PATENT DOCUMENT

Publication Number: US-8150063-B2
Application Number: US-32328408-A
Country: US
Kind Code: B2

Title: Stabilizing directional audio input from a moving microphone array

Abstract:
A device includes a microphone array fixed to the device. A signal processor produces an audio output using audio beamforming with input from the microphone array. The signal processor aims the beamforming in a selected direction. An orientation sensor—such as a compass, an accelerometer, or an inertial sensor—is coupled to the signal processor. The orientation sensor detects a change in the orientation of the microphone array and provides an orientation signal to the signal processor for adjusting the aim of the beamforming to maintain the selected direction. The device may include a camera that captures an image. An image processor may identify an audio source in the image and provide a signal adjusting the selected direction to follow the audio source. The image processor may receive the orientation signal and adjust the image for changes in the orientation of the camera before tracking movement of the audio source.

Claims:
What is claimed is: 
     
       1. A device to provide an audio output, the device comprising:
 a microphone array fixed to the device; 
 a signal processor coupled to the microphone array to produce the audio output using audio beamforming with input from the microphone array, the signal processor aiming the audio beamforming in a selected direction; and 
 an orientation sensor coupled to the signal processor, the orientation sensor detecting a change in the orientation of the microphone array and providing an orientation signal to the signal processor for adjusting the aim of the audio beamforming to maintain the selected direction. 
 
     
     
       2. The device of  claim 1 , wherein the orientation sensor is a compass that is mechanically fixed to the device such that there is no relative movement between the compass mounting and the microphone array. 
     
     
       3. The device of  claim 1 , wherein the orientation sensor is an accelerometer that is mechanically fixed to the device such that there is no relative movement between the accelerometer mounting and the microphone array. 
     
     
       4. The device of  claim 1 , wherein the orientation sensor is an inertial sensor that is mechanically supported by the device such that there is no relative movement between the inertial sensor mounting and the microphone array. 
     
     
       5. The device of  claim 1 , further comprising:
 a camera fixed to the device, the camera capturing an image; and 
 an image processor coupled to the camera, the signal processor, and the orientation sensor, the image processor identifying an audio source in the image received from the camera, tracking movement of the audio source, and providing a motion signal to the signal processor for adjusting the selected direction to follow the audio source, the image processor receiving the orientation signal and adjusting the image for changes in the orientation of the camera before tracking movement of the audio source. 
 
     
     
       6. A device to provide an audio output, the device comprising:
 a microphone array fixed to the device; 
 a signal processor coupled to the microphone array to produce the audio output using audio beamforming with input from the microphone array, the signal processor aiming the audio beamforming in a selected direction; and 
 an accelerometer coupled to the signal processor and mechanically supported by the device such that there is no relative movement between the accelerometer mounting and the microphone array, the accelerometer detecting a change in the orientation of the microphone array and providing an orientation signal to the signal processor for adjusting the aim of the audio beamforming to maintain the selected direction. 
 
     
     
       7. The device of  claim 1 , further comprising:
 a camera fixed to the device, the camera capturing an image; and 
 an image processor coupled to the camera, the signal processor, and the accelerometer, the image processor identifying an audio source in the image received from the camera, tracking movement of the audio source, and providing a motion signal to the signal processor for adjusting the selected direction to follow the audio source, the image processor receiving the orientation signal and adjusting the image for changes in the orientation of the camera before tracking movement of the audio source. 
 
     
     
       8. A device to provide an audio output, the device comprising:
 a microphone array fixed to the device; 
 a signal processor coupled to the microphone array to produce the audio output using audio beamforming with input from the microphone array, the signal processor aiming the audio beamforming in a selected direction; and 
 an inertial sensor coupled to the signal processor and mechanically supported by the device such that there is no relative movement between the inertial sensor mounting and the microphone array, the inertial sensor detecting a change in the orientation of the microphone array and providing an orientation signal to the signal processor for adjusting the aim of the audio beamforming to maintain the selected direction. 
 
