CA1091588A - Receiving system having a pre-selected directional rejection characteristic - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A receiving system includes a linear array of receivers, each of which is responsive to incident stimuli for producing an output signal, and signal processing means for processing the output signals to provide the array with pre-selected directional rejection characteristics. Such processing includes obtaining sum and difference signals from the outputs of pairs of the receivers, integrating the difference signal, and combining the integrated signal with the sum signal such that stimuli incident on the array at a predetermined angle and at a predetermined frequency are substantially rejected. The angle and frequency at which rejection takes place are selected on the basis of the spacing between the pairs of receivers whose outputs are added and subtracted, and on the basis of the relative gain applied to the integration and sum signals before they are combined.

Description

558 31.0Y~lti~

BAC~CGROU~ID OF l'HE: INVENTION

This invention relate!s to a receiving system having .I preselected directional re~ection characteristic, and more particularly to a receiving system utilizing a microphone array having a cardioidal-like rlesponse.
:-Amateur photographers who have made sound accompanied home movies with conventional equipment are familiar with the problem of minimizing camera ~ound pick~up during filming saquences. Failure to minimi~e camera sound pick-up is 10 evident during projection of film in that the camera noise will freq`uently mask the sounds whose recording is de~ired in connection with the film.
One approach to solving this problem is to physically separate the microphone from the camera, but this requires 15 an assistant to coordinate recording with picture taking.
In many circumstances, this is inappropriats. Therefore, to permit simultaneous recording and picture taking by a single person, it is conventional to attach a microphone to the -camera by way of an extension that positions the microphone 20 forwardly of the camera in the direction in which photography takes place, but out of the field of view of the camera. An .. : ~
inexpensive cardioid microphone so positioned on the camera and oriented so that the null of the cardioid faces the camera will normally be adequate for recording sounds associated with the scene being photographed. Unfortunately, the frequen~y spectrum of the noise associated with an operating camera is so wide, that a considerable amount of noise is also recorded.
Experience shows that the spectrum of many cameras extend from a relatively low frequency of around 100Hz to about 6000Hz : .
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with a peak occurring around 200Hz just in the region of maximum hearing perception. While th~ usual inexpensive cardioid microphone is often adequate for rejecting l~w f-requency sounds originating from the camera, its spatial pattern of response is not fixed with respect to frequency over the relatively wide spectr~n of sound usually associated with the mechanical drive of the camera. As a result, the sound of the camera in operation is superimposed on the recording of the sound associated with the scene being filmed. Being much closer to the microphone than the subject, i-t has been found that the camera noise dominates.
While it may be possible to design a special : ,:
microphone having the capability of rejecting noise from a `-~ camera over a relatively wide frequency band, such a micro-phone is likely to be very expensive and sensititve to mechanical damage by reason of the fragile nature of the ~; elements of the microphone. It is therefore an object of ; the present invention to provide a new and improved recording ~ystem whose rejection characteristics in terms of anqularity and frequency are determined by the type of signal proces~ing utilized rather than by mechanical details of the elemRnts of the microphone.
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SUMMARY OF THE INVENTION
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~ According to the present invention there is provided ,i ;~ 25 a receiving system having a preselected directional rejection characteristic for incident stimuli comprising an array of receiving members, each of which is responsive to incident time-variable s~imuli for producing a corresponding time variation output signal, and signal processing means to combine '' ~' , . .

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the output signals from the receiving members for cau~ing the system to reject stimuli at ~alues of frequency and angles of incidence which depend on the spacing of the receiving members. The signal processing means includes a summing channel for adding the output signals of a pair of the members to obtain a sum signal, means for subtracting the output signals of a pair of the members to obtain a difference signal, an integrating channel for integrating the difference signal to obtain an integrated signal, and combining means for combining the outputs of the two channels.
For a stimulus of a given frequency incident on the array, the sum signal and the integrated signal will be in phase and will vary with time in accordance with the time variation of the incident stimulus, while the magnitudes of the signals can be made equal for that frequency and fbr a pre-selected angle of incidence by a proper selection of the -gain applied to each of these signals before they are subtracted, and by a proper selection of the spacing of tlle receiving members of the array. Specifically, the relative gain of the gain controlled signals is selected such that upon subtraction, the result approaches zero for low frequency incident stimuli (i.e., stimuli at frequencies approaching zero) which make a predetermined angle with the axis of the array. Furthermore, the spacing between the pairs of receiving mer~ers may be selected so that the amplitudes of the gain controlled signals are also made equal for any given frequency for stimulus at ~ the predetermined angle with respect to the array.
:
- When the receiving system of the present invention is incorporated lnto a sound motion picture system, the signal processing means causes the array of receiving members to act as a cardioidal microphone at low frequencies, and ':~

