SlackBuildsOrg/audio/zynaddsubfx

ZynAddSubFX is a fully featured open source software synthesizer
capable of making a countless number of instruments, from some common
heard from expensive hardware to interesting sounds that you'll boost
to an amazing universe of sounds.

Beside the standalone application, lv2 and vst plugins are provided.

Optional dependencies, autodetected at buildtime:
jack, dssi, portaudio, ntk, lash

If ntk is detected at buildtime, fltk will not be used.

If compiled against jack, this package uses POSIX filesystem
capabilities to execute with elevated privileges (required for
realtime audio processing). This may be considered a security/stability
risk. Please read http://www.slackbuilds.org/caps/ for more information.
To disable capabilities, pass SETCAP=no to the script.