Hello Ian and welcome to the forum!

If you do not have it already, +++ HERE +++ is a link to the Korg EK-50 keyboard user manual.

The EK-50 has two USB ports. Port A accepts a USB memory stick that can be used for extra storage. Port B passes MIDI data between the EK-50 and a computer. Neither Port A or Port B supports audio over USB.

EK-50 audio would travel from the Output L & R jacks, through an audio interface, into your computer and into RealBand.

So the audio you're hearing is either coming from the MIDI synth associated with RealBand or from the speakers of your EK-50.

Attached Files (Click to download or enlarge) (Only available when you are logged in)
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Partial EK-50 Specifications Audio jacks and MIDI highlighted.

Jim Fogle - 2026 BiaB (Build 1224) RB (Build 7) - Ultra+ PAK
DAWs: Cakewalk Sonar - Standalone: Zoom MRS-8
Desktop: i7 Win 11, 12GB ram 256GB SSD, 4 TB HDD
Music at: https://fogle622.wix.com/fogle622-audio-home