Complex Modulated Filterbank for Shorter HRTF Subband Filtering
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Solution Overview
Problem
Current filter banks in audio signal processing, particularly for HRTF-related applications, face challenges in achieving efficient and flexible manipulation of time domain input signals with sufficient quality, as they often require long impulse responses that lead to high computational complexity and inadequate frequency resolution.
Innovation Solution
A filter apparatus and method utilizing a complex analysis filter bank to generate complex subband signals, with intermediate filters having shorter impulse responses than traditional filters, allowing for parallel processing and improved computational efficiency, and a filter generator to provide an intermediate filter definition signal that can accurately represent arbitrary filter characteristics in the subband domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional filters with long impulse responses are used to achieve accurate filtering with non-uniform amplitude/frequency characteristics, then filtering quality is improved, but computational complexity increases
Solution Approach 1:
The patent divides the traditional single filter into multiple intermediate filters operating in parallel subbands. Each intermediate filter has a shorter impulse response and operates on a specific frequency subband, collectively achieving the filtering effect of the original long-impulse-response filter with reduced computational complexity per filter.
Solution Approach 2:
The patent transitions from time-domain filtering to subband-domain filtering by applying complex exponential modulation. This dimensional change allows the filter bank to achieve frequency-selective processing with shorter impulse responses, as each subband filter operates independently on modulated signal components.
2Measurement precision
If traditional filter banks are used for audio signal processing, then basic filtering is achieved, but frequency resolution is insufficient for high-quality spatial audio processing
Solution Approach 1:
The patent applies different filtering characteristics to different frequency subbands. Each intermediate filter is designed with specific amplitude and phase characteristics tailored to its subband, enabling high frequency resolution where needed while maintaining processing efficiency. The complex exponential modulation provides local frequency selectivity across different subbands.
Solution Approach 2:
The patent uses complex exponential modulation with variable modulation indices to dynamically adjust the frequency resolution characteristics. By varying the modulation parameters, the filter bank can adapt its frequency resolution to match the spectral characteristics of the audio signal and the requirements of spatial audio processing.
3Measurement precision
If complex exponential modulated filter bank is used for spectral processing, then spectral resolution is improved, but the ability to accurately model intricate phase characteristics of HRTF filters is lost
Solution Approach 1:
The patent changes the parameter representation of filter characteristics by working in the subband domain with complex exponential modulation. Each intermediate filter's amplitude and phase characteristics are independently controlled through modulation parameters, allowing accurate modeling of HRTF phase characteristics while maintaining high spectral resolution through the modulated filter bank structure.
Data Source
Figure 1a~1c
Figure 1d~1e
Figure 2~4
AI summary
A filter apparatus for filtering a time domain input signal to obtain a time domain output signal, which is a representation of the time domain input signal filtered using a filter characteristic having an non-uniform amplitude/frequency characteristic, comprises a complex analysis filter bank for generating a plurality of complex subband signals from the time domain input signals, a plurality of intermediate filters, wherein at least one of the intermediate filters of the plurality of the intermediate filters has a non-uniform amplitude/frequency characteristic, wherein the plurality of intermediate filters have a shorter impulse response compared to an impulse response of a filter having the filter characteristic, and wherein the non-uniform amplitude/frequency characteristics of the plurality of intermediate filters together represent the non-uniform filter characteristic, and a complex synthesis filter bank for synthesizing the output of the intermediate filters to obtain the time domain output signal.