Help! Qjackctl is not able to shut down jack
This is a known bug with jackdbus on 12.04 LTS. To shut down jackdbus, use this command in a terminal:
killall -9 jackdbus
I can't seem to get sound when I use qjackctl
If you can start jack, but there's no sound, there are two likely reasons for this.
If you have multiple audio devices, you need to make sure to choose the right device after each boot in Qjackctl -> Setup -> Interface
Your audio device is muted, but the controls aren't visible to Pulseaudio. For PCI and USB, use alsamixer or a specific mixer for your device. For firewire use ffado-mixer.