Complex-Exponential Filterbank With Low-Delay Alias Minimization
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Solution Overview
Problem
Existing digital filter banks face challenges in minimizing aliasing artifacts and achieving low system delay while maintaining near-perfect reconstruction properties, especially when modifying subband signals, due to limitations in current filter bank design methods.
Innovation Solution
The development of an improved alias term minimization (IATM) method for designing low delay complex-exponential modulated filter banks using asymmetric prototype filters, which optimizes the design for reduced aliasing and pass band errors, and incorporates a composite objective function to iteratively determine the filter coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional filter bank design methods are used, then implementation is simpler, but aliasing artifacts increase and reconstruction precision deteriorates
Solution Approach 1:
The patent employs asymmetric prototype filters instead of symmetric ones, where the filter coefficients are specifically designed to minimize aliasing terms in the filter bank reconstruction. This asymmetry allows for optimized aliasing cancellation while maintaining practical implementability, directly resolving the contradiction between reconstruction precision and design complexity.
Solution Approach 2:
The patent optimizes specific parameters of the prototype filter, including the filter length, cutoff frequency, and coefficient values, to achieve near-perfect reconstruction. By carefully adjusting these parameters, the design achieves high reconstruction precision without requiring overly complex filter structures, thus balancing precision and complexity.
2Object-affected harmful factors
If filter bank is optimized for aliasing suppression, then aliasing artifacts decrease, but system delay increases
Solution Approach 1:
The patent applies partial aliasing suppression by targeting specific dominant aliasing terms rather than attempting to eliminate all aliasing components. The asymmetric prototype filter is designed to cancel the most significant aliasing terms while accepting residual aliasing from less critical terms, thereby achieving effective aliasing suppression without requiring excessive filter length that would increase system delay.
3Manufacturing precision
If prototype filter length is increased, then reconstruction precision improves, but computational complexity and delay increase
Solution Approach 1:
The asymmetric prototype filter design allows for more efficient use of filter coefficients compared to symmetric designs. By distributing the aliasing cancellation function across asymmetric coefficient patterns, the patent achieves high reconstruction precision with a moderate filter length, avoiding the need for excessively long filters that would increase computational complexity.
Data Source
AI summary
An apparatus and method are disclosed for processing an audio signal. The apparatus includes an input interface, a digital filterbank having an analysis part and a synthesis part, a first phase shifter, a spectral envelope adjuster, a second phase shifter, and an output interface. The first phase shifter and the second phase shifter reduce a complexity of the digital filterbank, which includes both analysis and synthesis filters that are complex-exponential modulated versions of a prototype filter.