PATENT DOCUMENT

Publication Number: US-7349849-B2
Application Number: US-20657202-A
Country: US
Kind Code: B2

Title: Spacing for microphone elements

Abstract:
A speech recognition device with a frequency range with an upper frequency limit f max  is provided. The speech recognition device has more than two microphones with distances between the microphones, wherein the greatest common factor of the distances between the microphones is less than the speed of sound divided by f max . More particularly, where the microphones are spaced a total distance, the number of the more than two microphones is less than the one half the total distance times the upper frequency limit divided by the speed of sound.

Claims:
1. A speech recognition device with a frequency range with an upper frequency limit (fmax), comprising:
 more than two microphones with distances between the microphones; 
 wherein the greatest common factor of the distances between the microphones is less than the speed of sound divided by the upper frequency limit (fmax); 
 wherein the microphones are spaced a total distance and the number of the more than two microphones is less than the one half the total distance times the upper frequency limit (fmax) divided by the speed of sound for receiving an input signal; and 
 a speech recognizer for recognizing speech in the input signal. 
 
     
     
       2. The speech recognition device, as recited in  claim 1 , further comprising a computer readable medium on which the distances between the microphones is stored. 
     
     
       3. The speech recognition device, as recited in  claim 2 , wherein each microphone has a microphone width and adjacent microphones are separated from each other by a separation distance, wherein the distances between may be any distance between the separation distance between two adjacent microphones and the sum of the separation distance between two adjacent microphones added to the widths of each of the two adjacent microphones. 
     
     
       4. The speech recognition device, as recited in  claim 3 , wherein the microphones are mounted on a display. 
     
     
       5. The speech recognition device, as recited in  claim 3 , further comprising a computer system, comprising:
 a display, upon which the microphones are mounted; 
 a chassis, connected to the microphones and display, wherein the computer readable medium is part of the computer system, and wherein the computer readable medium further comprises computer readable code to provide speech recognition, which uses the stored distances. 
 
     
     
       6. The speech recognition device, as recited in  claim 3 , further comprising a computer system a chassis, connected to the microphones wherein the computer readable medium is part of the computer system, and wherein the computer readable medium further comprises computer readable code to provide speech recognition, which uses the stored distances. 
     
     
       7. The speech recognition device, as recited in  claim 2 , further comprising a computer system, comprising:
 a display, upon which the microphones are mounted; 
 a chassis, connected to the microphones and display, wherein the computer readable medium is part of the computer system, and wherein the computer readable medium further comprises computer readable code to provide speech recognition, which uses the stored distances. 
 
     
     
       8. The speech recognition device, as recited in  claim 2 , further comprising a computer system comprises a chassis, connected to the microphones wherein the computer readable medium is part of the computer system, and wherein the computer readable medium further comprises computer readable code to provide speech recognition, which uses the stored distances. 
     
     
       9. The speech recognition device, as recited in  claim 1 , further comprising a computer system, comprising:
 a display, upon which the microphones are mounted; 
 a chassis, connected to the microphones and display; and 
 a computer readable medium with computer readable code to provide speech recognition. 
 
     
     
       10. The speech recognition device, as recited in  claim 1 , further comprising a computer system comprising:
 a chassis, connected to the microphones; and 
 a computer readable medium comprising computer readable code to provide speech recognition. 
 
     
     
       11. The speech recognition device, as recited in  claim 1 , further comprising a computer system, comprising:
 a display, upon which the microphones are mounted; 
 a chassis, connected to the microphones and display; and 
 a computer readable medium with computer readable code to provide speech recognition. 
 
     
     
       12. The speech recognition device, as recited in  claim 1 , further comprising a computer system comprising:
 a chassis, connected to the microphones; and 
 a computer readable medium comprising computer readable code to provide speech recognition.

