SFZ v2 header for effects controls.
In SFZ v1 only effect1 and effect2 opcodes was available
and only at ‹region› level.
From SFZ v2 this header was added together with the addition of
effect3 and effect4 opcodes also to modulate the related bus.
Other opcodes listed in the book are bus, type and dsp_order.
The specifics of what can be used under this header differ widely
between SFZ players. The information on available effects and
how to control them in ARIA and Cakewalk products can be found on
the type page.