Broadside small array microphone beamforming apparatus

A broadside small array microphone beamforming apparatus comprises first and second omni-directional microphones, a microphone calibration unit, and a directional microphone forming unit. The first and second omni-directional microphones respectively convert voice from a desired near-end talker into first and second signals. The second and first omni-directional microphones and the desired near-end talker are respectively arranged at three points of a triangle. The microphone calibration unit receives the first and second signals and correspondingly outputs first and second calibration signals. The directional microphone forming unit receives the first and second calibration signals to generate a first directional microphone signal with a bidirectional polar pattern. The adaptive channel decoupling unit receives the first calibration signal and the first directional microphone signal to generate a first main channel signal and a first reference channel signal for noise detection.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to small array microphone beamforming, and in particular to a broadside small array microphone beamforming apparatus with a narrow beam facing a near-end talker.

2. Description of the Related Art

Many communication system and voice recognition devices are designed for use in noisy environments. Examples of such applications include communication and/or voice recognition in cars or mobile environments (e.g., on street). For these applications, the microphones in the system pick up not only the desired voice but also noise as well. The noise can degrade the quality of voice communication and speech recognition performance if it is not dealt with in an effective manner.

Noise suppression is often required in many communication systems and voice recognition devices to suppress noise to improve communication quality and voice recognition performance. Noise suppression may be achieved using various techniques, which may be classified as single microphone techniques and array microphone techniques.

Thus, effective suppression of noise in communication system and voice recognition devices is desirable.

BRIEF SUMMARY OF THE INVENTION

An embodiment of a broadside small array microphone beamforming apparatus is provided. A broadside small array microphone beamforming apparatus comprises first and second omni-directional microphones, a microphone calibration unit, and a directional microphone forming unit. The first and second omni-directional microphones respectively convert voice from a desired near-end talker into first and second signals. The second and first omni-directional microphones and the desired near-end talker are respectively arranged at three points of a triangle. The microphone calibration unit receives the first and second signals and correspondingly outputs first and second calibration signals. The directional microphone forming unit receives the first and second calibration signals to generate a first directional microphone signal with a bidirectional polar pattern. The adaptive channel decoupling unit receives the first calibration signal and the first directional microphone signal to generate a first main channel signal and a first reference channel signal for noise detection.

Another embodiment of a broadside small array microphone beamforming apparatus is provided. A broadside small array microphone beamforming apparatus comprises first and second omni-directional microphones, a microphone calibration unit, and a directional microphone forming unit. The first and second omni-directional microphones respectively convert voice from a desired near-end talker into first and second signals. The second and first omni-directional microphones and the desired near-end talker are respectively arranged at three points of a triangle. The microphone calibration unit receives the first and second signals and correspondingly outputs first and second calibration signals. The directional microphone forming unit receives the first and second calibration signals to generate a first directional microphone signal with one side lobe polar pattern and a second directional microphone signal with another side lobe polar pattern. The adaptive channel decoupling unit receives the first calibration signal, the first directional microphone signal and the second directional microphone signal to generate a first main channel signal and a first reference channel signal for noise detection.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic diagram of broadside small array microphone beamforming apparatus100according to an embodiment of the invention. Broadside small array microphone beamforming apparatus100comprises omni-directional microphones Mic1and Mic2, microphone calibration unit110, directional microphone forming unit120, adaptive channel decoupling unit140, transformer150, noise suppression units160and170and inverse transformer180. Omni-directional microphones Mic1and Mic2respectively convert voice from desired near-end talker101into first and second signals S1and S2. Second and first omni-directional microphones Mic1and Mic2and desired near-end talker101are respectively arranged at three points of a triangle, referred to as a broadside way, as shown inFIG. 1. Microphone calibration unit110receives first and second signals S1and S2and correspondingly outputs first and second calibration signals X1and X2. Directional microphone forming unit120receives first and second calibration signals X1and X2to generate first directional microphone signal d1with a bidirectional polar pattern. Adaptive channel decoupling unit140receives first calibration signal X1and first directional microphone signal d1to generate first main channel signal m1and first reference channel signal r1for noise detection. In another embodiment of the invention, adaptive channel decoupling unit140receives the sum of the first calibration signal X1and the second calibration signal X2and receives first directional microphone signal d1to generate first main channel signal m1and first reference channel signal r1for noise detection.

