Audio Processor Bandwidth Extension Using WESPE Pulse Excitation
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Solution Overview
Problem
Existing bandwidth extension techniques in audio coding struggle to efficiently extract and smooth the time envelope for low complexity systems, leading to difficulties in controlling and steering the high-frequency content generation.
Innovation Solution
The proposed audio processor uses a Waveform Envelope Synchronized Pulse Excitation (WESPE) technique, which includes an envelope determiner, analyzer, excitation generator, extended band generator, and combiner to efficiently extract and smooth the time envelope, allowing for controlled pulse placement and high-frequency content generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional bandwidth extension techniques (copy-up, mirroring, non-linear operations) are used to generate high-frequency content, then the high-frequency fine structure can be preserved to some extent, but the control and steering of the generated content becomes difficult
Solution Approach 1:
The patent transforms the uncontrolled non-linear operations into a controlled process by changing the parameters of pulse placement. Instead of using complex non-linear operations, the invention places pulses at specific positions determined by the envelope maxima, with amplitudes controlled by envelope values. This allows precise control over the generated high-frequency content while preserving its natural structure.
2Ease of operation
If WESPE technique is used with pulse placement at envelope maxima, then control over high-frequency content generation is improved, but the extraction and smoothing of temporal envelope becomes more complex
Solution Approach 1:
The patent segments the envelope extraction process into distinct stages: initial envelope extraction from the signal, identification of envelope maxima positions, and smoothing of the envelope values. This segmentation allows each stage to be optimized independently, reducing overall complexity while maintaining control precision.
Solution Approach 2:
The patent performs preliminary extraction and analysis of the temporal envelope before the actual pulse placement and signal generation. By pre-computing the envelope maxima positions and values, the system prepares control parameters in advance, simplifying the real-time processing and reducing computational complexity during critical signal generation phases.
3Manufacturing precision
If extensive envelope extraction and smoothing is performed to achieve precise pulse placement, then the quality of bandwidth extension is improved, but the algorithmic delay and computational complexity increase
Solution Approach 1:
The patent applies partial smoothing to the temporal envelope - only enough smoothing to identify clear maxima positions for pulse placement, rather than extensive smoothing that would introduce significant delay. This partial action approach achieves sufficient precision for effective pulse placement while minimizing algorithmic delay and computational complexity.
Data Source
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AI summary
The audio processor (10) for extended a band-limited audio signal, comprising: an envelope determiner (12) for determining a temporal envelope (TDE) from a linear prediction residual of the band-limited audio signal (AS) or an excitation modelling the linear prediction residual of the band-limited audio signal (AS); an analyzer (14) for analyzing the temporal envelope (TDE) to determine certain values (V) of the temporal envelope (TDE); an excitation generator (16) for generating an excitation (E), by placing pulses in relation to the determined certain values (V), wherein the pulses are weighted using weights derived from the temporal envelope (TDE); an extended band generator (18) generating an extended-band audio signal (EBAS) by processing the generated excitation (E); a combiner (20) combining the band-limited audio signal (AS) with the generated extended-band audio signal (EBAS) to obtain a frequency enhanced audio signal (FEAS).