Description:
RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. 119(e) of the U.S. Provisional Application No. 60/311,025, entitled “INTEGRATED SOUND INPUT SYSTEM”, filed Aug. 8, 2001 by inventors Kim E. Silverman, Laurent J. Cerveau, and Matthias U. Neeracher, and to the U.S. Provisional Application No. 60/311,026, entitled “SPACING FOR MICROPHONE ELEMENTS”, filed Aug. 8, 2001 by inventors Kim E. Silverman and Devang K. Naik, which are incorporated by reference. 
     This application is related to the commonly assigned application Ser. No. 10/172,593 entitled “INTEGRATED SOUND INPUT SYSTEM” filed on Jun. 13, 2002 by inventors Kim E. Silverman, Laurent J. Cerveau, and Matthias U. Neeracher, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to computer systems. More particularly, the present invention relates to speech processing for computer systems. 
     BACKGROUND OF THE INVENTION 
     Computer systems, such as speech recognition systems use a microphone to capture sound. 
     To facilitate discussion,  FIG. 1  is a schematic view of a microphone array  102  that may be used in the prior art. Such an array may provide microphones  104  mounted on a display  108 . The spacing between the microphones  104  in the microphone array is an equal spacing “d” between each microphone. In this example the total distance between microphones is about 30 centimeters (cm), so that d is about 15 cm. In speech recognition systems, a microphone array may be used to increase the signal to noise ratio by adding signals from each microphone in the microphone array. A user  112  positioned in front of the microphones  104  would speak, so that the sound waves from the user  112  would reach each microphone  104  in the microphone array  102  at about the same time. The signals from each microphone  104  would then be added in a constructive manner. Background noise may be generated by a noise source  116  located off axis from the microphone array  102 . Sound  120  from the noise source  116  would reach the microphones  104  at different times, so that the signals from the different microphones would not normally be added in a constructive manner. However, if the background noise from the noise source has a wavelength (λ) of d/n, where n is an integer, then the microphones  104  would be simultaneously located at the maximums of the background noise causing a constructive addition of the signals from the microphones  104  (resonance interference). Generally, the speed of sound in dry air at about 1 atmospheres is about: v=331 m/s+(0.6 m/s/C)*T. So at about 20° C., the speed of sound in air is about 343 m/s. With distance being about 15 cm., the frequencies (f) that would cause the resonance interference so that the addition of signals from the microphones  104  would be constructively added would be f=(34,300 cm/s)*n/(15 cm)=n(1,143 Hz). For some voice recognition systems it may be desirable to process sounds with frequencies between 140 to 6,500 Hz. Therefore n=1, 2, 3, 4, 5 would yield frequencies of 1,143 Hz, 2,286 Hz, 3,429 Hz, 4,572 Hz, and 5,715 Hz, which would be within the range on a voice recognition system. 
       FIG. 2  is another schematic view of a microphone array  202  that may be used in the prior art. Such an array may provide microphones  204  mounted on a display  208 , in a manner similar to the array in  FIG. 1 . The spacing between the microphones  204  in the microphone array is an equal spacing “d” between each microphone. In this example the total distance between microphones is about 30 centimeters (cm), so that d is about 15 cm. However, an additional microphone  205  is added to the array  208  between two microphones  204 , so that the spacing between the additional microphone  205  and the two microphones  204  is ½ d (7.5 cm). A user  212  positioned in front of the microphone array  202  would speak, so that the sound waves from the user  212  would reach each microphone  204 ,  205  in the microphone array  202  at about the same time. The signals from each microphone  204 ,  205  would then be added in a constructive manner. Background noise may be generated by a noise source  216  located off axis from the microphone array  202 . Sound  220  from the noise source  216  would reach the microphones  204  at different times, so that the signals from the different microphones would not normally be added in a constructive manner. However, if the background noise from the noise source has a wavelength (λ) of (1/2)(d/n), where n is an integer, then the microphones  204 ,  205  would be simultaneously located at the maximums of the background noise causing a constructive addition of the signals from the microphones  204 ,  205  (resonance interference). Thus, the additional microphone  205  causes the wavelength to be 7.5 cm/n. Generally, the speed of sound in dry air at about 1 atmospheres is about: v=331 m/s+(0.6 m/s/C)*T. So at about 20° C., the speed of sound in air is about 343 m/s. With the extra microphone  205  spaced 7.5 cm from the other microphones  204 , the frequencies (f) that would cause the resonance interference so that the addition of signals from the microphones  204 ,  205  would be constructively added would be f=(34,300 cm/s)*n/(7.5 cm)=n(2,286 Hz). Therefore n=1 and 2, would yield frequencies of 2,286 Hz, 4,572 Hz, which would be within the range of a voice recognition system. 
