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What is Asynchronous USB?
Data from the PC is received by an asynchronous USB in sync with its own internal clock. The internal clock of the USB DAC must time perfectly with the computer’s clock. The computer must transfer data as USB packets down the USB connection IN HARMONY with the asynchronous USB’s internal clock. The converter is driven directly by the DAC, eliminating the need for the computer’s erratic clock since it forces the two clocks to synchronize at the same time.
The quality of the USB audio transfer accounts for the asynchronous DAC’s high level of excitement. There won’t be any pauses in the flow of data sent and received since the computer synchronizes with the USB DAC’s internal clock. With it, the sound from an asynchronous USB DAC won’t be distorted or jittered.
Asynchronous USB transfer mode basically implies that a “downstream” audio device regulates when and how much data is sent over the computer’s USB interface, without all the marketing guff. It takes on the role of bus “master” and is no longer dependent on the USB interface logic or the computer’s internal clocks. Since clocking information must be retrieved from USB packet and frame timing signals, which are rarely precise enough for high-end audio applications, products employing synchronous or adaptive USB transmission are fundamentally “slaved” to the computer.