Title: A 'Crackling' Sound Is Heard When Playing Qsynth
While playing Qsynth (or Fluidsynth), a 'crackling' (static) sound is heard occasionally.
Cause Of Problem:
Often this is caused by the volume being set too loud on Qsynth. I usually set the master volume of the Qsynth engine being used, to 67. Another cause could be that your machine is not fast enough to generate the sound, and you get under-run conditions (Qsynth can't keep up with the sound-card), producing 'clicks and pops' in the sound.
If reducing the Qsynth volume doesn't solve it, it's probably the under-run problem.
If you're using PulseAudio, re-configure Qsynth to use JACK, and run it with JACK (qjackctl). See the “Improving Your Linux System” documentation for instructions on how to do that.
If that doesn't solve the problem, your machine may be too slow to use Qsynth (or it may not have a floating-point-unit (FPU) in its processor, which really improves the ability of your machine to handle Qsynth. In such cases, you can't reliably use Qsynth (or Fluidsynth).
Fix Available (in version):
The only fix for this, if it's the latter problem, is to use a faster machine.