Hey people, Why do motorcycle sounds differ? Which is the deciding factor/s in getting the required sound for a motorcycle rather than ending up with an arbitrary sound? Is there a guide that such and such a construction will give you a certain sound?

One thing i know is higher the capacity and power more smoother and powerful the sound and also this depends on the quality of the materials used and the tolerances achieved on them while machining. For example: take P220, it has a rattling sound and a rather unharmonic noise,considering that its an aircooled engine! Coming to liquid cooled bikes like Yamaha R1 it has an awesome sound when revved and the idling noise is quite a smooth swish. Well, take a Ducati 1198, it sounds much more like a tractor and has higher quality materials than on R1! Then considering ducati and R1, why this sound difference, both are liquid cooled, have more or less same capacity and power! Any deciding factor? Please shed some light on this!