MIDI

If your hardware doesn't support MIDI, then you can use FluidSynth to do so.

I installe fluidsynth and qsynth.

After trying to run qsynth, then clicking "Start", it complained:

JACK is running in realtime mode, but you are not allowed to use realtime scheduling.
Please check your /etc/security/limits.conf for the following lines
and correct/add them:

  @audio          -       rtprio          100
  @audio          -       nice            -10

After applying these changes, please re-login in order for them to take effect.

You don't appear to have a sane system configuration. It is very likely that you
encounter xruns. Please apply all the above mentioned changes and start jack again!
fluidsynth: error: Failed to connect to Jack server.

I made the changes as recommended, closed qsynth, and ran it again, clicking on "Start". This time, it said:

JACK is running in realtime mode, but you are not allowed to use realtime scheduling.

Your system has an audio group, but you are not a member of it.
Please add yourself to the audio group by executing (as root):
  usermod -a -G audio jgardner

After applying these changes, please re-login in order for them to take effect.

You don't appear to have a sane system configuration. It is very likely that you
encounter xruns. Please apply all the above mentioned changes and start jack again!
fluidsynth: error: Failed to connect to Jack server.

I ran the command as root, then closed qsynth and started it again. It had the same error as before. I quit qsynth.

It's not detecting that I am in the audio group because I have to logout and login to make that change. (run 'groups' to see so.) So I tried 'ssh localhost', and sure enough, 'groups' said I am part of 'audio' now.

Running qsynth again complained because I don't have access to an X server. Logging out, then 'ssh -X localhost', and running 'qsynth' brought it up, and this time I didn't need to press 'start'.

I now wanted to get some MIDI magic going. I installed 'pianobooster', and configured it to use my new midi stuff. That is done with the setup menu, and choosing "FLUID synth" for the output device.

Now, when I press 'X' a little green light turns on in qsynth, but I hear no sound.

I'm going to try a proper logout/login.