|
USB is an almost universal PC connector standard, probably far more common than any optical or RCA digital output on PCs. External devices support USB for the simple reason it's the broadest market base to sell to. USB devices can be plugged into any PC out there, and only require a fairly standardised software driver to work. Non-PC USB devices will have their own internal, custom software and it may not necessarily sync with the DAC if they're not intended to transmit audio data. USB is a packetised serial bus, however its bandwidth greatly (USB1.1), massively (USB2.0) or mindboggingly (USB3.0) exceeds the modest requirements of Red Book audio or even 24/192 "hi res" audio. As such, unless your USB DAC is sharing USB packet space with HDDs, digital cameras, printers, etc all blasting out data via some ghastly passive hub, you simply will not ever have issues with audio data flow. Synchronous vs Asynchronous only matters if your cheapass DAC clocks off the USB... Any DAC worthy of the name has an internal clock and will FIFO buffer the data from the USB bus. USB also carries power of course, and some external USB DACs will use this power. It is likely to be noisy if the PC motherboard's power grid isn't well regulated. Independently powered USB DACs needn't connect the power pins in the USB plugs, providing isolation from the PC's potential power noise.
In short, the USB interface will work fine and exists to enable the broadest possible range of connectable computers and thus the greatest market to sell to. EVERY PC on earth these days has a USB port. Any reasonably well designed and modestly priced USB DAC will avoid the obvious pitfalls of relying on the USB clock and power rails, assuming you worry about these things. Some of course are just meant as products of convenience for casual 'desktop' users on microbudgets and DO rely on these, and that's a perfectly ok design solution, that USB offers on purpose. |
|