Electrical audio signal processing systems and devices – Directive circuits for microphones
Reexamination Certificate
1997-11-20
2001-02-20
Isen, Forester W. (Department: 2644)
Electrical audio signal processing systems and devices
Directive circuits for microphones
C381S122000, C367S119000, C367S121000, C367S129000
Reexamination Certificate
active
06192134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the field of microphones, and in particular, to a system and method for a monolithic directional microphone array.
2. Background Art
There are two general types of prior art microphones. The first type is the stand-alone microphone. Stand-alone microphones suffer from a number of disadvantages. First, these microphones cannot differentiate between two or more acoustic signals having different frequencies or originating from different spatial locations. Second, these microphones are unable to adapt to changing sources of sound, and are unable to track a moving source of sound.
The second type of prior art microphones is actually a microphone system which includes signal processing capabilities that can track and adapt to changing sources of sound. Unfortunately, these microphone systems are expensive, bulky and not suited for home use.
Noise cancelling microphones represent one type of prior art system that can track and adapt to changing sources of sound, and are commonly employed, for example, in helicopters. Such a noise cancelling microphone includes one microphone to record the speaker's voice, a second microphone to record the background noise, and a noise reduction circuit that subtracts the background noise from the speaker's voice to improve the signal quality of the speaker's voice. Although the noise cancelling microphone is suitable for noisy environments, these microphones suffer from several disadvantages. First, noise cancelling microphones cannot track a moving sound source, nor can they selectively adapt to a particular spatial angle. Second, they are costly.
Another example of prior art systems that can track and adapt to changing sources of sound are those employed by the military. Military directional acoustic detection systems are adept at tracking a changing sound source. These systems employ digital signal processing (DSP) techniques such as adaptive beam forming and noise reduction (commonly referred to as null steering) to improve signal quality. These systems, such as sonar systems, are commonly employed in submarines and ships. However, these prior art directional systems suffer from the drawbacks that they operate in a water medium and are bulky in nature. For example, the transducers employed in a towed array or mounted on the hull of a ship are large, heavy and unwieldy to maneuver. Moreover, the signal processing units are complex and often occupy several rooms of space.
Yet another example of prior art systems that can track and adapt to changing sources of sound are the ADAP 256 and ADAP 1024 systems that were sold by the assignee of the present application. These systems were used by law enforcement agencies, and are capable of performing functions such as frequency discrimination, separating the speakers' voices (i.e., sounds) based on correlation times, and removing background sounds. However, these systems are bulky (about 19 inches wide by 24 inches deep by 5 inches high) and expensive.
Accordingly, the size, complexity, and cost of the transducers and signal processing units required by the prior art systems that are capable of tracking and adapting to changing sources of sound hinder the use of these systems in consumer household electronics.
Accordingly, there remains a need for a system and method for a monolithic directional microphone array that can track and/or locate a changing source of acoustic waves or noise, that can separate components of a sound field, selectively enhance each component and selectively recombine them, and that is compact, portable, and cost effective.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a system and method for a monolithic directional microphone array is provided. The present invention can track and/or locate a moving and changing source of acoustic signals or noise.
According to another aspect of the invention, a directional microphone that adapts to a sound signal based upon spatial and/or frequency requirements is provided.
According to another aspect of the invention, a directional microphone that minimizes noise is provided. The directional microphone of the present invention can selectively block signals having certain frequencies and/or signals radiating from a certain spatial direction.
According to another aspect of the invention, unlike the prior art adaptive processing systems that have many bulky hardware components (e.g., transducers and processors), the present invention provides a directional adaptive microphone that is embodied in two or more monolithic chips. At least one monolithic detection unit includes at least one integrated transducer for detecting the sound signals, and a processor for executing local digital signal processing (DSP) programs to generate a signal representing the sound information of the sound signals. A monolithic base unit includes a processor for executing global digital signal processing (DSP) programs based on the sound information received from the detection unit(s) to generate globally processed sound information.
According to another aspect of the invention, a directional microphone is provided with a monolithic detection unit that integrates a transducer with signal processing elements so that adaptive processing, directional steering, and frequency steering can all be performed on the chip.
According to another aspect of the invention, a directional microphone that can separate components of a sound field, selectively enhance each component, and selectively recombine them is provided.
According to another aspect of the invention, a directional microphone that is light, compact, and useful in consumer household applications is provided.
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Cao, Y., et al.; “Speech Enhancement Using Microphone Array with Multi-Stage Processing”; IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences; Mar. 1, 1996; vol. E79-A; No. 3; pp. 386-394, 392.
Affes, S., et al.; “Robust Adaptive Beamforming Via LMS-Like Target Tracking”; Proceedings on the International Conference on Acoustics, Speech and Signal Processing (ICASSP), S. Statistical Signal and Array Processing Adelaid; Apr. 19, 1994; vol. 4; No. CONF. 19; pp. 269-272.
Andrews, Jr. Warner B.
Hale Kelly H.
Henderson P. Michael
Johnston James W.
Siann Jonathan I.
Conexant Systems Inc.
Isen Forester W.
Pendleton Brian Tyrone
Snell & Wilmer LLP
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