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causes complete rcjection along the axis o~ t'ne cardioid for the frequency that dominates camera noise.
~ he invention also consists in a sound motion picture system comprising a motion picture camera and a sound recording system associated with the camera. Such system includes a linear array of microphones fixed to the camera and located out of the field of view thereof, the array prefer-ably, but not necessarily, projecting forwardly and downwardly from the camera. Signal processing means are provided for combining the output signals of the microphones which are so spa~ed that the array preferentially rejects sound from the camera when it is operational. Specifically, low frequency sounds originating from a source aligned with the array are significantly rejected as are sounds originating at the camera at a frequency in the range within which hearing is most perceptive.
A sound recording system according to the present invention is thus capable of utilizing relatively simple and inexpensive microphones because the preselected directional rejection characteristics are derived entirely from the signal processing means employed and the spacing between the microphones.
According to the broadest aspect of the present invention, there is provided a receiving system comprising: a plurality of spaced apart receiving members, each of which is responsive to incident time-variable stimuli for producing corresponding time-variable output signals; signal ` processing means for combining the output signals from the rec0iving members to produce a selected response pattern for the stimuli, the signal process-ing means including means for subtracting the output signals of a pair of members to obtain a difference signal, the improvement wherein said signal processing means includes an integrating channel for integrating the differ-ence signal with respect to time to obtain an integrated signal.-The invention will now be described in greater detail with refer-ence to the accompanying drawing wherein:

FIG. 1 is a perspective view of a motion picture cc~mera into which .

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the present invention is incorporated and showing orthogonal, low frequency cardioidal response characteristics of the sound recording system;

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causes complete rejection along the axis of the cardioid for the frequency that dominates camera noise.
The invention also consists in a sound motion picture system comprising a motion picture camera and a sound recording system associated with the camera. Such system includes a linear array of microphones fixed to the camera and located out of the field of view thereof, the array preferably, but not necessarily, projecting forwardly and downwardly from the camera. Signal processing means are provided for combiining - l0 the output signals of the microphones which are so spaced that the array preferentially rejects sound from the camera -when it is operational. Specifically, low frequency sounds ~- originating from a source aligned with the array are!
- significantly rejected as are sounds originating at the camera at a frequency in the range within which hearing is most perceptive.
`~ A sound recording system according to the present : .
invention is thus capable of utilizing rela~ively simple and inexpensive microphones because the preselected directional rejection characteristics are derived entirely from the ~ signal processlng means employed and the spa~ing between the ; microphones.

; BRIEF DESCRIPTION OF THE DRAWING
. - --. . . _ Embodiments of the invention are shown in the accompanying drawing wherein:
FIG. l is a per~pective view of a motion picture camera into which the present invention is incorporated and showing orthogonal, low frequency cardioidal response ` characteristics of the sound recording system;

