USB noise filter, jitterbug or ifi

Thanks. I should have known. ASR covers it ;-)

recluse, jitter can be introduced with USB interface two ways - direct or indirect.  Direct happens when DAC uses average computer data rate as a source for D/A conversion rate (synchronous USB).  With asynchronous interface D/A clock and incoming data rate are independent and the problem of getting right amount of data is solved by signaling back to send more or less samples, but jitter can still be induced indirectly by injecting computer's electrical noise, that can affect D/A converter clock.  In either case computer initiates transfers and injects the noise.  Without computer DAC has to initiate transfers and there is no electrical noise to be injected.  I agree with Erik that such jitter reducing device should not make any difference with USB flash drive.

I'm using Wyred4Sound Recovery USB and find it highly effective. 

PS. The iFi noise filtering dongle has been proven to work as advertised by ASR, athough they were not able to measure effects at the DAC out.