Thanks again for your comments guys.
@mario
I had thought of a variation on what you suggest, but it is a bit complicated (isn't it always)
Basically, Zyn has three different sound generator methods. The one I used here starts off with white noise, and filters out everything
except the frequencies you want. Normally, you then get a set of harmonically related tones that form the overall sound, but what I did was to expand the range of noise that is allowed through (increased bandwidth). This then fairly naturally produced a breathy sound, as breath sounds are mostly filtered noise.
Using this method means that the 'breath' is always pitch related to the actual note - indeed it
is the note, which is exactly what would happen with real pipes. What I thought I needed to do for my 'second channel' was to duplicate this but with narrower bandwidth. Trouble is it doesn't seem to work