Complex-Exponential Filterbank for Low-Delay Spectral Envelope Adjustment
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Solution Overview
Problem
Existing digital filter banks face challenges in suppressing aliasing artifacts when modifying subband signals, while also maintaining low system delay and achieving near-perfect reconstruction.
Innovation Solution
The use of an improved alias term minimization (IATM) method for optimizing asymmetric or symmetric prototype filters in complex-exponential modulated filter banks, which reduces impairments from subband signal modifications and achieves low system delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional digital filter banks are used for subband signal processing, then the system can achieve basic spectral envelope adjustment, but aliasing artifacts are generated when modifying subband signals
Solution Approach 1:
The patent employs asymmetric prototype filters instead of traditional symmetric filters. The asymmetric filter design allows for optimized aliasing suppression characteristics while maintaining low system delay. The filter coefficients are specifically designed to minimize aliasing terms in the subband signals, enabling accurate spectral envelope adjustment without generating harmful aliasing artifacts.
Solution Approach 2:
The patent changes the fundamental parameters of the filter bank system by using complex-exponential modulation instead of traditional cosine modulation. This parameter change transforms the filter bank into a near-perfect reconstruction system that inherently suppresses aliasing. The modulation parameter ω is optimized to achieve both low delay and high aliasing suppression, resolving the contradiction between accuracy and harmful artifacts.
2Loss of time
If traditional cosine modulated filter banks are used, then the implementation is simple and effective, but the system delay is high and aliasing suppression is insufficient
Solution Approach 1:
The patent changes the modulation parameter from traditional cosine modulation to complex-exponential modulation with optimized frequency ω. This parameter change reduces the system delay by optimizing the filter bank structure while simultaneously improving aliasing suppression capabilities. The complex-exponential modulation allows for more flexible control of the frequency response and aliasing characteristics.
Solution Approach 2:
The asymmetric prototype filter design breaks the symmetry constraint of traditional filter banks, allowing for optimized delay characteristics. By removing the symmetry requirement, the filter can be designed to minimize both system delay and aliasing artifacts, achieving superior performance compared to conventional symmetric filter designs.
3Object-affected harmful factors
If filter banks are designed for near-perfect reconstruction, then aliasing is suppressed, but the device complexity increases
Solution Approach 1:
The complex-exponential modulated filter bank with asymmetric prototype filters serves multiple functions simultaneously: it provides near-perfect reconstruction, suppresses aliasing artifacts, maintains low system delay, and enables accurate spectral envelope adjustment. This multi-functional design achieves high performance without proportionally increasing complexity, as the same filter structure accomplishes multiple objectives that would otherwise require separate systems.
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.