Audio Processor Frequency Enhancement via Envelope-Synchronized Pulse Excitation
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Solution Overview
Problem
Current audio signal processing methods for bandwidth extension often result in undesired artefacts due to mismatched spectral and phase characteristics in high-frequency signal generation, leading to perceptual quality degradation, especially at low bitrates.
Innovation Solution
The Waveform Envelope Synchronized Pulse Excitation (WESPE) method generates a pulse train signal synchronized with the time domain envelope of the low-frequency signal, placing pulses at specific features to create a perceptually adapted high-frequency signal, minimizing the need for post-processing corrections and improving frequency domain characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If spectral patching is used to generate high-frequency content from low-frequency signal, then bandwidth extension is achieved, but spectral and phase mismatches cause artefacts and perceptual quality degradation
Solution Approach 1:
The patent replaces traditional spectral-domain patching operations with a time-domain pulse excitation approach. Instead of copying spectral coefficients, the system generates high-frequency content by exciting a synthesis filter bank with pulses synchronized to the temporal envelope of the low-frequency signal, thereby avoiding spectral mismatches inherent in coefficient copying methods
Solution Approach 2:
The patent changes the fundamental parameter representation from spectral coefficients to temporal envelope features. By analyzing the temporal envelope characteristics (amplitude modulation, zero-crossing rates) and using these to drive pulse excitation, the system adapts high-frequency generation to the actual temporal structure of the input signal, improving spectral fine structure matching
2Reliability
If post-processing is applied to correct spectral envelope and tonality, then perceptual properties are adjusted, but complexity increases and residual mismatches remain
Solution Approach 1:
The patent performs preliminary adaptation of high-frequency content by synchronizing pulse excitation to the temporal envelope before the signal enters the synthesis filter bank. This pre-adaptation ensures that spectral fine structure, tonality, and noisiness are correctly generated from the outset, eliminating the need for subsequent post-processing correction stages
3Manufacturing precision
If cross-over frequency is set high to avoid artefacts, then high-frequency quality improves, but low-frequency bandwidth is reduced
Solution Approach 1:
The patent replaces spectral copying with temporal envelope-driven pulse excitation, enabling the cross-over frequency to be lowered to 1-2 kHz. The temporal synchronization mechanism ensures that even at these lower cross-over frequencies, the generated high-frequency content maintains proper spectral fine structure and phase relationships, avoiding artefacts that would normally require higher cross-over frequencies
Data Source
AI summary
An audio processor for generating a frequency enhanced audio signal from a source audio signal has: an envelope determiner for determining a temporal envelope of at least a portion of the source audio signal; an analyzer for analyzing the temporal envelope to determine temporal values of certain features of the temporal envelope; a signal synthesizer for generating a synthesis signal, the generating having placing pulses in relation to the determined temporal values, wherein the pulses are weighted using weights derived from amplitudes of the temporal envelope related to the temporal values, where the pulses are placed; and a combiner for combining at least a band of the synthesis signal that is not included in the source audio signal and the source audio signal to obtain the frequency enhanced audio signal.