Audio Propagation Delay Phase Control Across Frequency Bands
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Solution Overview
Problem
Existing propagation delay correction methods for audio signals in vehicles suffer from degraded linearity of transmission characteristics and frequency characteristic disorders due to signal loss and phase interferences, particularly around crossover frequencies, which increase processing load and result in peaks and dips.
Innovation Solution
A propagation delay correction apparatus and method that utilize short-term Fourier transforms to generate frequency spectrum signals, calculate and smooth phase control amounts for each frequency band, and perform phase control to adjust propagation delay times without relying on high-order FIR filters, thereby improving linearity and suppressing frequency characteristic disorders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high order FIR filter with steep cutoff frequency is used to suppress peaks and dips, then frequency characteristic linearity is improved, but processing load increases
Solution Approach 1:
The audio signal is divided into multiple frequency bands using short-term Fourier transform, and phase control is applied independently to each band. This segmentation allows for targeted phase correction without requiring a high-order filter across the entire frequency spectrum, thereby reducing processing load while maintaining frequency characteristic linearity.
Solution Approach 2:
The invention changes the approach from time-domain filtering to frequency-domain phase control. By calculating and applying phase control amounts for each frequency band based on propagation delay times, the system achieves steep effective cutoff characteristics without the computational burden of high-order FIR filters.
2Manufacturing precision
If the number of delay circuits and multipliers is increased to improve frequency characteristic linearity, then transmission characteristic linearity is improved, but device complexity increases
Solution Approach 1:
The invention replaces the mechanical/filter-based approach (delay circuits and multipliers) with a mathematical approach (short-term Fourier transform and phase control calculations). This substitution achieves the same goal of improving transmission characteristic linearity while significantly reducing the number of physical components and computational operations required.
3Measurement precision
If band dividing circuit is used to correct sound image localization bias, then time alignment is improved, but signal loss and double additions occur degrading linearity
Solution Approach 1:
Instead of dividing the signal into bands and then recombining (which causes signal loss and double additions), the invention transforms the signal to the frequency domain, applies phase control, and then transforms back. This inverted approach avoids the problems of band dividing by working directly with the frequency spectrum where phase adjustments can be made without signal decomposition and recombination.
Data Source
AI summary
A propagation delay tune correction apparatus comprising a means for generating a frequency spectrum signal by performing short-term Fourier transform on an audio signal; a means for setting a propagation delay time for each of a plurality of predetermined frequency bands; a means for calculating a phase control amount for each of the plurality of predetermined frequency bands on a basis of the propagation delay time set for each of the plurality of predetermined frequency bands; a means for generating a phase control signal by smoothing the calculated phase control amount for each of the plurality of predetermined frequency bands; a means for controlling a phase of the frequency spectrum signal for each of the plurality of predetermined frequency bands on a basis of the generated phase control signal; and a means for generating an audio signal on which a propagation delay correction is performed by performing inverse short-term Fourier transform on the frequency spectrum signal of which the phase is controlled for each of the plurality of predetermined frequency bands.