reasonable synth LV2
(This URL of this page acts as identifier to reasonablesynth.LV2)
reasonablesynth.LV2 is a very simple synthesizer shipped with Ardour and intended to allow new users to "hear midi" without installing any 3rd party plugins.
It has no settings, no nothing. It's as simple as it can get while still making some reasonable sound (that is not just a sine-wave or beep). It may at some point also be used as default to audition midi-files.
For real work, you'll want to install instrument plugins: complex synths and samplers,... please see http://ardour.org/instruments.html