United States Patent (19)
`Sasaki et al.
`
`||||||I||
`US005471538A
`11
`Patent Number:
`5,471.538
`45) Date of Patent:
`Nov. 28, 1995
`
`(54) MICROPHONE APPARATUS
`75 Inventors: Tooru Sasaki, Tokyo, Kaoru Gyotoku,
`Kanagawa, both of Japan
`73 Assignee: Sony Corporation, Tokyo, Japan
`
`(21) Appl. No.: 57,821
`22 Filed:
`May 7, 1993
`30
`Foreign Application Priority Data
`May 8, 1992
`JP
`Japan .................................... 4-143209
`(51) Int. Cl. .........................
`HO4R 3100
`52 U.S. C. ................................................. 381/92; 381/94
`58 Field of Search .......................................... 381/92, 94
`
`(56
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`1/1983 Bäder ........................................ 38.192
`4,370,523
`4,589,137 5/1986
`... 381/92
`4,741,038 4/1988
`... 381/92
`4,802,227
`1/1989
`... 381192.
`4,888,807 12/1989 Reichel ..................................... 381A92
`
`5,033,082 7/199 Eriksson et al. .......................... 381/94
`5,243,661
`9/1993 Ohkubo et al. ........................... 381A94
`FOREIGN PATENT DOCUMENTS
`0084982 8/1983 European Pat. Off..
`0381498 8/1990 European Pat. Off..
`60097729 5/1985 Japan.
`9204781 3/1992 WIPO.
`Primary Examiner-Forester W. Isen
`Attorney, Agent, or Firm-Jay H. Maioli
`(57)
`ABSTRACT
`A microphone apparatus having a first microphone for
`picking up a desired sound and a second microphone with
`directionality in which sensitivity is low to the desired sound
`arrival direction. A sound signal from the second micro
`phone is supplied to a subtracting circuit through an adaptive
`filter. The subtracting circuit subtracts an output signal of the
`adaptive filter from the sound signal coming from the first
`microphone. A circuit is provided to adjust the adaptive filter
`so that the output power of the subtracting circuit is mini
`mized. The setup implements a microphone system which is
`compact in size and easily provides desired directionality.
`
`6 Claims, 7 Drawing Sheets
`
`
`
`S- O
`
`Page 1 of 14
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`GOOGLE EXHIBIT 1007
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`

`

`U.S. Patent
`
`Nov. 28, 1995
`
`Sheet 1 of 7
`
`5,471.538
`
`F G. A
`PROR ART
`
`
`
`/
`
`3.
`
`O
`
`O O O O O C O -
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`Page 2 of 14
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`

`

`U.S. Patent
`
`Nov. 28, 1995
`
`Sheet 2 of 7
`
`5,471.538
`
`F G 2
`
`
`
`S+ nC)
`
`e
`
`MAN NPUT
`
`MCROPHONE
`
`(OMND RECTIONAL)
`
`- a -
`
`a
`
`OdE
`
`REFERENCE INPUT
`MCROPHONE 2
`(UND RECTIONAL )
`
`-2OdB
`-----1-N1a- - - -
`CD
`
`Page 3 of 14
`
`

`

`U.S. Patent
`
`Nov. 28, 1995
`
`Sheet 3 of 7
`
`5,471.538
`
`F G 4
`
`24
`
`3OO
`
`n
`
`O
`
`Xok
`
`Xik
`
`X2k
`Z - - - - - - - -
`
`Z
`
`Z
`
`Xink
`
`3 O
`
`yk
`
`O
`
`c
`
`ek
`
`LMS
`COMPUTING
`CRCUT
`
`Page 4 of 14
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`

`

`U.S. Patent
`U.S. Patent
`
`Nov. 28, 1995
`Nov. 28, 1995
`
`Sheet 4 of 7
`Sheet 4 of 7
`
`5,471,538
`5,471.538
`
`FIG.5B
`
`FIG.5C
`
`FIG.SA
`
`Page 5 of 14
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`Page 5 of 14
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`

