Want your car to sound like an expensive muscle car? Now you can! DragFX requires a Bluetooth OBD adapter. The adapter allows DragFX to connect to your vehicle's OBD (On-board Diagnostic) interface, to allow the sound produced by DragFX to accurately match your engine's actual RPM in real time. Without the OBD adapter, a slider allows manual control of the RPM to preview the available engine sounds.