Adaptive Audio Feedback Filtering for Higher PA Loop Gain

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Solution Overview

Problem

Conventional audio feedback elimination systems in public address (PA) systems often rely on simple volume reduction or complex tuning, which are inefficient and require significant setup, failing to effectively remove the entire feedback spectrum and leading to poor convergent properties and perceptual artifacts.

Innovation Solution

The Howling-Killer system employs a dual-subband data structure with adaptive filters and a crossover frequency, using two filter taps and normalized non-linear echo suppression to holistically model and systematically remove the feedback signal, allowing operation at higher loudspeaker volumes with reduced feedback and easy setup.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If conventional feedback elimination systems use simple volume reduction, then feedback is reduced, but the system cannot operate at higher loudspeaker volumes and requires complex tuning for sophisticated systems

Engineering Contradiction:

Improvefeedback elimination effectivenessVSAvoidsystem setup complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The system performs self-adjustment through automatic feedback path identification and adaptive filter coefficient updating. The adaptive filters continuously monitor the acoustic environment and automatically adjust their parameters to eliminate feedback, eliminating the need for manual tuning while maintaining effectiveness at higher volumes

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The system dynamically changes filter parameters (coefficients) based on real-time acoustic conditions. By continuously adapting the filter characteristics to match the actual feedback path, the system maintains effective feedback elimination without requiring complex manual setup or tuning

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If adaptive filters are used to model feedback paths, then feedback elimination effectiveness improves, but computational complexity and processing delay increase

Engineering Contradiction:

Improvefeedback spectrum removalVSAvoidprocessing delay

Core Design Contradiction:

Object-affected harmful factorsVSLoss of time

Solution Approach 1:

The feedback elimination is divided into frequency subbands, with each subband processed independently by dedicated adaptive filters. This segmentation allows parallel processing of multiple frequency regions, reducing overall processing delay while maintaining comprehensive feedback spectrum removal across all frequencies

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system applies adaptive filtering selectively to frequency regions where feedback is actually present, rather than uniformly processing the entire spectrum. This partial action approach reduces unnecessary computational overhead and processing delay while maintaining effective feedback elimination where needed

Inventive Principle:

Principle #16Partial or excessive action

3Object-affected harmful factors

If multiple adaptive filters are used to remove the entire feedback spectrum, then feedback elimination completeness improves, but device complexity increases

Engineering Contradiction:

Improvefeedback spectrum coverageVSAvoidfilter structure complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The frequency spectrum is divided into multiple subbands, each handled by a dedicated adaptive filter. This segmentation enables comprehensive feedback spectrum coverage through parallel simple filter structures, avoiding the complexity of a single complex full-spectrum filter while maintaining complete feedback elimination

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each adaptive filter in the subband structure serves multiple functions: frequency-specific feedback elimination, adaptive parameter adjustment, and automatic gain control. This multi-functionality reduces the need for separate dedicated components, thereby reducing overall device complexity while maintaining comprehensive feedback spectrum removal

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS10117021B1Audio feedback reduction utilizing adaptive filters and nonlinear processing

Publication Date: 2018.10.30 HEWLETT PACKARD DEVELOPMENT COMPANY LP

AI summary

Systems and methods for holistically modelling audio feedback and removing the entire feedback signal corresponding thereto. The systems can operate at a much larger loop-gain (and hence with a much higher loudspeaker volume), than those conventional systems which seek to remove singing frequencies with PEQs. The systems are an improvement over traditional audio feedback elimination systems which attempt to reduce the effect of the audio feedback by simply scaling down the audio volume of the signal frequencies that are prone to howling, and those feedback elimination systems which simply employ adaptive notch filtering to detect and “notch” the so-called “singing” or “howling” frequencies as they occur in real-time. Such devices may typically have several knobs and buttons needing tuning, for example: the number of adaptive parametric equalizers (PEQs) versus fixed PEQs; attack and decay timers; and/or PEQ bandwidth. The systems set forth herein obviate the need for tuning knobs or buttons, making set up easy.