(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2009/0141907 A1
`Kim et al.
`(43) Pub. Date:
`Jun. 4, 2009
`
`US 20090141907A1
`
`(54) METHOD AND APPARATUS FOR
`CANCELING NOISE FROMSOUND INPUT
`THROUGH MCROPHONE
`
`(75) Inventors:
`
`Kyu-hong Kim, Yonging-si (KR);
`Kwang-cheol Oh, Yonging-si (KR);
`Jae-hoon Jeong, Yonging-si (KR);
`So-Young Jeong, Seoul (KR)
`
`Correspondence Address:
`STAAS & HALSEY LLP
`SUITE 700,1201 NEW YORKAVENUE, N.W.
`WASHINGTON, DC 20005 (US)
`
`(73) Assignee:
`
`SAMSUNGELECTRONICS
`CO.,LTD., Suwon-si (KR)
`
`(21) Appl. No.:
`
`12/076,281
`
`(22) Filed:
`
`Mar. 14, 2008
`
`(30)
`
`Foreign Application Priority Data
`
`Nov.30, 2007 (KR) ........................ 10-2007-0 1238.19
`
`Publication Classification
`
`(51) Int. Cl
`(2006.01)
`Giokii/16
`(52) U.S. Cl. ....................................................... 381/71.7
`(57)
`ABSTRACT
`Provided is a method and apparatus for canceling noise from
`a sound signal input through a microphone. The method
`includes filtering a high-frequency signal having a frequency
`that is higher than a reference frequency and a low-frequency
`signal having a frequency that is lower than the reference
`frequency from input signals obtained through a microphone
`array, obtaining a high-frequency target signal by canceling a
`noise signal from the filtered high-frequency signal using a
`beam forming method, obtaining a low-frequency target sig
`nal by canceling a noise signal having a phase difference that
`is different from a phase difference of a target signal from the
`filtered low-frequency signal, and obtaining a sound source
`signal from which noise is cancelled, by synthesizing the
`obtained high-frequency target signal with the obtained low
`frequency target signal. Thus, it is possible to accurately
`obtain a target Sound Source signal by minimizing signal
`distortion occurring in a low-frequency band in a digital
`Sound obtaining apparatus having a small-size microphone
`array and accurately canceling or attenuating unnecessary
`noise.
`
`3OO
`F------------------------------ -4------------------
`31
`
`HIGH-PASS
`FILTERED
`SIGNAL
`
`
`
`
`
`
`
`
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`
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`TARGET SIGNAL
`REINFORCEMENT
`UNIT
`
`NOSE SIGNAL
`REINFORCEMENT
`UNIT
`
`320
`NOISESIGNAL
`CANCELLATIONH
`UNIT
`
`HIGH
`FREQUENCY
`TARGET
`SIGNAL
`
`|
`
`-------------------------------------------------------- J
`
`Page i
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`IPR PETITION
`US RE48,371
`Amazon Ex. 1023
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`

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`Patent Application Publication
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`Jun. 4, 2009 Sheet 1 of 7
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`US 2009/O141907 A1
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`& O
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`3
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`Patent Application Publication
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`Jun. 4, 2009 Sheet 2 of 7
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`US 2009/0141907 A1
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`
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`GENERATION UNT
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`GENERATION UNIT
`
`FIG. 3A
`
`OUTPUT
`SIGNAL
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`SIGNAL
`SYNTHESIS
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`- -a - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4.-------------
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`TARGET SIGNAL
`RENFORCEMENT
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`NOSE SIGNAL
`REINFORCEMENT
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`HIGH
`FREQUENCY
`TARGET
`SIGNAL
`
`NOISE SIGNA
`CANCELLATION
`UN
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`Page iii
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`Patent Application Publication
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`Jun. 4, 2009 Sheet 3 of 7
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`US 2009/0141907 A1
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`
`
`TARGET
`DOMINANT
`SIGNAL
`
`NOISE
`DOMINANT
`SIGNAL
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`'g's
`SIGNAL
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`FREQUENCY
`TARGET
`SIGNAL
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`DIFFERENCE
`CALCULATION
`UNIT
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`NOISE SIGNAL
`CANCELLATION
`UNIT
`
`LOW
`FREQUENCY
`TARGET
`SIGNAL
`
`Page iv
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`Patent Application Publication
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`Jun. 4, 2009 Sheet 4 of 7
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`US 2009/O141907 A1
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`Page v
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`Patent Application Publication
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`Jun. 4, 2009 Sheet 6 of 7
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`US 2009/0141907 A1
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`2. ‘OI H
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`S-O. O. O. O.
