Improving Speech Recognition in Noise: Directional Microphone and FM Systems

Recent estimates suggest that over 29 million individuals in the United States exhibit some degree of hearing impairment (National Institutes of Deafness and Communication Disorders (NIDCD). A major consequence of sensorineural hearing loss (SNHL) is communicative difficulty, especially with the addition of noise and/or reverberation (Dubno, Dirks and Morgan 1984; Hawkins and Yacullo 1984; Suter 1985; Helfer and Wilber 1990; Crandell 1991; Helfer and Huntley 1991; Needleman and Crandell 1995; Killion 1997a; Moore 1997). Unfortunately, conventional amplification with omnidirectional microphone technology may provide little or no improvement to the signal-to-noise ratio (SNR) in adverse listening environments (Duquesnoy and Plomp 1983; Plomp 1986; Crandell and Smaldino 2000; 2001). In fact, a lack of perceptual improvement in noisy listening environments is one of the major reasons why individuals with SNHL report dissatisfaction with and reject amplification (Kochkin 1994). At present, there are various technologies that have been shown to improve speech recognition in poor listening environments. These technologies include directional microphones and personal frequency modulation (FM) systems (Hawkins and Yacullo 1984; Hawkins 1984; Fabry 1994; Valente, Fabry and Potts 1995; Gravel, Fausel, Liskow and Chobot 1999; Kuk, Kollofski, Brown, Melum and Rosenthal 1999; Pittman, Lewis, Hoover and Stelmachowicz, 1999; Preves, Sammeth and Wynne 1999; Ricketts and Dhar, 1999; Pumford Seewals, Scollie and Jenstad