Audio system based on at least second-order eigenbeams

Abstract

A microphone array-based audio system that supports representations of auditory scenes using second-order (or higher) harmonic expansions based on the audio signals generated by the microphone array. In one embodiment, a plurality of audio sensors are mounted on the surface of an acoustically rigid sphere. The number and location of the audio sensors on the sphere are designed to enable the audio signals generated by those sensors to be decomposed into a set of eigenbeams having at least one eigenbeam of order two (or higher). Beamforming (e.g., steering, weighting, and summing) can then be applied to the resulting eigenbeam outputs to generate one or more channels of audio signals that can be utilized to accurately render an auditory scene. Alternative embodiments include using shapes other than spheres, using acoustically soft spheres and/or positioning audio sensors in two or more concentric patterns.

What is claimed is:  
     
         1 . A method for processing audio signals, comprising: 
 receiving a plurality of audio signals, each audio signal having been generated by a different sensor of a microphone array; and    decomposing the plurality of audio signals into a plurality of eigenbeam outputs, wherein each eigenbeam output corresponds to a different eigenbeam for the microphone array and at least one of the eigenbeams has an order of two or greater.    
     
     
         2 . The invention of  claim 1 , wherein the eigenbeams correspond to spheroidal harmonics based on a spherical, oblate, or prolate configuration of the sensors in the microphone array.  
     
     
         3 . The invention of  claim 1 , wherein at least one of the eigenbeams has an order of at least three.  
     
     
         4 . The invention of  claim 1 , wherein the microphone array comprises the plurality of sensors mounted on an acoustically rigid sphere.  
     
     
         5 . The invention of  claim 4 , wherein one or more of the sensors are pressure sensors.  
     
     
         6 . The invention of  claim 5 , wherein at least one pressure sensor comprises a patch sensor operating as a spatial low-pass filter to avoid spatial aliasing resulting from relatively high frequency components in the audio signals.  
     
     
         7 . The invention of  claim 6 , wherein at least one patch sensor comprises a number of proximally configured, individual pressure sensors, wherein, for each such patch sensor, analog signals generated by the number of individual pressure sensors are combined before sampling to generate a digital audio signal for that patch sensor.  
     
     
         8 . The invention of  claim 6 , wherein the at least one pressure sensor further comprises a point sensor positioned below the patch sensor, wherein: 
 the point sensor is used to generate relatively low frequency audio signals; and    the patch sensor is used to generate relatively high frequency audio signals.    
     
     
         9 . The invention of  claim 4 , wherein one or more of the sensors are elevated over the surface of the sphere.  
     
     
         10 . The invention of  claim 1 , wherein the microphone array comprises the plurality of sensors mounted on an acoustically soft sphere.  
     
     
         11 . The invention of  claim 10 , wherein one or more of the sensors are cardioid sensors configured with their nulls pointing towards the center of the sphere.  
     
     
         12 . The invention of  claim 1 , wherein the number and positions of sensors in the microphone array enable representation of a beampattern as a series expansion involving at least second-order spheroidal harmonics.  
     
     
         13 . The invention of  claim 12 , wherein the number of sensors is based on the highest-order spheroidal harmonic in the series expansion.  
     
     
         14 . The invention of  claim 1 , wherein the arrangement of the sensors in the microphone array satisfies a discrete orthogonality condition.  
     
     
         15 . The invention of  claim 1 , wherein decomposing the plurality of audio signals further comprises treating each sensor signal as a directional beam for relatively high frequency components in the audio signals.  
     
     
         16 . The invention of  claim 1 , further comprising generating an auditory scene based on the eigenbeam outputs and their corresponding eigenbeams.  
     
     
         17 . The invention of  claim 16 , wherein generating the auditory scene comprises independently generating two or more different auditory scenes based on the eigenbeam outputs and their corresponding eigenbeams.  
     
     
         18 . The invention of  claim 16 , wherein generating the auditory scene comprises: 
 applying a weighting value to each eigenbeam output to form a weighted eigenbeam; and    combining the weighted eigenbeams to generate the auditory scene.    
     
     
         19 . The invention of  claim 1 , further comprising storing data corresponding to the eigenbeam outputs for subsequent processing.  
     
     
         20 . The invention of  claim 19 , further comprising: 
 recovering the eigenbeam outputs from the stored data; and    generating an auditory scene based on the recovered eigenbeam outputs and their corresponding eigenbeams.    
     
     
         21 . The invention of  claim 1 , further comprising transmitting data corresponding to the eigenbeam outputs for remote receipt and processing.  
     