     To provide improved signal to noise output more microphones may be provided to the array.  FIG. 3  is another schematic view of a microphone array  302  that may be used in the prior art. Such an array may provide four microphones  304  mounted on a display  308 . The spacing between the microphones  304  in the microphone array is an equal spacing “d” between each microphone. In this example the total distance between microphones is about 30 centimeters (cm), so that d is about 10 cm. In speech recognition systems, a microphone array may be used to increase the signal to noise ratio by adding signals from each microphone in the microphone array. A user  312  positioned in front of the microphones  304  would speak, so that the sound waves from the user  312  would reach each microphone  304  in the microphone array  302  at about the same time. The signals from each microphone  304  would then be added in a constructive manner. Background noise may be generated by a noise source  316  located off axis from the microphone array  302 . Sound  320  from the noise source  316  would reach the microphones  304  at different times, so that the signals from the different microphones would not normally be added in a constructive manner. However, if the background noise from the noise source has a wavelength (λ) of d/n, where n is an integer, then the microphones  304  would be simultaneously located at the maximums of the background noise causing a constructive addition of the signals from the microphones  304  (resonance interference). With distance being about 10 cm., the frequencies (f) that would cause the resonance interference so that the addition of signals from the microphones  304  would be constructively added would be f=(34,300 cm/s)*n/(10 cm)=n(3,430 Hz). Therefore n=1, would yield frequencies of 3,430 Hz, which would be within the range of some voice recognition systems. 
     It would be desirable to provide a computer system with speech recognition, with a microphone array where the frequency of resonance interference would be outside of or near the outside of the human voice range and may even be outside of a microphone sound range or even outside of the voice recognition range. 
     SUMMARY OF THE INVENTION 
     To achieve the foregoing and other objects and in accordance with the purpose of the present invention, a variety of techniques is provided for a speech recognition device with a frequency range where an upper frequency limit f max  is provided. The speech recognition device has more than two microphones with distances between the microphones, wherein the greatest common factor of the distances between the microphones is less than the speed of sound divided by f max . 
     These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a schematic view of a microphone array that may be used in the prior art. 
         FIG. 2  is another schematic view of a microphone array that may be used in the prior art. 
         FIG. 3  is another schematic view of a microphone array that may be used in the prior art. 
         FIG. 4  is a schematic bird&#39;s eye view of a preferred embodiment of the invention. 
         FIG. 5  is another schematic illustration of another embodiment of the invention, using four microphones. 
         FIGS. 6A and 6B  illustrate a computer system, which is suitable for implementing embodiments of the present invention. 
         FIG. 7  is a schematic illustration of another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. 
     To facilitate discussion,  FIG. 4  is a bird&#39;s eye view of a top view of a an array of a first, second, and third microphones  404 ,  406 ,  408  mounted on a computer system comprising a display  410 , and a chassis  412 , which supports a speech recognition system  414 . A distance d, is between the first microphone  404  and the second microphone  406 . A distance d 2  is between the second microphone  406  and the third microphone  408 . A distance “g” is also shown in  FIG. 4 , where “g” is the greatest common factor between d 1  and d 2 . In the specification and claims the greatest common factor is defined as the largest distance that is evenly divisible into two or more distances. Since “g” is the greatest common factor between d 1  and d 2 , then “g” is the greatest distance where the relationship of m 1 *g=d 1  and m 2 *g=d 2 , where m 1  and m 2  are integers greater than zero. In the embodiment illustrated in  FIG. 4 , m 1 =3 and m 2 =2. 
     In operation, a user  430  positioned in front of the microphones  404 ,  406 ,  408  would speak, so that the sound waves from the user  430  would reach each microphone  404 ,  406 ,  408  at about the same time. The signals from each microphone  404 ,  406 ,  408  would then be sent to the voice recognition system  414  in the chassis, where the signals may be added in a constructive manner. Background noise may be generated by a noise source  416  located off axis from the microphones. Sound  420  from the noise source  416  would reach the microphones  404 ,  406 ,  408  at different times, so that the signals from the different microphones would not normally be added in a constructive manner. However, if the background noise from the noise source has a wavelength (λ) of g/n, where n is an integer, then the microphones  404 ,  406 ,  408  would be simultaneously located at the maximums of the background noise causing a constructive addition of the signals from the microphones  404 ,  406 ,  408  ( resonance interference). The invention uses the upper frequency f max  of the voice recognition system to obtain a minimum wavelength λ min . In this embodiment, the frequency range of the voice recognition system  414  is 140 to 6,500 Hz. Therefore f max  is 6,500 Hz. The invention then specifies that g&lt;v/f max =λ min , where v is the speed of sound in air. For example, generally, the speed of sound in dry air at about 1 atmospheres is about: v=331 m/s+(0.6 m/s/C)*T. So at about 20° C., the speed of sound in air is about 343 m/s. Therefore, the invention would require that g&lt;λ min =343 m/s/6,500 Hz=0.0528 m=5. Therefore, if the greatest common factor is less than 5.28 cm, then the lowest frequency that would cause resonance interference would have a wavelength less than 5.28 cm. Since signals with a wavelength less than λ min =5.28 cm have a frequency beyond the range of the voice recognition system  414 , such sounds should not be registered as background noise by the voice recognition system. Therefore if the first microphone  404  is placed a distance 3*5.20 cm=15.6 cm from the second microphone  406  and the second microphone is placed a distance of 2*5.20 cm.=10.4 cm from the third microphone  408 , then frequencies that would cause resonance interference would be beyond the range of the voice recognition system  414 . This would result in the first microphone  404  being spaced from the third microphone a total distance of 15.6 cm+10.4 cm=26 cm. 
