Virtual Microphone for Adaptive Noise Cancellation
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Solution Overview
Problem
Existing adaptive noise cancellation systems in personal audio devices fail to accurately cancel ambient noise at the listener's eardrum due to the distance between the error microphone and the eardrum, resulting in incomplete noise reduction.
Innovation Solution
Incorporating a personal audio device with a transducer, a reference microphone, an error microphone, and a processing circuit that implements an adaptive filter and filters to model the electro-acoustic and acoustic paths from the error microphone to the eardrum, generating a synthesized playback corrected error signal to minimize ambient noise, and adapting the anti-noise signal accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an error microphone is used to sense acoustic pressure proximate to the transducer output, then the noise cancellation system can generate an error microphone signal for adaptive filtering, but the noise cancellation is incomplete because the error microphone signal is only an approximation and not a perfect indication of acoustic pressure at the eardrum
Solution Approach 1:
The patent introduces an intermediary computational model (acoustic transfer function) that bridges the gap between the error microphone location and the eardrum. This model acts as a virtual intermediary to translate measurements from one location to another, allowing the system to estimate eardrum-level noise without physically placing a microphone at the eardrum.
Solution Approach 2:
The patent creates a virtual copy of the acoustic environment at the eardrum by computing what the noise signal would be at that location based on measurements from the error microphone. This virtual copying allows the system to work with accurate eardrum-level noise representations without requiring physical presence at the measurement location.
2Ease of manufacture
If the error microphone is positioned away from the eardrum for practical reasons, then the device structure is simplified and easier to implement, but the noise cancellation performance deteriorates because the system cannot accurately cancel noise present at the drum reference point
Solution Approach 1:
The patent replaces the mechanical solution of placing a microphone physically at the eardrum with a computational approach. Instead of mechanically positioning the sensor at the optimal location, the system uses signal processing and acoustic modeling to achieve the same effect, substituting mechanical complexity with computational intelligence.
3Adaptability or versatility
If the acoustic environment changes dramatically depending on noise sources and device position, then the system must be highly adaptable to maintain performance, but the complexity of the noise cancellation system increases
Solution Approach 1:
The patent implements dynamic adaptation through the adaptive filter that continuously adjusts its coefficients based on the changing acoustic environment. The system transitions from a static noise cancellation approach to a dynamic one that can respond to environmental changes, making the noise cancellation effective across varying conditions without requiring multiple fixed configurations.
Data Source
AI summary
A processing circuit may implement an adaptive filter having a response that generates an anti-noise signal from a reference microphone signal, one or more filters for modeling an electro-acoustic path of the anti-noise signal from a location of an error microphone to an eardrum of a listener and having a response that generates a filtered reference microphone signal from the reference microphone signal, one or more filters for modeling an acoustic path of ambient audio sounds from the location of the error microphone to the eardrum and having a response that generates a synthesized playback corrected error signal based on the error microphone signal, wherein the synthesized playback corrected error signal is indicative of ambient audio sounds present at the eardrum, and a coefficient control block that shapes the response of the adaptive filter in conformity with the filtered reference microphone signal and the synthesized playback corrected error signal by adapting the response of the adaptive filter to minimize the ambient audio sounds in the synthesized playback corrected error signal.