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`Page vii
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`Patent Application Publication
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`Jun. 4, 2009 Sheet 7 of 7
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`US 2009/0141907 A1
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`FIG. 8
`
`
`
`
`
`
`
`
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`
`
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`FILTER HIGH-FREQUENCY SIGNAL HAVING
`FREQUENCY THAT ISHIGHER THAN REFERENCE
`FREQUENCY AND LOW-FREQUENCY SIGNAL
`HAVING FREOUENCY THAT IS LOWER THAN
`REFERENCE FREQUENCY FROM INPUT SIGNALS
`OBTANED THROUGH MCROPHONE ARRAY
`
`
`
`81 O
`
`OBTAN HIGH-FREQUENCY TARGET SIGNAL
`BY CANCELNG NOISE SIGNAL FROM
`FILTERED HIGH-FREOUENCY SIGNAL
`USING BEAMFORMING METHOD
`
`- 820
`
`OBTAIN LOW-FREGUENCY TARGET SIGNAL
`BY CANCELNG NOSE SIGNAL HAVING
`PHASE DIFFERENCE THAT IS DIFFERENT
`FROM PHASE DIFFERENCE OF TARGET SIGNAL
`FROM FILTERED LOW-FREGUENCY SIGNAL
`
`OBTAIN SOUND SOURCE SIGNAL FROM WHICH
`NOISE IS CANCELED BY SYNTHESIZING OBTANED
`HIGH-FREQUENCY TARGET SIGNAL WITH
`OBTAINED LOW-FREQUENCY TARGET SIGNAL
`
`
`
`830
`
`840
`
`Page viii
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`

`

`US 2009/O 141907 A1
`
`Jun. 4, 2009
`
`METHOD AND APPARATUS FOR
`CANCELING NOISE FROMSOUND INPUT
`THROUGH MCROPHONE
`
`CROSS-REFERENCE TO RELATED PATENT
`APPLICATION
`0001. This application claims the benefit of Korean Patent
`Application No. 10-2007-0123819, filed on Nov.30, 2007, in
`the Korean Intellectual Property Office, the disclosure of
`which is incorporated herein in its entirety by reference.
`
`BACKGROUND
`
`0002 1. Field
`0003. One or more embodiments of the present invention
`generally relates to a method, medium and apparatus for
`canceling noise from an input Sound, and more particularly, to
`a method and apparatus whereby a sound Source signal cor
`responding to interference noise is canceled from a Sound that
`is input through a small-size digital sound obtaining appara
`tus having a microphone array in order to obtain only a Sound
`Source signal radiated from a target Sound source.
`0004 2. Description of the Related Art
`0005. An age has emerged in which making of phone
`conversations, recording of external Voice, or taking of mov
`ing pictures using portable digital devices is a routine. In
`various digital devices such as consumer electronics (CE)
`devices, portable phones, and digital camcorders, a micro
`phone is used as a means for obtaining Sounds. In order to
`implement a stereo sound using two or more channels instead
`of a mono Sound using a single channel, a microphone array
`including a plurality of microphones is generally used.
`0006. The microphone array can obtain an additional fea
`ture regarding directivity, such as the direction or position of
`a sound to be obtained, as well as the sound itself. Directivity
`involves increasing sensitivity with respect to a Sound Source
`signal radiated from a sound source located in a particular
`direction, by using differences in time at which sound Source
`signals arrive at a plurality of microphones of the microphone
`array. Thus, a sound source signal input from a specific direc
`tion can be reinforced or Suppressed by obtaining the Sound
`Source signal using the microphone array.
`0007 Environment where a sound source signal is
`recorded or a sound signal is input through a portable digital
`device is more likely to include noise and neighboring inter
`ference Sound and less likely to be a calm environment having
`no interference Sound. For this reason, techniques for rein
`forcing a particular Sound Source signal required by a user
`from composite sounds or canceling unnecessary interfer
`ence noise from the composite sounds have been developed.
`Recently, there has been increasing demands to accurately
`obtain only a Sound source signal desired by a user, such as in
`Video conference or Voice recognition.