`

`U.S. Patent
`U.S. Patent
`
`Nov. 28, 1995
`Nov. 28, 1995
`
`Sheet 5 of 7
`Sheet 5 of 7
`
`5,471,538
`5,471.538
`
`F G 6
`FIG.6
`
`AR
`AR
`
`- 90°
`~----\_,----- — 90°
`
`900
`
`Page 6 of 14
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`Page 6 of 14
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`

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`U.S. Patent
`U.S. Patent
`
`Nov. 28, 1995
`Nov. 28, 1995
`
`Sheet 6 of 7
`Sheet 6 of 7
`
`5,471,538
`5,471.538
`
`F G. 7
`FIG. 7
`
`AR
`AR
`
`~----1_-4.-}------ 90°
`
`|
`
`Page 7 of 14
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`Page 7 of 14
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`

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`U.S. Patent
`
`Nov. 28, 1995
`
`Sheet 7 of 7
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`5,471.538
`
`F G. 8
`
`& A
`
`3.
`
`
`
`
`
`
`
`
`
`
`
`F G 9
`
`
`
`
`
`FREQUENCY
`CHARACTERSTC
`CORRECTING
`CRCUT
`
`F G. O
`
`is . .
`
`C CIRCUIT
`
`.
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`Page 8 of 14
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`

