Audio Bandwidth Extension Decoder Using Temporal Spreading
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Solution Overview
Problem
Existing bandwidth extension methods for audio signals result in high complexity and quality loss, particularly at low bitrates, with artifacts such as roughness and timber perception issues due to harmonic relations being overlooked.
Innovation Solution
A decoder-based method using temporal signal spreading and decimation, combined with bandpass filtering, to generate a high-frequency signal portion without requiring complex harmonic transposition or analysis/synthesis filterbanks, utilizing a phase vocoder for efficient bandwidth extension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If harmonic transposition with filterbank patching is used for bandwidth extension, then audio quality is improved, but computational complexity increases significantly
Solution Approach 1:
The patent extracts only the essential spectral envelope information from the lower band signal and applies it to synthesize the upper band, rather than performing complete harmonic transposition with filterbank patching. This extraction approach maintains audio quality while significantly reducing computational complexity by eliminating the need for complex filterbank operations.
Solution Approach 2:
The patent changes the approach from time-domain filterbank operations to frequency-domain spectral envelope manipulation. By transforming the problem into parameter-based spectral shaping rather than signal-based filterbank processing, computational complexity is reduced while preserving audio quality.
2Device complexity
If copying function of low-frequency signals into high-frequency range is used, then computational complexity is reduced, but audio quality deteriorates with artifacts
Solution Approach 1:
The patent introduces spectral envelope as an intermediary that mediates between the simple copying approach and the complex harmonic transposition. The spectral envelope captures the essential harmonic structure and uses it to shape the synthesized upper band, eliminating artifacts while maintaining low computational complexity.
Solution Approach 2:
The patent combines elements of both approaches: the simplicity of signal copying with the quality enhancement of spectral envelope modeling. The synthesized upper band is formed by combining copied low-frequency content with spectrally-shaped components, creating a composite signal that achieves high quality with low complexity.
3Manufacturing precision
If complex spectral envelope adjustment and post-processing is applied, then audio quality is improved, but processing delay increases
Solution Approach 1:
The patent applies partial spectral envelope adjustment rather than complete post-processing. By applying spectral shaping only to the essential spectral envelope parameters and leaving the temporal structure intact, audio quality is improved while processing delay is minimized through selective rather than comprehensive processing.
Data Source
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AI summary
For a bandwidth extension of an audio signal, in a signal spreader the audio signal is temporally spread by a spread factor greater than 1. The temporally spread audio signal is then supplied to a decimator to decimate the temporally spread version by a decimation factor matched to the spread factor. The band generated by this decimation operation is extracted and distorted, and finally combined with the audio signal to obtain a bandwidth extended audio signal. A phase vocoder in the filterbank implementation or transformation implementation may be used for signal spreading.