     In the preferred embodiment, the first microphone  404 , second microphone  406 , and third microphone  408  are mounted on the display  410 , although the microphones may be mounted on other parts of the computer system. The distance d 1  between the first microphone  404  and the second microphone  406  and the distance d 2  between the second microphone  406  and the third microphone  408  is set in a program of the voice recognition system  414 , so that the voice recognition system  414  makes use of these distances during the voice recognition process. One way for allowing these distances to be placed in the voice recognition system  414  is by fixing the microphones to the computer system so that the microphones  404 ,  406 ,  408  may not be moved relative to each other, so that these distances cannot be changed. Integers m 1  and m 2  may not have a common factor. This is because if m 1  and m 2  had a common factor “c”, then the greatest common factor would not be “g”, but would instead be g*c. In a more preferred embodiment of the invention, m 1  and m 2  would be prime numbers to ensure that they do not have a common factor. 
     In voice recognition systems, it may be desirable to spread the microphones further apart. One way of this may be achieved is by increasing m 1  and m 2 . For example, if m 1  is 9 and m 2  is 11 with the greatest common factor “g” being 5.20 cm., then d 1 =m 1 *5.20 cm=46.80 cm. and d 2 =m 2 *5.20=57.20 cm. This would allow the first microphone  404  to be separated from the third microphone  408  by a distance of 104.00 cm. 
     Other embodiments may use more than three microphones.  FIG. 5  is a schematic illustration of a display  504  with a first microphone  508 , a second microphone  512 , a third microphone  516 , and a fourth microphone  520  mounted on the display  504 . The first distance between the first microphone  508  and the second microphone  512  is distance d 1 . The second distance between the second microphone  512  and the third microphone  516  is distance d 2 . The third distance between the third microphone  516  and the fourth microphone  520  is distance d 3 . In this example, the greatest common factor “g” is divisible into the first distance d 1 , the second distance d 2 , and the third distance d 3 , such that m 1 *g=d 1 , m 2 *g=d 2 , and m 3 *g=d 3 , where m 1 =3, m 2 =2, and m 3 =4. Although m 2  and m 3  have a common factor of 2, m 1 , m 2 , and m 3  do not have a common factor, and therefore “g” is the greatest common factor between d 1 , d 2 , and d 3 . 
     The use of too many microphones may cause additional problems, since microphones may fail and add additional costs. Therefore, it may be desirable to limit the number of microphones used by the invention. In the preferred embodiment, if the total distance between the first and last microphone (the sum of all distances between adjacent microphones) is D total , then the number of microphones N is preferably less than ½*(D total /λ min )=½* (D total *f max /v). If there are N microphones, there will be N1 distances d 1 , d 2 , . . . d N   1 . 
       FIGS. 6A and 6B  illustrate a computer system, which is suitable for implementing embodiments of the present invention.  FIG. 6A  shows one possible physical form of the computer system. Of course, the computer system may have many physical forms ranging from an integrated circuit, a printed circuit board, and a small handheld device up to a desktop personal computer. Computer system  900  includes a monitor  902  with a display  904 , first microphone  905 , a second microphone  907  and a third microphone  909 , a chassis  906 , a disk drive  908 , a keyboard  910 , and a mouse  912 . Disk  914  is a computer-readable medium used to transfer data to and from computer system  900 . 
       FIG. 6B  is an example of a block diagram for computer system  900 . Attached to system bus  920  are a wide variety of subsystems. Processor(s)  922  (also referred to as central processing units, or CPUs) are coupled to storage devices including memory  924 . Memory  924  includes random access memory (RAM) and read-only memory (ROM). As is well known in the art, ROM acts to transfer data and instructions uni-directionally to the CPU and RAM is used typically to transfer data and instructions in a bi-directional manner. Both of these types of memories may include any suitable of the computer-readable media described below. A fixed disk  926  is also coupled bi-directionally to CPU  922 ; it provides additional data storage capacity and may also include any of the computer-readable media described below. Fixed disk  926  may be used to store programs, data, and the like and is typically a secondary storage medium (such as a hard disk) that is slower than primary storage. It will be appreciated that the information retained within fixed disk  926 , may, in appropriate cases, be incorporated in standard fashion as virtual memory in memory  924 . Removable disk  914  may take the form of any of the computer-readable media described below. A speech recognizer  944  is also attached to the system bus  920 . The speech recognizer  944  may be connected to the first microphone  905 , the second microphone  907 , and the third microphone to form an integrated speech recognition system in which known distances between the microphones are used by the speech recognizer  944 . 