`

`5,471.538
`
`1.
`MICROPHONE APPARATUS
`
`BACKGROUND OF THE INVENTION
`
`2
`desired sound is low, an adaptive filter means 24 to which a
`sound signal is supplied from the second microphone, and a
`subtracting means 15 for subtracting an output signal of the
`adaptive filter means 24 from a sound signal of the first
`microphone 11, wherein the adaptive filter means 24 is
`adjusted to minimize an output power of the subtracting
`means 15.
`If the directions in which sounds to be recorded come are
`different, it indicates that their sources are different and
`correlation between then is often low. In the above-men
`tioned novel constitution, directionality of the second micro
`phone 21 is low in sensitivity in the direction of the desired
`sound. Therefore, correlation is low between a sound signal
`from the second microphone 21 and a sound signal from the
`first microphone 11. If the sound signal from the second
`microphone 21 is assumed to be noise, the microphone
`apparatus according to the invention has a constitution of an
`adaptive noise reduction system. In this system, when the
`output power of the subtracting means is minimized, the
`sound signal of the second microphone 21 is removed from
`the sound signal of the first microphone 11, providing only
`a desired sound from the first microphone 11 as an output
`sound signal. The adaptive noise reduction system is dis
`closed in U.S. Patent application Ser. No. 07/680,408 for
`example.
`That is, the microphone apparatus according to an inven
`tion has the adaptive noise reduction system which makes a
`distinction between desired sound and noise depending on
`sound arrival direction wherein the directionality of the
`second microphone 21 is arranged to make the system
`mainly sensitive to the arrival direction of desired sound.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIGS. 1A-1C are a diagram illustrating an example of a
`prior-art microphone apparatus,
`FIG. 2 is a block diagram of an embodiment of the
`microphone apparatus according to the invention;
`FIG. 3 is a diagram illustrating an example of direction
`alities of the first and second microphones;
`FIG. 4 is a diagram illustrating an example of an adaptive
`filter circuit of FIG. 2;
`FIG. 5A-5C are diagram describing the operation of the
`microphone apparatus according to the invention;
`FIG. 6 is a diagram illustrating another example of the
`directionalities of the first and second microphones;
`FIG. 7 is a diagram illustrating still another-example of
`the directionalities of the first and second microphones;
`FIG. 8 is a diagram explaining an example of constituting
`the microphone with a plurality of microphone units;
`FIG. 9 is a diagram illustrating the example of constitut
`ing the microphone with a plurality of microphone units; and
`FIG. 10 is a diagram illustrating another example of a part
`of the constitution of FIG. 9.
`
`1. Field of the Invention
`The present invention relates to a microphone apparatus.
`2. Description of the Related Art
`With a so-called camcorder, a lightweight television cam
`era with an incorporated video cassette recorder, for
`example, sound around an object is recorded while the
`object is being pictured. In recording the sound, the micro
`phone is designed so that only the sound coming from the
`direction of the object is recorded. That is, the camcorder is
`provided with a directional microphone that picks up the
`sound coming into the front of the camcorder.
`One example of a microphone apparatus of this type is
`known as a "gun microphone.' This microphone is pro
`vided, as shown in FIG. 1, with a pipe 2 extending from a
`diaphragm 1. The pipe 2 is provided with many through
`holes 3 in its side wall, providing directionality so that the
`microphone is highly sensitive to a sound coming from its
`front and long along the center line of the pipe 2, or the
`opposite side of the diaphragm 1.
`To be more specific, as shown in FIG. 1A, acoustic waves
`coming from the front of the microphone (the right-hand in
`the figure) have the same path length to the diaphragm 1
`whether they arrive at it from the top of the pipe 2 or any one
`through-hole 3, so that they arrive in the same phase to be
`added together.
`In contrast, as shown in FIG. 1B, acoustic waves coming
`from a side of the pipe 2 through different through-holes 3
`differ in phase because their path lengths from the through
`holes, or incident positions, to the diaphragm 1 are different.
`Likewise, as shown in FIG. 1C, an acoustic wave coming
`from the backside of the microphone arrives via different
`through-holes 3 at the diaphragm 1, causing a phase differ
`ence in the acoustic wave, or an incident signal. A plurality
`of holes 3 in the pipe 2 are arranged so that incident acoustic
`signals weaken each other. The microphone shown in FIG.
`1 has a directionality in which sensitivity is low to acoustic
`waves coming from the side or back of the pipe.
`Thus, the gun microphone as shown in FIG. 1 provides a
`directional microphone having a high sensitivity to an
`45
`acoustic wave coming from the front of the microphone.
`However, as described above, this microphone requires a
`pipe 2, which is long, thereby increasing the microphone's
`external dimensions.
`Additionally, this unidirectional microphone has a high
`sensitivity only to acoustic waves coming from the front of
`the microphone, providing fixed, inflexible directionality.
`This makes it difficult to record not only sound coming from
`the desired direction of source, but also sound coming, for
`example, from the sides of the camcorder.
`
`15
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`25
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`35
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`40
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`50
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`55
`
`SUMMARY OF THE INVENTION
`It is therefore an object of the present invention to provide
`a microphone apparatus which is compact in size and easily
`provides desired directionality.
`In carrying out the invention and according to one aspect
`thereof, there is provided a microphone apparatus compris
`ing a first microphone 11 (this and other reference characters
`below are identified in the accompanying drawings) for
`recording a desired sound, a second microphone having
`directionality in which sensitivity in the direction of the
`
`60
`
`65
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`For a general understanding of the features of the present
`invention, references are made to the embodiment of the
`microphone apparatus according to the invention as shown
`in FIG. 2.
`Referring to FIG. 2, reference numeral 11 is a main input
`microphone for recording a desired sound and reference
`numeral 21 is a reference input microphone for picking up
`
`Page 9 of 14
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`

