Adaptive Noise Cancellation with Shaped Noise for Secondary Path Training

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Solution Overview

Problem

Existing adaptive noise cancellation systems in personal audio devices face challenges in effectively training the secondary path estimate filter due to source audio signals with silent intervals or lacking spectral density, particularly in stereo playback modes.

Innovation Solution

The system incorporates a noise injection mechanism that generates a broadband noise signal, combined with the source audio signal, to ensure the filter adapts to all frequency ranges, using a white noise source filtered by a frequency shaping filter to match the playback corrected error, and an inverse secondary path estimate filter to minimize perceptibility.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If source audio signal is used to train the secondary path estimate filter, then the system can adapt to the acoustic environment, but the filter training becomes ineffective during silent intervals or when spectral density is insufficient

Engineering Contradiction:

Improvefilter training effectivenessVSAvoidadaptability to all frequency ranges

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The system pre-generates test signals with known spectral characteristics before filter training begins. These test signals are injected into the audio path in advance to ensure continuous spectral content is available for training the secondary path estimate filter, even when source audio is silent or spectrally deficient.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A test signal injection mechanism acts as an intermediary between the audio source and the filter training process. This intermediary ensures that sufficient spectral content is always available for training by adding test signals when source audio lacks the necessary frequency content.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If noise injection is used to maintain filter adaptation, then all frequency ranges can be covered, but the injected noise may become perceptible to the listener

Engineering Contradiction:

Improvespectral coverageVSAvoidperceptibility of injected noise

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The system applies different processing to different frequency bands by shaping the test signal spectrum to match the playback corrected error spectrum. This ensures that test signals are injected only where needed for training, and at levels that match the existing audio content in each frequency band, making them imperceptible.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The system dynamically adjusts the spectral characteristics and amplitude of injected test signals based on the current audio state. By matching the test signal spectrum to the playback corrected error spectrum and controlling injection levels, the system maintains spectral coverage while keeping injected signals imperceptible.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If the test signal spectrum matches the playback corrected error spectrum, then filter training is optimized, but the system complexity increases

Engineering Contradiction:

Improvefilter training precisionVSAvoidsignal processing complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The system uses the playback corrected error spectrum as feedback to shape the test signal spectrum. This feedback mechanism allows the test signals to automatically adapt to the current acoustic environment and filter state, optimizing training precision without requiring complex manual configuration.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

Instead of generating complex test signals from scratch, the system copies the spectral characteristics from the existing playback corrected error signal. This copying approach simplifies the signal generation process while ensuring the test signals have the appropriate spectral content for effective filter training.

Inventive Principle:

Principle #26Copying

Data Source

PatentEP3044780B1Systems and methods for adaptive noise cancellation by adaptively shaping internal white noise to train a secondary path

Publication Date: 2021.10.06 CIRRUS LOGIC INC

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AI summary

A processing circuit may include: (i) an adaptive filter having a response that generates an anti-noise signal from a reference microphone signal, wherein the response is shaped in conformity with the reference microphone signal and a playback corrected error; (ii) a secondary path estimate filter configured to model an electro-acoustic path of a source audio signal and having a response that generates a secondary path estimate from the source audio signal; (iii) a secondary coefficient control block that shapes the response of the secondary path estimate filter in conformity with the source audio signal and the playback corrected error by adapting the response of the secondary path estimate filter to minimize the playback corrected error; and (iv) a noise injection portion for injecting a noise signal into the source audio signal, wherein the noise signal is shaped based on the playback corrected error.