Al - at 192 sample-rate, the frequency is only 50MHz.
Steve, note that I said that "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)."
Surely the risetimes and falltimes of USB 2.0 signals don't change as a function of data rate. Or so it seems to me, at least in situations where the link is actually being used in USB 2.0 mode, and is not falling back to USB 1.1 operation. And therefore the risetimes and falltimes would have to be compatible with the fastest rate USB 2.0 can support.
Also, isn't 192 kHz/24 bit/2 channel data more like 10 MHz, plus a bit more for protocol overhead, rather than 50?