     
     
       9. The device of  claim 1 , further comprising:
 a camera fixed to the device, the camera capturing an image; and 
 an image processor coupled to the camera, the signal processor, and the inertial sensor, the image processor identifying an audio source in the image received from the camera, tracking movement of the audio source, and providing a motion signal to the signal processor for adjusting the selected direction to follow the audio source, the image processor receiving the orientation signal and adjusting the image for changes in the orientation of the camera before tracking movement of the audio source.

Description:
BACKGROUND 
     1. Field 
     Embodiments of the invention relate to the field of audio beamforming; and more specifically, to the aiming of audio beamforming. 
     2. Background 
     Under typical imperfect conditions, a single microphone that is embedded in a mobile device does a poor job of capturing sound because of background sounds that are captured along with the sound of interest. An array of microphones can do a better job of isolating a sound source and rejecting ambient noise and reverberation. 
     Beamforming is a way of combining sounds from two or more microphones that allows preferential capture of sounds coming from certain directions. In a delay-and-sum beamformer sounds from each microphone are delayed relative to sounds from the other microphones, and the delayed signals are added. The amount of delay determines the beam angle—the angle in which the array preferentially “listens.” When a sound arrives from this angle, the sound signals from the multiple phones are added constructively. The resulting sum is stronger, and the sound is received relatively well. When a sound arrives from another angle, the delayed signals from the various microphones add destructively—with positive and negative parts of the sound waves canceling out to some degree—and the sum is not as loud as an equivalent sound arriving from the beam angle. 
     For example, if the sound comes into the microphone on the right before it enters the microphone on the left, then you know the sound source is to the right of the microphone array. During sound capturing, the microphone array processor can aim a capturing beam in the direction of the sound source. Beamforming allows a microphone array to simulate a highly directional microphone pointing toward the sound source. The directivity of the microphone array reduces the amount of captured ambient noises and reverberated sound as compared to a single microphone. This may provide a clearer representation of a speaker&#39;s voice. 
     A beamforming microphone array may made up of distributed omnidirectional microphones linked to a processor that combines the several inputs into an output with a coherent form. Arrays may be formed using numbers of closely spaced microphones. Given a fixed physical relationship in space between the different individual microphone transducer array elements, simultaneous digital signal processor (DSP) processing of the signals from each of the individual microphones in the array can create one or more “virtual” microphones. Different algorithms permit the creation of virtual microphones with extremely complex virtual polar patterns and even the possibility to steer the individual lobes of the virtual microphones patterns so as to home-in-on, or to reject, particular sources of sound. Beamforming techniques, however, rely on knowledge of the location of the sound source. Therefore it is necessary to aim the beamforming at the intended sound source to benefit from the use of a microphone array. It would be desirable to maintain the aim of the beamforming when the microphone array is part of a mobile device. 
     SUMMARY 
     A device includes a microphone array fixed to the device. A signal processor produces an audio output using audio beamforming with input from the microphone array. The signal processor aims the beamforming in a selected direction. An orientation sensor—such as a compass, an accelerometer, or an inertial sensor—is coupled to the signal processor. The orientation sensor detects a change in the orientation of the microphone array and provides an orientation signal to the signal processor for adjusting the aim of the beamforming to maintain the selected direction. The device may include a camera that captures an image. An image processor may identify an audio source in the image and provide a signal adjusting the selected direction to follow the audio source. The image processor may receive the orientation signal and adjust the image for changes in the orientation of the camera before tracking movement of the audio source. 
     Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention by way of example and not limitation. In the drawings, in which like reference numerals indicate similar elements: 
         FIG. 1A  is a block diagram of a mobile device to provide an audio output. 
         FIG. 1B  shows the mobile device after having moved from the orientation shown in  FIG. 1A . 
         FIG. 2  is a block diagram of another mobile device to provide an audio output. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. 
