I am experimenting with audio production under Linux Mint 20.3  (based on Ubuntu 20.04). I managed to install a low latency kernel, then I have installed JACK, and Qsynth, following the steps described in this tutorial:

http://www.tedfelix.com/linux/linux-midi.html

Everything seems to work fine if I use Qsynth and pulseaudio: I use the vmpk simple virtual keyboard, and I have good output sound.

I have also tested JACK, as suggested in the tutorial using

$ jack-play test.wav

and I hear the right clean output.

However, when I tell Qsynth to use JACK, I have a lot of noise. When I hit a key I have "white noise" for few milliseconds instead of the key sound, and only when it fades I have a little bit of the note that I was supposed to play.

I have the same "white noise" problem is I use Rose Garden.

I have tried to change the sample rate and the frames/period settings, and also the Timeout, in JACK, but the problem stays the same.

Thank you in advance for any help you can give.

Best,

Fabio