`
`SUMMARY OF THE INVENTION
`0008. One or more embodiments of the present invention
`provides a method, medium and apparatus for canceling noise
`whereby it is possible to solve a conventional problem that
`unnecessary noise cannot be appropriately canceled from a
`Sound obtained through a microphone array because of a
`Small size of a digital sound obtaining apparatus having the
`microphone array and to overcome a conventional limitation
`that a target Sound source signal cannot be accurately
`obtained due to the problem.
`
`0009. According to an aspect of the present invention,
`there is provided a method of canceling noise. The method
`includes filtering a high-frequency signal having a frequency
`that is higher than a reference frequency and a low-frequency
`signal having a frequency that is lower than the reference
`frequency from input signals obtained through a microphone
`array, obtaining a high-frequency target signal by canceling a
`noise signal from the filtered high-frequency signal using a
`beam forming method, obtaining a low-frequency target sig
`nal by canceling a noise signal having a phase difference that
`is different from a phase difference of a target signal from the
`filtered low-frequency signal, and obtaining a sound source
`signal from which noise is cancelled, by synthesizing the
`obtained high-frequency target signal with the obtained low
`frequency target signal.
`0010. According to another aspect of the present inven
`tion, there is provided a computer-readable recording
`medium having recorded thereon a program for executing the
`method of canceling noise.
`0011. According to another aspect of the present inven
`tion, there is provided an apparatus for canceling noise. The
`apparatus includes a filtering unit filtering a high-frequency
`signal having a frequency that is higher than a reference
`frequency and a low-frequency signal having a frequency that
`is lower than the reference frequency from input signals
`obtained through a microphone array, a high-frequency target
`signal generation unit obtaining a high-frequency target sig
`nal by canceling a noise signal from the filtered high-fre
`quency signal using a beam forming method, a low-frequency
`target signal generation unit obtaining a low-frequency target
`signal by canceling a noise signal having a phase difference
`that is different from a phase difference of a target signal from
`the filtered low-frequency signal, and a signal synthesis unit
`obtaining a sound source signal from which noise is can
`celled, by synthesizing the obtained high-frequency target
`signal with the obtained low-frequency target signal.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0012. The patent or application file contains at least one
`drawing executed in color. Copies of this patent or patent
`application publication with color drawing(s) will be pro
`vided by the Office upon request and payment of the neces
`sary fee. The above and other features and advantages of the
`present invention will become more apparent by describing in
`detail embodiments thereof with reference to the attached
`drawings in which:
`(0013 FIGS. 1A and 1B illustrate beam patterns with
`respect to sizes of a microphone array in order to explain a
`problem to be solved by the embodiments;
`0014 FIG. 2 is a block diagram of an apparatus for can
`celing noise according to an embodiment of the present
`invention;
`(0015 FIGS. 3A and 3B are detailed block diagrams of a
`high-frequency target signal generation unit of the apparatus
`illustrated in FIG. 2 according to an embodiment of the
`present invention;
`0016 FIG. 4 is a detailed block diagram of a low-fre
`quency target signal generation unit of the apparatus illus
`trated in FIG. 2 according to an embodiment of the present
`invention;
`0017 FIG. 5 is a detailed block diagram of a signal syn
`thesis unit of the apparatus illustrated in FIG. 2 according to
`an embodiment of the present invention;
`
`

`

`US 2009/O 141907 A1
`
`Jun. 4, 2009
`
`0018 FIG. 6 is a block diagram of an apparatus for can
`celing noise, which includes a means for detecting a direction
`of a sound source, according to another embodiment of the
`present invention;
`0019 FIG. 7 is a block diagram of an apparatus for can
`celing noise, which includes a means for canceling an acous
`tic echo, according to still another embodiment of the present
`invention; and
`0020 FIG. 8 is a flowchart illustrating a method of can
`celing noise according to still another embodiment of the
`present invention.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`Hereinafter, embodiments of the present invention
`0021
`will be described in detail with reference to the accompanying
`drawings. In the description of the embodiments, a Sound
`Source is used as a term that means a source from which a
`Sound is radiated, a Sound pressure expresses a force exerted
`by acoustic energy using the physical amount of pressure, and
`a Sound source field conceptually expresses a region affected
`by the Sound pressure around the Sound Source.