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FI~. 2 is a qualitative showing of a typic~l noi.~e spectrum associated with a movie camera;
FIG. 3 is a prespectilve view of a linear array of receiving members showing ~le il~cidence thereon of a plane wave of arbitrary frequency and making an ar~itrary angle of incidence with the array;
FIG. 4 is a block diagram of a receiving system according to the present invention showing details of the ~ :
signal processing means;
FIG. 5 is a polar-plot of the response chara~teristic of a receiving system according to the present invention for a particular value of relative gain as between the sum channel and the integrated channel for low frequency stimuli;
FI~. 6 is a composite plot of the respective lS amplitudes of the sum signal and the integrating signal for -. the system shown in FIG. 4, and showing the effect on the ~ difference in magnitudes of the amplitudes of the sum and integrated channels for two situations,when the spacing betwe~n the pair of microphones whose output is subtracted i8 the same : 20 as, and is twice the spacing between the pair of microphones whose output is added for stimuli aligned with the incident : on the array;
FIG. 7 is a plot similar to that shown in FIG. 6 except the spacing between the pairs of microphones has been selected so that the difference in magnitudes of the amplitud~
` of the sum and integrated channels is made zero for ~timuli : of a predetermined, ~on-zero frequency, incident on and aligned . :
with the array;
. FIG. 8 is a plot similar to FIG. 7 but showing ~-` 30 the amplitudes of the sum and integra~ing signals for stimuli ',.j ' ~ - 6- , .
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incident on the array at an angle of approximately 30;
FI~. 9 is a plot similar to ~IG. 8 but showing the situation when the stimuli is incident on the ~rray at an angle of cibout 60 ~; and FIG. 10 is a block diagram of signal processing equipment suitable for carrying out the signal processing technique of the present invention as it is applied to a four~microphone version o the present invention.

DESCRIPTION OF THE PREF13R~ED EMBODI~ql3NTS

Referring now to FIG~ 1, reference numeral 10 designates a sound motion picture system according tv the ~-rcsent invention comprising a motion picture camera 11 and a sound recording system 12 associated with the camera.
System 12 comprises a linear array of microphone elements ~not shown), collectively referred to as a microphone and designated by reference numeral 13, secured in fixed position to the camera 11 by boom 14, and signal processing means 15 connected to the camera by cable 16.
Camera 11 includes a conventional housing 17 containing film, film drive means (not ~hown), and lens assembly lB
through which light from a scene being photographed pa~se~
onto the film contained within the camera housing.
Aligned witll the optical axis Z of the lens , system of the camera is a viewfinder sys~em 19 through which an operator views the scene being filmed~ In addition, the camera is provided with grip 20 allowing the operator, with one hand~ to hold the camera and actuate the same by :- .
~ squeezing trigger switch 21 with one finger, and, with the ,. .

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other hand, to steady tlle camera.
The linear array oE microphone elements that constitute micropllone 13 are aligned along the X-axis w}~ich is do~nwardly inGlined at a small angle (e.g., 20) ~ 5 to ~eoptical axis z and lies in a plane co~non to the `~ Z-axis and grip 20. Microphone 13 thus projects forwardly and downwardly from the camera by reason of boom 14 and is ~ out of the field of view of lens assembly 18.
-~ In operation, an operator grasps grip 20 with one hand, steadies the camera with the other hand, and views the scene to be filmed through the viewfinder means l9.
Squeezing the trigger causes the camera and the microphone to be actuated whereby the scene withln the field of view of the viewfinder means is photographed, and sound3 from the scene are synchronously recorded. By reason of the orientation of boom 14, microphone 13 is positioned to receive :` :
sound from the scene being photographed. As explained -below, microphone 13 has a cardioidal-like response (multiplied by the response of each element).- The spatial - 20 characteristics of the response, as a function of ~reqyency, are determined in accordance with signal processing means 15.
- Essentially, microphone 13 rejects sound incident on the microphone within a predetermined rejection cone having a - solid angle that comprehends camera ll as suggested by chain-lines 22 of FIG. 1. The angularity of the X-axis relative to th~e Z~axis, and the distance of the microphone ` from the camera are factors that depend upon the solid angle - of the re~ection cone whose apex coincides with microphone 13, such solid angle depending upon the operation of signal processing mPans 15 and selectable within wide li~its to ~ .
` accomodate a given camera.

