SlackBuildsOrg/multimedia/dssi

DSSI (pronounced "dizzy") is an API for audio processing plugins,
particularly useful for software synthesis plugins with user
interfaces.

DSSI is an open and well-documented specification developed for use
in Linux audio applications, although portable to other platforms. It
may be thought of as LADSPA-for-instruments, or something comparable
to VSTi.

qt4 is an optional dependency. If found, the package will include a
qt-based 'trivial_sampler_qt' plugin.