FIG. 2is a schematic diagram of bidirectional polar pattern201and omni-directional polar pattern203according to an embodiment of the invention. Bidirectional polar pattern201comprises two main lobes. One lobe points left and another lobe points right, one lobe points up and another lobe points down, or one lobe points right up and another lobe points left down. Desired talker205faces the null of bidirectional polar pattern201, as shown inFIG. 2. According to an embodiment of the invention, first and second omni-directional microphones Mic1and Mic2form a directional microphone with bidirectional polar pattern201for noise detection, and one of first and second omni-directional microphones Mic1and Mic2is used as a main microphone.

FIG. 3is a schematic diagram of two single main lobe polar patterns301and302and omni-directional polar pattern303according to an embodiment of the invention. Two single main lobe polar patterns301and302can be formed by two omni-directional microphones. One lobe points left and another lobe points right, one lobe points up and another lobe points down, or one lobe points right up and another lobe points left down. Desired talker205faces the cross point or the equal gain point of two single lobes301and302, as shown inFIG. 3.

FIG. 4is a schematic diagram of directional microphone forming unit120according to an embodiment of the invention. Directional microphone forming unit120comprises phase adjustment units401and402and subtractor407. Phase adjustment unit401shifts first calibration signal X1phase P1to generate first shifted signal XP1. Phase adjustment unit402shifts second calibration signal X2phase P2to generate second shifted signal XP2. Subtractor407subtracts second shifted signal XP2from first shifted signal XP1to generate first directional microphone signal d1with a bidirectional polar pattern, as shown inFIG. 2. According to an embodiment of the invention, phase P1is zero and Phase P2is also zero. Thus, first directional microphone signal d1is equal to second calibration signal X2subtracted by first calibration signal X1(d1=X1−X2). First microphone signal d1is a signal with a bidirectional polar pattern.

FIG. 5is a schematic diagram of adaptive channel decoupling unit500according to another embodiment of the invention. Adaptive channel decoupling unit500comprises first voice activity detector (VAD1)511, first adaptive filter501, second voice activity detector (VAD2)512and second adaptive filter502. First voice activity detector511receives first calibration signal X1and first directional microphone signal d1to generate first voice activity signal V1for indicating the presence of desired voice. First adaptive filter501receives first calibration signal X1, first directional microphone signal d1and first voice activity signal V1and suppresses the desired voice of first directional microphone signal d1to generate first reference channel signal r1. Second voice activity detector512receives first voice activity signal V1, first reference channel signal r1and first calibration signal X1to generate second voice activity signal V2for indicating the presence of noise or interference. Second adaptive filter502receives second voice activity signal V2, first calibration signal X1, and first reference channel signal r1and suppresses noise of first calibration signal X1to generate first main channel signal m1.

FIG. 6is a schematic diagram of adaptive channel decoupling unit600according to another embodiment of the invention. The difference between adaptive channel decoupling units600and500is the presence of adder620. Adaptive channel decoupling unit600comprises adder620, first voice activity detector (VAD1)611, first adaptive filter601, second voice activity detector (VAD2)612and second adaptive filter602. Adder adds first calibration signal X1and second calibration signal X2to output third calibration signal X3. First voice activity detector611receives third calibration signal X3and first directional microphone signal d1to generate first voice activity signal V1for indicating the presence of desired voice. First adaptive filter601receives third calibration signal X3, first directional microphone signal d1, and first voice activity signal V1and suppresses the desired voice of first directional microphone signal d1to generate first reference channel signal r1. Second voice activity detector612receives first voice activity signal V1, first reference channel signal r1and third calibration signal X3to generate second voice activity signal V2for indicating the presence of noise or interference. Second adaptive filter602receives second voice activity signal V2, third calibration signal X3and first reference channel signal r1and suppresses noise of third calibration signal X3to generate first main channel signal m1.

