To everyone-

I own a Susato set, C, D, and Bb. The tones are clear and best of all - they are loud. The best session whistles I have.

Mine demand a bit more air in the upper octaves, but in all my D is fine. The upper octaves demand alot of air to simply stay put (on mine) and this technique - if you want to call it that - works NOT on other whistle brands.

Hope this helps.