Output Phase Modulation for Digital Filter Entrainment Containment
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Solution Overview
Problem
Digital filter systems face entrainment issues, leading to degraded feedback cancellation, attenuation of input signals, increased instability, and sustained oscillations, particularly when stimulated with sinusoidal or periodic signals, which affect their performance in applications like hearing aids.
Innovation Solution
The implementation of a phase adjustment module that gradually changes the phase of the output signal between zero and 180 degrees, or up to 360 degrees, using all-pass filters or complex multipliers, to reduce or prevent entrainment, thereby stabilizing the system and improving feedback cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an adaptive digital filter is stimulated with a sinusoidal signal, then the filter correlates the output with the feedback signal and stimulus signal, but this causes degraded response to the feedback signal and decreased feedback cancellation
Solution Approach 1:
The patent extracts the harmful sinusoidal component from the input signal using a notch filter before it can entrain the adaptive filter. By removing this specific frequency component that causes entrainment, the adaptive filter can accurately estimate feedback signals without being distracted by the periodic stimulus, thus resolving the contradiction between measurement precision and reliability
Solution Approach 2:
The patent introduces a phase modulator as an intermediary component between the adaptive filter and the output. This phase modulator applies a time-varying phase shift to the filter output, which prevents the adaptive filter from becoming entrained by sinusoidal inputs while maintaining accurate feedback signal estimation and cancellation performance
2Productivity
If the adaptive filter processes periodic input signals with high autocorrelation, then the system responds to these signals, but this causes attenuation of the input stimulus signal
Solution Approach 1:
The phase modulator acts as an intermediary that prevents the adaptive filter from attenuating the input stimulus signal. By applying a time-varying phase shift to the filter output rather than allowing direct feedback cancellation, the system maintains signal transmission while still processing periodic inputs effectively
3Productivity
If the adaptive filter is stimulated by periodic input signals, then the filter processes these signals, but this increases system instability and can cause sustained oscillation
Solution Approach 1:
The notch filter extracts and removes the periodic input signal component before it can cause instability in the adaptive filter. By eliminating these high-autocorrelation signals that lead to sustained oscillations, the system maintains stability while preserving the ability to process general audio signals
Solution Approach 2:
The phase modulator introduces a stabilizing intermediary effect by applying time-varying phase shifts to the filter output. This prevents the feedback loop from becoming unstable when processing periodic signals, eliminating sustained oscillations while maintaining normal signal processing functionality
4Measurement precision
If a longer digital filter is used to improve feedback cancellation, then the filter provides better response, but under entrainment the smaller coefficients at the tail are more sensitive to mistuning
Solution Approach 1:
The notch filter removes the entraining sinusoidal signals before they can affect the adaptive filter coefficients. This protection allows longer filters to be used with improved feedback cancellation accuracy without the risk of coefficient mistuning, as the harmful periodic inputs that cause sensitivity issues are extracted beforehand
Solution Approach 2:
The phase modulator serves as an intermediary that protects the adaptive filter coefficients from entrainment effects. By applying time-varying phase shifts to the output, it prevents periodic signals from causing coefficient mistuning, enabling the use of longer filters with stable coefficients and improved cancellation performance
Data Source
AI summary
Method and apparatus for entrainment containment in digital filters using output phase modulation. Phase change is gradually introduced into the acoustic feedback canceller loop to avoid entrainment of the feedback canceller filter. Various embodiments employing different output phase modulation approaches are set forth and time and frequency domain examples are provided. Additional method and apparatus can be found in the specification and as provided by the attached claims and their equivalents.