     CPU  922  is also coupled to a variety of input/output devices such as display  904 , keyboard  910 , mouse  912  and speakers  930 . In general, an input/output device may be any of: video displays, track balls, mice, keyboards, microphones, touch-sensitive displays, transducer card readers, magnetic or paper tape readers, tablets, styluses, or handwriting recognizers, biometrics readers, or other computers. CPU  922  optionally may be coupled to another computer or telecommunications network using network interface  940 . With such a network interface, it is contemplated that the CPU might receive information from the network, or might output information to the network in the course of performing the above-described method steps. Furthermore, method embodiments of the present invention may execute solely upon CPU  922  or may execute over a network such as the Internet in conjunction with a remote CPU that shares a portion of the processing. The chassis  906  may be used to house the fixed disk  926 , memory  924 , network interface  940 , and processors  922 . 
     In addition, embodiments of the present invention may further relate to computer storage products with a computer-readable medium that have computer code thereon for performing various computer-implemented operations, such as voice recognition using the distances between the microphones. The media and computer code may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well known and available to those having skill in the computer software arts. Examples of computer-readable media include, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and holographic devices; magneto-optical media such as floptical disks; and hardware devices that are specially configured to store and execute program code, such as application-specific integrated circuits (ASICs), programmable logic devices (PLDs) and ROM and RAM devices. Examples of computer code include machine code, such as produced by a compiler, and files containing higher level code that are executed by a computer using an interpreter. 
       FIG. 7  is a schematic illustration of another embodiment of the invention. In the previous embodiment, the microphones were approximated as single points with no width. This approximation is satisfactory, if the width of the sensitive region of the microphone is small compared to the distances separating the microphone. In this embodiment the width of the sensitive region of the microphones is accounted for. In  FIG. 7  a first microphone  704 , a second microphone  708 , and a third microphone  712  are mounted on a mounting device  716 , which forms part of a computer system. The first microphone  704  has a first active width d m1 . The first active width is a width of the sensitive region of the microphone, which may be the width of an aperture in the microphone through which the sound passes. For this reason, the first microphone  704  is illustrated as a circular aperture. In the same way, the second microphone  708  has a second active width d m2  and the third microphone  712  has a third active width d m3 . The active widths of the first, second and third microphones may be all the same width or may be different widths. The first microphone  704  is spaced from the second microphone  708  by a first separation distance s 1 . This separation distance is from a side of the first microphone  704  to a side of the second microphone  708 , as shown in  FIG. 7 . Likewise, the second microphone  708  is spaced from the third microphone  712  by a separation distance s 2 . A signal  716  with a wavelength of “g” is also shown in  FIG. 7 . As shown in  FIG. 7 , two wavelengths 2g extend across the second separation distance s 2  and almost the entire second active width d m2  and almost the entire third active width d m3 . Therefore, 2g≈s 2 +d m2 +d m3 . On the other hand, three wavelengths 3g extend across the first separation distance s 1  and just a little of the second active width d m2  and almost the entire first active width d m1 . Therefore, 3g≈s 1 +d m1 . Therefore in this embodiment the invention then specifies that g&lt;v/f max , where v is the speed of sound in air and where g is the greatest common factor for all distances between microphones. The distance d n  between a microphone n and microphone n+1 is any length between the separation distance s n  between microphone n and microphone n+1 and the separation distance s n  between microphone n and microphone n+1 added to the active width d mn  of microphone n and the active width d mn+1  of microphone n+1 (s n ≦d n ≦s n +d mn +d mn+1 ). 
     While this invention has been described in terms of several preferred embodiments, there are alterations, modifications, permutations, and substitute equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and substitute equivalents as fall within the true spirit and scope of the present invention.

Metadata:
Filing Date: 20020725
Publication Date: 20080325
Grant Date: 20080325
Priority Date: 20010808
Inventors: SILVERMAN KIM E.
NAIK DEVANG K.
Assignee: APPLE INC
CPC Classifications: [{"code": "G10L2021/02165", "inventive": false, "first": false, "tree": "[]"}, {"code": "G10L15/20", "inventive": true, "first": true, "tree": "[]"}, {"code": "G10L2021/02165", "inventive": false, "first": false, "tree": "[]"}, {"code": "G10L2021/02166", "inventive": false, "first": false, "tree": "[]"}, {"code": "G10L15/20", "inventive": true, "first": true, "tree": "[]"}, {"code": "G10L2021/02166", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 27394954