`

`5,471.538
`
`4
`subtraction error e from the subtracting circuit 15 is mini
`mized.
`Here, suppose that s, n0, and n1 are statistically stationary
`and their average is 0, then an output is:
`
`Because there is no correlation between s and n0 and
`between sandy, an expected value obtained by squaring this
`result becomes as follows:
`
`10
`
`Ele'
`
`15
`
`3
`sound coming from a direction to be removed from the
`recording. In this example, the arrival direction of desired
`sound is mainly a direction indicated by an arrow AR in FIG.
`3, or a direction from up to down (hereinafter referred to as
`the front direction). This setup is intended to implement a
`microphone apparatus which generally does not pick up any
`sound coming from a direction (hereinafter referred to as a
`rear direction) opposite to the front direction.
`In the above-mentioned example, the main input micro
`phone 11 is constituted by an omnidirectional microphone as
`shown in FIG.3, while the reference input microphone 21 is
`constituted by a unidirectional microphone which is mainly
`sensitive to the rear direction, not to the front direction or the
`desired sound arrival direction as shown in FIG. 3.
`A sound signal picked up by the main input microphone
`11 and converted into an electrical signal is fed to an A-D
`converter 13 through an amplifier 12 to be converted into a
`digital equivalent which is fed to a subtracting circuit 15
`through a delay circuit 14.
`A sound signal picked up by the reference microphone 21
`and converted into an electrical signal is fed to an A-D
`converter 23 through an amplifier 22 to be converted into a
`digital equivalent which is fed to an adaptive filter circuit 24.
`The output signal of the adaptive filter circuit 24 is fed to the
`subtracting circuit 15. The output signal of the subtracting
`circuit 15 is fed back to the adaptive filter circuit 24 and, at
`the same time, converted into an analog signal by a D-A
`converter 16 to be fed to an output pin 17.
`It should be noted that the sound signal may be output
`without passing it through the D-A converter 16, or the
`signal may be output in digital form. The delay circuit 14 is
`provided to compensate a time delay required by the adap
`tive filter circuit 24 for adaptive processing and a propaga
`tion time in the filter.
`The adaptive filter circuit 24 controls so that a reference
`input sound signal approximates a sound signal other than
`that coming from the front direction included in a main input
`sound signal, as will become apparant. Consequently, if
`there is no correlation between a desired sound signal in the
`sound signal picked up by the main input microphone 11 and
`a sound signal other than that coming from the front direc
`tion, the sound signal picked up by the reference input
`microphone 21 is subtracted by the subtracting circuit 15
`from the sound signal picked up by the main input micro
`phone, making the subtracting circuit 15 put out only the
`desired sound signal.
`In other words, the above-mentioned setup provides an
`adaptive noise reduction system to which the output sound
`signal of the main input microphone 11 is supplied as a main
`input and the output sound signal of the reference input
`microphone 21 is supplied as a reference input. This system
`operates as follows.
`The main input sound signal from the A-D converter 13
`is obtained by adding the desired sound signal s coming
`from the direction of arrow AR or the front direction to the
`sound signal n0 coming from the rear direction (hereinafter
`referred to as a noise) which is supposed to have no
`correlation with the main input sound signal. On the other
`hand, letting the reference input sound signal from the A-D
`converter 23 be n1, then, as seen from the above description,
`this reference input sound signal n1 has correlation with the
`noise n0, not with the desired sound signal. An adaptive
`processing algorithm makes the adaptive filter circuit 24
`filter the reference input sound signal n1 to output a signal
`y and controls the adaptive filter circuit 24 so that a
`
`The adaptive filter circuit 24 is adjusted to minimize E
`(e). At this time, Es’) is not affected;
`Emin (e=E (s-Emin (n0-y)
`That is, minimizing E (e' in turn minimizes E (n0-y),
`making the outputy of the adaptive filter circuit 24 equal to
`an estimator of the noise n0. And an expected value of the
`output from the subtracting circuit 15 becomes only the
`desired signal. In other words, adjusting the adaptive filter
`circuit 24 to minimize a total output power is equal to
`making the subtracting outpute be a least square estimator
`of the desired sound signals.
`Referring to FIG. 4, one embodiment of the adaptive filter
`circuit 24 is exemplarily shown by using the algorithm of
