Acoustic source location using a microphone array

• US 6,469,732 B1
• Filed: 11/06/1998
• Issued: 10/22/2002
• Est. Priority Date: 11/06/1998
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Vtel Corporation
• Inventors: Ning, Aidong, Haas, Wayne J., Chang, Pi Sheng, Lambert, Michael G.
• Primary Examiner(s): Ramakrishnaiah, Melur
• Application Number:
  US09/187,081
• Time in Patent Office: 1,446 Days
• Field of Search: H04/N.714, 381/92, 348/14, 348/15, 348/14.01, 348/14.02, 348/14.03, 348/14.04, 348/14.06, 348/14.07, 348/14.08, 348/14.09, 348/14.1
• US Class Current: 348/14.08
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10
• CPC Class Codes: H04N 7/15 Conference systems
• CPC Class Codes: H04R 1/406 microphones
• CPC Class Codes: H04R 2201/401 2D or 3D arrays of transducers
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407

Abstract

An apparatus and method in a video conference system provides accurate determination of the position of a speaking participant by measuring the difference in arrival times of a sound originating from the speaking participant, using as few as four microphones in a 3-dimensional configuration. In one embodiment, a set of simultaneous equations relating the position of the sound source and each microphone and relating to the distance of each microphone to each other are solved off-line and programmed into a host computer. In one embodiment, the set of simultaneous equations provide multiple solutions and the median of such solutions is picked as the final position. In another embodiment, an average of the multiple solutions are provided as the final position.

Claims

1. A method for locating a speaking participant in a video conference, comprising:

receiving sound from said speaking participant at each of a plurality of microphones positioned in a predetermined 3-dimensional configuration;

from said received sound, computing three or more time delays using a cross-correlation function computed in a frequency domain, each time delay being representative of the difference in arrival times of said sound at a selected pair of said microphones;

based on the positions of said microphones and said time delays, determining one or more possible positions of said speaking participant; and

deriving from said possible positions of said speaking participant a final position, said deriving said final position comprising;

(a) computing for each of said possible positions a radial distance from a reference position;

(b) obtaining from said possible positions a group of positions by discarding positions corresponding to the p₁ furthest and the p₂ closest radial distances from said reference position; and

(c) computing a weighted average position from said group of positions.

2. A video conference system, comprising:

a plurality of microphones and a camera positioned in a predetermined configuration, each microphone providing an audio signal representative of sound received at said microphone;

a time delay module receiving said audio signals of said microphones and based on said audio signals, providing for each pair of said microphones a time delay estimate associated with said pair of microphones using a cross correlation function in a frequency domain;

a position determination module, based on said time delay estimates and said predetermined configuration, providing a plurality of possible positions of a sound source, and selecting from said possible positions a final position of said sound source, said position computation module (1) computing, for each of said possible positions, a radial distance from a reference position;

(2) obtaining from said possible positions a group of positions by discarding positions corresponding to the p₁ farthest and the P₂ closest radial distances from said reference position; and

(3) computing a weighted average position from said group of positions; and

a camera control module directing said camera towards said sound source using said final position of said sound source.

3. A video conference system, comprising:

a plurality of microphones and a camera positioned in a predetermined configuration, each microphone providing an audio signal representative of sound received at said microphone;

a time delay module receiving said audio signals of said microphones and based on said audio signals, providing for each pair of said microphones a time delay estimate associated with said pair of microphones using a cross correlation function in a frequency domain;

a position determination module, based on said time delay estimates and said predetermined configuration, providing a plurality of possible positions of a sound source, and selecting from said possible positions a final position of said sound source, said position determination module (a) solving a set of simultaneous equations relating the location of said sound source to the positions of said microphones, and relating positions of said microphones to each other; and

(b) applying said computed time delays to said solutions; and

a camera control module directing said camera towards said sound source using said final position of said sound source, wherein when said final position corresponds to a position outside a predetermined boundary, said camera control module directs said camera to an adjusted position within said boundary.

4. A system as in claim 3, wherein said predetermined boundary is determined based on the minimum and maximum heights expected of a conference participant.

5. A video conference system, comprising:

a plurality of microphones and a camera positioned in a predetermined configuration, each microphone providing an audio signal representative of sound received at said microphone;

a time delay module receiving said audio signals of said microphones and based on said audio signals, providing for each pair of said microphones a time delay estimate associated with said pair of microphones using a cross correlation function in a frequency domain;

a position determination module, based on said time delay estimates and said predetermined configuration, providing a plurality of possible positions of a sound source, and selecting from said possible positions a final position of said sound source, said position determination module (a) solving a set of simultaneous equations relating the location of said sound source to the positions of said microphones, and relating positions of said microphones to each other; and

(b) applying said computed time delays to said solutions; and

a camera control module directing said camera towards said sound source using said final position of said sound source, wherein said camera control module divides the view from said camera into 3-dimensional zones, each zone being specified by a radial distance from said camera and angular positions from said camera in two orthogonal directions.

6. A system as in claim 5, wherein said camera control module, upon receiving said final position from said position determination module, compares said final position with a current position of said camera, and wherein when said final position is separated from said current position by less than a predetermined number of zones, said camera control module does not direct said camera to said final position.

7. A system as in claim 6, wherein when said final position and said current position both correspond to the same speaker, said predetermined number of zones is two zones.

8. A system as in claim 6, wherein when said final position and said current position correspond to positions of different speakers, said predetermined number of zones is one zone.