Complex-Exponential Filterbank for Low-Aliasing Spectral Adjustment
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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 subband signals are modified, leading to issues with aliasing and phase dispersion.
Innovation Solution
The development of an improved alias term minimization (IATM) method for designing asymmetric prototype filters in complex-exponential modulated filter banks, which optimizes the design of analysis and synthesis filters to reduce aliasing and pass-band errors, and incorporates a composite objective function to iteratively determine filter coefficients that minimize errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional cosine modulated filter banks are used, then implementation is simple and effective, but aliasing artifacts occur when subband signals are modified
Solution Approach 1:
The patent applies asymmetry by using asymmetric prototype filters instead of traditional symmetric cosine modulated filters. The asymmetric filter design allows for different impulse response characteristics that can suppress aliasing artifacts while maintaining implementation feasibility through modified modulation schemes.
Solution Approach 2:
The patent changes key parameters of the filter bank system, including the modulation type (from cosine to complex exponential), the prototype filter symmetry (from symmetric to asymmetric), and the sampling structure. These parameter changes enable the filter bank to achieve low sensitivity to aliasing while preserving implementation effectiveness.
2Manufacturing precision
If filter bank design optimizes for near-perfect reconstruction, then reconstruction accuracy improves, but system delay increases
Solution Approach 1:
The asymmetric prototype filter design enables the filter bank to achieve near-perfect reconstruction with reduced group delay variation across frequency bands. The asymmetric structure allows for optimized phase characteristics that minimize time delay while maintaining reconstruction accuracy.
Solution Approach 2:
The patent employs dynamic optimization of the filter coefficients through the IATM method, which iteratively adjusts parameters to achieve the desired balance between reconstruction accuracy and system delay. This dynamic approach allows the filter bank to adapt its characteristics for optimal performance.
3Productivity
If sub-sampled filter banks are used, then computational efficiency improves, but aliasing sensitivity increases when subband signals are modified
Solution Approach 1:
The patent converts the harmful aliasing effect into a beneficial property by designing the asymmetric filter bank such that aliasing terms naturally cancel out when subband signals are modified. The complex exponential modulation with asymmetric prototypes transforms aliasing from a detrimental artifact into a mechanism that supports the near-perfect reconstruction property.
Solution Approach 2:
The patent changes the sampling structure and modulation parameters to achieve a critically sampled or sub-sampled filter bank that is inherently less sensitive to aliasing. By modifying the prototype filter symmetry and modulation type, the system maintains computational efficiency while reducing aliasing sensitivity.
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.