i've been having a problem with the volume of one of the instruments (sometimes voice 1, sometimes 2), it's not the same instrument, but sometimes, piano, strings, guitar, etc. Partway thru playing (!!) the sound for that instrument just fades out, it only returns when the voice is de-selected and then re-selected,(not a good idea for a faultless performance!!!). does anyone have any ideas, I'd be eternally grateful.Thanks