Complex Modulated Filterbank With Short Subband Filters
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Solution Overview
Problem
Current filtering technologies, particularly in the context of HRTF-related applications, face challenges in achieving efficient and flexible manipulation of time domain audio signals with sufficient quality, as they often require long impulse responses that lead to high computational effort or introduce aliasing effects when transformed into the frequency domain.
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, allowing for parallel processing and efficient filtering in the subband domain, while a filter generator provides an intermediate filter definition signal that can accurately represent arbitrary filter characteristics without aliasing, enabling flexible and high-quality audio signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If filtering is performed in the time domain using a filter with non-uniform amplitude/frequency characteristic, then the filter can accurately model complex filter characteristics (e.g., HRTF), but the impulse response is long leading to high computational complexity
Solution Approach 1:
The patent divides the filtering operation into multiple subbands using a complex modulated filter bank. Each subband is processed independently with shorter impulse response filters, and the results are synthesized back to the time domain. This segmentation reduces the computational complexity of each individual filter while maintaining the overall filter characteristic accuracy through the combined effect of all subband filters.
2Ease of operation
If the time domain signal is transformed into the frequency domain for filtering, then filtering operations become simpler, but aliasing effects are introduced and transformation overhead increases computational effort
Solution Approach 1:
The patent introduces a complex modulated filter bank as an intermediary structure that operates in the subband domain. This filter bank transforms the time domain signal into complex subband signals, processes them with simple filtering operations, and synthesizes the result back to time domain. The intermediary subband representation allows simple filtering operations without introducing aliasing effects, as the filter bank structure inherently handles the transformation and reconstruction.
3Device complexity
If simple gain modifications are applied in each subband, then computational complexity is reduced, but the resolution is insufficient to truthfully model complex filter characteristics
Solution Approach 1:
The patent applies different filtering operations to different subbands based on their local requirements. Instead of uniform gain modification, each subband receives tailored filtering with appropriate impulse response characteristics. This local quality approach allows computational efficiency in each subband while maintaining overall filter characteristic accuracy through the combined effect of all subbands, each optimized for its specific frequency range.
Data Source
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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.