Non-linear Acoustic Feedback Suppression in Telephone Devices
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Solution Overview
Problem
Existing telephone devices struggle to efficiently suppress non-linear acoustic feedback, particularly harmonics of the speaker signal picked up by the microphone, which are not effectively addressed by conventional echo cancellers using finite impulse response filters.
Innovation Solution
The telephone device determines substantial similarity between frequency components of the speaker and microphone signals, attenuating harmonics that are in harmonic relation with the fundamental frequency, using a processing unit to transform signals into the frequency domain and apply spectral subtraction techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional echo cancellers using finite impulse response filters are used, then linear echo effects are suppressed, but non-linear acoustic feedback (harmonics) remains ineffective
Solution Approach 1:
The patent segments the echo cancellation problem into two distinct parts: linear echo cancellation using FIR filters and non-linear echo cancellation using harmonic detection. By dividing the frequency spectrum into fundamental frequencies and their harmonics, the system can apply different cancellation strategies to each segment, effectively addressing both linear and non-linear feedback
Solution Approach 2:
The patent changes the approach from purely time-domain FIR filtering to frequency-domain analysis by transforming signals and examining harmonic relationships. This parameter change enables the system to identify and suppress non-linear feedback components that were invisible to conventional linear filters
2Object-affected harmful factors
If the microphone signal is heavily filtered to remove echo, then acoustic feedback is reduced, but speech quality and naturalness deteriorate
Solution Approach 1:
The patent applies local quality by selectively attenuating only the harmonic frequency components that correspond to non-linear feedback, while leaving other frequency components of the speech signal intact. This targeted approach removes harmful feedback without degrading overall speech quality
Solution Approach 2:
The system uses feedback by continuously monitoring the relationship between speaker signal harmonics and microphone signal harmonics, dynamically adjusting attenuation levels based on detected similarity, thereby adaptively suppressing feedback while preserving speech
Data Source
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AI summary
The invention relates a telephone device (TD) arranged to receive a microphone signal (TX) from a microphone (MI) and a speaker signal (RX) from a line interface (LIF). The telephone device is arranged to transmit the microphone signal (TX) to the line interface (LIF) and the speaker signal (RX) to a speaker (SP). The telephone device (TD) is further arranged to determine a substantial similarity between a first frequency component of the speaker signal (RX) and a second frequency component of the microphone signal (TX) for at least a predetermined time interval, and attenuate the second frequency of the microphone signal (TX) for the at least predetermined time interval if a substantial similarity is determined.