Audio Decorrelator Using Phase-Flip and Delay for Artifact-Free Upmixing
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Solution Overview
Problem
Conventional upmixing devices face challenges in achieving sufficient psychoacoustic decorrelation of audio signals without introducing audible artifacts, while maintaining signal discreteness and compatibility with non-decorrelated signals for effective audio width enhancement.
Innovation Solution
The implementation of a psychoacoustic decorrelation technique using a decorrelator with a phase-flip filter and frequency-dependent delay, which processes audio signals through separate paths with phase-flip and high-pass/low-pass filters to achieve zero average correlation across critical bandwidths, ensuring the decorrelated signals sound distinct and artifact-free.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional decorrelation techniques (all-pass filters with random phase responses) are used, then decorrelation is achieved, but audible artifacts are generated and signal discreteness is compromised
Solution Approach 1:
The patent changes the phase response parameters of the all-pass filters from random to specific patterns (0, π/2, or -π/2) that are adapted based on frequency band and signal characteristics. This parameter change enables the system to achieve decorrelation while avoiding audible artifacts by selecting optimal phase values that maintain signal quality.
Solution Approach 2:
The patent implements dynamic adaptation of the decorrelation technique based on real-time analysis of the audio signal. The system determines whether to apply decorrelation and which specific decorrelation method to use based on the signal's characteristics, allowing flexible adjustment to maintain both decorrelation effectiveness and audio quality without artifacts.
2Reliability
If strong decorrelation is applied to ensure distinct audio images, then audio width is enhanced, but mixing with non-decorrelated signals generates audible artifacts
Solution Approach 1:
The patent applies different phase shift parameters (0, π/2, or -π/2) based on the frequency band and signal characteristics. This selective parameter application ensures sufficient decorrelation for audio width enhancement in appropriate frequency ranges while avoiding excessive decorrelation that would cause artifacts when mixing with non-decorrelated signals.
Solution Approach 2:
The patent applies different decorrelation strengths and types to different frequency bands and signal components. High-frequency components receive different treatment compared to low-frequency components, allowing optimal decorrelation for audio width where needed while preserving compatibility with non-decorrelated signals in other regions.
3Reliability
If psychoacoustic decorrelation is achieved through numerical correlation manipulation, then signal discreteness is improved, but the process complexity increases
Solution Approach 1:
The patent uses simplified models of psychoacoustic correlation based on critical bandwidth filtering and standardized phase shift patterns. Instead of complex numerical correlation calculations, the system uses copied and transformed versions of the input signal through predetermined filter patterns that replicate the essential psychoacoustic effects with reduced computational complexity.
Solution Approach 2:
The patent divides the audio signal into different frequency bands using critical bandwidth filtering, then applies specific decorrelation techniques to each segment independently. This segmentation allows the system to achieve psychoacoustic decorrelation through simpler, band-specific processing rather than complex full-signal manipulation.
Data Source
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AI summary
An improved decorrelator is disclosed that processes an input audio signal in two separate paths. In one path, a banded phase-flip filter is applied to lower frequencies of the input audio signal. In a second path, a frequency-dependent delay is applied to higher frequencies of the input audio signal. Signals from the two paths are combined to obtain an output signal that is psychoacoustically decorrelated with the input audio signal. The decorrelated signal can be mixed with the input audio signal without generating audible artifacts.