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FIG. 1 shows orthogona] response patterns 23 and ~4, respectively, of the microphone showing the dependency of the response on the direction of incidence of sound, the patterns being symmetrical about the X-axis. The patterns are shown qualitatively, but are typical of microphone 13 - o~er a band of frequencies of interest.
FIG. 2 shows, in a qualitative way, the frequency distribution of noise associated with a typical movie camera. It has been found that noise associated with operation of the camera has very low frequency components, and a significant peak around 2000Hz, which is within the range - most perceptible by the human ear. The higher frequençy components of naise associated with the operation of the camera decrease significantly about 6000Hz. By reason of ... .
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the operation of signal processing means lS, the response characteristic of micropllone 13 can be ad~usted to preferentially reject noise emanating from the c~mera throughout a relatively wide band of frequencies with particular emphasis on re~ection around 2000Hz~
In order to explain the manner in which the signal processing means of the present invention preferentially modifies the re~ection characteristics of microphone 13, reference is made to FIG. 3 which sllows the interaction between plane sound wave 30 and a linear array of four microphone elements M1, M2, M3 and M4 which, collectively, constitute microphone 13. The microphone elements are shown uniformly spaced along the X-axis to facilitate the analysis that follows, but the spacing need not be uniform.
The intermediate pair of elements M2 and M3 are spaced apart a distance dl, and the outer pair of elements Ml and M4 are spaced apart a distance d2. For purposes of simplifying the analysis, it is assumed that the space between elements Ml and M2 is the same as the space between elements M3 and M4.
The sinusoidal plane sound wave 30 has a frequency ~, and is incident on the array of elements. The direction of propagation of the wave is generally from the positive X-axis and along the ~-axis which makes an angle ~ with the X-axis, intersecting the same at the point 31, midway ~5 between elemen~s M2, M3. Because the plane wave varies with ` time, FIG. 3 shows the position of the wave at an instant in time. The amplitude of the wave at this instant along the X-axis is shown by the chain line 32 which is defined ~ b~ the intersection of a plane containing the Y-axi~ passing - 30 through the X-axis and being perpendicular to the plane :.

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defined by the A - and X-axes. The Y-axis passes through point 31. The amplitude of wave 32 at any instantl w.ith respect ~o a point on the X-axis, is a measure of the instantaneous sound ~nplitude at that point.
The distance between corresponding points on the plane wave, as measured along the ~A~-axis, is related to the distance between these points as measured along the X-axis by the cosine of d , the angle of incidence of the plane wave. Designating the wavelength of wave 30 along the ~h~-axis is ~O , the wavelength xO along the wave in plane 33 defined by the X-Y
axes, is related to ~O as follows:

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where V is the speed of propagation of the plane wave, and f = ~lr. The ; speed of sound at 20C at sea-level is 344 m/s.
. The period To of the plane wave is as follows:

~ (2) rO = ~ X o Cl~S C~C

- From equation (2), it can be seen that time ~ for point 34 on ~ wave 30, whose projection on the X-axis is the point 31 midway between -~
- elements M2 and M3, to move to point 35, whose projection on the X-axis is ` a distance ~1/2)dl from point 31 where element M3 is located is as follows:
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The time ~or the pOil~t 34 on the plane wave to reach microphone M4 is;

~ (4) ~ = dZ G~cx - r~ith equations (3) and (4) in mind, it can be ;- 5 seen that an assumption of the analytical form of the wave ?
at point 31 will yield the analytical expression for the wave at ~he four locations of the microphone elements in - terms of phase differences with respect to the assumed form of the wave. If it is assumed that the wave at point 31 - 10 has the form Sin(~- ~d)~ then the wave at each of the four elements will be given as follows:
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(5B) At M2: SJn ~-~o f ~ ) (SC) At M3; Srn ~-7~ - 2 - 15 (5D) At M4: S/n ~(~

where Z represents the time required for the wave to move i;: ~ :
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. t~e expressions that follow to be applicable to either a - sine or cosine wave of unit amplitude). ~ecause any complex .~ 20 wave can be synthesized by a Fourier sine or cosine seriesi .
` the analysis that follows is of general applicability even . though the equations refer to a single sinusoidal wave having an angular frequency of ~. -~.
~ Reference is now made to FIG. 4 which shows details of the signal processing means 15. Each of the microphone , . . ~
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elements ~1 and ~4 is responsive to an incident time-variable stimuli, such as a sound wave, for producing a corresponding time-variable output signal which is processed in accordance with the block diagram shown in FIG. 4. Specifically, means 15 includes, in addition to the microphone elements, summing channel 40 in the form of an adder for adding the output signals of the inner pair of microphone elements M2 and M3, ~ and subtractor 41 for subtracting the output signals of ~ the outer pair of microphone elements Ml and M4. The difference signal produced by subtractor 41 is integrated in integrating channel 42 which is in the form of an integrator whose output is termed an integrated signal. Finally, means - 15 includes combining means 43 for combining the outputs -~- of the summing channel andthe integrating channel.
` 15 Specifically, combining means 43 includes a gain control means in each of the channels for setting the gain of one channel relative to the other to define a gain controlled -: integrated signal that appears at the output of amplifier 44 which has a gain B, and a gain controlled sum signal which appears at the output of amplifier 45 which has a gain A.
Combining means 43 also includes means for adding the two gain controlled signals and is in the form of adder 46.
The output of adder 46, which appears in line 47, constitutes the output of microphone 13.
: 25 Where the inputs to microphones Ml and ~14 are as indicated in equation (5) above, the sum signal S appearing at the output of adder 40 is as follows:

