New feedback‐cancellation algorithm reported to increase usable gain

A hearing aid amplifies all sounds picked up by its microphone. Some of these sounds may be the output of the hearing aid traveling back into the microphone through an acoustic feedback path. The schematic in Figure 1 illustrates the relationship between the feedback path and the direct path inside the hearing aid. The feedback path may consist of a vent, or gaps between a loosely fitted earmold and the ear canal. Once it is picked up by the microphone, the feedback will be amplified by the hearing aid again. The direct path from the microphone to the receiver inside the hearing aid and the feedback path outside the aid form a loop. If at any frequency the total gain exceeds the total attenuation in this loop, the system will become unstable and will oscillate. When that happens, the hearing aid has a feedback problem. The oscillation is heard as an annoying whistle, distorting the original signal. To avoid feedback problems, the gain of the hearing aid must be held below a certain limit. However, doing this can create a new problem, since very often patients would benefit from gains above that limit. That extra gain may translate into improved audibility and speech understanding. Thus, feedback problems compromise the effectiveness of hearing aids, particularly for patients with severe losses. Therefore, to realize the full potential benefit of hearing aids, effective management of feedback problems is essential.