`0022 FIGS. 1A and 1B illustrate beam patterns with
`respect to sizes of a microphone array in order to explain a
`problem to be solved by the embodiments. Here, a beam
`pattern means a graph of measurements of electric field
`strengths of electromagnetic waves formed around a micro
`phone array when a sound source field having directivity is
`formed using the microphone array.
`0023. As mentioned previously, a microphone array is
`used to make use of a directional feature of a sound. Such as
`directivity. Generally, in order to receive a target signal mixed
`with background noise with high sensitivity, a microphone
`array functions as a filter capable of spatially reducing noise
`by increasing an amplitude of each signal received by the
`microphone array using the application of an appropriate
`weight to the signal when directions of a target signal and an
`interference noise signal are different from each other. Such a
`sort of spatial filter is referred to as a beam former.
`0024 FIGS. 1A and 1B illustrate beam patterns formed in
`the implementation of directivity for obtaining a Sound Source
`signal radiated from a sound source located in a particular
`direction using the beam former. The beam patterns illustrated
`in FIGS. 1A and 1B are formed for a microphone array having
`an aperture size of 20 cm and a microphone array having an
`aperture size of 3 cm, respectively. In graphs illustrated in
`FIGS. 1A and 1B, a vertical axis represents an array response
`formed by a microphone array and two horizontal axes rep
`resent a frequency and an angle with respect to the micro
`phone array, respectively. As can be seen from FIGS. 1A and
`1B, each of the graphs is symmetric to a center 0° in the
`horizontal angle axis. In other words, FIGS. 1A and 1B visu
`ally illustrate the degree of beam forming of the microphone
`arrays with respect to frequencies.
`0025. When FIGS. 1A and 1B are compared with each
`other, in the graph illustrated in FIG. 1A corresponding to the
`microphone array having an aperture size of 20 cm, beam
`forming is performed stably without greatly changing with
`frequencies in the horizontal axis. In other words, a constant
`array response pattern is formed regardless of a change in
`frequency. On the other hand, in the graph illustrated in FIG.
`1B corresponding to the microphone array having an aperture
`size of 3 cm, the performance of beam forming degrades
`sharply from a frequency of about 500 Hz or lower in the
`
`horizontal axis. In the graph illustrated in FIG. 1B, a flat beam
`pattern is shown in a frequency interval between 0 Hz and 500
`HZ.
`0026. As can be seen from the graphs illustrated in FIGS.
`1A and 1B, it is known that an aperture size of a microphone
`array is closely related to a wavelength of an input signal. In
`particular, as the aperture size of the microphone array
`decreases, performance degradation occurs in beam forming
`for a low-frequency domain where the wavelength of the
`input signal is large. Moreover, the size of the low-frequency
`domain where any beam is not formed increases as the size of
`the microphone array decreases. For example, if a low-fre
`quency domain where any beam is not formed ranges from 0
`HZ to 500 Hz for an aperture size 3 cm of a microphone array,
`the low-frequency domain may extend up to 700 Hz for an
`aperture size 1 cm of the microphone array. Thus, in a digital
`Sound obtaining apparatus for obtaining an external Voice
`signal and a particular target Sound source signal using a
`beam forming method, an aperture size of a microphone array
`has a direct influence upon the performance of obtaining a
`Sound source signal.
`0027. In a small-size sound obtaining apparatus Such as a
`portable phone or a digital camcorder carried by a user, unlike
`in an audio device generally used in home or recording equip
`ment used in a professional recording studio, an aperture size
`of a microphone array mounted in the Sound obtaining appa
`ratus is inevitably small because of the small-size of the sound
`obtaining apparatus. As a result, the performance of the Sound
`obtaining apparatus degrades in obtaining a sound source
`signal for a low-frequency Sound source signal having a large
`wavelength. Consequently, signal distortion or signal drop
`ping which does not occur in a high-frequency domain may
`occur when the Sound source signal obtained by the Sound
`obtaining apparatus is processed.
`0028 Embodiments of the present invention to be
`described will suggest an apparatus and method in which an
`input signal obtained through a microphone array is divided
`into a high-frequency band and a low-frequency band based
`on their frequency bands and then are processed so that a
`Sound source signal of the low-frequency band is not distorted
`or dropped.
`0029 FIG. 2 is a block diagram of an apparatus for can
`celing noise according to an embodiment of the present
`invention. Referring to FIG. 2, the apparatus includes a
`microphone array 200, a filtering unit 210 having a high-pass
`filter (HPF) 211 and a low-pass filter (LPF) 212, a high
`frequency target signal generation unit 221, a low-frequency
`target signal generation unit 222, and a signal synthesis unit
`23O.
