Immersive Audio Bitstream Superframes for Downmix and Metadata Coding
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Solution Overview
Problem
Existing technologies face challenges in efficiently transmitting and storing immersive audio signals with high perceptual quality in a bandwidth-efficient manner, particularly for soundfield representation signals like ambisonics, which require a large number of channels and directivity patterns.
Innovation Solution
A method for generating a bitstream that includes a superframe structure comprising coded audio data and metadata, using a joint coding module to downmix and encode immersive audio signals, allowing for efficient transmission and reconstruction of immersive audio signals across various speaker arrangements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If immersive audio signals are transmitted using existing standards (MPEG‑1 Audio Layer‑2, MPEG‑4 AAC, MP3) then compatibility with current audio equipment is maintained, but the signals cannot be decoded by current equipment and require new decoders
Solution Approach 1:
The immersive audio signal is segmented into two separate streams: a downmix signal containing downmixed audio data that can be decoded by existing equipment, and a separate stream containing metadata and coded audio data for reconstructing the full immersive signal. This segmentation allows current equipment to process the downmix while new decoders can utilize all components for immersive playback
Solution Approach 2:
A downmix signal acts as an intermediary between traditional audio systems and immersive audio systems. The downmix contains coded audio data that serves as a bridge, allowing existing decoders to process the signal while preserving the ability to reconstruct the full immersive audio experience with appropriate metadata
2Loss of information
If the entire immersive audio signal is coded and transmitted, then complete audio information is preserved, but the data rate increases significantly
Solution Approach 1:
The essential immersive audio information is extracted and separated into two components: a compressed downmix signal that contains the core audio content at reduced data rates, and separate metadata that contains only the essential parameters needed for reconstruction. This extraction eliminates redundant information while preserving audio quality
Solution Approach 2:
The audio signal undergoes parameter transformation where the immersive audio is converted into a downmix representation with modified parameters (downmixed channels, reduced sample rates where applicable). The metadata captures the transformation parameters, allowing reconstruction without transmitting the full original signal data
3Device complexity
If downmix audio data is transmitted without separate metadata streams, then transmission simplicity is maintained, but the immersive audio signal cannot be accurately reconstructed
Solution Approach 1:
The downmix audio data and metadata are merged into a unified bitstream structure that can be transmitted as a single cohesive signal. The metadata is interleaved or appended with the downmix data in a way that preserves both components while maintaining transmission efficiency and enabling accurate reconstruction at the decoder
Data Source
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AI summary
The present document describes a method (500) for generating a bitstream (101), wherein the bitstream (101) comprises a sequence of superframes (400) for a sequence of frames of an immersive audio signal (111). The method (500) comprises, repeatedly for the sequence of superframes (400), inserting (501) coded audio data (206) for one or more frames of one or more downmix channel signals (203) derived from the immersive audio signal (111), into data fields (411, 421, 412, 422) of a superframe (400); and inserting (502) metadata (202, 205) for reconstructing one or more frames of the immersive audio signal (111) from the coded audio data (206), into a metadata field (403) of the superframe (400).