Adaptive ANC Circuit Handling Direction-Dependent Ambient Sound
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Solution Overview
Problem
Existing personal audio devices, such as wireless telephones, face challenges in providing effective noise cancellation due to frequency and direction-dependent ambient sounds, leading to improper adaptation and erroneous operation of active noise cancellation systems.
Innovation Solution
A personal audio device with an adaptive noise-canceling (ANC) processing circuit that includes a transducer, microphones, and an integrated circuit, which detects frequency and direction-dependent ambient sounds to adapt the anti-noise signal generation, avoiding disruptive or ineffective noise cancellation by using error microphones and signal processing techniques like FFT and direction determination logic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive noise canceling is used to improve noise cancellation performance, then noise cancellation effectiveness is improved, but the system may become ineffective or provide unexpected results for certain ambient sounds with frequency and direction-dependent characteristics
Solution Approach 1:
The patent implements dynamic control of the adaptive filter by detecting frequency and direction-dependent characteristics of ambient sounds, then adjusting or pausing adaptation in response to these conditions. This allows the system to maintain reliability for typical noise while avoiding the pitfalls of adaptive behavior for problematic sound conditions.
Solution Approach 2:
The system uses feedback from analyzing ambient sound characteristics (frequency content and direction-dependency) to control the adaptation process. When problematic characteristics are detected, the system modifies its adaptation behavior accordingly, creating a closed-loop control mechanism that prevents erroneous operation.
2Productivity
If the adaptive filter continuously adapts to cancel ambient noise, then noise cancellation is improved, but improper adaptation occurs for sounds with frequency and direction-dependent characteristics leading to erroneous operation
Solution Approach 1:
The adaptive filter's behavior is dynamically adjusted based on real-time analysis of ambient sound characteristics. The system transitions between adaptive and non-adaptive states depending on whether frequency and direction-dependent characteristics are present, preventing improper adaptation while maintaining productivity for suitable conditions.
Solution Approach 2:
The system changes operational parameters of the adaptive filter based on detected sound characteristics. When problematic frequency or direction-dependent characteristics are detected, the system modifies adaptation parameters or pauses adaptation entirely, thereby maintaining operational stability while preserving noise cancellation productivity.
3Productivity
If noise cancellation is applied to all ambient sounds, then overall noise reduction is improved, but high-frequency and low-frequency noise become difficult to cancel effectively
Solution Approach 1:
The patent segments the noise cancellation process by frequency characteristics and direction-dependency. Rather than applying uniform cancellation to all ambient sounds, the system analyzes and segments sounds based on their characteristics, then applies appropriate cancellation strategies only to suitable frequency ranges and sound types, improving precision for challenging frequencies.
Solution Approach 2:
The system applies different noise cancellation qualities to different frequency bands and sound conditions. High-frequency and low-frequency sounds with direction-dependent characteristics receive different treatment compared to typical mid-range noises, allowing optimized performance across the frequency spectrum rather than uniform but suboptimal cancellation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The ANC system effectively cancels ambient audio sounds by adapting to frequency and direction characteristics, improving intelligibility and reducing noise interference, even in challenging acoustic environments like cars, where high-frequency and low-frequency noise are typically difficult to cancel.
Implementation Method 1
a transducer mounted on the housing for reproducing an audio signal that includes both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds
Implementation Method 2
At least one microphone is mounted on the housing to provide a microphone signal indicative of the ambient audio sounds
Implementation Method 3
An adaptive noise canceling (ANC) processing circuit within the housing for adaptively generating an anti-noise signal from the microphone signal such that the anti-noise signal causes substantial cancellation of the ambient audio sounds
Data Source
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Figure 3A
AI summary
A personal audio device, such as a wireless telephone, includes noise canceling circuit W(z) that adaptivcly generates an anti-noise signal from a reference microphone signal (ref) and injects the anti- noise signal into the speaker or other transducer output to cause cancellation of ambient audio sounds. An error microphone (err) may also be provided proximate the speaker to measure the output of the transducer in order to control the adaptation of the anti-noise signal and to estimate an electro-acoustical path (SE) from the noise canceling circuit through the transducer. A processing circuit that performs the adaptive noise canceling function also detects frequency-dependent characteristics (54) in and/or direction of the ambient sounds and alters adaptation of the noise canceling circuit in response to the detection.