For instrument design 0.5ms is not significant, as long as there is no click. To put things into perspective, given a speed of sound of 350 m/s (at roughly 20 C), it takes the sound from an acoustic guitar you are playing 1.5ms to get to your ear (0.5 m). If you are playing with an amp that's 3m away, there is a ~9ms delay before you hear the sound.
when running your audio device with block sizes of 64 samples, it means, that audio data have to be computed within 1.3 ms. it you block the process for 0.5 ms the rest of the computation has to be done within 0.8 ms, having a cpu utilization of more than 60 % won't be possible without a dropout ...
but i have to admit, vanilla pd has some other problems, that don't allow to run audio computation with these latency settings (wini's alsamm code won't run with latencies below 10ms on my machine)
cheers ... tim
-- TimBlechmann@gmx.de ICQ: 96771783 http://www.mokabar.tk
Linux is like a wigwam: no windows, no gates, apache inside, stable.