How does ReSound combat feedback squeal in hearing instruments?
A new algorithm for controlling and cancelling feedback, DFS Ultra, was introduced with the ReSound Alera product line. Like earlier versions of digital feedback suppression in ReSound instruments, a phase-inverted signal relative to the feedback pathway is applied in the output of the hearing aid to cancel out feedback squeal. However, DFS Ultra now uses more advanced modeling techniques of the input and feedback signals to combat feedback in the most difficult situations. DFS Ultra also employs two feedback filters: a static filter that is customized to the specific hearing aid and the person wearing it, and a dynamic filter that responds to feedback-critical situations in everyday hearing aid use, such as receiving a hug. The static system can distinguish between feedback and other feedback-like sounds, such as flute music and phone rings. In situations that have been traditionally troublesome for feedback management, such as an object being brought close to the ear, the dynamic system uses gain reduction for the feedback spike only, to bring the hearing aid gain and output back to non-feedback levels. When the offending object is removed the system immediately ceases any gain reduction and the hearing instrument cancels feedback through phase cancellation only. This means that important everyday sounds can be amplified to desired levels without feedback or gain reduction for the original signal.
Tammara Stender, Au.D., CCC-A is a Senior Audiologist at GN ReSound, where she plans and conducts clinical trials for newly developed hearing aid technology and prepares documentation for released products. Her research interests include hearing aid benefit and satisfaction, the occlusion effect and spatial localization abilities with hearing aids. She received her Master of Science degree from Vanderbilt University, and her Doctor of Audiology degree from the University of Florida.