专利名称：Method and apparatus for improving
effective signal to noise ratios in hearing aidsand other communication systems used innoisy environments without loss of spectralinformation
发明人：David Franklin,Michael Steele申请号：US08/687014申请日：19960716公开号：US05794187A公开日：19980811
摘要：Improved signal to noise ratio to help speech comprehension in a noisyenvironment is accomplished by selectively downwardly expanding a speech and noisecomposite signal when the speech signal is absent, thereby lowering signal componentswhich represent noise. An expansion control signal is extracted from the composite inputsignal. Operation is based on the assumption that when noise alone is present, the inputsignal amplitude is less than some reference level and that when speech and noise arepresent together, the input signal amplitude is greater than the reference level. Theresponse rates of gain changes are quite rapid, and do not introduce distortion or otheraudibly noticeable artifacts of the processing. The amount of downward expansion of thenoise alone is small compared to noise gates to further reduce processing artifacts. Themethods of realization include use of, in combination and alone, analog compressors andexpanders, analog expanders in combination with voltage clamps and/or automatic levelcontrol circuits, two-quadrant multipliers in conjunction with digital control, entirely
digital means for obtaining the requisite sensing and gain control, and expandor designsthat are analogs of conventional filter designs where the notion of amplitude replacesfrequency. Automatic noise suppression may be employed to pre- process the inputsignal, thereby rendering the control circuit self adjusting for better performance over awide range of background sound levels. Various microphone, preferably providingdirectional characteristics, may be used to reduce noise levels in the received input signal.
申请人：AUDIOLOGICAL ENGINEERING CORPORATION
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