Rosegarden

1. Install QSynth:

   sudo apt-get install fluidsynth

2. Install a soundfont library:

   sudo apt-get install fluid-soundfont-gs
3. Open QSynth:
   1. Enable MIDI Input. Click on Setup..., select Enable MIDI Input
   2. Configure it to use ALSA Audio Driver. Click on Setup... button, Audio tab and select Audio Driver: alsa
   3. Set up soundfont. Click on Setup..., select Soundfonts tab and point to /usr/share/sounds/sf2/FluidR3_GM.sf2 or other soundfont location
   4. Allow QSynth to restart when it prompts and leave it running

4. install Rosegarden:

   sudo apt-get install rosegarden
5. If necessary, run QSynth.
6. Run Rosegarden.
   1. Tell Rosegarden to play through QSynth: select Studio > Manage MIDI Devices and set the General MIDI Device to whatever QSynth broadcasts as its MIDI input option, e.g. 129:0 Synth input port...* or similar.