Symmetry-Based Downmix Matrix Encoding for Flexible Spatial Audio
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Solution Overview
Problem
Existing spatial audio coding and decoding technologies face inefficiencies in encoding and decoding downmix matrices due to the lack of flexibility and precision in handling speaker configurations, leading to increased bit usage and reduced compatibility with varying speaker setups.
Innovation Solution
Exploiting symmetries in speaker pair configurations to create a compact downmix matrix, using significance values and run-length coding, along with limited Golomb-Rice encoding to reduce the number of gain values and improve encoding efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional downmix matrix encoding methods are used, then all mixing gains are encoded with full precision, but the bit usage increases significantly
Solution Approach 1:
The patent applies local quality by differentiating the encoding precision for different groups of mixing gains. Symmetric speaker group mixing gains are encoded with reduced precision (e.g., 3 bits) while asymmetric speaker group mixing gains are encoded with full precision (e.g., 6 bits). This selective precision approach maintains audio quality where needed while reducing bit usage where symmetry allows for lower precision representation.
2Quantity of substance
If symmetry exploitation is applied to encode downmix matrix, then the number of bits required is reduced, but the complexity of encoding/decoding increases
Solution Approach 1:
The patent applies preliminary action by pre-identifying and categorizing speaker groups into symmetric and asymmetric categories before the actual encoding process. The encoder determines symmetry relationships in advance and prepares the appropriate encoding strategy for each group. This preliminary classification simplifies the subsequent encoding process by providing a clear framework for applying different precision levels to different speaker groups.
3Quantity of substance
If reduced precision encoding is used for symmetric speaker groups, then bit usage decreases, but the compatibility with varying speaker configurations is reduced
Solution Approach 1:
The patent applies dynamics by making the encoding precision adaptive rather than fixed. The encoder dynamically determines which speaker groups exhibit symmetry relationships and applies reduced precision encoding only to those groups. Asymmetric speaker groups or configurations that don't meet symmetry criteria are encoded with full precision. This dynamic approach maintains compatibility with varying speaker configurations while still achieving bit rate reduction where applicable.
Data Source
AI summary
A method is described which decodes a downmix matrix for mapping a plurality of input channels of audio content to a plurality of output channels, the input and output channels being associated with respective speakers at predetermined positions relative to a listener position, wherein the downmix matrix is encoded by exploiting the symmetry of speaker pairs of the plurality of input channels and the symmetry of speaker pairs of the plurality of output channels. Encoded information representing the encoded downmix matrix is received and decoded for obtaining the decoded downmix matrix.