     
         22 . The invention of  claim 21 , further comprising: 
 recovering the eigenbeam outputs from the received data; and    generating an auditory scene based on the recovered eigenbeam outputs and their corresponding eigenbeams.    
     
     
         23 . The invention of  claim 1 , further comprising applying an equalizer filter to each eigenbeam output to compensate for frequency dependence of the corresponding eigenbeam.  
     
     
         24 . The invention of  claim 1 , wherein receiving the plurality of audio signals further comprises generating the plurality of audio signals using the microphone array.  
     
     
         25 . The invention of  claim 24 , wherein receiving the plurality of audio signals further comprises calibrating each sensor of the microphone array based on measured data generated by the sensor.  
     
     
         26 . The invention of  claim 25 , wherein receiving the plurality of audio signals comprises calibrating each sensor of the microphone array using a calibration module comprising a reference sensor and an acoustic source configured on an enclosure having an open side, wherein the open side of the volume is held on top of the sensor in order to calibrate the sensor relative to the reference sensor.  
     
     
         27 . The invention of  claim 1 , wherein the plurality of sensors are arranged in two or more concentric arrays of sensors, wherein each array is adapted for audio signals in a different frequency range.  
     
     
         28 . The invention of  claim 27 , wherein audio signals from different arrays are combined prior to being decomposed into a plurality of eigenbeams.  
     
     
         29 . The invention of  claim 1 , wherein all of the sensors are used to process relatively low-frequency signals, while only a subset of the sensors are used to process relatively high-frequency signals.  
     
     
         30 . The invention of  claim 29 , wherein only one of the sensors is used to process the relatively high-frequency signals.  
     
     
         31 . A microphone, comprising a plurality of sensors mounted in an arrangement, wherein the number and positions of sensors in the arrangement enable representation of a beampattern for the microphone as a series expansion involving at least one second-order eigenbeam.  
     
     
         32 . The invention of  claim 31 , wherein the series expansion involves an eigenbeam having order of at least three.  
     
     
         33 . The invention of  claim 31 , wherein the arrangement is one of spherical, oblate, or prolate.  
     
     
         34 . The invention of  claim 31 , wherein the plurality of sensors are mounted on an acoustically rigid sphere.  
     
     
         35 . The invention of  claim 34 , wherein the sensors are pressure sensors.  
     
     
         36 . The invention of  claim 35 , wherein at least one pressure sensor comprises a patch sensor operating as a spatial low-pass filter to avoid aliasing resulting from relatively high frequency components in the audio signals.  
     
     
         37 . The invention of  claim 36 , wherein at least one patch sensor comprises a number of proximally configured, individual pressure sensors, wherein, for each such patch sensor, analog signals generated by the number of individual pressure sensors are combined before sampling to generate a digital audio signal for that patch sensor.  
     
     
         38 . The invention of  claim 36 , wherein the at least one pressure sensor further comprises a point sensor positioned below the patch sensor, wherein: 
 the point sensor is used to generate relatively low frequency audio signals; and    the patch sensor is used to generate relatively high frequency audio signals.    
     
     
         39 . The invention of  claim 34 , wherein one or more of the sensors are elevated over the surface of the sphere.  
     
     
         40 . The invention of  claim 31 , wherein the plurality of sensors are mounted on an acoustically soft sphere.  
     
     
         41 . The invention of  claim 40 , wherein the sensors are cardioid sensors configured with their nulls pointing towards the center of the sphere.  
     
     
         42 . The invention of  claim 31 , wherein the second-order eigenbeam corresponds to a second-order spheroidal harmonic.  
     
     
         43 . The invention of  claim 42 , wherein the number of sensors is based on the highest-order spheroidal harmonic in the series expansion.  
     
     
         44 . The invention of  claim 31 , wherein the arrangement of the sensors satisfies a discrete orthogonality condition.  
     
     
         45 . The invention of  claim 31 , further comprising a processor configured to decompose a plurality of audio signals generated by the sensors into a plurality of eigenbeam outputs, wherein each eigenbeam output corresponds to a different eigenbeam for the microphone array and at least one of the eigenbeams has an order of two or greater.  
     
     
         46 . The invention of  claim 45 , wherein the processor is further configured to generate an auditory scene based on the eigenbeam outputs and their corresponding eigenbeams.  
     
     
         47 . The invention of  claim 31 , wherein the plurality of sensors are arranged in two or more concentric arrays of sensors, wherein each array is adapted for audio signals in a different frequency range.  
     
     
         48 . The invention of  claim 47 , wherein the sensors in the different arrays are located at the same spherical coordinates.  
     
     
         49 . The invention of  claim 31 , wherein all of the sensors are used to process relatively low-frequency signals, while only a subset of the sensors are used to process relatively high-frequency signals.  
     
