Electrical audio signal processing systems and devices – Directive circuits for microphones
Reexamination Certificate
1998-04-06
2001-06-05
Nguyen, Duc (Department: 2743)
Electrical audio signal processing systems and devices
Directive circuits for microphones
C381S122000, C348S014090, C348S014160, C348S169000
Reexamination Certificate
active
06243471
ABSTRACT:
REFERENCE TO APPENDICES
The disclosure of this patent document contains material which is subject to copyright protection. Once the patent document or the patent disclosure are duly released from secrecy in accord with standard procedure of the U.S. Patent and Trademark Office, the owner has no objection to facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
FIELD OF INVENTION
The invention pertains to sensor arrays and, more particularly, to methods and apparatus for locating a source based on receipt of signals generated by it at a sensor array. The invention has application, for example, in steering cameras for video teleconferencing.
BACKGROUND OF THE INVENTION
An array microphones (or other sensors) can be advantageously used to detect sounds (or other transmitted energy waves) emitted by objects. An advantage of using an array, as opposed to a single such sensor, is that its output can be electronically processed to emphasize sounds from a particular location and to de-emphasize sounds from other locations—in other words, to reduce background noise. One form of electronic processing is beamforming, which makes it possible to electronically “steer” an array by emphasizing sounds from objects as they move from location to location.
For these reasons, a microphone array can be advantageously used to pick up speech in situations such as teleconferences, where hands-free speech acquisition is desired, where there are multiple talkers or where there the talkers are moving. Through the use of beamforming and other such techniques, the array's directivity pattern can be updated rapidly to follow a moving talker or to switch between several alternating or simultaneous talkers.
The increased popularity of multimedia (or video) teleconferencing presents the art with new challenges. In addition to speech, manufacturers and service providers must provide conference participants with quality images of one another. Conventionally, only single, fixed camera installed at each site to obtain those images. This is problematic where there are more than a few conferees, especially, where those conferees are situated around a large area (e.g., a conference table) or are pacing about.
An object of this invention is to resolve this and related problems by providing methods and apparatus for steering cameras used in a teleconferencing system. A still more particular object is to provide such systems as will automatically steer the camera toward an active talker in the teleconference.
A more general object of the invention provide improved methods and apparatus for locating a source that emits sounds, or other such energies.
Still another object of the invention is to provide source localization systems that can be readily and inexpensively implemented using current digital data processing and/or signal processing technologies.
Yet another object is to provide such systems as can be readily implemented in connection with beamforming or other such steering circuitry.
SUMMARY OF THE INVENTION
The invention meets the foregoing objects, among others, by providing in one aspect an apparatus for determining the location of a signal-generating source (e.g., a conferee in a telephone conference). The apparatus includes at least three sensors (e.g., microphones) arranged in a plurality of sets, each having two or more sensors. A surface-finding element responds to receipt at each sensor set of signals (e.g., speech) from the source for identifying a geometric surface (e.g., the surface of a hyperboloid or cone) representing potential locations of the source as a function of sensor locations and time difference of arrival of the signals. A location-approximating element coupled to two or more of the sets identifies a line that further defines potential source locations at the intersection of the surfaces. A location signal representing those potential locations is generated in accord with parameters of that line.
In a further aspect of the invention, the sensor sets each include two sensors and at least two of those sets are orthogonally centered with respect to one another. For each such orthogonally centered set, the midpoint of the locations of one of the sensor sets is substantially aligned with the midpoint of the other and the line segments defined by those pairs are substantially perpendicular to one another. Put in other way, the sensors lie on the endpoints of a cross (“+”) configuration.
For each sensor set (e.g., two microphones), the surface-finding element includes functionality for identifying, as potential source locations, a substantially conical surface having a direction angle &thgr; defined as a function of a speed of propagation of the signal from the source, a measured time difference of arrival of that signal at the sensors of the sensors set, a location of a first sensor in the sensor set, and a location of a second sensor in the sensor set.
For each pair of sensor sets (e.g., four microphones), the surface-finding element can include functionality for identifying, as potential source locations, a line defining an intersection of conical surfaces associated with each sensor set (e.g., two microphones). That line, more particularly, is defined as having direction angles &agr;, &bgr; and &ggr; from the centerpoint of the sensor sets (e.g., the center of the cross configuration).
According to further aspects of the invention, the location-approximating element includes functionality for generating the location signal as a function of closest intersections the plural ones of the aforementioned lines. This functionality can identify points of closest intersection, s
jk
and s
jk
, of two such lines, l
j
and l
k
, as a function of a vector of cosines of direction angles &agr;
j
, &bgr;
j
and &ggr;
j
of the line l
j
from the centerpoint of the corresponding pair of sensor sets rotated relative to a global coordinate system, a vector of cosines of direction angles &agr;
k
, &bgr;
k
and &ggr;
k
of the line l
k
from the centerpoint of the corresponding pair of sensor sets rotated relative to a global coordinate system, locations of the centerpoints of the pairs of sensor sets, a range of a point on the line l
j
from the corresponding pair of sensor sets, and a range of a point on the line l
k
from the corresponding pair of sensor sets.
In still further aspects of the invention, the location signal is generated as a weighted function of closest intersections the plural ones of the aforementioned lines. Thus, that signal can be generated as a function of a point ŝ defined as a function of a number of pairs of sensor sets, a location of the first sensor in the first sensor set of the lth sensor set pair, a location of the second sensor in the first sensor set of the lth sensor set pair, a location of the first sensor in the second sensor set of the lth sensor set pair, a location of the second sensor in the second sensor set of the lth sensor set pair, a measured time difference of arrival of the source signal at the sensors of a first sensor set of the lth pair of sensor sets, a measured time difference of arrival of the source signal at the sensors of a second sensor set of the lth pair of sensor sets, a variance of a measured time difference of arrival of the source signal at the sensors of a first sensor set of the lth pair of sensor sets, and a variance of a measured time difference of arrival of the source signal at the sensors of a second sensor set of the lth pair of sensor sets.
In still other aspects, the invention provides an apparatus for steering a camera for use in a video teleconferencing system. The apparatus can be configured and operated in accord with that described above, wherein the aforementioned sensors are microphones and wherein the apparatus includes further functionality for steering the camera as a function of said location signal.
Other aspects of the invention provide methods for
Adcock John E.
Brandstein Michael S.
Silverman Harvey F.
Brown University Research Foundation
Lahive & Cockfield LLP
Lauro, Esq. Peter C.
Nguyen Duc
Rikkers, Esq. David J.
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