Delayless Adaptive Filter for Hearing Aid Feedback Cancellation
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Solution Overview
Problem
Traditional frequency domain adaptive filters introduce additional delay in signal paths, which is unacceptable in certain applications, and existing delayless adaptive filters have limitations in convergence and steady-state behavior for feedback and echo cancellation systems with long impulse responses.
Innovation Solution
A new delayless adaptive filter structure that transforms input signals into the frequency domain, applies adaptive algorithms to estimate the feedback path, and inversely transforms the estimate back into the time domain to control filter coefficients, ensuring efficient convergence and steady-state performance without additional delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional frequency domain adaptive filters are used to reduce computational complexity for long impulse responses, then computational complexity is reduced, but additional delay is introduced in the signal path
Solution Approach 1:
The patent segments the frequency domain processing into multiple independent filters operating in parallel at different frequency bands. Each bandpass filter processes a specific frequency range separately, allowing the system to achieve frequency-dependent adaptation while avoiding the delay associated with traditional frame-based frequency domain processing. This segmentation enables real-time processing by eliminating the need to wait for complete signal frames.
Solution Approach 2:
The patent implements dynamic adaptation by continuously updating filter coefficients for each frequency band in real-time based on incoming signal characteristics. The adaptive filters adjust their parameters dynamically without requiring frame-based processing delays, enabling the system to track and cancel feedback paths with long impulse responses while maintaining zero delay in the signal path.
2Loss of time
If existing delayless adaptive filter structures are used to eliminate additional delay, then signal delay is eliminated, but convergence and steady-state behavior are limited for long impulse responses
Solution Approach 1:
The patent transitions from traditional time-domain or single-frequency-domain approaches to a multi-dimensional frequency domain representation by processing multiple frequency bands simultaneously. This dimensional expansion allows the adaptive filter to capture and cancel long impulse response characteristics more effectively while maintaining real-time performance, as each frequency band can be optimized independently for its specific convergence requirements.
Solution Approach 2:
The patent employs parameter changes by adapting filter coefficients dynamically for each frequency band based on local signal characteristics and feedback path properties. This localized parameter adaptation enables better convergence behavior for long impulse responses compared to uniform time-domain approaches, as each frequency band can be tuned to its optimal convergence parameters without being constrained by global processing delays.
3Adaptability or versatility
If frequency domain adaptive filters are used to provide frequency dependent control, then frequency dependent control is achieved, but additional delay is introduced due to frame processing
Solution Approach 1:
The patent segments the frequency spectrum into multiple independent bands, each processed by its own adaptive filter. This segmentation enables frequency-dependent control to be applied to each band separately in real-time, eliminating the need for frame-based processing that introduces delay. The segmented approach allows continuous adaptation across frequencies without waiting for complete signal frames.
Solution Approach 2:
The patent creates a universal processing framework where the same adaptive filtering methodology is applied across multiple frequency bands simultaneously. This multi-functional approach achieves frequency-dependent control for the entire spectrum through parallel processing of segmented bands, providing both the adaptability of frequency-specific control and the real-time performance of delayless operation.
Data Source
AI summary
A hearing device includes a feedback control system that applies an adaptive filtering algorithm. The adaptive algorithm provides a filter control signal to adaptively control filter coefficients based on first and second algorithm input signals of a forward path. The feedback control system further includes first and second transform units for transforming the first and second algorithm input signals to the transform domain, and an inverse transform unit to convert an estimate of the current feedback path in the transformed domain to a time domain estimate, and a combination unit in the forward path to subtract the estimate of the current feedback signal from a signal of the forward path to provide a feedback corrected signal.