The Arp Omni is an analogue synthesizer used by Prince and his band from the late 1970s to the mid 1980s. Prince first acquired one in the late 1970s, and it probably appears on the Prince album. Along with the Oberheim OB series, it is the main synth on the Dirty Mind, Controversy and 1999 albums.
This record was so minimalist... I mean, "Dirty Mind": it's just the ARP Omni, a guitar part, the bass is handled by the ARP Omni and the main chords of the rhythm, and then you've got the guitar chunky-part going on, and the drums. And that was the whole song. And the vocals. Real simple layering of music.
It is a "string sythesizer", meaning it could play preset orchestral sounds (violin, viola, cello and bass) with limited sound-shaping capabilities. Dr Fink played the riff to the song Dirty Mind on the Omni and it was layered with an OB-Xa for the riff to the song 1999. At different points, Prince and his band used Omni and Omni-2 models.
The only other thing that really sticks out would be the ARP Omni. It had a kind of funny, nasal quality to it. But that’s the Dirty Mind sound. That one was written on the ARP Omni, and played by [Dr] Matt Fink. If you play those chords on that keyboard, you’ll swear you just put the album on. Those were very simple things. There wasn’t a lot of editing going on.
It was used live by Dr Fink and Lisa Coleman on the Dirty Mind, Controversy and 1999 tours, with Lisa using it on the Purple Rain tour as well. When the Revolution reunited, Lisa bought an Omni-2 out of retirement for their first show.