FIG. 7is a schematic diagram of adaptive channel decoupling unit700according to another embodiment of the invention. Adaptive channel decoupling unit700comprises first voice activity detector (VAD1)711, first adaptive filter701, second voice activity detector (VAD2)702, second adaptive filter702, third adaptive filter703and selection criteria unit721. First voice activity detector711receives first calibration signal X1and first directional microphone signal d1to generate first voice activity signal for indicating the presence of desired voice. First adaptive filter701receives first calibration signal X1, first directional microphone signal d1and first voice activity signal V1and suppresses the desired voice of first directional microphone signal d1to generate first reference channel signal r1. Second voice activity detector712receives first reference signal r1and first calibration signal X1to generate second voice activity signal V2for indicating the presence of noise or interference. Second adaptive filter702receives second voice activity signal V2, first calibration signal X1and first reference channel signal r1and suppresses one side (right side, one lobe of bidirectional polar pattern) noise of first calibration signal X1to generate first adaptive filter signal Xn1. Third adaptive filter703receives second voice activity signal V2, first calibration signal X1and first reference channel signal r1and suppresses another side (left side, another lobe of bidirectional polar pattern) noise of first calibration signal X1to generate second adaptive filter signal Xn2. Selection criteria unit721does a selection from first adaptive filter signal Xn1and second adaptive filter signal Xn2to output first main channel signal m1according to first calibration signal X1. For example, m1=a*Xn1+b*Xn2.

Referring toFIG. 1, a transformer, such as Fast Fourier Transformer,150transforms first main channel signal m1and first reference channel signal from time domain to frequency domain to correspondingly output first main signal m1and first reference signal R1. First noise suppression unit160comprises noise estimating unit162and noise suppression unit164. Noise estimating unit162generate ambient noise signal N1by estimating noise of first reference signal R1. Noise suppression unit receives ambient noise signal N1, suppresses low frequency internal noise caused by forming the bidirectional microphone and generates first ambient noise signal N1′. Second noise suppression unit170comprises entire estimating unit172, frequency domain voice activity detector171and noise suppression unit174. Entire noise estimating unit172generates entire ambient noise signal N2by estimating entire noise from first main signal M1and first ambient noise signal N1′. Frequency domain voice activity detector171receives first main signal M1and entire ambient noise signal N2to generate third voice activity signal V3for indicating noise. Noise suppression unit174receives entire ambient noise signal N2, first main signal M1and third voice activity signal V3to generate first clean voice signal M0with ambient noise suppression. Inverse transformer, such as Inverse Fast Fourier Transformer,180transforms first main signal from frequency domain to time domain to generate second clear voice signal m0.

FIG. 8is a schematic diagram of broadside small array microphone beamforming apparatus800according to another embodiment of the invention. Broadside small array microphone beamforming apparatus800comprises omni-directional microphones Mic11and Mic12, microphone calibration unit810, directional microphone forming unit820, adaptive channel decoupling unit840, transformer850, noise suppression units860and870and inverse transformer880. Omni-directional microphones Mic3and Mic2respectively convert voice from desired near-end talker801into first and second signals S1and S2. Second and first omni-directional microphones Mic12and Mic11and desired near-end talker801are respectively arranged at three points of a triangle, referred to as a broadside way, as shown inFIG. 8. Microphone calibration unit810receives first and second signals S1and S2and correspondingly outputs first and second calibration signals X1and X2. Directional microphone forming unit120receives first and second calibration signals X1and X2to generate first directional microphone signal d1with one side polar pattern and second directional microphone signal d2with another side lobe polar pattern, as shown inFIG. 3. Adaptive channel decoupling unit840receives first calibration signal X1, first directional microphone signal d1and second directional microphone signal d2to generate first main channel signal m1and first reference channel signal r1for noise detection. In another embodiment of the invention, adaptive channel decoupling unit840receives the sum of the first calibration signal X1and the second calibration signal X2and receives first directional microphone signal d1and second directional microphone signal d2to generate first main channel signal m1and first reference channel signal r1for noise detection.