(6) S = [2 c~ ] sin ~(Y ~0) , `'" ~ ' ~ . , . ' `':

~93.~88 while the difference signal D aE)pearing at the output of subtractor 41 is as follows: '.

(7~ D = [- 2 S~n ~ ~ c~s~f~ z~) where the minus sign indicatès a phase inversion with respect :: 5 to the sum signal.
Integrating the difference siynal in integrator 42 yields an integrated signal I given as follows: :

; (8) I = [_ ZS~C~ S~n ~J~ 0) `: After the sum and integrated signals are passed ` 10 through amplifiers 45 and 44 respectively, it can be seen that each of the resultant gain controlled signals has the ~-` same phase allowing arithmetic addition of the amplitudes of .,. ; . .
the signals to take place. The amplitude of the gain controlled sum signal ~ ) is given by:
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while the magnitude of the ga.in controlled integrated signal :~
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~i The output of adder 46 is ~(~,~) and is ~ .
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given by:
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.~ where the minus sign takes into account the inversion that occurs due to subtractor 4l.
From inspection of equation tl2), it can be seen that the output of adder 46 can be reduced to zero, : indicating the complete rejection of the incident wave, at ~ any desired frequency or angle oE incidence of the incidént :~ wave on the array of microphone elements, by suitable `-; selection of the relative gain A/B of the gain controlled . lO signals and the spàcing dl, d2 between the microphone elements. For low frequency incident waves where ~ tends . to zero, equation (12) reduces to:
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(12A) ~(O~X) = Z ~ L~ - Z~ Cr9S~]

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From inspection of èquation (l2A), it can be seen that the output of adder 46 will be zero when the .: expression contained wi~hin the square brackets in this equation is equal to zero. For a given angle of incidence CCo, the relative gain A/B of the gain controlled signals to achieve complete rejection at low frequencies is given as follows:
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. Inserting the relative gain from equation ~12B) - into equation (12) provides the general expression for the output of adder 46 that insures rejection of low frequency ., .
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waves incident on tlle array of microphone elements at an angle ~O ;

~ ) = ZB(z v) [c~so(; ~o~(z~ c~ o50~ Sin(~cOsP~)]

To re~ect low frequency sounds incident on the array at ~O= o , equation (13) reduces to:
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; (13A) ~(o,c~J- z ~ d~ cos~) Inspection of equation (13A) reveals the low frequency response of the composite microphone is cardioidal, with the axis of symmetry lying along the axis of the array (i.e., along the X-axis), and arises solely as a consequence ` of the processing of the signals from the elements of the array. The higher frequency response of the composite `
-- microphone for stimuli aligned with the array is obtained from equation (13) with cyc o - 15 (13B) a(c),o) C ZB(z~)[~os(~)-- ~i) ]

The spacing of ~le microphone elements from which - the sum signal is derived, dl can also be selected to insure rejection of a wave at any frequency ~ having an angle of `71 incidence C~l . The value of dl is obtained by setting the expression in the square brackets of eqUation (13) equal to zero and solving for dl. This process yields the following:
;~i (14) d~= Z~- afi~ cos r ~7)]

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If C~ = ~ = O, which is to say that rejection is achieved for waves of frequency approaching the linear array along the X axi,s from the positive direction, equation (14) reduces to the following;

~ 5 (14~) d, = Zv o~c ~05 [~ ]

