Delay time of digital hearing aids

Abstract

Delays, in digital signal processing by hearingaids may be perceived as an echo by wearers: their ears receive an unprocessed sound through the head and airway, while a delayed sound reaches the eardrum through the hearing aid because of the complexity of the digital processing. Recently, we prescribed a digital product (A) for a patient (I), who complained of an echo-like noise, presumably resulting from this kind of delay. To study the etiology of the noise, we retrospectively examined 98 ears of 77 patients (35 men and 42 women) who tried or bought Product A between 2002 and 2003 (age range, 24-89 years; mean age 67.9 years) (hearing acuity range, 25-92.5dB; mean, 52.6dB), We found that 8 ears in 6 patients, including Patient I, were improperly fitted. We analyzed the reasons for the improper fitting and compared the audiograms of fitted and unfitted patients. Among the 6 patients, Patient I and two others were delay-sensitive-their hearing was better, especially for lower frequencies. Further, we measured the delay levels (0.2-10.2ms) of Product A and 4 other products and observed that Product A had the longest delay. The productoriented delay time should be considered during the fitting of digital hearing aids in such patients.