If you are using an Octamic XTC in USB class compliant mode with Logic Pro, you may be getting dreaded, periodic I/O errors, as do I. There is a workaround.
The XTC's default config in Audio/MIDI Setup in OSX is 24-in, 24-out. My 2010 MBP apparently has trouble with this (I/O and MIDI sync errors), but I found that the errors do not occur in the XTC's resource-saving 8-in, 4-out mode. But, there is a catch. The config must be set after Logic Pro is launched, because LP will force the config back to 24-in, 24-out upon launch.
So, make sure to set the audio config to 8-in, 4-out after launching Logic, and you'll be able to record without errors.
Enjoy!