Headphone Active Noise Cancellation Using Analog Prediction Filtering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing active noise cancellation systems in headphones are limited in their ability to effectively cancel environmental noise without compromising the quality of the intended audio signal, and they typically struggle to reduce noise levels beyond 10dB.
Innovation Solution
The proposed active noise cancellation system employs a feedforward approach with an analog-to-digital converter (ADC) and a prediction filter operating at a higher clock frequency to predict and invert environmental noise samples, while maintaining low latency and preserving audio quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional digital noise cancellation techniques are used, then noise cancellation is provided for typical environmental noise, but the noise reduction level is limited to approximately 10dB
Solution Approach 1:
The patent changes the fundamental parameters of noise cancellation by transitioning from conventional digital sub-band filtering to analog prediction filtering. The analog prediction filter operates continuously in the time domain rather than in discrete frequency bands, enabling deeper noise reduction beyond the 10dB limitation of digital techniques while maintaining audio signal integrity.
2Object-affected harmful factors
If noise cancellation is increased, then environmental noise is reduced, but the quality of the intended audio signal deteriorates
Solution Approach 1:
The patent segments the audio processing into distinct analog paths: one path processes the noise signal through the prediction filter, while another path preserves the original audio signal. These segmented paths are then combined at the summation point, allowing noise cancellation to be applied selectively without degrading the overall audio quality.
Solution Approach 2:
The analog prediction filter acts as an intermediary that processes only the noise component of the signal. By isolating and filtering the noise path separately from the audio signal path, the system can aggressively cancel noise while leaving the audio signal untouched, thus maintaining audio quality.
3Loss of information
If filtering is applied to preserve audio signal, then audio quality is maintained, but noise cancellation performance is compromised
Solution Approach 1:
Instead of applying filtering to the combined audio and noise signal (conventional approach), the patent inverts the approach by applying the prediction filter exclusively to the noise signal path. The filtered noise is then subtracted from the original audio signal, achieving both noise cancellation and audio preservation simultaneously.
4Ease of manufacture
If analog noise cancellation techniques are used, then implementation is simple, but noise reduction capability is limited
Solution Approach 1:
The patent replaces conventional digital signal processing mechanisms with an analog prediction filter mechanism. This substitution maintains the simplicity of analog implementation while achieving superior noise reduction capability, as the analog filter operates continuously in the time domain rather than requiring complex digital algorithms.
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
This system achieves effective noise cancellation with minimal impact on audio quality, capable of reducing noise levels beyond the limitations of current technologies, while maintaining low latency and cost-effectiveness.
Implementation Method 1
a prediction filter working at a multiple N times higher clock frequency (N × fs) than the clock frequency (fs) of the ADC and configured for predicting a plurality D of inverted digital environmental noise samples
Implementation Method 2
an analog-to-digital converter (ADC) working at a clock frequency (fs) and arranged to convert the sensed environmental noise to a digital environmental noise signal
Implementation Method 3
a digital-to-analog converter (DAC) to convert the digital inverted environmental noise signal to an analog inverted environmental noise signal for cancelling the environmental noise
Implementation Method 4
the measured noise signal is used to generate a feedback signal that is processed through an amplifier to adjust the level and then inverted and applied to a speaker of the headphone for cancellation of the noise signal
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An active noise cancellation system (2) comprising an active noise cancellation circuit connected to a microphone (10) arranged to sense environmental noise, the active noise cancellation circuit comprising : - an analog-to-digital converter (ADC) (14) arranged to convert the sensed environmental noise to a digital environmental noise signal, - a prediction filter (16) configured for predicting a plurality D of inverted digital environmental noise samples and generating a digital inverted environmental noise signal, - a digital-to-analog converter (DAC) (24) to convert the digital inverted environmental noise signal to an analog inverted environmental noise signal for cancelling the environmental noise.