Audio Feedback Detection Using Allpass Phase Shift
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Solution Overview
Problem
Existing audio systems face challenges in distinguishing feedback tones from environmental sounds, as detectors often react to similar signals, leading to incorrect identification and inefficient feedback cancellation.
Innovation Solution
The audio system employs an allpass filter to change the phase of the audio signal at specific frequencies, allowing for differentiation between feedback tones and external tones by comparing frequency shifts before and after phase alteration, enabling more effective feedback cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a detector is used to identify feedback tones, then feedback cancellation can be controlled, but the detector also reacts to environmental sounds with pure tones causing false positives
Solution Approach 1:
The patent introduces a phase shift element as an intermediary component in the feedback path. This element shifts the phase of feedback tones by a predetermined amount (e.g., 180 degrees) while leaving environmental tones unchanged. The detector then compares the phase of the original signal with the phase-shifted signal to distinguish feedback tones from environmental sounds, thereby reducing false positives while maintaining reliable feedback detection
Solution Approach 2:
The patent changes the phase parameter of the feedback path by introducing a phase shift element. This parameter change creates a distinctive characteristic for feedback tones (phase difference relative to the shifted signal) that environmental sounds do not possess. The detector utilizes this phase parameter difference to accurately identify feedback tones while ignoring environmental pure tones, thus improving both detection reliability and measurement precision
2Object-generated harmful factors
If gain is reduced at detected frequencies to suppress feedback, then feedback is controlled, but environmental tones are also suppressed causing audio quality degradation
Solution Approach 1:
The phase shift element serves as a mediator that enables selective identification of feedback tones without affecting environmental tones. By comparing phase characteristics between the original and phase-shifted signals, the system can distinguish feedback from environmental sounds, allowing gain reduction to be applied only to genuine feedback tones rather than all detected tones, thus preserving audio quality while suppressing feedback
Solution Approach 2:
The patent applies local quality by making the gain reduction selective rather than blanket. The phase comparison mechanism enables the system to apply different gain adjustments to different frequency components based on their origin: feedback tones receive gain reduction while environmental tones maintain their original gain levels. This localized application of feedback suppression preserves overall audio signal quality while effectively controlling harmful feedback
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 allows for efficient control of feedback cancellation systems by accurately identifying feedback tones, reducing false positives and enabling targeted countermeasures to mitigate feedback.
Implementation Method 1
means are provided for changing the phase of the audio signal at a given frequency
Data Source
AI summary
The invention concerns an audio system comprising a microphone, audio signal processing means, an output transducer and mans for detecting a possible feedback tone and the corresponding frequency of the feedback tone in the audio system between the output transducer and the microphone. According to the invention means for counteracting feedback are provided. Further, mans are provided for changing the phase of the audio signal at a given frequency.