An audio signal in a hearing aid is enhanced by detecting the power of the desired audio signal and the power of the total audio signal, generating a power value and making a noise reduction adjustment or no noise-reduction adjustment based on the power value. In one embodiment, the power

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E l e c t r i c a l E n g i n e e r i n g U n i v e r s i t y of Colorado Boulder, Colorado 80309The recent development of high-speed quantizers which digitize t o f e w e r t h a n six b i t s a c c u r a c y s u g g e s t s t h e p o s s i b i l i t y of d i g i t a l a d a p t i v e beamforming a t bandwidths up t o s e v e r a l GHt. This paper d e s c r i b e s t h e s i g n a l p r o c e s s i n g a s p e c t s of i n c o r p o r a t i n g a low-order q u a n t i z e r i n t o a d i g i t a l a d a p t i v e beamformer. The p a r t i c u l a r s t r u ct u r e c o n s i d e r e d is a noise-cancelling system in which an adaptive beam i s s u b t r a c t e d f r o m a c o n v e n t i o n a l a r r a y s i g n a l . Two types of a d a p t i v e a r r a y p r o c e s s o r s a r e d e s c r i b e d .Both employ a n a n a l o g conventional beamformer and an analog prefilter which blocks the d e s i r e d s i g n a l f r o m t h e q u a n t i z e r s a t each of t h e p r e p r o c e s s o r o u t p u t s . T h e s e d i g i t i z e d s i g n a l s are t h e n combined through high-speed d i g i t a l tapped delay lines. The output i s converted back to analog and subtracted from t h e c o n v e n t i o n a l beam. I n t h e s e c o n d t y p e , a n a l o g d e l a y l i n e s w i t h d i g i t a l l y c o n t r o l l e d w e i g h t s a r e employed.This paper summarizes t h e r e s u l t s of a n a l y t i c a l s t u d i e s and computer simulation experiments designed to quantitatively measure performance of t h e two systems, as a f u n c t i o n of t h e number of q u a n t i z e r b i t s . S u r p r i s i n gl y good c a n c e l l a t i o n is d e m o n s t r a t e d i n t h e 2-6 b i t r a n g e .

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