Binaural Hearing Aid Inter-Aural Feedback Cancellation
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Solution Overview
Problem
Traditional feedback cancellation methods in hearing aids often lead to signal distortions and loss of intelligibility due to correlation between output and input signals, causing acoustic feedback instability and oscillation.
Innovation Solution
A binaural hearing aid system with spatially separated instruments that transmit inter-aural signals and use binary gain patterns to process input sounds, ensuring the loop gain is kept below one across all frequencies to prevent feedback oscillation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional feedback cancellation algorithms are used with adaptive filters, then feedback reduction is achieved, but signal distortions and loss of intelligibility occur due to correlation between output and input signals
Solution Approach 1:
The patent introduces an intermediary probe noise signal that is uncorrelated with the input speech signal. This probe noise serves as a mediator to train the adaptive filter without causing the filter to mistakenly cancel speech components. The probe noise allows the filter to learn the feedback path characteristics while preserving the integrity of the actual speech signal.
Solution Approach 2:
The patent applies preliminary action by pre-training the adaptive filter using probe noise before processing actual speech signals. This preliminary training establishes the feedback cancellation capability in advance, allowing the filter to be ready to cancel feedback without distorting subsequent speech signals. The filter coefficients are adapted beforehand using the uncorrelated probe noise.
2Power
If gain in hearing aid is increased above a certain point, then amplification performance is improved, but feedback instability or oscillation occurs
Solution Approach 1:
The patent implements a feedback mechanism where the adaptive filter continuously monitors and cancels the feedback signal. By using the probe noise to train the filter and the residual signal to update coefficients, the system creates a closed-loop feedback cancellation path that actively suppresses feedback oscillations even at high gain settings.
Solution Approach 2:
The patent changes the parameter of the reference signal by introducing probe noise with specific statistical properties (uncorrelated with input speech). This parameter change in the reference signal allows the adaptive filter to distinguish feedback from speech, enabling high gain operation without feedback instability.
3Object-affected harmful factors
If output signal is used as reference signal in feedback cancellation, then feedback reduction is achieved, but components of input signal are removed leading to signal distortions
Solution Approach 1:
The patent replaces the problematic reference signal (output signal correlated with input) with an intermediary probe noise signal that is uncorrelated with the input speech. This intermediary reference signal allows the adaptive filter to learn feedback cancellation without mistakenly identifying speech components as feedback to be cancelled.
Data Source
AI summary
The invention relates to a hearing aid system comprising first and second spatially separated hearing instruments, the system being adapted for processing input sounds to output sounds according to a user's needs. The invention further relates to a method and use. The object of the present invention is to provide an alternative scheme for reducing the effect of acoustic feedback in a hearing aid system. The problem is solved in that the hearing instruments comprises, respectively, first and second input transducers for converting a first input sound to first and second electric input signal, and first and second output transducers for converting first and second processed electric output signal to first and second output sounds, wherein the system is adapted to provide that a first Tx-signal originating from the first electric input signal of the first hearing instrument is transmitted to the second hearing instrument and used in the formation of the second processed electric output signal, and that a second Tx-signal originating from the second electric input signal of the second hearing instrument is transmitted to the first hearing instrument and used in the formation of the first processed electric output signal. This has the advantage of providing a scheme for reducing or effectively eliminating acoustic feedback in a pair of hearing instruments. The invention may e.g. be used in listening devices, e.g. hearing aids, head sets, or active ear plugs.