Hi, Djim:
Well, that's the much-dreaded computer latency. Your 'puter is having difficulty processing everything in time and stutters and hiccoughs over notes.
When using internal sounds and/or virtual instruments, remember that the computer has to calculate all of the audio as well as send midi messages (and do the housekeeping stuff within Composer) (and run your anti-virus software and your network etc.). So, it takes serious processing horsepower to make it work.
If the host for your virtual instruments can use ASIO drivers (
www.asio4all.com), then that may fix some of it or even all of it. Setting the number of read buffers used by your host to a higher number or using fewer virtual instruments, ie., smaller processing demands will also help.
Of course, outboard (read: REAL) instruments don't take that kind of internal processing power, so they would likely eliminate it altogether. But they rarely come as freeware.
Merry Christmas
David