       FIG. 1A  is a block diagram of a mobile device  10  to provide an audio output. The device may be an audio recorder, a cellular telephone, or other device for capturing an audio source and providing an audio output. A microphone array  12 ,  14  is fixed to the device. The microphone array includes at least two individual microphones. A signal processor  24  is coupled to the microphone array to produce the audio output using audio beamforming with input from the microphone array. The signal processor aims the audio beamforming in a selected direction, as suggested by the dashed line directed toward a speaker  30 . The audio beamforming provides a directional audio sensitivity so that the sound from the speaker  30  at whom the audio beamforming is aimed is emphasized. Other sound, such as a conversation between people  32 ,  34  adjacent the speaker, may be attenuated by the beamforming. 
       FIG. 1B  shows the mobile device  10  having moved relative to the speaker  30 . The device  10  includes an orientation sensor  22  coupled to the signal processor  24 . The orientation sensor  22  detects a change in the orientation of the device and hence the microphone array since the orientation sensor and the microphone array are both fixed to the device so that they all move in unison. The orientation sensor  22  provides an orientation signal to the signal processor  24  for adjusting the aim of the audio beamforming to maintain the selected direction of the beamforming despite the movement of the device  10 . 
     It will be appreciated that the amount of adjustment made by signal processor  24  to maintain the selected direction of the beamforming is dependent on both the magnitude and the direction of movement of the device  10 . For example, moving the device up and down perpendicular to the axis of a linear microphone array will not change the aiming of the audio beamforming. On the other hand, rotating the device around an axis that is perpendicular to the axis of a linear microphone array will have a large effect on the aiming of the audio beamforming. The signal processor will use both magnitude and direction information in the orientation signal to make an appropriate adjustment to the aiming of the audio beamforming. 
     Any of a variety of devices may be used, either singly or in combination, as an orientation sensor  22 . For example, the orientation sensor  22  may be a compass that is mechanically fixed to the device  10  such that there is no relative movement between the compass mounting and the microphone array  12 , 14 . For the purposes of the invention, a compass includes any device that provides an orientation signal based on the position of the device within the Earth&#39;s magnetic field. 
     The orientation sensor  22  may be an accelerometer that is mechanically fixed to the device  10  such that there is no relative movement between the accelerometer mounting and the microphone array  12 , 14 . An accelerometer provides an orientation signal based on acceleration and gravity induced reaction forces. Thus the accelerometer provides an inertial reference platform that can determine changes in the position and orientation of the device  10  without using external references. 
     The orientation sensor  22  may be an inertial sensor that is mechanically supported by the device  10  such that there is no relative movement between the inertial sensor mounting and the microphone array  12 , 14 . For the purposes of the invention, an inertial sensor includes any device that senses changes in the orientation of a support structure relative to a structure that resists changes in orientation. A gyroscope is an exemplary inertial sensor. Various devices which may be described as vibrating structure gyroscopes may be used as an inertial sensor. 
     The orientation sensor  22  may be a micro-electro-mechanical systems (MEMS) device. 
       FIG. 2  is a block diagram of another mobile device  40  to provide an audio output. The device  40  includes the elements of the device  10  shown in  FIG. 1A . The device  40  further includes a camera  42  fixed to the device. The camera  42  captures an image that includes the audio source  30  at which the audio beamforming is aimed. An image processor  44  is coupled to the camera  42 , the signal processor  46 , and the orientation sensor  22 . The image processor  44  may identify the audio source in the image received from the camera, track movement of the audio source, and provide a motion signal to the signal processor  46  for adjusting the selected direction to follow the audio source. The image processor  44  may identify the audio source based on a user input to select the audio source at which to aim of the audio beamforming. In other embodiments, the image processor  44  may identify the audio source in various automatic or semi-automatic ways. The image processor  44  further receives the orientation signal from the orientation sensor  22  and adjusts the image for changes in the orientation of the device, and hence the camera, before tracking movement of the audio source  40 . The speed and accuracy of the tracking of movement of the audio source may be improved by first adjusting the image to remove the effects of camera movements. 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those of ordinary skill in the art. The description is thus to be regarded as illustrative instead of limiting.

Metadata:
Filing Date: 20081125
Publication Date: 20120403
Grant Date: 20120403
Priority Date: 20081125
Inventors: CHEN SHAOHAI
TAMCHINA PHILLIP GEORGE
LEE JAE HAN
Assignee: APPLE INC
CPC Classifications: [{"code": "H04R3/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04N7/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R27/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R27/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R3/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R3/00", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 42196288