Complex-Exponential Filter Bank for Low-Delay 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, which is crucial for real-time applications like audio and video streaming.
Innovation Solution
The design of a low delay complex-exponential modulated filter bank using an improved alias term minimization method for asymmetric prototype filters, which optimizes the filter bank to reduce aliasing and pass band errors, and incorporates a composite objective function to iteratively determine the filter coefficients for minimal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional digital filter banks are used, then aliasing suppression is achieved, but system delay increases
Solution Approach 1:
The patent employs asymmetric prototype filters instead of conventional symmetric filters. The asymmetric filter design allows for optimized frequency response characteristics that reduce aliasing artifacts while maintaining lower group delay, thereby resolving the contradiction between aliasing suppression and system delay reduction.
Solution Approach 2:
The patent optimizes filter bank parameters including prototype filter length, modulation type (complex-exponential), and decimation factors. By carefully selecting and adjusting these parameters, the system achieves near-perfect reconstruction with reduced aliasing while minimizing system delay compared to conventional designs.
2Adaptability or versatility
If sub-sampled filter banks are used for spectral modification, then aliasing emerges, but near-perfect reconstruction is required
Solution Approach 1:
The patent acknowledges that sub-sampling inherently causes aliasing, but converts this harmful effect into a beneficial one by designing the filter bank to exploit aliasing cancellation properties. The complex-exponential modulation and asymmetric prototype filters are specifically designed so that aliasing terms cancel each other out, enabling near-perfect reconstruction even with sub-sampling for spectral modifications.
Solution Approach 2:
The patent implements near-perfect reconstruction through feedback mechanisms where the aliasing introduced by sub-sampling is compensated by carefully designed synthesis filters that reverse the analysis filter effects. This feedback approach ensures that spectral modifications can be made with minimal aliasing artifacts.
3Manufacturing precision
If filter coefficients are optimized for minimal distortion, then near-perfect reconstruction is achieved, but device complexity increases
Solution Approach 1:
The patent divides the filter bank into distinct components: asymmetric prototype filter design, complex-exponential modulation stage, and sub-sampling/synthesis stage. Each segment can be independently optimized and implemented, reducing overall design complexity while achieving near-perfect reconstruction through the coordinated operation of these segmented components.
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.