I know nothing about music, and I don't play piano, but I have played with these when they first came out. I was manager of a public hall and a shop brought a load of them for demonstration. It sounds like an Effects setting and I know that is one called 'Leslie', which if I remember correctly is the effect of a speaker spinning in a speaker enclosure.Here is your manual
http://www.synthmanuals.com/manuals/roland/kr-3500/owners_manual/kr-3500_om.pdfService Manual and a link to Roland, to ask them direct.Roland KR-3500 Service Manual, Analog Alley Manuals
www.analogalley.com > osccart > product_infoProduct: Roland Digital Intelligent Piano, model KR-3500. Service Manual , First Edition. Contains/Contents: specifications location of controlsSupport - Manual Archive - Roland
www.roland.com > support > manual_archiveHP-3500S Owner's Manual · HP-3800 Owner's ... KR-1070 Owner's Manual · KR-117 Owner's ... KR-4500 Owner's Manual · KR-4700 Owner's Manual · KR-4700 ...Roland USA5100 S. Eastern Ave.Los Angeles, CA90040USPhone: 323-890-3700Fax: 323-721-4875