Audio Phase Control by Band-Specific Delay Update and Smoothing
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Solution Overview
Problem
Existing phase control signal generation methods for time alignment in vehicle audio systems face high processing loads and frequency characteristic dips due to the need for multiple delay circuits and multipliers, especially as the number of frequency bands increases.
Innovation Solution
A phase control signal generation device and method that uses weighting coefficients and filter coefficients tailored to each frequency band, with a rectangular attenuation curve for weighting coefficients and varying filter orders and cut-off frequencies based on the number of frequency spectral signals, to reduce processing load and minimize dips by only updating and smoothing the phase control signal for the specific frequency band adjusted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an FIR filter with a steep cutoff frequency is used to suppress dips, then frequency characteristic linearity is improved, but the processing load increases due to the need for multiple delay circuits and multipliers
Solution Approach 1:
The patent divides the frequency spectrum into multiple bands and applies different filter orders and cutoff frequencies to each band. This segmentation allows the system to achieve good frequency characteristic linearity in each band without requiring a single high-order filter that would increase processing load. The filter parameters are optimized per band to balance performance and computational complexity.
Solution Approach 2:
The patent applies different filter characteristics (order and cutoff frequency) to different frequency bands based on their specific requirements. Lower frequency bands may use different filter parameters than higher frequency bands, allowing each local region of the frequency spectrum to be optimized independently. This local optimization achieves overall good linearity without requiring excessive processing power across the entire spectrum.
2Measurement precision
If the number of frequency bands is increased to improve time alignment precision, then delay adjustment accuracy is improved, but the processing load further increases due to more delay circuits and multipliers
Solution Approach 1:
The patent segments the frequency spectrum into multiple bands and processes each band independently with its own filter parameters. This allows precise delay adjustment for each frequency band while avoiding the need for a single complex high-order filter that would be required to achieve the same precision across all frequencies, thereby reducing overall processing load.
Solution Approach 2:
The patent dynamically adjusts filter parameters (order and cutoff frequency) based on the specific characteristics of each frequency band and the required delay adjustment. This dynamic adaptation allows the system to use lower processing power where high precision is not critical while maintaining high precision where needed, optimizing the trade-off between accuracy and computational load.
3Stability of the object's composition
If a high order FIR filter is used to achieve linear phase characteristic, then phase constant in all frequency bands is improved, but the number of delay circuits and multipliers increases
Solution Approach 1:
The patent divides the frequency spectrum into multiple bands and applies different filter orders to each band. This segmentation allows the system to achieve linear phase characteristics within each frequency band using lower-order filters, rather than requiring a single high-order filter for the entire spectrum. The sum of the orders of individual band filters is less than the order of a single filter covering all bands.
Data Source
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Figure 4A~4B
AI summary
A phase control signal generation device generating a phase control signal for each of frequency bands for an audio signal converted into a frequency domain, the phase control signal generation device comprising: a setting change means that is able to change setting of a propagation delay time for each of predetermined frequency bands; a difference obtaining means that obtains a difference between propagation delay times before and after setting change; an updating means that updates a phase control amount of the frequency band for which the propagation delay time is changed, based on the obtained difference; and a phase control signal generating means that generates a phase control signal of each frequency band by performing a smoothing process for the phase control amount in a frequency domain using the updated phase control amount.