`0030 The microphone array 200 obtains sound source
`signals. A way to control the microphone array 200, e.g., the
`direction of a sound source or the magnitude of a Sound
`Source signal, can be designed variously according to a situ
`ation in which and a goal for which the current embodiment of
`the present invention is implemented.
`0031. The filtering unit 210 filters a high-frequency signal
`having a frequency that is higher than a reference frequency
`and a low-frequency signal having a frequency that is lower
`than the reference frequency from the input signal obtained
`through the microphone array 200. Here, the reference fre
`quency means a frequency that serves as a criterion for filter
`ing the high-frequency signal and the low-frequency signal
`from the input signal, and is also called a cut-off frequency. A
`high frequency or a low frequency is a relative concept, and it
`
`

`

`US 2009/O 141907 A1
`
`Jun. 4, 2009
`
`is necessary to select a frequency from the entire band of the
`input signal for division into a high frequency and a low
`frequency.
`0032. As mentioned previously, in embodiments of the
`present invention, the input signal is divided based on their
`frequency bands because beam forming is not performed
`properly in a low-frequency domain. Consequently, the ref
`erence frequency has to be higher than or equal to a start point
`of a frequency at which beam forming is not performed prop
`erly. Thus, an ideal reference frequency may be set higher
`than or equal to a frequency at which beam forming of an input
`signal obtained through the microphone array 200 results in
`signal distortion, in consideration of an aperture size of the
`microphone array 200.
`0033. The reference frequency can be adjusted according
`to products or environments in which the embodiments of the
`present invention are actually implemented. Alternatively, the
`reference frequency may be experimentally calculated as a
`particular value in advance. Alternatively, the reference fre
`quency may be set using a separate device in consideration of
`an aperture size of the microphone array 200, instead of being
`set to a fixed value in advance.
`0034 Referring back to FIG. 2, an input signal obtained
`through the microphone array 200 is filtered by the HPF 211
`and the LPF 212 which pass a high-frequency signal having a
`frequency that is higher than the reference frequency and a
`low-frequency signal having a frequency that is lower than
`the reference frequency, respectively.
`0035. When the number of individual microphones of the
`microphone array 200 is M, an input signal X(t) obtained
`through the microphone array 200 can be expressed as fol
`lows.
`
`0036. When pass functions of the HPF 211 and the LPF
`212 are h(t) and h(t), respectively, the high-frequency
`signal and the low-frequency signal filtered by the HPF 211
`and the LPF 212 can be defined as follows:
`
`0037 where x, "(t) and X,*(t) denote sound source sig
`nals filtered from an input signal obtained through an ith
`microphone of the microphone array 200, respectively. In the
`following description, a process of canceling a noise signal
`from the filtered high-frequency signal and the filtered low
`frequency signal and a process of extracting only a target
`sound source signal desired by a user will be described
`sequentially.
`0038. The high-frequency target signal generation unit
`221 obtains a high-frequency target signal by canceling a
`noise signal from the filtered high-frequency signal using a
`beam forming method. As described previously, beam form
`ing is used to amplify or extract a Sound source signal, i.e., a
`target signal, radiated from a Sound source located in a par
`ticular direction through a microphone array. To this end, a
`beam pattern formed through the microphone array and sig
`nal information input to each individual microphone of the
`microphone array are used. Various beam forming methods
`Such as a fixed beam forming method or an adaptive beam
`forming method have been introduced to obtain the signal
`information, and various algorithms for extracting a target
`signal from an input signal using the beam forming methods
`have been developed. Hereinafter, the adaptive beam forming
`
`method will be described by way of example with reference to
`FIGS. 3A and 3B. Among various adaptive beam forming
`methods, a generalized sidelobe canceller (GCS) algorithm,
`which is known as a representative adaptive beam forming
`method, will be introduced in the following description.
