Low Complexity Speech Bandwidth Expansion via Frequency Folding
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Solution Overview
Problem
Audio communication networks often suffer from bandwidth limitations, resulting in low-quality speech due to the absence of low and high frequency content, with existing solutions either requiring excessive resources and introducing latency or being impractical for audio applications.
Innovation Solution
The method involves frequency folding of narrow bandwidth signals, determining features such as signal band energy slope, and modifying the expanded signals using a shelf filter to enhance bandwidth, while adding noise to reduce harmonic signal characteristics, utilizing a processor and modules like signal fold and feature extraction to create an expanded audio signal spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If frequency folding and shelf filter modification are used to expand bandwidth, then audio quality is improved, but computational complexity increases
Solution Approach 1:
The audio signal is divided into multiple frequency bands (low, mid, high) that are processed independently through frequency folding operations. Each band is folded separately and then combined, allowing complex bandwidth expansion to be broken into manageable segments that reduce overall computational burden while maintaining audio quality
Solution Approach 2:
The patent applies shelf filters with different cutoff frequencies and gain parameters to different frequency bands. By dynamically adjusting filter parameters based on the folded signal characteristics, the system achieves high-quality bandwidth expansion without requiring overly complex processing for all frequency ranges simultaneously
2Manufacturing precision
If complex algorithms are used to reconstruct missing frequencies, then bandwidth is expanded, but processing latency increases
Solution Approach 1:
The patent performs frequency folding operations on the incoming narrowband signal in real-time as each audio frame arrives. Rather than waiting to collect multiple frames for complex reconstruction, the folding and shelf filter processing is applied immediately to each frame, minimizing buffering delays while still achieving bandwidth expansion
Solution Approach 2:
Different processing approaches are applied to different frequency regions. The shelf filters are configured with specific cutoff frequencies and slopes tailored to each band's requirements, allowing efficient processing in regions where full reconstruction is less critical while maintaining quality where it matters most, thereby reducing overall latency
3Manufacturing precision
If resource-intensive processing is applied to envelope and excitation signals, then bandwidth is expanded, but system resources are depleted
Solution Approach 1:
The patent extracts only the essential spectral characteristics from the narrowband signal through frequency folding, rather than performing full decomposition into envelope and excitation components. By taking out only the necessary frequency information and using shelf filters to shape the spectrum, the system achieves bandwidth expansion with significantly reduced computational resource consumption
Data Source
AI summary
Audio signal bandwidth expansion is performed on a narrow bandwidth signal received from a far end source. The far end source may transmit the signal over the audio communication network. The narrow band signal bandwidth is expanded such that the bandwidth exceeds that of the audio communication network. The signal may be expanded by performing frequency folding on the signal. One or more features are determined for the narrow bandwidth signal, and the expanded signal is modified based on a feature. The feature may be signal band energy slope, narrow band signal energy, or some other feature. The modification may be performed by a shelf filter selected based on the feature. The modified signals are provided for additional processing. In some embodiments, a noise component is added to the narrow band signal prior to folding to create an excitation that reduces the appearance of a fully harmonic signal characteristic.