`so-called LMS (Least Mean Square).
`As shown in FIG.4, an adaptive linear coupler 300 of FIR
`filter type is used in this example. This linear coupler
`comprises a plurality of delay circuits DL1, DL2, . . . DLm
`(m is a positive integer) respectively having a delay time Z'
`of unit sampling time, multipliers MX0, MX1, ... MXm for
`multiplying an output signal of each of the delay circuits
`DL1, DL2,... DLm by the input signal n1, and an adder 310
`for adding outputs of the multipliers MX0 through MXm.
`An output of the adder 310 is equivalent to y shown in FIG.
`2.
`A weight to be supplied to the multipliers MX0 through
`MXm is formed based on the residual signal e coming from
`the subtracting circuit 15 in an LMS computing circuit
`consisting of a microcomputer for example. An algorithm to
`be executed in the LMS computing circuit 320 is as follows:
`As shown in FIG.4, let an input vector X at time k be:
`X32 (xok x1 x2, ... xm."
`and an output be y and the weight be w. G=0,1,2,... m),
`then a relation between input and output is an shown in
`equation (1).
`
`g
`yk = 2 wikik
`j=0
`If a weight vector W. at time k is defined as
`W-two wik was . . . wind
`then, the relation between input and output is given as
`
`(1)
`
`Y-XT.W.
`Let a desired response be d, then an error e with the
`output is represented as follows:
`
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`5,471.538
`
`ek = di-ye
`d:- X. W.
`
`With the LMS technique, the weight vector is updated by
`the following relation:
`
`6
`shown in FIG. 5A. An output sound waveform appearing on
`the output pin 17 is as shown in FIG. 5B, which approxi
`mates an ideal output sinusoidal wave of 1 kHz as shown in
`FIG. 5C, proving the effect of the microphone apparatus
`according to the present invention.
`FIG. 6 and FIG.7 respectively illustrate directional char
`acteristics of the main input microphone 11 and the refer
`ence input microphone 21 of another embodiment of the
`present invention. In these examples, like the above-men
`tioned example, the main input microphone 11 is placed in
`front of the reference input microphone 21, both placed
`along the desired sound arrival direction indicated by the
`arrow AR.
`In the example of FIG. 6, the main input microphone 11
`is unidirectional and placed with its most sensible side in the
`front direction. The reference input microphone is also
`unidirectional and is placed with its most sensible side in the
`rear direction for example. In other words, the reference
`input microphone 21 has a low sensibility in the desired
`sound arrival direction and a high sensitivity in the rear
`direction or noise arrival direction.
`Consequently, the example of FIG. 6 also may implement
`a microphone apparatus that outputs only a desired sound. In
`this example, if a noise signal arrives at an angle between the
`rear direction and about 90 degrees to it, a noise level in the
`main input becomes low because the sensitivity of the main
`input microphone 11 is low at that angle. Therefore, the main
`input microphone 11 itself contributes to noise reduction to
`SOre eXtet.
`In the example of FIG. 7, the noise arrival direction is
`limited to around 90 degrees to the desired sound arrival
`direction and the sensitivity of the reference input micro
`phone 21 is made high in a direction 90 degrees to the arrow
`AR direction. In this example, the reference input micro
`phone 21 is bidirectional. As with the example of FIG. 6, the
`main input microphone 11 is unidirectional and is placed so
`that its sensitivity becomes highest in the desired sound
`arrival direction. The main input microphone 11 may also be
`non-directional in this example.
`The above-mentioned examples use single microphone
`units having the discussed directional characteristics for the
`main input microphone 11 and the reference input micro
`phone 21. For these microphones, a plurality of microphone
`units may also be used to implement respective microphones
`having desired directionality.
`Implementation of a unidirectional microphone system by
`using two non-directional microphone units will be
`described as follows by referring to FIG. 8 and FIG. 9.
`Referring to FIG. 8, the non-directional microphone units
`30 and 31 are spaced by a distanced. As shown in FIG. 9,
`an output sound signal of the microphone unit 30 is fed to
`a subtracting circuit 32 through an amplifier not shown.
`Likewise, an output sound signal of the microphone unit 31
`is fed to the subtracting circuit 32 through an amplifier not
`shown and a filter 33. In this example, the filter 33 comprises
`a resistor 34 and a capacitor 35. Now, let resistance of the
`resistor 34 be R1 and capacity of the capacitor 35 be C1,
`then R1 and C1 are set so that a relation shown below is
`established:
`
`CR-dic
`
