Adaptive Filter Coefficient Initialization for Vehicle Noise Reduction
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Solution Overview
Problem
Conventional active noise reduction devices in vehicles take time to achieve noise reduction effects due to initial adaptive filter coefficient calculations starting from zero, which delays the effectiveness of cancelling sounds.
Innovation Solution
The active noise reduction device uses a stored adaptive filter coefficient from a previous operation as the initial value for the update equation when starting the output of cancelling sound, allowing for early adaptation and faster noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the adaptive filter coefficient is calculated from zero at the start of cancelling sound output, then the initial calculation is simple and systematic, but the time required to achieve noise reduction effect is prolonged
Solution Approach 1:
The patent applies preliminary action by calculating and storing the adaptive filter coefficient at a timing prior to when the cancelling sound output is started (e.g., when the vehicle is off or in a previous operating state). This pre-calculated coefficient is then reused as the initial value when noise reduction begins, eliminating the need to start from zero and significantly reducing the adaptation time of the adaptive filter.
2Loss of time
If the adaptive filter coefficient is pre-calculated and stored, then the noise reduction response time is improved, but the memory storage requirement increases
Solution Approach 1:
The patent changes the parameter of the adaptive filter coefficient from being dynamically calculated in real-time to being pre-calculated and stored as a static parameter. This parameter change allows the system to trade minimal storage space for significant improvements in noise reduction response time, as the coefficient values are computed once and reused across multiple operating cycles.
3Reliability
If the adaptive filter coefficient is continuously updated from zero, then the system maintains simplicity in coefficient management, but the noise reduction effectiveness is delayed
Solution Approach 1:
The system performs preliminary coefficient calculation before the noise reduction function is activated. By storing the pre-calculated coefficient in memory, the system achieves both rapid noise reduction effectiveness and maintains relatively simple coefficient management, as the coefficient is updated only when necessary (e.g., when vehicle operating conditions change significantly) rather than being continuously recalculated from zero.
Data Source
AI summary
An active noise reduction device includes: an adaptive filter that generates a cancelling signal by applying an adaptive filter to a reference signal that has a correlation with noise in a space in an automobile, the cancelling signal being used to output a cancelling sound for reducing the noise; and a filter coefficient updater that calculates a coefficient of the adaptive filter based on a predetermined update equation. At a first timing at which the output of the cancelling sound is started, the filter coefficient updater uses a first coefficient as an initial value of the update equation, the first coefficient being the coefficient of the adaptive filter calculated by the filter coefficient updater at a second timing that is prior to the first timing.