I want to do a lot of music editing, recording, etc. First of all I installed Hydrogen and along with it came this 'Jack'. After I use hydrogen, my system sounds stop working and start again only after restarting. I tried Googling this problem and seems like several others have this problem too. The solutions there are actually some explanations and I don't have the patience to read all those pages! What I want regarding JACK audio is:

  1. A simple and proper understanding of what this software does so that solutions to this problem make sense. When we go to their actual website, they have all this long story of "Do you want to .... blah blah". When we go to the Wikipedia article, they straight away demoralize us with all technical terms.

  2. How I can close it along with Hydrogen so that my system sounds return to normal (OR) How I can make all my system functions works along with JACK. In this case, Jack will have to start with every boot.

  3. Hydrogen's default MIDI driver is ALSA (even when there is a jackmidi option); then why is jack needed at all?

2 Answers 2


Ubuntu uses PulseAudio by default. This is a sound server application based on ALSA with customizations to integrate it well in the Ubuntu desktop environment, and to operate well with all default applications.

This is very much different for JACK, a more professional sound server aimed at music production applications, possibly in a realtime environment. Therefore the more ambitious a software is the more likely it will make use of JACK. Which sound server a software uses is entirely up to the developers.

Because of the more professonal audience we do need to have the patience to read the documentation as only then we are able to make use use JACK's features aimed at our special tasks.

To be able to run both JACK, and PulseAudio there is quite some effort to integrate JACK into pulseaudio.



You've got all the JACK info in Takkat's answer.

However, it doesn't tell how to restore sound after using Hydrogen. I've run into the same problem, and after a little experimenting and talking to the Hydrogen guys, I've found out the only way that works for me is to kill the jackd process:

killall jackd

This is what happens:

The cause for that behaviour is that hydrogen starts jack if it is installed and if no other audio system was explicitly set in the hydrogen preferences. Hydrogen does not stop jack on shutdown, so the service is still running and may block other audio.

So how to solve that problem?

A) You can remove jackd if you don't need it

B) You can select an appropriate audio driver in the preferences panel

From: https://github.com/hydrogen-music/hydrogen/issues/134

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