[LAT] A guide to optimize JACK?

Hi there!, I want to optimize JACK capabilities in running Linux PCs. What JACK configuration parameters do I have to vary (and in what way) to achieve that? (by "that" I mean: minimum latency, zero noise and zero xruns). I'm looking for something like a "standard procedure"... ...not just trying all the possible configurations of JACK and picking up the most convenient. (... maybe an "autoJACKtuning" program can be done for this purpose, but there MUST be a procedure to follow) Maybe you just can't tune the best of every system by following the same pattern, but making the average best is what i'm looking for. I'm working in a program that's a metronome that reacts to human synchronization errors (to the very same metronome). That errors are just some milliseconds, and a further advance in the program would need reacting as quickly as that - Fast!. In some ways, the program is similar to a tap-tempo thing, but it's meant for synchronization experiments. That experiments are aimed at researching how do people sync themselves to outer stimuli, like... the beat of a song. Results of that can end up in cool stuff - e.g., the possibility of making the sync of drum-machines REALLY human-like. Well... This program should be as "portable" as it can be.... but I'm having trouble with some audio cards. I don't think powerful sound cards are needed for this task... the bottleneck seems much more of a OS scheduling thing. I turned to JACK because of the promised low latencies and throughput (and an easy API)... ... but sometimes the audio crackles, has xruns, can't get it to work even with high latency, etc... and I don't have a clue about what to vary to fix that. Besides that, I'm kind of a musician too and it seems everybody who uses JACK wants low low low latency and good sound, so a "guide" to tune up that would be a step forward to the self promotion of JACK-based software. Sorry for my Neanderthal-ish English and cheers from Argentina, Trece.