FIG. 5, which is a plot of equation (13A) r is the response of an array of microphone elements to low frequency waves as a function o theirangles of incidence on the array wllen the outputs of the ~lements are processed in accordance ` 10 with ~G. 4. Thus, it is seen that, a linear array of omni-directional receiving members in the form of micxophone elements is converted into a composite microphone having a cardioidal re~ponse by rea~on of the signal processing that is carried out by means 15. If the elements themselves ~, 15 have cardioidal responses, the signal processing creates a higher order cardioidal response of the composite microphone.
The response of an array of microphone elements ' to higher frequency waves incident on the array in alignment ~` tnerewith ~i.e., C~ =o) is sh~n in FIG. 6 which is based ~; 20 on equation (13B). Curve 50 represents the variation of co~ ( Z~d~ ) with the parameter ( ~Zd~ ~ for dl=d2 and -`~i is the gain controlled sum signal at the output of amplifier ~ 45; and curve 51 represents the variation of 5; -(- ~
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-~ with the parameter ( ~~ ) and is the gain controlled integrated signal at the output of amplifier 43. It should be noted that when dl-d2, elements Ml and M2 merge and elements M3 and ~4 merge creating a composite microphone of ~ - 17 -:' .~ ;

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two, rather than four elements. Such a microphone has good low frequency re~ection characteristics, but the ability of the microphone to re~ect higher frequency waves decreases markedly with frequency as indicated by curve 52 which is the difference between curves 50 and 51 and represents equation (13B) whicll is the output of adder 47.
- For the condition that dl~l/2 d2, elements Ml-M4 are equally spaced with the result that the microphone has four elements. Curve 53 represents cos( ~kJ~ ) for the condition indicated, and it is apparent that curve 53 approximates curve 51 rather closely. The difference between curves 51 and 53 is curve 54; and it is obvious that the use of four elements with dl=1/2 d2 provides significantly improved rejection characteristics as compared with a two -, element microphone.
- The frequency scale in FIG. 6 has been selected by choosing d2=1" so that both curves 51 and 53 are zero at ~d~ = 13~548EIz.~ A further improvement in rejection of waves aligned with the array and in the band up to : 20 6000Hz, which i5 the noise band of a camera, is pos~ible by suitable choice of the ratio of dl to d2. Presently, it is preferred to select dl such that the amplitude of the gain controlled sum signal (i.e., the frequency of the cosine curve) equals the gain controlled integrated signal (i.e., ~ 25 the sinc curve) at a frequency of about 59~ of the gain -1 controlled integrated signal. For d2~1"~, the e~uality occur-at 8000Hz; and from equation (14A), dl_0.55".
Curve 60 in FIG. 7 represents the gain controlled sum signal under these conditions, and curve 61 represents the g~in controiled integrated signal which equal each other :

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at 800~Hz. At frequencies less than this, the rejection is extremely good as shown by curve 62 which is the difference between curves 60 and 61 and represents the output 47 of adder 46.
The curves shown in FIG. 7 are applicable to input waves aligned with the ar~ay. FIGS. 8 and 9 show the rej~ction at angles of incidence of 30 and 60 respectively. In FIG. 8, curve 63 represents the gain controlled sum signal for = 30, and curve 64 represents the gain controlled integrated signal. Curve 65 repr~sents the difference between curves 63 and 64. In FIG. 9, curve 66 represents the gain controlled sum signal for ~ =60, and curve 67 represents the gain controlled integrated signal. Curve 68 represents the difference betwecn curves 66 and 67. It is evident, that the selcction of dl=0.55 inches and d2=1 inch provides 15 ~ extremely good rejection at C~ = 0 and through CX = 30 (which corresponds to a rejection conc whos~ apical angle is 60).
Other rejection patterns can be created by suitable selection of relative gain between the sum and integrated channels, and the relative distances between the sum and difference pairs of elements. Furthermore, other analytical solutions are available when the spacing of the elements is not uniform.
While the above description refers to sound waves and microphones, it is clear that the present invention is applicable to other stimuli to which elements respond by producing output signals. For example, the invention is applicable to radio waves and receiving antennae.

