.
[0085] This preferred embodiment of the present invention can determine if wind noise is
currently present and perform noise reduction control to eliminate wind noise if wind noise is
present.
[0086] According to another aspect of the present invention, there is further provided an active
noise reduction earphone, wherein one feed forward microphone and one feedback microphone
are disposed on each one of the active noise reduction earphones, wherein , The feedforward
microphone is located outside the earphones, the feedback microphones are located in the
coupling cavity of the earphones, and in each one of the active noise reduction earphones a noise
reduction control system according to the above technical solution It is arranged.
[0087] Referring to FIG. 5, FIG. 5 is a structural diagram of an active noise reduction earphone
07-05-2019
18
according to an embodiment of the present invention. The active noise reduction earphone
includes an environmental noise detection module 51, a noise analysis control module 52, a
feedforward noise reduction module 531, and a feedback noise reduction module 532, the
feedforward noise reduction module 531 being active with the feedback noise reduction module
532 The noise reduction module 53 is configured. The functions performed by the
environmental noise detection module 51 and the noise analysis control module 52 may be
realized by a noise reduction control system applied to the active noise reduction earphone
shown in FIG.
[0088] When the active noise reduction earphone is activated, the environmental noise detection
module 51 collects a noise signal of the current time in real time by a feedforward microphone to
detect environmental noise. The noise analysis control module 52 performs weighted energy
calculation on the noise signal collected by the feedforward microphone at the current time, and
based on the energy after weighting, whether active noise reduction control is necessary at the
current time or not Analyze and judge. If it is determined that active noise reduction control is
required, then the feedforward noise reduction amount and feedback noise reduction amount are
calculated and determined, and active noise reduction is performed according to the feedforward
noise reduction amount. The feedforward noise reduction module 531 in the reduction module
53 is controlled, and the feedback noise reduction module 532 in the active noise reduction
module 53 is controlled to perform feedback noise reduction according to the feedback noise
reduction amount.
[0089] Summarizing the above, the noise reduction control method, system and active noise
reduction earphone applied to the active noise reduction earphone according to the embodiment
of the present invention detect the environment of the active noise reduction earphone, the
current noise type and frequency Dynamically adjustable noise reduction means can be used to
reduce ambient noise relative to the distribution, achieving superior noise reduction effects
compared to conventional fixed noise reduction active noise reduction techniques Can.
[0090] In one preferred solution, the invention places a feedback microphone on each one of the
active noise reduction earphones and utilizes the feedback microphones in the combined cavity
of the earphone and the human ear. The feedback noise reduction amount of the feedback noise
reduction system may be finely adjusted to ensure that the maximum effect of noise suppression
can be achieved. In another preferred solution, the present invention uses dynamic dual
thresholding to make the dynamic adjustment process a gradual process, avoiding noise due to
frequent adjustment of the noise reduction level Do. In a further preferred solution, the present
invention determines the presence or absence of wind noise at present by correlation of the noise
signals collected by the two feed-forward microphones, and if wind noise is present, Noise
07-05-2019
19
reduction control may be performed.
[0091] The above description is just a preferred embodiment of the present invention, and does
not limit the protection scope of the present invention. Any corrections, equivalent replacements,
improvements, etc. made within the spirit and principle of the present invention shall fall within
the protection scope of the present invention.
07-05-2019
20