Partially Complex Filter Bank for Low-Aliasing Subband Processing
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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 severe aliasing and reduced frequency selectivity at lower frequencies.
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 increased computational efficiency, allowing for better quality manipulation by using a multiband filter and calculator to combine real-valued signals into complex-valued signals, and vice versa, maintaining the advantages of complex filter banks with reduced computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a cosine modulated (real-valued) filter bank is used to reduce computational complexity, then computational complexity is reduced, but severe aliasing is encountered and frequency selectivity is reduced at lower frequencies
Solution Approach 1:
The patent applies different filter bank types to different frequency regions: complex exponential modulated filter bank for low frequencies (where aliasing is more audible and frequency selectivity is needed) and cosine modulated filter bank for high frequencies (where computational efficiency is more important). This local differentiation resolves the contradiction by optimizing each frequency region according to its specific requirements.
Solution Approach 2:
The frequency spectrum is segmented into low-frequency and high-frequency regions, with different filter bank implementations applied to each segment. The low-frequency segment uses complex exponential modulation to minimize aliasing, while the high-frequency segment uses cosine modulation for computational efficiency, thereby resolving the overall contradiction through分段处理.
2Object-generated harmful factors
If a complex exponential modulated filter bank is used to achieve low aliasing and high frequency resolution, then aliasing is reduced and frequency selectivity is improved, but computational complexity increases
Solution Approach 1:
The patent applies complex exponential modulated filter bank only to the low-frequency region where aliasing is most problematic and frequency selectivity is most needed for spatial audio processing. The high-frequency region uses the computationally simpler cosine modulated filter bank, thus achieving low aliasing where needed without incurring computational complexity everywhere.
Solution Approach 2:
The frequency spectrum is divided into segments with different processing strategies: complex exponential modulation for low frequencies to minimize aliasing, and cosine modulation for high frequencies to reduce computational load, thereby resolving the contradiction through frequency-based segmentation.
3Object-generated harmful factors
If gain locking is applied to reduce aliasing in cosine modulated filter banks, then aliasing is alleviated, but frequency selectivity is strongly reduced and sound source placement becomes problematic
Solution Approach 1:
The patent avoids applying gain locking to the low-frequency region where frequency selectivity is critical for spatial audio processing. Instead, it uses complex exponential modulated filter bank in this region which provides inherent aliasing reduction without compromising frequency selectivity. Gain locking is only applied where it does not degrade spatial audio 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.