Dynamic Notch Filter Release for Acoustic Howling Suppression
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Solution Overview
Problem
Existing howling cancellers face challenges in efficiently releasing notch filters, leading to potential deterioration in sound quality due to prolonged insertion of notch filters, especially when howling frequencies change, and hardware limitations restrict the number of filters that can be inserted.
Innovation Solution
A howling canceller that dynamically adjusts the insertion and release of notch filters based on frequency, using a filter insertion unit, setting unit, and release unit, with shorter insertion times for higher frequencies and considering microphone movement, to optimize notch filter usage and prevent sound quality degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If notch filters are inserted to suppress howling, then howling suppression performance is improved, but sound quality deteriorates due to prolonged filter insertion
Solution Approach 1:
The patent applies dynamics by making the notch filter insertion time variable rather than fixed. The release time is dynamically adjusted based on the frequency band (shorter for high-band, longer for low-band) and microphone movement detection, allowing the system to adaptively optimize the balance between howling suppression and sound quality preservation.
Solution Approach 2:
The patent changes the parameter of filter insertion time based on different conditions. Specifically, it sets different release times for low-band and high-band frequencies, and adjusts the insertion time based on detected microphone movement, thereby optimizing both howling suppression effectiveness and sound quality.
2Adaptability or versatility
If the number of notch filters is increased to handle multiple howling frequencies, then howling suppression capability is improved, but hardware complexity increases
Solution Approach 1:
The patent uses dynamics by implementing a release mechanism that automatically removes notch filters after predetermined time periods. This allows the limited number of hardware filters to be reused for different howling frequencies over time, effectively increasing the system's adaptability without requiring additional hardware filters.
Solution Approach 2:
The patent applies discarding and recovering by releasing notch filters after they have served their purpose for a predetermined time. This allows the same hardware filters to be recovered and reused for suppressing different howling frequencies, maximizing the utilization of limited hardware resources.
3Productivity
If notch filters are released based on longest insertion time, then filter reuse is improved, but howling suppression reliability decreases when acoustic feedback changes
Solution Approach 1:
The patent applies local quality by differentiating the release time strategy between low-band and high-band frequencies. High-band filters are released after shorter periods while low-band filters are released after longer periods, recognizing that different frequency bands have different characteristics regarding acoustic feedback stability and howling persistence.
Solution Approach 2:
The patent uses feedback by continuously monitoring for new howling occurrences and detecting microphone movement. When movement is detected or new howling is identified, the system adjusts filter release timing accordingly, ensuring that filters remain inserted long enough to suppress active howling while allowing timely release for filter reuse.
Data Source
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AI summary
A howling canceller applied to an acoustic system having a speaker and a microphone comprises: a filter insertion unit for inserting a notch filter at a frequency of an audio signal picked up by the microphone; a setting unit for setting the insertion time of the notch filter on the basis of the frequency at which the notch filter is inserted; and a releasing unit for, when the insertion time set by the setting unit has elapsed, releasing the notch filter, the insertion time of which has elapsed. The setting unit sets the insertion time of the notch filter to be shorter as the frequency at which the notch filter is inserted increases.