Complex-Exponential Filter Bank With Asymmetric Low-Delay Prototype
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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, due to limitations in current filter bank design methods.
Innovation Solution
The proposed method employs an improved alias term minimization (IATM) technique for optimizing asymmetric prototype filters, which involves designing a low delay complex-exponential modulated filter bank with a specific objective function that balances pass band errors and aliasing errors, allowing for near-perfect reconstruction and low system delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If cosine modulated filter banks are used, then implementation effectiveness is improved, but aliasing artifacts increase when subband signals are modified
Solution Approach 1:
The patent employs asymmetric prototype filters instead of symmetric ones used in conventional cosine modulated filter banks. This asymmetry allows for optimized control of aliasing terms while maintaining implementation efficiency, directly addressing the contradiction between ease of manufacture and aliasing suppression.
Solution Approach 2:
The patent changes the modulation approach from standard cosine modulation to complex exponential modulation with specifically designed asymmetric prototypes. This parameter change in the filter bank design enables simultaneous achievement of implementation effectiveness and reduced aliasing artifacts when subband signals are modified.
2Object-generated harmful factors
If complex exponential modulated filter banks are used, then aliasing freedom is improved, but system delay increases
Solution Approach 1:
The patent uses asymmetric prototype filters in the complex exponential modulated filter bank design. This asymmetry enables optimization of the frequency response to achieve aliasing suppression while controlling the group delay characteristics, thereby reducing system delay compared to conventional symmetric designs.
Solution Approach 2:
The patent employs dynamic optimization of the asymmetric prototype filter coefficients to balance aliasing suppression and delay reduction. The filter design allows adaptive control of the frequency response characteristics to minimize both aliasing artifacts and system delay simultaneously.
3Adaptability or versatility
If subband samples are modified for equalization or quantization, then signal processing flexibility is improved, but aliasing artifacts increase
Solution Approach 1:
The patent applies preliminary anti-action by designing the asymmetric complex exponential modulated filter bank to preemptively suppress aliasing terms before subband signal modification. The filter bank structure is optimized in advance to cancel aliasing components, ensuring that subsequent modifications for equalization or quantization do not generate significant aliasing artifacts.
Solution Approach 2:
The patent changes the filter bank parameters to asymmetric complex exponential modulation, which fundamentally alters the aliasing behavior. This parameter change enables the filter bank to maintain aliasing suppression even when subband samples are modified, thus preserving signal processing flexibility without introducing harmful artifacts.
Data Source
AI summary
The document relates to modulated sub-sampled digital filter banks, as well as to methods and systems for the design of such filter banks. In particular, the present document proposes a method and apparatus for the improvement of low delay modulated digital filter banks. The method employs modulation of an asymmetric low-pass prototype filter and a new method for optimizing the coefficients of this filter. Further, a specific design for a (64) channel filter bank using a prototype filter length of (640) coefficients and a system delay of (319) samples is given. The method substantially reduces artifacts due to aliasing emerging from independent modifications of subband signals, for example when using a filter bank as a spectral equalizer. The method is preferably implemented in software, running on a standard PC or a digital signal processor (DSP), but can also be hardcoded on a custom chip. The method offers improvements for various types of digital equalizers, adaptive filters, multiband companders and spectral envelope adjusting filterbanks used in high frequency reconstruction (HFR) or parametric stereo systems.