KORG PA4X 76 - Manual (Page 813)

Connecting MIDI devices |809
Converting notes to RX Noises
RX Noises are special ambience or mechanical sounds that allow Sounds
to be more realistic. They are usually located above C7, depending on the
Sound.
1 Go to the Global > MIDI > General Controls page.
2 Select the Note to RX Noise checkbox to convert incoming notes to RX
Noises.
When this parameter is turned on, notes received from the MIDI IN or USB
DEVICE ports, or performed by the internal Players, in the RX Noises range,
are recognized and converted to RX Noises.
This parameter is automatically activated each time the instrument is turned
on.