`where c stands for acoustic velocity.
`Then, in this example, an output of the subtracting circuit
`32 is sent as an output sound signal to the output pin 37
`through a frequency characteristic correcting circuit 36 such
`as an integrator for flattening the frequency characteristic of
`the signal. As will appear, this frequency characteristic
`correcting circuit 36 is provided as required.
`
`WW2-eX
`where, u is a step gain for determining adaptivity speed and
`stability.
`Thus, the sound signal mainly consisting of the desired
`sound signal, with the noise removed, appears on the output
`pin 17.
`Meanwhile, to reduce the noise in the main input by using
`the reference input by means of the adaptive processing as
`described above, there should be no correlation between
`desired sound and reference noise as mentioned above. For
`this reason, conventional adaptive noise reduction systems
`of this type take such measures as preventing reception of a
`desired sound in a reference input by sound-proofing the
`reference input microphone or placing it as near a noise
`source as possible to separate it from a main input micro
`phone. However, these measures make the systems large and
`inconvenient to move around.
`In contrast, the present invention makes the distinction
`between desired sound and noise depending on the sound
`arrival direction. And it is so arranged that the main input
`microphone 11 has a directionality (including non-direction
`ality) in which a sound coming from the desired sound
`arrival direction may be picked up and the reference input
`microphone 21 has a directionality in which there is no or
`little sensitivity in the desired sound arrival direction,
`thereby providing no correlation between the desired sound
`in the sound picked up by the main input microphone 11 and
`the noise picked up the reference input microphone 21.
`Therefore, the present invention may only consider the
`directionalities of the main input microphone and the refer
`ence input microphone. This makes it possible to place both
`microphones in proximity, resulting in a compact implemen
`tation as compared with the conventional microphone sys
`telS.
`The constitution according to the present invention
`adequately eliminates the noise signal from the main input,
`making it possible to easily implement a microphone system
`having directionality in which there is no or little sensitivity
`in the noise arrival direction. FIG. 5 illustrates an effect
`brought about by an experimental system based on this
`example.
`To be specific, in the above-mentioned experimental
`system, the main input microphone 11 is placed in front of
`the reference input microphone 21, both placed along the
`desired sound arrival direction indicated by the arrow AR, as
`shown in FIG. 3. For a sound pickup operation, a sinusoidal
`wave signal of 1 kHz for example is introduced in the arrow
`AR direction as a desired sound and a sinusoidal-wave
`signal of 600 Hz is introduced in a direction 30 degrees to
`the rear side as a noise.
`In this example, sensitivity of the omnidirectional main
`input microphone is 0 dB and that of the reference input
`microphone 21 is -20 dB to a sound coming from the front
`side, 0 dB to a sound coming from the rear side, and -0.7 dB
`to a sound coming from a direction 30 degrees to the rear
`side.
`An input waveform on the main input microphone 11 is a
`composite of the 1 kHz and 600 Hz sinusoidal waves as
`
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`5,471.538
`
`7
`The microphones in this example operate as follows. As
`shown in FIG. 8, let outputs of two microphone units 30 and
`31 be P0 and P1 where a sound source is located at angle-to
`the direction in which the two microphone units are arranged
`and a sound arrives from the source at each microphone unit,
`then output P1 is:
`
`8
`the filter circuit 24 may also be constituted by an analog
`circuit to make the entire system analog. It is also possible
`to make only the filter circuit 24 digital in an analog system.
`Thus, according to the present invention, simply modify
`ing the directional characteristics of the first and second
`microphones may implement a microphone system having
`desired directional characteristics. Further substituting the
`second microphone with a microphone having a different
`directional characteristic may change the directional char
`acteristic of the entire microphone system, thus providing
`wide freedom in implementation of the directional charac
`teristics. These features allow the embodiments to be used in
`a variety of applications, bringing about a remarkable prac
`tical effect.
`Additionally, according to the present invention, the first
`and second microphones may be placed in proximity to each
