用一阶DirAC改进3维声场编码，低码率下实现沉浸式音频传输
A first-order DirAC-based parametric Ambisonic coder for immersive communications
- 将合成过程移到球谐函数域，降低延迟与码率
- 在32-128kbps下成功编码三阶声场，性能优于现有方案
- 专为3GPP标准中的沉浸通信设计，适合低带宽实时场景
方向性音频编码（DirAC）是一种成熟的参数化方法，可用于以B格式表示三维音频场景，并能在任意扬声器布局上还原。尽管该方法看似适合低码率的全向声场传输，但实际系统构建研究较少。本文基于一阶DirAC模型，提出一种用于高阶全向声场（HOA）的编码方案，作为将3GPP EVS编解码器扩展至沉浸式通信标准的一部分。通过将完整合成过程引入球谐函数域，有效降低了算法延迟、参数码率和计算复杂度。在32至128 kbps码率下对三阶全向声场的评估表明，该参数化方法相比现有方案具有明显优势。
原文摘要 · Abstract (English)
Directional Audio Coding (DirAC) is a proven method for parametrically representing a 3D audio scene in B-format and is capable of reproducing it on arbitrary loudspeaker layouts. Although such a method seems well suited for low bitrate Ambisonic transmission, little work has been done on the feasibility of building a real system upon it. In this paper, we present a DirAC-based coding for Higher-Order Ambisonics (HOA), developed as part of a standardisation effort to extend the 3GPP EVS codec to immersive communications. Starting from the first-order DirAC model, we show how to reduce algorithmic delay, the bitrate required for the parameters and complexity by bringing the full synthesis in the spherical harmonic domain. The evaluation of the proposed technique for coding 3\textsuperscript{rd} order Ambisonics at bitrates from 32 to 128 kbps shows the relevance of the parametric approach compared with existing solutions.
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