Gain of the region's send into the 4th effect bus.
Effects handling varies across SFZ versions. In SFZ v1 only effect1 and effect2 opcodes were available and only at ‹region› level. In SFZ v2 the ‹effect› header was added, and effect3 and effect4. ARIA uses the effect header as well, with the MDA effects built in and the possibility to support vendor-specific effects as well.
The below example should work in Cakewalk Rapture.
<group> sample=../samples/soundfx.wav ... <region> ... effect4=50 <effect> type=filter bus=fx4 ...
|effect4||SFZ v2||float||0||0 to 100||%|