Partially Complex Filter Bank for Low-Aliasing Audio Subbands
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Solution Overview
Problem
Existing audio signal processing technologies face challenges in achieving high-quality spectral envelope adjustment and frequency selectivity while minimizing aliasing, especially when using cosine-modulated filter banks, which can result in narrow sound impressions and incorrect sound source placement due to increased computational complexity and aliasing issues.
Innovation Solution
A partially complex modulated filter bank is introduced, which processes real-valued subband signals to generate complex-valued signals with minimal aliasing and reduced computational complexity, allowing for efficient manipulation and reconstruction quality comparable to complex filter banks, while maintaining the stability of energy estimation and frequency selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a complex exponential modulated filter bank is used for spectral envelope adjustment, then the quality of signal processing is improved, but the computational complexity increases
Solution Approach 1:
The filter bank is segmented into two distinct parts: a complex exponential modulated filter bank for low-frequency subbands and a cosine modulated filter bank for high-frequency subbands. This segmentation allows each part to be optimized for its specific frequency range, achieving high signal processing quality where needed while reducing overall computational complexity by using the simpler cosine modulation for high frequencies where complex modulation provides minimal additional benefit.
Solution Approach 2:
Different modulation types are applied to different frequency regions based on their specific requirements. The complex exponential modulation is applied locally to low-frequency subbands where high spectral resolution and accurate envelope adjustment are critical for perceptual quality. The cosine modulation is applied locally to high-frequency subbands where computational efficiency is more important and the human ear is less sensitive to spectral inaccuracies.
2Device complexity
If a cosine modulated filter bank is used to reduce computational complexity, then the computational complexity is reduced, but aliasing increases
Solution Approach 1:
The frequency spectrum is segmented into low-frequency and high-frequency regions, with different filter bank types assigned to each segment. The complex exponential modulated filter bank is assigned to low-frequency subbands where aliasing would be most perceptible and detrimental to signal quality. The cosine modulated filter bank is assigned to high-frequency subbands where aliasing is less perceptible, thus reducing overall computational complexity while maintaining acceptable signal quality.
Solution Approach 2:
The modulation parameter (complex exponential vs. cosine) is changed based on the frequency subband being processed. This parameter change allows the system to adapt the level of aliasing tolerance to the specific frequency region, using complex modulation with its superior anti-aliasing properties for low frequencies and simpler cosine modulation for high frequencies.
3Object-generated harmful factors
If gain locking is applied to reduce aliasing in cosine modulated filter banks, then aliasing is reduced, but frequency selectivity is reduced
Solution Approach 1:
The filter bank processing is segmented by frequency range, with gain locking applied only to high-frequency subbands where aliasing can be tolerated and frequency selectivity is less critical. Low-frequency subbands process without gain locking, preserving their frequency selectivity and spectral resolution where it is most needed for accurate envelope adjustment and perceptual quality.
Data Source
AI summary
An apparatus for processing a plurality of real-valued subband signals using a first real-valued subband signal and a second real-valued subband signal to provide at least a complex-valued subband signal comprises a multiband filter for providing an intermediate real-valued subband signal and a calculator for providing the complex-valued subband signal by combining a real-valued subband signal from the plurality of real-valued subband signals and the intermediate subband signal.