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FIG. 10 is a circuit diayram for siynal processing means according to the present invention for ~tfectinc3 a desired signal rejection characteri~tic.
Me~ns 15~ includes four microphonc ~lements Ml-M4 and a pre-amplifier 70 associated with each element. The pre-amplified output signals from elements M2 and M3 are added in analog adder 71 to develop the sum signal. The pre-amplified signals from~elements Ml and M4 are subtracted and integrated in ~orton difference integrator 72, the output of which is the integrated signal. The sum and integrated signal are added in analog adder 73 to provide the output signal.
It is believed that the advantages and improved i results furnished by the method and apparatus of the present - 15 invention are apparent from the foregoing description of the several embodiments of the invention. Various changes ; and modifications may be made without departlng from the spirit and scope of the invention as sougllt to be defined in the claims that follow.

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Claims (32)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A receiving, system comprising:
a plurality of spaced apart receiving members, each of which is responsive to incident time-variable stimuli for producing corresponding time-variable output signals;
signal processing means for combining the output signals from the receiving members to produce a selected response pattern for the stimuli, the signal processing means including means for subtracting the output signals of a pair of members to obtain a difference signal, the improvement wherein said signal processing means includes an integrating channel for integrating the difference signal with respect to time to obtain an integrated signal.

2. A receiving system according to claim 1 wherein the signal processing means additionally includes:
a summing channel for adding the output signals of a pair of the members to obtain a sum signal; and combining means for combining the outputs of the summing and integrating channels.

3. A receiving system according to claim 2 wherein the combining means includes means for adding the outputs of the summing and integrating channels.

4. A receiving system according to claim 2 wherein said combining means includes means for subtracting the outputs of the summing and integrating channels.

5. A receiving system according to claim 4 wherein said combining means further includes means for adding the outputs of the summing and integrating channels.

6. A receiving system according to claim 2 wherein the combining means includes gain control means for setting the gain of at least one of said channels relative to the other.

7. A receiving system according to claim 2 wherein there are four aligned receiving members, the members the outputs of which are added in the sum channel to form the sum signal being positioned between the members the outputs of which are subtracted to form the difference signal.

8. A receiving system comprising: a plurality of receiving members, each of which is responsive to incident time-variable stimuli for producing corresponding time-variable output signals; and signal processing means for combining the output signals from the receiving members to produce a selected response pattern for stimuli at preselected values of frequency and angles of incidence, said signal processing means including: a summing channel for adding the output signals of a pair of the members to obtain a sum signal; means for subtracting the output signals of a pair of the members to obtain a difference signal; an integrating channel for integrating the difference signal with respect to time to obtain an integrated signal;
and combining means for combining the outputs of the summing and integrating channels.

9. A receiving system according to claim 8 wherein the combining means includes gain control means for setting the gain of one channel relative to the other to define a gain controlled integrated signal and a gain controlled sum signal, and means for adding the two gain controlled signals.

10. A receiving system according to claim 9 wherein the relative gain of the gain controlled signals is selected such that the output of the combining means approaches zero for incident stimuli at low frequencies making a predetermined angle with the axis of the array.

11. A receiving system according to claim 9 wherein the members are laterally spaced in an elongated array and the relative gain of the gain controlled signals is selected such that the output of the combining means approaches zero for incident stimuli at low frequencies and oriented in a given direction with respect to the array.

12. A receiving system according to claim 8 wherein the plurality of members includes four receiving members, the members the outputs of which are added in the sum channel to form the sum signal being located between the members the outputs of which are subtracted to form the difference signal.

13. A receiving system according to claim 11 wherein the receiving members are microphones and the incident stimuli are sound waves having a component in the audio range.

14. A receiving system according to claim 13 in combina-tion with a source of noise and mounting means for mounting the microphones oriented with respect to the source of noise such that the receiving system rejects noise from the source.

15. A receiving system according to claim 8 wherein the array includes two receiving members the outputs of which are added to obtain the sum signal and the outputs of which are sub-tracted to obtain the difference signal.

16. In a receiving system having a plurality of receiv-ing members arranged in an array with each member being responsive to incident time-variable stimuli for producing corresponding time-variable output signals, the improvement comprising signal processing means for combining the output signals from the receiving members to create a cardioidal response pattern over a band of frequencies of the stimuli, said signal processing means including:
a summing channel for adding the output signals of a pair of members to obtain a sum signal;
means for subtracting the output signals of a pair of the members to obtain a difference signal;
an integrating channel for integrating the difference signals with respect to time to obtain an integrated signal; and combining means for combining the outputs of the summing and integrating channels.

