Audio Interface
Digital audio interface
同轴（Coaxial）
The transmission is a digital signal, the protocol is SPDIF, and the transmission medium is a cable, and different manufacturers may use different interfaces. For example: Type-C, RCA, 3.5mm interface, etc.
Fiber (or Toslink Optical)
The transmitted signal is a digital signal, the protocol is SPDIF, and the transmitted medium is an optical fiber
USB audio signal
USB audio input and output, sometimes called USB Audio, USB DAC, and UAC. Refers to the transmission of USB audio signals through a USB cable.
It is necessary to be careful to distinguish it from coaxial (Type-C -> RCA). The coaxial and USB audio of the HiBy player are connected through the Type-C interface, but the transmitted signals are different.