     
         50 . The invention of  claim 49 , wherein only one of the sensors is used to process the relatively high-frequency signals.  
     
     
         51 . A method for generating an auditory scene, comprising: 
 receiving eigenbeam outputs, the eigenbeam outputs having been generated by decomposing a plurality of audio signals, each audio signal having been generated by a different sensor of a microphone array, wherein each eigenbeam output corresponds to a different eigenbeam for the microphone array and at least one of the eigenbeam outputs corresponds to an eigenbeam having an order of two or greater; and    generating the auditory scene based on the eigenbeam outputs and their corresponding eigenbeams.    
     
     
         52 . The invention of  claim 51 , wherein generating the auditory scene comprises: 
 applying a weighting value to each eigenbeam output to form a weighted eigenbeam; and    combining the weighted eigenbeams to generate the auditory scene.    
     
     
         53 . The invention of  claim 51 , wherein generating the auditory scene further comprises applying an equalizer filter to each eigenbeam output to compensate for frequency dependence of the corresponding eigenbeam.  
     
     
         54 . The invention of  claim 51 , wherein the microphone array comprises a plurality of sensors mounted in a spheroidal arrangement.  
     
     
         55 . The invention of  claim 54 , wherein the plurality of sensors are mounted on an acoustically rigid sphere.  
     
     
         56 . The invention of  claim 55 , wherein the sensors are pressure sensors.  
     
     
         57 . The invention of  claim 56 , wherein at least one pressure sensor comprises a patch sensor operating as a spatial low-pass filter to avoid aliasing resulting from relatively high frequency components in the audio signals.  
     
     
         58 . The invention of  claim 57 , wherein at least one patch sensor comprises a number of proximally configured, individual pressure sensors, wherein, for each such patch sensor, analog signals generated by the number of individual pressure sensors are combined before sampling to generate a digital audio signal for that patch sensor.  
     
     
         59 . The invention of  claim 57 , wherein the at least one pressure sensor further comprises a point sensor positioned below the patch sensor, wherein: 
 the point sensor is used to generate relatively low frequency audio signals; and    the patch sensor is used to generate relatively high frequency audio signals.    
     
     
         60 . The invention of  claim 55 , wherein one or more of the sensors are elevated over the surface of the sphere.  
     
     
         61 . The invention of  claim 54 , wherein the plurality of sensors are mounted on an acoustically soft sphere.  
     
     
         62 . The invention of  claim 61 , wherein one or more of the sensors are cardioid sensors configured with their nulls pointing towards the center of the sphere.  
     
     
         63 . The invention of  claim 54 , wherein the number and positions of sensors in the microphone array enable representation of a beampattern as a series expansion involving at least second-order spheroidal harmonics.  
     
     
         64 . The invention of  claim 63 , wherein the number of sensors is based on the highest-order spheroidal harmonic in the series expansion.  
     
     
         65 . The invention of  claim 54 , wherein the arrangement of the sensors satisfies a discrete orthogonality condition.  
     
     
         66 . The invention of  claim 51 , wherein generating the auditory scene further comprises treating each sensor signal as a directional beam for relatively high frequency components in the audio signals.  
     
     
         67 . The invention of  claim 51 , wherein receiving the eigenbeam outputs further comprises recovering the eigenbeam outputs from data stored during previous processing.  
     
     
         68 . The invention of  claim 51 , wherein receiving the eigenbeam outputs further comprises recovering the eigenbeam outputs from data received after transmission from a remote node.  
     
     
         69 . The invention of  claim 51 , wherein the number of higher-order eigenbeams used in generating the auditory scene is limited to maintain a minimum value of signal-to-noise ratio (SNR).  
     
     
         70 . The invention of  claim 69 , wherein the SNR is characterized using white noise gain.  
     
     
         71 . The invention of  claim 51 , wherein generating the auditory scene comprises independently generating two or more different auditory scenes based on the eigenbeam outputs and their corresponding eigenbeams.  
     
     
         72 . The invention of  claim 51 , wherein the plurality of sensors are arranged in two or more concentric patterns, each pattern having a plurality of sensors adapted to process signals in a different frequency range.  
     
     
         73 . The invention of  claim 72 , wherein the sensors arranged in the innermost patterns are mounted on the surface of an acoustically rigid sphere.  
     
     
         74 . The invention of  claim 51 , wherein all of the sensors are used to process relatively low-frequency signals, while only a subset of the sensors are used to process relatively high-frequency signals.  
     
     
         75 . The invention of  claim 74 , wherein only one of the sensors is used to process the relatively high-frequency signals.