ThomasH | Jean Michel Jarre - Equinoxe 7 Bass - Live by ThomasH @thhedk | Uploaded May 2023 | Updated October 2024, 2 hours ago.
Full version: youtu.be/LxBrGPwslTE

This was how Jean Michel Jarre and Michel Geiss made the famous Equinoxe Bass.
Geiss' Matrisequencer played two sequencer patterns and Jean Michel changed the notes with the ARP 2600 keyboard.

This cover version is made with Propellerhead Reason 7 and the bass is played live on this clip.

Michel Geiss has confirmed to me this was how they did it.