Hi Graham, I don't know to be honest. They supply normal, tired and overhauled engine sound variations for 141s and 181s (i.e. 6 variants with PD and 6 without PD). All I know is their LokSound projects sound better than the authentic recordings made here from actual IR/IE prototypes. I've a mix of PD and non-PD LokSounds, but to be honest I prefer driving the non-PD versions, just simpler to operate. Zimo/RealDrive remains my favourite to drive but the 141/181 sound is not as good as ESU, so I've gone ESU. Jeepers we are spoiled nowadays with sound options for Irish diesel models. Noel