`other and they need not be provided with a special shape
`such that of a gun microphone, thereby providing a compact,
`easy-to-transport implementation.
`While preferred embodiments of the invention have been
`described using specific terms, such description is for illus
`trative purpose only, and it is to be understood that changes
`and variations may be made without departing from the
`spirit or scope of the appended claims.
`What is claimed is:
`1. A microphone apparatus comprising:
`a first microphone for picking up at least a desired sound
`coming from an arrival direction;
`a second microphone arranged in proximity to arid adja
`cent said first microphone and having a directionality in
`which said second microphone has a low sound-pickup
`sensitivity in said arrival direction of said desired sound
`wherein said second microphone comprises a plurality
`of non-directional microphone units axially aligned and
`placed in proximity to each other so as to be spaced
`apart by a predetermined distance, a filter receiving an
`output from one of said plurality of microphone units
`and wherein output sound signals of remaining ones of
`said plurality of nondirectional microphone units and
`an output of said filter are combined to provide an
`output representing a directional microphone;
`adaptive filter means to which said output from said
`second microphone is supplied; and
`subtracting means for subtracting an output of said adap
`tive filter means from a signal picked up by said first
`microphone for producing an output signal of said
`microphone apparatus;
`wherein said adaptive filter means is adjusted in response
`to the output signal of said subtracting means to mini
`mize a power of the output signal of said subtracting
`CaS.
`2. A microphone apparatus as defined in claim 1, wherein
`said adaptive filter means controls a filter weight to mini
`mize the power of the output signal of said subtracting
`CalS.
`3. A microphone apparatus comprising:
`a first microphone having a first directionality;
`a second microphone arranged in proximity to said first
`microphone and having a second directionality differ
`ent than said first directionality of said first micro
`phone, wherein said second microphone comprises a
`plurality of non-directional microphone units axially
`aligned and placed in proximity to each other so as to
`be spaced apart by a predetermined distance, a filter
`receiving an output from one of said plurality of
`microphone units and wherein output sound signals of
`
`5
`
`10
`
`where-w is an angular frequency.
`The output of the microphone unit 31 is fed to the
`subtracting circuit 32 through the filter 33, so that an output
`signalPa of the subtracting circuit 32 is as given by equation
`(2):
`
`P0(1-Ae Jodocos)
`
`15
`
`(2)
`
`POjode) (
`+ cose )
`1 - A
`jod/c
`In the equation (2), A indicates a filter function of the filter
`33, andja) d/cC<1.
`In the equation (2), if equation (3) below is satisfied, the
`output Pa is unidirectional:
`
`20
`
`1 - A = jod/c
`
`A = 1 -jode-
`
`1
`1 + iode
`
`)
`
`25
`
`(3)
`
`That is, if the equation (3) is satisfied, the equation (2)
`becomes:
`
`making the output Pa unidirectional to angle 0.
`Meanwhile, in the above-mentioned example, the filter
`function A of the filter 33 is represented by
`A=1/(1+joCl-Rl)
`and is configured to be Cl-Rl)
`and is configured to be Cl-Rl-d/c, so that
`A=1/(1+jod/c)
`Therefore, it is clear from the equation (3) that the
`microphone units in the embodiment of FIG. 8 are unidi
`rectional, provided that, however, frequency characteristics
`of these microphone units are going upward to the right (that
`is, the higher the frequency, the greater the response). In this
`example, the frequency characteristic correcting circuit 36 is
`provided to flatten this characteristic.
`It should be noted that, in the example of FIG.9, the filter
`33, the subtracting circuit 32, and the frequency character
`istic correcting circuit 36 may also be implemented by a
`digital filter or a program (software).
`For example, the filter 33 may be constituted by a digital
`filter comprising an adder 41, a delay circuit 42, and a
`transfer function A feedback amplifier 43 as shown in FIG.
`10.
`Although the microphone apparatus according to the
`present invention has been described as applied to the
`microphone unit for the camcorder, the present invention is
`also applicable to any microphone systems, including a
`stand-alone microphone unit, a microphone for a profes
`sional-use video camera, and an instrumentation micro
`phone.
`It should also be noted that, although, in the above
`mentioned example, the adaptive filter circuit 24 is consti
`tuted by a digital circuit to make the entire system, digital,
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Page 12 of 14
`
`

