Martijn Sipkema wrote: > > > It's not unusable, but IIRC it can get to several ms of jitter. > > > > Why is that? The USB iso clock is every ms IIRC, so naively you > > would expect the maximum jitter to be just under 1ms (if the bus was > > saturated by audio transfers), and less in proportion to the degree of > > saturation.
USB transfers always wait for the beginning of the next frame, so the maximum jitter is never less than 1 ms, even on an otherwise free bus. > Yes, one would expect that (if there are no other bulk transfers), but > somehow this does not seem to be the case: > > http://www-2.cs.cmu.edu/~eli/papers/icmc01-midiwave.pdf These measurements include the jitter added by the drivers and by the high-quality realtime-capable (yeah :-) Windows 98 scheduler. I did some similar measurements under Linux, and it seems the jitter isn't bigger than the expected 1 or 2 ms (2 because MIDI through involves two USB transfers). Regards, Clemens
