Hearing Device Feedback Cancellation via Periodic Gain Modulation
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Solution Overview
Problem
Acoustic feedback in audio systems, particularly in hearing devices, leads to audible artifacts and howling due to the loop between the microphone and loudspeaker, which existing adaptive feedback cancellation methods struggle to effectively manage, especially in dynamic environments.
Innovation Solution
A hearing device with a feedback reduction unit that modulates the forward gain over time, applying a higher gain in one period and a lower gain in another, with these periods determined by the loop delay to break the feedback loop and prevent howling, while conserving signal energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If adaptive feedback cancellation methods are used to reduce acoustic feedback, then feedback artifacts and howling are reduced, but the system becomes unstable in dynamic environments and sound quality degrades
Solution Approach 1:
The patent applies periodic gain modulation to the forward path signal with a period matching the feedback loop delay. By periodically varying the gain in sync with the feedback loop, the system creates destructive interference for the feedback path while maintaining forward signal integrity, thereby reducing acoustic feedback without compromising system stability
Solution Approach 2:
The patent introduces dynamic gain modulation that adapts to the feedback loop characteristics. The gain is dynamically adjusted in the forward path based on the estimated feedback loop delay, allowing the system to respond to changing acoustic environments while maintaining stability through continuous adaptation
2Object-affected harmful factors
If adaptive feedback cancellation methods are used to reduce acoustic feedback, then feedback artifacts and howling are reduced, but sound quality is degraded
Solution Approach 1:
The periodic gain modulation is synchronized with the feedback loop delay, creating nulls in the feedback path at specific intervals while leaving the forward audio signal intact. This temporal selectivity allows feedback reduction without degrading the quality of the desired audio signal
Solution Approach 2:
The patent applies gain modulation locally in the frequency-time domain, targeting specific frequency bands and time intervals where feedback occurs. By applying feedback reduction only where needed rather than uniformly across all frequencies and time, the system preserves sound quality in regions unaffected by feedback
3Object-affected harmful factors
If feedback cancellation systems are implemented in hearing devices, then acoustic feedback is reduced, but the device complexity increases
Solution Approach 1:
The patent changes the gain parameter in the forward path as a function of time, specifically modulating it periodically according to the feedback loop delay. This parameter modulation approach simplifies the system architecture compared to traditional feedback cancellation methods by avoiding complex adaptive filters and feedback path estimation mechanisms
Data Source
Figure 1A~1C
Figure 1D
Figure 2A~2B
AI summary
A hearing device is provided, e.g. a hearing aid, comprising an input transducer for converting an input sound to an electric input signal representing sound, an output transducer for converting a processed electric output signal to an output sound or mechanical vibration, and a signal processing unit operationally coupled to the input and output transducers and configured to apply a requested forward gain to the electric input signal or a signal originating therefrom, the input transducer, the signal processing unit and the output transducer forming part of a forward path of the hearing device, the forward path applying a resulting forward gain to the electric input signal and providing a resulting signal, the hearing device further comprising a feedback reduction unit for reducing a risk of howl due to acoustic or mechanical feedback of an external feedback path from the output transducer to the input transducer, the forward path and the external feedback path defining a loop path exhibiting a roundtrip loop delay. The application further relates to a method of operating a hearing device and to the use of a hearing device. The object of the present application is to provide an alternative scheme for reducing or eliminating external feedback in a hearing device. The problem is solved in that the feedback reduction unit is configured to modulate said requested forward gain in time, to provide that the resulting forward gain exhibits a first, increased gain AH in a first time period TH and a second, reduced gain AL in a second time period TL, wherein at least one of the first gain AH, the second gain AL, the first time period TH, and the second time period TL is/are determined according to a predetermined or adaptively determined criterion. Thereby a reduction or elimination of external feedback can be provided. The invention may e.g. be used in hearing aids, headsets, ear phones, active ear protection systems, handsfree telephone systems, mobile telephones, teleconferencing systems, public address systems, karaoke systems, classroom amplification systems, etc.