Phase Modulation for Digital Filter Entrainment Containment
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Solution Overview
Problem
Digital filter systems face entrainment issues, leading to degraded feedback signal estimation, attenuation of input stimuli, increased system instability, and potential sustained oscillations, especially when stimulated with sinusoidal or periodic signals, which affects 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 avoid entrainment, thereby stabilizing the system and improving feedback cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an adaptive digital filter is used for feedback cancellation, then feedback signal estimation is improved, but entrainment occurs when stimulated with sinusoidal signals causing degraded response and system instability
Solution Approach 1:
The patent applies periodic phase modulation to the filter output signal, cycling through different phase shifts (e.g., 0°, 90°, 180°, 270°) at a predetermined rate. This periodic phase variation prevents the adaptive filter from becoming entrained by sinusoidal input signals, as the changing phase relationship disrupts the correlation between input and output that causes entrainment, while maintaining effective feedback cancellation through the modulated signal.
2Measurement precision
If the digital filter length is increased to improve feedback cancellation, then feedback estimation is enhanced, but entrainment effects are amplified causing worse response
Solution Approach 1:
By implementing periodic phase modulation on the filter output, the patent prevents entrainment of longer filter lengths. The phase modulation ensures that even with more taps in the adaptive filter, the coefficients do not become excessively correlated with sinusoidal inputs, thereby maintaining both the benefits of longer filters (better feedback cancellation) and avoiding their drawbacks (amplified entrainment effects).
3Reliability
If phase modulation is applied to contain entrainment, then system stability is improved, but device complexity increases due to additional processing modules
Solution Approach 1:
The patent introduces a phase modulation module as an intermediary component that processes the filter output signal. This module applies predetermined phase shifts (such as 0°, 90°, 180°, 270°) at regular intervals, serving as a mediator between the adaptive filter and the output stage. The phase modulation effectively contains entrainment and improves system stability while adding a manageable level of complexity through a dedicated processing stage.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively contains entrainment, preventing coefficient drift, enhancing feedback signal estimation, increasing system stability, and allowing for longer filter lengths without introducing perceivable artifacts, thus improving the overall performance of digital filter systems in reducing acoustic feedback.
Implementation Method 1
The present subject matter provides method and apparatus for entrainment containment of digital filter designs... a phase adjustment module processing the error signal E(z) in series to produce an output signal X(z)... wherein the phase adjustment module gradually changes phase applied to the output signal X(z)
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.