Any sound I get from PD is full of clicks and other unpleasant, weird 'effects'. Even if I put just a noise~ and dac~ I cannot get clear sound. I'm sure it's because my computer is too slow. However, on every patch I've ever measured CPU, pd uses maximum 20% cpu, while about 5% is used by system & other apps. So I still have 75% cpu free. Anyway, pd cannot make use of this power and in the result the audio quality is quite poor. Running pd as root, in realtime mode doesn't help too much. Is there any way to simply improve pd's performance? I dunno, maybe changing bitrate or sth like that may result in better cpu usage, or maybe pd had a hardcoded limit forcing using less than f.e. 30% cpu?
Maybe a good tip is that I get many DIO errors, about 2 times / second there is a 'A/D/A sync error'. I use pd on Ubuntu Linux, and I always connect it to Jack Server.

did you try it without jack, just with the normal OSS or ALSA audio? i never had any success with jack. it's possibly the most illogical piece of software i have ever seen. i'm sure there's a way to tweak it to work with my system, but i have never found it.