Sorry, I was totally wrong. I was looking only at the initialization
code when I answered originally.
Later, when frequency is set, the center frequencies are multiplied by
the desired frequency value.
(This is in the controlChange() function, handling the ModWheel parameter.)
Does the following code work for you?
For me it creates the bamboo sound decending in frequency.
Yes, this works perfectly! I'm now wondering what went wrong with my experiments of this morning (sadly those were lost in a little crash). I did think it used to work and that it was odd. Perhaps I made a typo or tried too small a range with a preset with too much noisy characteristics but I do think I tried a rather large range of numbers...