Second, while trying to convert ABC contents to MIDI, I discovered that a MIDI synthesizer must be open, like this:

Synthesizer synth = MidiSystem.getSynthesizer(); synth.open();

... conversion ...

synth.close();

I left out the exception handling. It would be nice to know this little fact, because without doing so one will surely wonder why he is getting all those NullPointerException-s trying to convert ABC to MIDI.