LinPlug Spectral - Manual (Page 97)

MIDI CC 16 to 19 These are MIDI Controllers, which are available when
your DAW/host transmits them to the plugin. The
reason to have them in the Matrix is, that you might
want to control more aspects of the sound from your
Keyboard/Controller than is possible with Velocity,
Modulation Wheel and Pressure/Aftertouch.