17. The improvement of claim 16 wherein the combining means includes gain control means for setting the gain of one channel relative to the other to define a gain controlled integrated signal and a gain controlled sum signal, and means for adding the two gain controlled signals.

18. A receiving system having a preselected directional rejection characteristic of incident stimuli, comprising:

a plurality of receiving members, each of which is responsive to incident time-variable stimuli for producing a corresponding time-variable output: signal; and signal processing means for combining the output signals from the receiving members to cause the system to reject stimuli at preselected values of frequency and angles of incidence, said signal processing means including:
means for subtracting the output signals of a pair of members to obtain a difference signal; and an integrating channel for integrating the difference signal with respect to time to obtain an integrated signal.

19. A sound photographic system, comprising:
a camera having a lens assembly with a predetermined field of view which defines the camera taking axis, said camera during its operation generating sound extending over a given range of frequencies; and a sound recording apparatus associated with said camera, said system comprising:
an array of microphones fixed to said camera outside of said field of view such that said camera sound is oriented at a pre-determined angle of incidence to said array; and means for spacing the microphones in said array and for combining the output signals thereof so that array preferentially rejects sound from said camera when the latter is made operative, said spacing and combining means includes means for subtracting the output signals of a pair of said microphones to obtain a difference signal, and integrating channel for integrating said difference signal with respect to time.

20. The sound photographic system of claim 19 wherein said microphones are omnidirectional microphones and in combina-tion with said spacing and combining means provide a cardioidal response pattern having its area of maximum rejection of said range of camera sound frequencies located at said predetermined angle of incidence.

21. A sound receiving system for use with a camera having a lens assembly with a predetermined field of view which defines the camera taking axis, said camera during its operation generating camera sound extending over a given range of frequencies, said sound system comprising:
an array of spaced microphones;
means for mounting said array on said camera outside of said field of view such that said camera sound is oriented at a predetermined angle of incidence to said array;
means for combining the output signals of said microphones so that said array preferentially rejects sound from said camera when the latter is made operative, said combining means including:
means for subtracting the output signals of a pair of said microphones to obtain a difference signal; and an integrating channel for integrating said difference signal with respect to time.

22. A sound receiving system according to claim 21 additionally including:

a summing channel for adding the output signals of a pair of microphones to obtain a sum signal; and means for combining the outputs of said summing and said integrating channels.

23. A sound receiving system according to claim 22 wherein said combining means includes means for adding the outputs of said summing and integrating channels.

24. A sound receiving system according to claim 22 wherein said combining means includes means for subtracting the outputs of said summing and integrating channels.

25. A sound receiving system according to claim 22 wherein said combining means further includes means for also adding the outputs of said summing and integrating channels.

26. A sound receiving system according to claim 22 wherein said combining means includes gain control means for setting the gain of one channel relative to the other to define a gain controlled integrated signal and a gain controlled sum signal, and said combining means comprises means for adding the two gain controlled signals.

27. A sound receiving system according to claim 26 wherein the relative gain of said gain controlled signals is selected such that the output of said combining means approaches zero for low frequency sound incident on said array at said pre-determined angle, and the spacing between said microphones is selected to provide an equal amplitude of both gain controlled signals for a given frequency incident at said predetermined angle.

28. A sound receiving system according to claim 22 wherein said array includes four microphones, the microphones the outputs of which are added in said summing channel to form said sum signal being positioned between the microphones the out-puts of which are subtracted to form said difference signal.

29. A sound receiving system according to claim 28 wherein said four microphones are spaced generally side by side in a plane.

30. A sound receiving system according to claim 28 wherein the distance between said intermediate microphones is approximately one-half the distance between the outer microphones of said array.

31. A sound receiving system according to claim 26 wherein said gain control means and the spacing of said micro-phones in said array are selected to provide an equal amplitude of both gain controlled signals for a frequency of approximately 8,000 Hz incident on said array at said predetermined angle.

32. A sound receiving system according to claim 31 wherein said given range of frequencies extends from low frequen-cies up to approximately 6,000 Hz.