The Sound Devices USBPre2 could be considered an industry standard audio interface for 2 channel measurement purposes. I own so many audio interfaces already that I haven’t really given the USBPre2 a second thought but I’ve recently seen a need for a smaller 2 channel audio i/o that is buss powered and USB based.
Of special interest for measurement purposes is the units internal loop through feature. This is a quote from the user guide (PDF page 20).
“Input 2 Loop Source – Input 2 has an additional source labeled LOOP. This input source does not correspond to any physical connections on the USBPre 2. When LOOP is selected, input 2’s source is derived from the left channel of the computer audio signal (post digital-to-analog conversion). The input 2 Gain Control
affects signal The Output Gain Control does not affect the level of the signal going in to input 2.The LOOP source is useful for test and measurement applications where a reference signal is required to be routed back to an input.”
What this means is that instead of needing a cable to jump from an output back into an input to provide a reference signal that follows the same circuitry and has the same latency as the measurement, select the loop through and no cable is necessary. Many times I have to go hunt for a TRS to TRS cable for this purpose so having an audio i/o with an internal loop through removes one more external element which is always a good thing when seconds count.