The xsynth-dssi package contains the Xsynth-DSSI plugin, a classic-analog (VCOs-VCF-VCA) style software synthesizer with an editor GUI. Xsynth-DSSI was written by Sean Bolton, and was based on Steve Brooke's Xsynth code, but has since acquired polyphonic operation, band-limited oscillators, a better filter mode, and velocity-sensitive envelopes.

DSSI is an API for audio processing plugins, particularly useful for software synthesis plugins with user interfaces.