As shown inFIG. 8, first and second omni-directional microphones Mic11and Mic12form two directional microphones with single lobe polar patterns for noise detection, and one of the first and second omni-directional microphones is used as a main microphone. Desired near-end talker801faces a cross point or a point of equal gains of two single polar pattern.

FIG. 9is a schematic diagram of directional microphone forming unit820according to another embodiment of the invention. Directional microphone forming unit820comprises phase adjustment units901,902,903and904and subtractors907and908. Phase adjustment unit901shifts first calibration signal X1phase P10to generate first shifted signal XP10. Phase adjustment unit902shifts second calibration signal X2phase P20to generate second shifted signal XP20. Phase adjustment unit911shifts first calibration signal X1phase P11to generate third shifted signal XP11. Phase adjustment unit912shifts second calibration signal X2phase P21to generate fourth shifted signal XP21. Subtractor907subtracts second shifted signal XP20from first shifted signal XP10to generate first directional microphone signal d1with one side single polar pattern301, as shown inFIG. 3. Subtractor908subtracts fourth shifted signal XP21from third shifted signal XP11to generate second directional microphone signal d2with another side single polar pattern302, as shown inFIG. 3.

According to an embodiment of the invention, phases P10and P21are zero and Phases P20and P11are T (the delay for sound propagation between two microphones). Thus, omni-directional microphones Mic11and Mic12can form a first directional microphone with a single lobe polar pattern and second directional microphone with another single lobe polar pattern.

FIG. 10is a schematic diagram of adaptive channel decoupling unit1000according to another embodiment of the invention. Adaptive channel decoupling unit1000comprises voice activity detectors1011,1012,1013and1014and adaptive filter1001,1002,1003and1004. First Voice activity detector (VAD1)1011receives first calibration X1and first directional microphone signal d1to generate first voice activity signal V1for indicating desired voice. First adaptive filter1001receives first calibration signal X1, first directional microphone signal d1and first voice activity signal V1, and suppresses the desired voice of first directional microphone signal d1to generate reference channel signal r1′. Second voice activity detector (VAD2)1012receives first voice activity signal V1, reference channel signal r1′ and first calibration signal X1to generate second voice activity signal V2for indicating noise or interference. Second adaptive filter1002receives second voice activity signal V2, first calibration signal X1and reference channel signal r1′ and suppresses noise of first calibration signal X1to generate main channel signal m1′. Third voice activity detector (VAD3)1013receives reference channel signal r1′ and second directional microphone signal d2to generate third voice activity signal V3for indicating the desired voice. Third adaptive filter1003receives reference channel signal r1′, second directional microphone signal d2and third voice activity signal V3, and suppresses the desired voice of second directional microphone d2to generate first reference channel signal r1. Fourth voice activity detector (VAD4)1014receives third voice activity signal V3, first reference channel signal r1and main channel signal m1′ to generate fourth voice activity signal V4for indicating noise of interference. Fourth adaptive filter1004receives fourth voice activity signal V4, main channel signal m1′, first reference channel signal r1and suppresses noise of main channel signal m1′ to generate first main channel signal m1.

FIG. 11is a schematic diagram of adaptive channel decoupling unit1100according to another embodiment of the invention. The difference between adaptive channel decoupling units1000and1100is adder1101. Adder1101adds first calibration signal X1and second calibration signal X2to output calibration signal X0. Since the operation of adaptive channel decoupling unit1100inFIG. 11is similar to the operation of adaptive channel decoupling unit1000inFIG. 10, it is not detailed here.

Referring toFIG. 1, first noise suppression unit860comprises noise estimating unit862and noise suppression unit864and second noise suppression unit870comprises entire estimating unit872, frequency domain voice activity detector871and noise suppression unit874. The operation of transformer850, noise suppression units860and870and inverse transformer880is the same as that of transformer150, noise suppression units160and170and inverse transformer180. Thus, it is not detailed here.