USB Playback Messed up

Lets start with specs:
Dual Core AMD Athlon, 2.1 Ghz
64-bit Realtime kernel (2.6.31-10-rt)
Ubuntu 10.04
Jack (or “jackd” as its called in ubuntu) v 0.118.0
NVidia High Definition Audio (internal soundcard)

Jack works great with my NVidia soundcard. But i use an Edirol UA-25 for recording and stuff. Playback using other servers such as PulseAudio, direct connection to ALSA, etc. works great. But no matter what i do, Playback using Jack through my UA-25 card is really messed up. There is this weird distortion. Its like this crunching sound. Jack is running with realtime priority, i have set the limits.conf file as recommended, i joined the audio group, and nothing has worked. I am lost as to what to do. It seems the problem is in Jack as i have managed to play audio smoothly using other sound servers, and yet Jack works perfectly fine on my crappy little internal soundcard. any suggestions?

What are your settings for jack?

Here are my current jack settings. before taking the screenshot, timeout was at 1000, but im going to try 9000.

I have the same card, and works flawlessly, on 10.04. Try to set Timeout (msec) to 9000, and 3 periods/buffers. Frames/period must be no less than 128 for recording, better 256. But if you are mixing something with a lot of tracks and effects, set it even higher to have it reliable.

Does it work? Try seq as MIDI driver, and 3 buffers instead of 4, everything else is ok, it should work that way. Also, make sure the advance mode switch in the Edirol UA-25 is on, and the freq switch is set on 48k.