Multichannel Audio Coding Phase Compensation
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Solution Overview
Problem
Existing audio signal processing technologies, such as the AC-3 digital audio encoding and decoding system, face challenges in efficiently representing and reconstructing multiple audio channels at low bitrate conditions, particularly in reducing coupling cancellation artifacts and improving spatial dimensionality of the reproduced signal.
Innovation Solution
The implementation of an N:1:N spatial audio coding technique that includes improved phase compensation, decorrelation mechanisms, and signal-dependent variable time-constants, allowing for continuous channel coupling at lower frequencies than traditional systems, and employing angle rotation and energy normalization to minimize out-of-phase signal cancellations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple audio channels are combined into a composite channel at high frequencies to reduce bitrate, then data rate requirements are reduced, but coupling cancellation artifacts occur due to out-of-phase signal components
Solution Approach 1:
The system performs preliminary phase alignment and angle rotation on audio channels before combining them into a composite channel. By pre-adjusting the phase relationships and applying angle rotation transformations, the system prevents out-of-phase cancellations from occurring during the coupling process, thereby eliminating coupling cancellation artifacts while maintaining bitrate reduction benefits
Solution Approach 2:
The system dynamically changes phase and angle parameters of audio channels based on signal characteristics. By adjusting phase angles and applying signal-dependent transformations, the system optimizes the coupling process to minimize cancellation artifacts while maintaining data rate efficiency
2Quantity of substance
If channel coupling is performed to reduce bitrate, then data rate requirements are reduced, but spatial dimensionality of the reproduced signal deteriorates
Solution Approach 1:
The system employs dynamic decorrelation mechanisms that adaptively adjust the degree of decorrelation based on signal characteristics and listening conditions. By dynamically modifying phase relationships and spatial parameters during playback, the system restores spatial dimensionality while maintaining the bitrate benefits of channel coupling
Solution Approach 2:
The system introduces auxiliary sidechain information as an intermediary that carries phase and spatial relationship data between the encoder and decoder. This sidechain information enables the decoder to reconstruct spatial dimensions by applying appropriate phase compensation and decorrelation, thereby maintaining spatial dimensionality despite channel coupling for bitrate reduction
3Device complexity
If fixed time-constants are used in channel coupling, then system complexity is reduced, but accuracy of phase compensation deteriorates
Solution Approach 1:
The system replaces fixed time-constants with signal-dependent variable time-constants that adapt to the characteristics of the audio signal. By dynamically adjusting the time-constants based on signal energy, frequency content, and temporal variations, the system achieves accurate phase compensation without requiring overly complex fixed-parameter systems
Data Source
AI summary
Multiple channels of audio are combined either to a monophonic composite signal or to multiple channels of audio along with related auxiliary information from which multiple channels of audio are reconstructed, including improved downmixing of multiple audio channels to a monophonic audio signal or to multiple audio channels and improved decorrelation of multiple audio channels derived from a monophonic audio channel or from multiple audio channels. Aspects of the disclosed invention are usable in audio encoders, decoders, encode/decode systems, downmixers, upmixers, and decorrelators.