Comment 7 for bug 347307

Hmm...could you be suffering from alsa underruns?

What if you specify

-o audio.period-size=4096

...that will probably give timing errors as well, but does it help against the distortions? If so, you could try changing 4096 to the smallest possible value that does not cause distortions (to get less and less timing problems). There is more information on the subject here:

http://fluidsynth.resonance.org/trac/wiki/LowLatency