`0039 FIGS. 3A and 3B are block diagrams of a high
`frequency target signal generation unit 300 in an apparatus for
`canceling noise according to an embodiment of the present
`invention. In FIGS. 3A and 3B, the high-frequency target
`signal generation unit 300 is illustrated based on a GSC
`algorithm. The GSC algorithm is an adaptive filtering method
`for extracting only a target signal desired by a user by can
`celing a noise signal from a sound source signal obtained
`through a microphone array. The GSC algorithm can be easily
`construed by those of ordinary skill in the art (Lloyd J. Grif
`fiths and Charles W. Jim, “An alternative approach to linearly
`constrained adaptive beam forming, IEEE Transaction on
`antennas and propagation, Vol. AP-30, No. 1, January 1982).
`0040. Referring to FIG.3A, the high-frequency target sig
`nal generation unit 300 includes a target signal reinforcement
`unit 311, a noise signal reinforcement unit 312, and a noise
`signal cancellation unit 320.
`0041. The target signal reinforcement unit 311 inputs
`therein a high-frequency signal generated by a HPF (not
`shown) and reinforces a target signal from the high-frequency
`signal. In order to reinforce the target signal, a directivity
`adjustment factor, i.e., a delay, has to be adjusted so that the
`target signal has directivity toward a direction of a Sound
`source that radiates the target signal. By means of such direc
`tivity adjustment, a target dominant signal is generated. The
`target signal reinforcement unit 311 may be implemented
`with a beam forming means such as a fixed beam former.
`0042. The noise signal reinforcement unit 312 inputs
`therein the high-frequency signal generated by the HPF (not
`shown) and reinforces a noise signal from the high-frequency
`signal. This process is similar to the above-described process
`of reinforcing the target signal except that a signal that is
`Subject to reinforcement is a noise signal instead of a Sound
`Source signal radiated from a target Sound source. By means
`of the noise signal reinforcement unit 312, a noise dominant
`signal is generated. A means for reinforcing a noise signal
`instead of a target signal is also called a target blocker.
`0043. When the target dominant signal generated by the
`target signal reinforcing unit 311 and the noise dominant
`signal generated by the noise signal reinforcing unit 312 are
`implemented in the form of filters, they can be expressed as
`follows:
`
`K
`
`ya(k) =XX anx" (k-1)
`
`(3)
`
`i
`
`K
`
`y,(k) =XX by" (k-1),
`
`n=l i=1
`
`0044 where y(k) denotes a target dominant signal gen
`erated by the target signal reinforcing unit 311, y,(k) denotes
`a noise dominant signal generated by the noise signal rein
`forcing unit 312, M denotes the number of individual micro
`phones of a microphone array, Kdenotes the number of filter
`tabs of channels of the microphone array, a denotes a pass
`function of a beam former, and b, denotes a pass function of
`a target blocker.
`
`

`

`US 2009/O 141907 A1
`
`Jun. 4, 2009
`
`0045 Although the target dominant signal and the noise
`dominant signal are expressed in the form of FIR filters in
`Equation 3, various methods of implementing a beam former,
`Such as multiplication of signals in a frequency domain, as
`well as the use of the FIR filters, can be used.
`0046. The noise signal cancellation unit 320 generates the
`high-frequency target signal using the target dominant signal
`generated by the target signal reinforcing unit 311 and the
`noise dominant signal generated by the noise signal reinforc
`ing unit 312. A detailed process for the generation of the
`high-frequency target signal will be described with reference
`to FIG. 3B.
`0047 Referring to FIG. 3B, the noise signal cancellation
`unit 320 includes a subtraction unit 322 for noise cancellation
`and an adaptive filter 321. The subtraction unit 322 subtracts
`the noise dominant signal from the target dominant signal.
`The subtraction result is input to the adaptive filter 321 in
`order to properly adjust a noise signal to be canceled. As a
`result, the noise signal cancellation unit 320 outputs the high
`frequency target signal from which the noise signal is can
`celed and which includes only a clear target signal.
`0048. In order to generate the target signal from which the
`noise signal is canceled, a filter coefficient has to be deter
`mined first. To this end, various cost calculation methods such
`as a least mean square (LMS) algorithm, a normalized least
`mean square (NLMS) algorithm, and a recursive least square
`(RLS) algorithm can be used. By using a representative LMS
`algorithm, a cost function can be defined as follows:
`
`J(n) = Elysc(n)|
`
`(4)
`
`0049 where ys(n) denotes a target signal, y(n) and
`y,(n) denote a target dominant signal and a noise dominant
`signal, respectively, and f'(k) denotes a coefficient of the
`adaptive filter 321. The coefficient of the adaptive filter 321
`can be expressed in more detail as follows:
`
`6 J(n)
`a f(n) (m)
`
`(5)
`
`0050 where u denotes a learning coefficient involved in
`convergence speed, and has a value between 0 and 1. A signal
`resulting from Subtracting a signal filtered by the adaptive
`filter 321 from the target dominant signal can be expressed as
`follows.