`

`9
`remaining ones of said plurality of non-directional
`microphone units and an output of said filter are
`combined to provide an output representing a direc
`tional microphone;
`adaptive filter means to which said output from said
`second microphone is supplied; and
`subtracting means for subtracting an output of said adap
`tive filter means from a signal picked up by said first
`microphone for producing an output signal of said
`microphone apparatus,
`wherein said adaptive filter means is adjusted in response
`to the output signal of said subtracting means to mini
`mize a power of the output signal of said subtracting
`CS.
`4. A microphone apparatus as defined in claim3, wherein
`said adaptive filter means controls a filter weight to mini
`mize the power of the output signal of said subtracting
`2S.
`5. A microphone apparatus used on a lightweight hand
`held television camera with an incorporated video cassette
`recorder comprising:
`a first microphone having a first directionality for picking
`up at least a sound arriving from a direction in which
`a lens of said television camera is directed;
`a second microphone arranged proximate and adjacent
`said first microphone and having a second directional
`ity different than said first directionality of said first
`
`O
`
`15
`
`20
`
`25
`
`5,471.538
`
`O
`microphone and having a low sensitivity to a sound
`arriving from said direction, wherein said second
`microphone comprises a plurality of non-directional
`microphone units axially aligned and placed in prox
`imity to each other so as to be spaced apart by a
`predetermined distance, a filter receiving an output
`from one of said plurality of microphone units and
`wherein output sound signals of remaining ones of said
`plurality of nondirectional microphone units and an
`output of said filter are combined to provide an output
`representing a directional microphone;
`adaptive filter means to which said output from said
`second microphone is supplied; and
`subtracting means for subtracting an output of said adap
`tive filter means from a signal picked up by said first
`microphone for producing an output signal of said
`microphone apparatus;
`wherein said adaptive filter means is adjusted by the
`output signal of said subtracting means to minimize a
`power of the output signal of said subtracting means.
`6. A microphone apparatus as defined in claim 5, wherein
`said adaptive filter means controls a filter weight to mini
`mize the power of the output signal of said subtracting
`eaS.
`
`Page 13 of 14
`
`

`

`UNITED STATES PATENT ANDTRADEMARK OFFICE
`CERTIFICATE OF CORRECTION
`
`DATED
`INVENTOR(S) :
`
`November 28, 1995
`Tooru Sasaki
`Kaoru Gyotoku
`it is certified that error appears in the above-indentified patent and that said Letters Patent is hereby
`Corrected as shown below:
`
`Col.
`Col.
`
`line 22, delete "long"
`line 48, after "another" delete "-"
`line 49, change "*k-oxal to x
`line 51 change "an" to -as
`line 3, change "-" to -O-
`line 9, delete "-"
`delete line 40- "and is configured to be Clrl)"
`8 line l8, after "such" insert -as
`
`xOk x x2k
`
`In the claims:
`g
`Colio 87 tine 29, change "arid" to -and
`line 32, after "sound" insert --
`
`Signed and Sealed this
`Twentieth Day of May, 1997
`
`Attesting Officer
`
`Commissioner of Patents and Trademarks
`
`BRUCE LEHMAN
`
`
`
`Page 14 of 14
`
`