[linux-audio-user] Noise problem, qsynth, jack

Hi all, I use my midi keybord to play soundfonts on qsynth (via jack). The problem is that a lot of soundfonts sound bad. I hear some ssshhhhh noise when I play a note. On some soundfonts this problem appears with a simple key press (this might be a bad soundfonts), but on others, it appears only when I hit the key with more power, or if I play multiple notes at the same time (then there is sound saturation) Also, I have jack Xruns (more and more when using at the same time freewheeling, mutiple qsynth, hydrogen..) In general, the sound quality is bad (even when not using qsynth but zynadd, ...). All of my records are bad. My PC : - 1GB ram - 2.6 Ghz Sound card : well..an old soundblaster 128 (could this be the problem?) My jack configuration is : - real time - no memory lock - soft mode - force 16bit - priority : 50 - frames/perdio : 512 - sample rate : 48000 - periods/buffer : 2 - port maximum : 128 - timeout : 2000 it shows as result latency : 21.3 msec qsynth config : - sample rate : 48000 - buffer size : 512 - buffer count : 2 - polyphony : 256 - sample format : 16bits How can I improve sound quality ? (ps : mic & capture are turned off) thanks a lot !