@Michael_TW no worries mate - glad it's sorted, I haven't quite nailed it yet as not had much time but it definitely sounds like the multiple messages is the problem - I just need to unpick the responses and apply to my setup then hopefully get back to the music

Just got around to trying to apply some of these fixes and finally sussed it - the problem ony occured with my M-Audio Oyxgen 49 controller and not my Roland digital piano. I was using the M-Audio and happened to accidentally catch one of the sliders which altered the synth sound (made it sound like a Bontempi piano) so after a process of elimination and setting all but one of the sliders and their corresponding pots on the controller to zero - that has fixed the problem. Digital audio eh - never fails to rock up something new to scratch your head over.
 
Thanks all.
 
Andy