Audio Signal Gain Estimation for Howling Prevention
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Solution Overview
Problem
Existing communication systems face challenges in reducing howling and echo cancellation, particularly during calls between hands-free devices, due to unknown gain changes introduced by dedicated audio signal processing modules, which can lead to system gain exceeding unity and causing howling.
Innovation Solution
The method involves estimating the gain introduced by the audio signal processing module using noise levels of the far-end signal before and after processing, and selectively applying a system gain reduction step to prevent howling by ensuring the system gain remains below unity across all frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the system gain is increased to improve audio signal quality, then the audio signal quality is improved, but howling occurs due to system gain exceeding unity
Solution Approach 1:
The patent implements a feedback mechanism where the communication client application receives loopback audio data from the audio signal processing module, estimates the gain applied, and uses this information to control the system gain. This closed-loop feedback allows the system to monitor and adjust gain levels to prevent howling while maintaining audio quality.
Solution Approach 2:
The patent dynamically adjusts the system gain parameter based on estimated gain values derived from noise level comparisons. By changing the gain parameter adaptively rather than using a fixed value, the system can optimize audio quality while preventing the gain from exceeding unity and causing howling.
2Productivity
If dedicated audio signal processing modules are used to improve audio processing, then audio processing capability is improved, but the gain introduced by the module becomes unknown leading to howling
Solution Approach 1:
The patent uses feedback by capturing loopback audio data from the dedicated audio signal processing module and comparing noise levels before and after processing. This allows the system to estimate the gain introduced by the module without requiring internal information from the module itself.
Solution Approach 2:
The patent introduces an intermediary measurement approach using noise level estimation as a mediator to indirectly determine the gain introduced by the audio processing module. Instead of directly accessing the module's internal gain settings, the system uses the noise level ratio as an intermediary indicator of the applied gain.
3Object-affected harmful factors
If noise attenuation is applied to reduce background noise, then background noise is reduced, but system gain may exceed unity causing howling
Solution Approach 1:
The patent dynamically adjusts the noise attenuation parameter based on the estimated system gain. When the estimated gain approaches unity, the noise attenuation is reduced or disabled to prevent the system gain from exceeding unity and causing howling. This adaptive parameter adjustment resolves the contradiction between noise reduction and howling prevention.
Data Source
AI summary
A method of reducing noise in an acoustic system, the method comprising at a first user terminal: receiving an audio signal from at least one further user terminal over a network; executing a communication client on a processing unit, the client configured so as when executed to: supply the audio signal to an audio signal processing module of the first user terminal, wherein the processing module processes the audio signal, whereby a level of gain is applied to the audio signal, and outputs a processed audio signal to a speaker; estimate a noise level of the audio signal and the processed audio signal and estimate the gain applied by the processing module taking into account both the noise level estimates; selectively apply a system gain reduction step to at least one of the audio signal and an audio signal received via a microphone, based on at least the estimated gain.