High-frequency whistling (feedback) is a problem often associated with hearing aids and their use.
Feedback occurs because the amplified sound from the hearing aid is picked up at the hearing aid microphone and allowed to pass through the hearing aid again. If the amplification is large enough, the signal passing through the feedback loop will become louder and louder, eventually resulting in the high-frequent whistling sound.
Fortunately, the feedback cancelling systems of modern top range hearing aids are very effective in minimising the problem of feedback.
The feedback cancelling system in our newst hearing aid series consists of two main parts.
One is the Feedback Path Simulator, which continuously monitors the part of the signal played back by the receiver that returns to the hearing aid microphones.
The purpose of the Feedback Path Simulator is to remove this part of the input signal before it is re-amplified. This means more gain can be provided by the hearing aid without the occurrence of feedback than would be possible if no feedback cancelling system was available.
The second main part of the feedback cancelling system is the Dynamic Cancellation Optimiser, which analyses the incoming signal. If the signal is found to be audible feedback whistling, gain will be reduced at the affected frequency to provide a stable sound without feedback whistling.
Even though the Feedback Path Simulator has been designed to prevent re-amplification of the hearing aid signals in order to avoid whistling, it may not always be fast enough. In these situations, the Dynamic Cancellation Optimiser takes over.
Relying on an ongoing analysis of the incoming sound, the Dynamic Cancellation Optimiser is able to determine whether it is a feedback sound that should be removed or a desirable sound for the client to hear.
If it is feedback, the Dynamic Cancellation Optimiser will adjust gain in the affected frequency area to stop the whistling.
Experience has shown that the Multi-directional active feedback cancelling system in Widex hearing aids is extremely efficient in controlling dynamic feedback problems.
When an external, auto-correlated sound (i.e., a sound with a repeating pattern) like a whistle or an alarm is picked up by the hearing aid, the InterEar coordination between the hearing aids means that Dynamic Cancellation Optimiser is able to compare detected sound from both sides of the head.
If the feedback-like signal is the same on both sides, it can be deducted that it is an external sound rather than a feedback signal. Thus, with InterEar feedback cancelling, we are able to avoid unnecessary gain regulation resulting from “false positives”.