`
`Equation 6 means that a result of subtracting a signal
`0051
`obtained by filtering the noise dominant signaly(n) from the
`target dominant signaly(n) is a target signalys(n)
`0052. The configuration of the high-frequency target sig
`nal generation unit 221 and a target signal generation process
`
`have been described so far. Next, the low-frequency target
`signal generation unit 222 will be described in detail.
`0053. The low-frequency target signal generation unit 222
`obtains the low-frequency target signal by canceling the noise
`signal having a phase difference that is different from a phase
`difference of the target signal from the low-frequency signal
`filtered by the LPF 212. Unlike a general beam forming
`method which uses an amplitude of a Sound Source signal, the
`low-frequency target signal generation unit 222 uses a phase
`difference of the Sound source signals that are input through a
`microphone array including a plurality of microphones.
`0054. In order to cancel only a noise signal from the input
`low-frequency signal, the low-frequency target signal genera
`tion unit 222 calculates phase differences between input sig
`nals according to frequency components of the input signals.
`The input signals may include a target Sound source signal
`radiated from a Sound source desired by a user and a noise
`signal to be canceled. If a phase difference for the target signal
`is known, only the target signal can be obtained by removing
`the remaining signals except for a signal corresponding to the
`phase difference for the target signal based on the calculated
`phase differences. This is because sound source signals hav
`ing phase differences that are not the same as or are not similar
`to the phase difference for the target signal correspond to the
`noise signal.
`0055. The low-frequency target signal generation unit 222
`has to previously know the phase difference for the target
`signal before calculating the phase differences between the
`input signals and canceling the noise signal. When a sound is
`obtained using a portable sound obtaining apparatus, it is a
`general feature thana target Sound Source is located in front of
`a microphone array. In this case, since input signals obtained
`through the microphone array have arrived at the almost same
`time as each other in individual microphones of the micro
`phone array, they have little phase differences. In other words,
`when a target Sound source is located in frontofa microphone
`array, a target signal can be obtained by removing the remain
`ing signals except for a signal having no phase difference
`between input signals.
`0056. When a target sound source is not located in front of
`a microphone array, if a phase difference at the moment when
`a sound source signal radiated from a direction in which the
`target Sound source is located arrives at the microphone array
`is known in advance, a target signal can be obtained by
`removing the remaining sound source signals except for a
`Sound Source signal corresponding to the known phase dif
`ference. The foregoing embodiments will be described with
`reference to FIG. 4.
`0057 FIG. 4 is a detailed block diagram of a low-fre
`quency target signal generation unit 400 in an apparatus for
`canceling noise according to an embodiment of the present
`invention. Referring to FIG. 4, the low-frequency target sig
`nal generation unit 400 includes signal transformation units
`411 and 412, a phase difference calculation unit 420, and a
`noise signal cancellation unit 430. In the current embodiment
`of the present invention, it is assumed that 2 channels are
`selected from among a plurality of channels, i.e., individual
`microphones, of the microphone array in order to be used for
`calculation of phase differences between input signals.
`0058. The signal transformation unit 411 performs a dis
`crete Fourier transform (DFT) on an input low-pass signal
`that is a signal of a time domain. In order to calculate a phase
`
`

`

`US 2009/O 141907 A1
`
`Jun. 4, 2009
`
`difference for each frequency component, it is necessary to
`transform the low-pass signal into a signal of a frequency
`domain.
`0059. The phase difference calculation unit 420 calculates
`a phase difference between input signals that are transformed
`by the signal transformation unit 411 for each frequency
`component of the input signals.
`0060. The noise signal cancellation unit 430 cancels the
`remaining frequency components except for a frequency
`component having no phase difference calculated by the
`phase difference calculation unit 420 from the input signal
`transformed by the signal transformation unit 411. This can
`cellation process is based on anassumption that a target Sound
`Source is located in front of a microphone array. If the target
`Sound source is not located in front of the microphone array
`and is located in a particular direction, the noise signal can
`cellation unit 430 compares the phase differenc