Preferred delay and phase-frequency response of open-canal hearing aids with music at low insertion gain.

OBJECTIVE: Preferences between low delays and phase-frequency responses of behind-the-ear, open-canal hearing aids were investigated with acoustic conditions deemed sensitive to delay effects by normal-hearing listeners. DESIGN: Hearing aids with the following selectable delay and phase response options were fitted at low insertion gain: (1) 1.4 ms delay, minimum phase; (2) 3.4 ms delay, minimum phase; and (3) 3.4 ms delay, linear phase. Blind paired comparisons were made between processing options and between each option and a muted hearing-aid output with two music stimuli. The three alternative forced choice responses were "Slightly prefer", "Prefer", or "Strongly prefer". STUDY SAMPLE: Twelve hearing-impaired musicians. RESULTS: At the 3.4-ms delay, the minimum-phase response was significantly preferred to the linear-phase response for one music sample and vice-versa for the other sample with a sign test (p < 0.04) but not a Wilcoxon signed rank test that accounted for the low preference strength. Preferences between all other processing conditions were not significant. CONCLUSIONS: In acoustic conditions sensitive to delay effects, delays of 1.4 or 3.4 ms were either not detected or no less preferable than no delayed aided signal. It is unclear whether different phase-frequency responses may be preferred with different music stimuli.

Improving speech intelligibility in background noise with an adaptive directional microphone.

Omnidirectional, supercardioid, and adaptive directional microphones (ADM) were evaluated in combination with the ADRO amplification scheme for eight participants with moderate sloping hearing losses. The ADM produced better speech perception scores than the other two microphones in all noise conditions. Participants performed the Hearing in Noise Test sentences at -4.5 dB SNR or better, which is similar to the level achievable with normal hearing. The Speech, Spatial and Qualities of Hearing Scale indicated no disadvantages of using the ADM relative to the omnidirectional microphone in real-life situations. The ADM was preferred over the omnidirectional microphone in 54% of situations, compared to 17% preferences for the omnidirectional microphone, and 29% no preference. The combination of the ADM to improve SNR, and ADRO to keep the signal output comfortable and audible provided near-normal hearing performance for people with moderate hearing loss. The ADM is the recommended microphone configuration for ADRO hearing aids.