Matrix-Coded Stereo Downmixing for Spatial Audio Continuity
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Solution Overview
Problem
Existing audio processing technologies struggle to preserve spatial relationships between audio elements when downmixing multi-channel audio signals into two-channel stereo signals for spatial audio reconstruction, particularly in surround sound systems.
Innovation Solution
A matrix coded stereo signal with periphonic elements is constructed using a mixing matrix that applies complex gain elements and phase corrections to preserve spatial relationships, adhering to specific matrix encoding rules and phase-preference rules to minimize discontinuities in panning functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional downmixing method is used to transform M-channel audio signal to two-channel stereo signal, then the audio signal can be transported over a two-channel connection, but the spatial relationships between audio elements are not accurately preserved and discontinuities occur in the panning function
Solution Approach 1:
The patent applies parameter changes by modifying the panning function parameters to include phase information. The mixing matrix coefficients are defined as complex values with magnitude and phase components, allowing continuous phase transitions as audio elements move across the sound field. This resolves the discontinuity problem while maintaining spatial accuracy in the downmixed stereo signal.
Solution Approach 2:
The patent introduces a phase dimension to the traditional magnitude-only panning function. By representing mixing coefficients as complex numbers with both magnitude and phase components, the system adds an extra dimension to control spatial relationships, enabling continuous transitions and accurate positioning that cannot be achieved with magnitude-only approaches.
2Device complexity
If a simple downmixing approach is used, then the processing complexity is low, but the panning behavior has discontinuities and spatial accuracy deteriorates
Solution Approach 1:
The patent changes the parameter representation from real-valued magnitudes to complex-valued coefficients with phase information. This allows the panning function to maintain continuity by utilizing phase wrapping, where phase transitions smoothly from 0 to 2π as audio elements cross boundaries, eliminating discontinuities without significantly increasing processing complexity.
3Ease of manufacture
If traditional panning functions are used without phase consideration, then the implementation is simple, but phase incompatibility occurs between different gain elements
Solution Approach 1:
The patent extends the panning function to include phase parameters, defining mixing coefficients as complex values. The phase component is calculated based on the audio element's position and the panning function, ensuring that phase relationships between different gain elements are consistent and compatible, which is essential for accurate spatial reconstruction during upmixing.
Data Source
AI summary
Embodiments are disclosed for a matrix coded stereo signal with periphonic elements. A mixing matrix, suitable for processing a multi-channel audio input signal, is constructed so that the resulting multi-channel output signal contains the same audio elements from the input signal, wherein the spatial relationships between audio elements, as defined by panning rules associated with the input signal format, are preserved in the output signal, as defined by matrix encoding rules associated with the output signal format. The choice of the coefficients of the mixing matrix is governed by a phase-preference rule that is used to determine the appropriate phase to apply to each input signal channel.