Communications – electrical: acoustic wave systems and devices – Distance or direction finding – With time interval measuring means
Reexamination Certificate
1999-11-05
2001-06-05
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
With time interval measuring means
C367S124000
Reexamination Certificate
active
06243322
ABSTRACT:
TECHNICAL FIELD
This invention relates to systems and methods for estimating the distance of the source of an acoustic signal within a reverberant space.
BACKGROUND
In the area of human-machine speech interface, or in hands-free telecommunication such as audio phones, it is usually desired to process only the voice of the speaker(s) that are close to a microphone, and ignore background noise. Some degree of interference rejection can be achieved through the use of a voice detector, such as the ones described in U.S. patent application Ser. No. 09/375,309, entitled “METHOD FOR ENHANCEMENT OF ACOUSTIC SIGNAL IN NOISE” and U.S. patent application Ser. No. 09/385,975, entitled “SYSTEM AND METHOD FOR CLASSIFICATION OF SOUND SOURCES”, both of which are assigned to the assignee of the present invention. However, such voice detectors still let voice interference's, such as remote conversations, television sets, and public announcement systems, be processed.
Most prior art approaches rely on sound volume (loudness) to determine whether a sound source is sufficiently near the microphone to warrant processing it. However, even though the volume of a source is somewhat correlated to its distance to a microphone, a distant loud source can often be perceived as louder than a weaker, albeit closer source.
Another way to determine the range of an acoustic source is to use triangulation through the use of several pairs of microphones. This approach is computationally onerous, and necessitates much significant additional hardware.
The inventor has determined that it would be desirable to be able to estimate the range of a sound source independently of its inherent loudness using only two microphones. The present invention provides a system and method for determining the range of an acoustic signal within a reverberant space that avoids the limitations of prior techniques.
SUMMARY
The invention includes a method, apparatus, and computer program to determine whether a sound source is situated near or far from a pair of microphones situated in a reverberant space. The input signal may represent human speech, but it should be recognized that the invention could be used to localize any type of acoustic data, such as musical instruments and transient noise.
The preferred embodiment of the invention localizes input signals as follows. Sound input signals from a pair of microphones are digitized into binary data. A signal detector is applied to the data; only the data that passes the signal detector is processed any further. The signal at the two microphones is compared to obtain the angular distribution of acoustic power. The concentration of acoustic power in the direct path versus reverberant paths is determined and used to compute a direct-to-reverberant ratio. If this ratio is greater than a threshold, the source is determined to be near the microphones. Otherwise, the source is determined to be far from the microphones, and ignored by the system.
More particularly, in one aspect, the invention includes a method for estimating the distance of an acoustic signal within a reverberant space utilizing two microphones, including: optionally passing the acoustic signal through a signal detector to discriminate against noises that are not of the same class as the acoustic signal; determining the angular distribution of acoustic power from the acoustic signal with respect to the two microphones; estimating the direct-to-reverberant ratio from the angular distribution of acoustic power; optionally passing the direct-to-reverberant ratio through a threshold detector; and outputting an indication as to whether the distance of the acoustic signal to the pair of microphones is near or far based on the output of the threshold detector.
The invention has the following advantages: since the direct-to-reverberant ratio is independent of source volume or loudness, the range estimate will also be independent of volume; and, the invention needs only two microphones to work.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
REFERENCES:
patent: 4312053 (1982-01-01), Lipsky
patent: 5673327 (1997-09-01), Julstrom
patent: 5778082 (1998-07-01), Chu et al.
patent: 6160758 (2000-12-01), Spiesberger
Coudert Brothers
Pihulic Daniel T.
WaveMakers Research, Inc.
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