Encoded Audio Scene Parameter Conversion for Low-Delay Stereo
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Solution Overview
Problem
Existing audio processing systems face challenges in rendering immersive audio scenes at low bitrates with high delay and complexity, particularly in mono or stereo setups, due to the use of Directional Audio Coding (DirAC) which requires additional filter-bank analysis, leading to suboptimal delay and complexity.
Innovation Solution
A parameter conversion approach using Short-Time Fourier Transform (STFT) filterbank for upmixing a single downmix channel into stereo output without additional delay, combined with bandwidth extension and parameter smoothing to reduce overall delay and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DirAC renderer with CLDFB filter-bank analysis is used for spatial restoration, then spatial information is restored, but overall delay increases significantly
Solution Approach 1:
The patent changes the parameter representation from DirAC's filter-bank domain parameters to STFT-based frequency domain parameters. This allows the same spatial restoration function to be achieved with different mathematical tools that have lower computational delay, specifically using Short-Time Fourier Transform instead of Complex-valued Low-Delay Filter-Bank
Solution Approach 2:
The patent replaces the mechanical filter-bank processing system with a frequency-domain STFT-based system. This substitution eliminates the need for complex filter-bank analysis and synthesis operations, thereby reducing the processing delay while maintaining spatial restoration capability
2Ease of operation
If FOA upmix with L/R conversion is used for stereo output, then stereo output is achieved, but processing complexity and delay increase
Solution Approach 1:
The patent extracts and eliminates the unnecessary FOA upmix and L/R conversion steps from the traditional DirAC processing chain. By using STFT-based parameter conversion directly to stereo parameters, the system achieves stereo output without the intermediate FOA representation, thereby reducing processing complexity
Solution Approach 2:
Instead of converting from mono to FOA to stereo (the traditional DirAC path), the patent inverts the approach by directly converting from mono to stereo parameters using STFT. This reverse engineering of the processing path eliminates unnecessary intermediate steps and reduces overall complexity
3Measurement precision
If additional filter-bank analysis is performed for spatial restoration, then spatial accuracy is improved, but processing time increases
Solution Approach 1:
The patent changes the mathematical representation of spatial parameters from filter-bank domain to STFT frequency domain. This parameter transformation allows spatial accuracy to be maintained through frequency-domain convolution operations that are computationally more efficient than time-domain filter-bank analysis, thereby improving processing speed
Data Source
AI summary
An apparatus for processing an encoded audio scene representing a sound field related to a virtual listener position, the encoded audio scene including information on a transport signal and a first set of parameters related to the virtual listener position includes a parameter converter for converting the first set of parameters into a second set of parameters related to a channel representation including two or more channels for a reproduction at predefined spatial positions for the two or more channels, and an output interface for generating a processed audio scene using the second set of parameters and the information on the transport signal.