Evaluation of an Adaptive Directional System in a DSP Hearing Aid

Abstract

The effectiveness of an adaptive directional microphone design, as implemented in the Phonak Claro behind-the-ear hearing aid, is evaluated. Participants were fit bilaterally and tested in 2 environments, an anechoic chamber and a moderately reverberant classroom, with the microphones in the fixed (cardioid) setting and the adaptive setting. Five speakers were placed between 110 degrees and 250 degrees azimuth around the listener. Speech-weighted noise was presented from those speakers at an overall level (OAL) of 65 dB (A). Noise was increased by 8 dB from 1 speaker at a time, using 2-s modulation and random assignment, while the output from the other speakers was reduced to maintain the constant OAL. Results of 2 speech perception tasks used as outcome measures indicated that the adaptive system was not able to follow the dominant noise source in the presence of lower level noise sources. Self-report measures obtained after blinded home trials were consistent with laboratory findings that the participants did not perceive this adaptive microphone design to be more effective than the default fixed-microphone option.

Noise reduction technologies implemented in head-worn preprocessors for improving cochlear implant performance in reverberant noise fields

“…These data are generally consistent with previous studies that the effectiveness of adaptive directional microphone decreases with the number of noise sources (Ricketts and Henry, 2002;Bentler et al, 2004;Chung, 2004). The exception was that the multichannel adaptive directional microphone algorithm tested in the current study provided comparable amounts of SNR improvement in environments with one or three noise sources.…”

“…Adaptive directional microphones are reported to be more effective than fixed-pattern directional microphones in laboratory environments with a limited number of noise sources or with dominant sources coming from focused spatial locations (Ricketts and Henry, 2002;Bentler et al, 2004;Valente and Mispagel, 2004;Spriet et al, 2007;Chung and Zeng, 2009). Advantages of adaptive-over fixed-pattern directional microphones usually diminish or disappear as the number of the noise sources increases or as the sound field becomes more diffuse (Ricketts and Henry, 2002;Bentler et al, 2004;Valente and Mispagel, 2004;Spriet et al, 2007;Chung and Zeng, 2009). In general, the higher the microphone order (i.e., more microphones/ports) and the less the number of noise sources, the higher the directional effects (Spriet et al, 2007;Chung and Zeng, 2009;Kokkinakis and Loizou, 2010).…”

Effects of in-the-ear microphone directionality on sound direction identification

“…These microphones, by design, can reduce the level of sounds coming from the sides and back. In situations where the desired signal is in front and noise sources are located at the sides or back, directional microphones can enhance speech recognition performance and improve perceived sound quality for hearing aid and cochlear implant users ͑Hawkins and Yacullo, 1984; Killion et al, 1998;Ricketts and Dhar, 1999;Kuhnel et al, 2001;Ricketts and Henry, 2002;Bentler et al, 2004;Walden et al, 2004;Amlani et al, 2006;Mackenzie and Lutman, 2005;Valente et al, 2006;van Hoesel and Clark, 1995;Wouters et al, 1999;Blamey et al, 2006;Chung et al, 2006;Spriet et al, 2007;van der Beek et al, 2007͒. It is possible that they can produce similar advantages for HPD users.…”

Wind noise in hearing aids with directional and omnidirectional microphones: Polar characteristics of custom-made hearing aids

“…The wind noise problem for hearing instrument users can be exacerbated by the use of directional microphones, which are implemented in many highperformance digital hearing aids and some cochlear implants. Directional microphones have gained popularity in hearing instruments in recent years because they can reduce background noise and increase speech recognition in environments with low reverberation ͑Studebaker et al., 1980;Hawkins and Yacullo, 1984;Valente et al, 1995;Killion et al, 1998;Ricketts and Dhar, 1999;Ricketts, 2000;Valente et al, 2000;Amlani, 2001;Ricketts and Henry, 2002;Bentler et al, 2004;Chung et al, 2006;Spriet et al, 2007͒. First-order directional microphones employ either one microphone with two ports ͑single-cartridge design͒ or two omnidirectional microphones ͑dual-microphone design͒ to sense the pressure difference or gradient between two points in space. They are often referred to as pressure gradient microphones in the engineering literature ͑Carlson and Killon, 1974;Eargle, 2004;Baumhaur and Marcus, 1997͒.…”