08-24-13: AudioengrThanks, Steve. Based on your experience I don't doubt that 1.5 meters is a good length for a USB computer-to-DAC cable. The rationale still puzzles me, though. Given that USB 2.0 supports a theoretical maximum bit rate of 480 mbps, using both the positive-going and negative-going clock edges, the risetimes and falltimes of USB 2.0 signals would seem to have to be able to support a clock period of around 4 ns (approximately 1/240 MHz). Which would say that risetimes and falltimes have to be in the vicinity of 1 ns at most. Very different than the 25 ns or thereabouts upon which the rationale for 1.5 meter S/PDIF cables is based.
Al - risetimes may be a bit faster with some USB interfaces, but the length minimum still applies.
Regards,
-- Al