Directional Audio Downmixing for Low-Bitrate Object Encoding
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Solution Overview
Problem
Existing audio encoding technologies face challenges in efficiently encoding multiple audio objects at low bitrates while maintaining high-quality reproduction, particularly when using Directional Audio Coding (DirAC) for object-based audio content, as they often require significant bitrate increases with the number of objects, leading to audible signal degradation.
Innovation Solution
A parametric approach is introduced that uses multiple directional cues per time/frequency unit, incorporating power ratios and object indices to downmix and decode audio objects efficiently, employing covariance synthesis and direction-dependent downmixing to enhance audio quality and reduce bitrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If discrete coding approach is used to encode multiple audio objects individually, then audio quality is maintained, but bitrate consumption increases prohibitively with the number of objects
Solution Approach 1:
The patent combines multiple audio objects into a single multichannel downmix signal for transmission, rather than encoding each object separately. This merging approach significantly reduces bitrate consumption while preserving spatial audio information through efficient covariance synthesis at the decoder side.
Solution Approach 2:
The downmix signal serves multiple functions simultaneously: it carries the combined audio content of multiple objects, encodes spatial positioning information through covariance matrices, and provides a basis for reconstructing individual object streams at the decoder, eliminating the need for separate encoding of each object.
2Quantity of substance
If parametric approaches are used to reduce bitrate, then bitrate consumption is reduced, but audio quality and spatial accuracy deteriorate
Solution Approach 1:
The patent transforms the audio signal into the frequency domain and represents spatial characteristics using covariance matrices in the spectral domain. This parameter transformation enables efficient compression while preserving spatial information, as the covariance synthesis can accurately reconstruct temporal correlations from the spectral parameters.
Solution Approach 2:
The patent replaces traditional time-domain audio processing with frequency-domain covariance synthesis. Instead of directly processing audio waveforms, the system uses spectral representation and covariance matrices to encode and reconstruct spatial audio, achieving both compression and high fidelity.
3Productivity
If standard covariance synthesis is used for decoding, then audio objects are reconstructed, but decorrelator-induced artifacts degrade audio fidelity
Solution Approach 1:
The patent converts the harmful decorrelator artifacts into beneficial spatial diffusion effects. By intentionally introducing controlled decorrelation in the covariance synthesis process, the system creates natural-sounding spatial ambient effects that mask the artifacts and enhance the perception of spatial audio environment.
Solution Approach 2:
The patent modifies the covariance synthesis parameters to optimize the balance between reconstruction accuracy and artifact suppression. By adjusting the regularization parameter and covariance matrix computation method, the system achieves high-fidelity reconstruction while minimizing decorrelator-induced artifacts.
Data Source
AI summary
An apparatus for encoding a plurality of audio objects and related metadata indicating direction information on the plurality of audio objects has: a downmixer for downmixing the plurality of audio objects to obtain one or more transport channels; a transport channel encoder for encoding one or more transport channels to obtain one or more encoded transport channels; and an output interface for outputting an encoded audio signal comprising the one or more encoded transport channels, wherein the downmixer is configured to downmix the plurality of audio objects in response to the direction information on the plurality of audio objects.