I discovered this thread kindof late... To the V-DAC owners: I know the V-DAC quite well, have tweaked it alot, I even wrote my own firmware for it. Don't use its USB input if you have other options, better use coax or optical if coax gives you ground loop problems.
The PCM2706 is used as USB->SPDIF converter, feeding one of the 4 inputs of the upsampler, the other inputs being the coax and optical plugs. So if you use USB, your chain is longer by that chip making S/PDIF from it again. The USB input chip is sub-par with the capabilities of the DAC, only capable of 16 bit and up to 48 kHz. To my only partial understanding, USB Adaptive mode is a pretty bad idea, introducing a lot of jitter. The host (normally the PC) sends data with its own pace, jittered like hell because e.g. it is chopped into USB packets. The poor device (USB DAC) has the tough job to recover a steady clock from that. This works far less well than recovering a SPDIF clock. Asynchronous mode is the current hype. In this case the *device* sets the clock, the host has to deliver with that speed. No need for the DAC to recover a clock at all, it can use a fixed internal ultraclock. Only by using this scheme a USB DAC can outperform SPDIF in terms of jitter. Jörg -- [IDC]Dragon ------------------------------------------------------------------------ [IDC]Dragon's Profile: http://forums.slimdevices.com/member.php?userid=5111 View this thread: http://forums.slimdevices.com/showthread.php?t=82110
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