12-13-2017, 11:09 PM
Citation :Timing is everything
The importance of a clean stable clock in digital audio is well documented, and transferring audio over USB isno exception. UAC offers three clocking mechanisms:
•Synchronous: The audio clock is derived from the USB start-of-frame signal and so is synchronous to the US
B host.
•Asynchronous: The audio clock is derived from an independent clock source, typically a crystal oscillator
in the USB audio device, or an external clock supplied to the USB audio device.
•Adaptive: The audio clock is derived from the flow of audio da
ta itself.
Each clocking method has pros and cons and best-fit applications. For example, asynchronous is particularly favoured for audiophile playback systems where a high stability clock source is implemented in the device, or
audio is synchronised to an external digital stream such as S/PDIF. Whereas synchronous enables audio content from multiple USB devices to be more easily aggregated by a host, without the need for complex
sample-rate conversion and so is often used in professional mixing systems.
UAC1 only allows for a single audio clock. UAC2 introduces the concept of ‘clock domains’ (one or more sample clocks synchronized to a common master clock) and the ability to support one or more clock domains, each derived from a different ‘clock entity’.
Both UAC1 and UAC2 offer the same three clocking schemes. However, UAC2 offers 8x the timing resolution in synchronous and adaptive modes, and allows complex multi-clocking domains to be configured and
controlled.
trouvé sur http://www.epsglobal.com/downloads/XMOS/...lass-2.pdf
l'UAC 1 ne veut pas dire forcément synchrone puisqu'il supporte les trois modes (le protocole).