Data processing: measuring – calibrating – or testing – Measurement system – Measured signal processing
Reexamination Certificate
1997-10-17
2001-11-13
Isen, Forester W. (Department: 2644)
Data processing: measuring, calibrating, or testing
Measurement system
Measured signal processing
C702S191000, C381S094300
Reexamination Certificate
active
06317703
ABSTRACT:
DESCRIPTION
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to acoustic signal processing and, more particularly to a method and apparatus for reconstructing an acoustic signal that substantially matches one of a plurality of sources while eliminating other interfering sources.
2. Background Description
In a typical scenario, two or more acoustic sources, at different locations, are simultaneously active. The composite sound pressure level is measured at a number of locations that is typically less than the number of acoustic sources. The problem is to reconstruct an acoustic signal that substantially matches any selected one of the sources, while substantially eliminating the other interfering sources. This is often referred to as the “cocktail-party” processing problem. A solution to this problem has applications to enhanced speech recognition, hearing aids, and improved detection of speech or other sound sources in acoustically cluttered environments.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a signal processing method which is reconstructs an acoustic signal that substantially matches a selected one of a plurality of sources.
It is another object of the invention to provide a signal processing apparatus which measures a composite sound pressure level at a number of locations less than a number of acoustic sources and reconstructs an acoustic signal that substantially matches a selected one of a plurality of sources.
According to the invention, two or more microphones are positioned at different locations to detect the variations in sound pressure level resulting from the activity of a plurality of acoustic source at different locations. The outputs of the microphones are sampled and digitized, and the resulting digital waveform from each microphone is provided as an input to a corresponding filter bank. The outputs of the filter banks are input to a comparison unit. A comparison control unit generates “signature” information that characterizes each source with respect to the microphones. The comparison unit receives “signature” information of a selected source from the comparison control unit and provides an output to a synthesizer unit which produces a synthesized digital waveform for the selected source. Optionally, the synthesized digital waveform is input to a digital-to-analog (D/A) converter to generate an analog signal of the reconstructed source.
In operation, the digital waveforms are provided as input to the filter banks. The filter banks are chosen so as to produce “sparse representations” as output. The filters which comprise the filter banks are preferably digital filters, and the output values of each digital filter at each of a plurality of discrete times is a complex-valued number, called the “filter output value”. For each of the digital waveforms, the set of these filter output values (over a plurality of times, and for the entire set of filters) is referred to as a “filter output pattern”. Any particular filter output value of a filter output pattern is identified by a “label” that uniquely describes both (a) the index of the filter that generated that filter output value and (b) the time at which it was generated. The comparison control unit generates control information including a set of comparison parameters and information specifying which labels from each filter bank are to be used in a comparison of filter output values. The filter output values Of the specified labels from the several filter banks are compared by the comparison unit. The comparison consists of computing a function of (a) these quantities and (b) the comparison parameters. The result of the comparison is a decision that the filter output values are a “match” or a “non-match”. If the result is a “match”, the filter output values are used to compute a complex-valued number called the “filter target value”. If the result is a “non-match”, the filter target values are defined to be zero.
In this way, there is generated a set of filter target values. These filter target values, taken as a whole, form a “filter target pattern”. The next and last step is to use these filter target values to produce a “synthesized digital waveform”. The synthesizer unit takes these filter target values as input, and produces as output a synthesized digital waveform that has the property that if the synthesized digital waveform were provided as input to the set of digital filters, then the resulting output pattern would be similar to the filter target pattern. The synthesized digital waveform is the output of the invention. Optionally, the synthesized digital waveform is provided as input to a digital-to-analog (D/A) converter to produce an analog synthesized acoustic signal.
REFERENCES:
patent: 5315532 (1994-05-01), Comon
patent: 5539832 (1996-07-01), Weinstein et al.
patent: 5825671 (1998-10-01), Deville
patent: 5848163 (1998-12-01), Gopalakrishnan et al.
patent: 6002776 (1999-12-01), Bhadkamkar et al.
International Business Machines - Corporation
Isen Forester W.
McGuireWoods LLP
Morris, Esq. Daniel P.
Pendleton Brian Tyrone
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