I love it when folks knowledgeably describe how a whistle plays and what its tone sounds like with those interesting terms like having a lot of “chiff,” “backpressure,” and so forth. Trouble is, I can’t correlate these terms with the actual whistles. Can someone do a quick run down of how you would describe whistles by the following makers – Copeland, Burke, Sindt, Humphrey, Susato and O’Riordan?
Susato (the two I’ve played, which are both low ones)
Moderately Clear
Fair amount of back pressure
Not especially chiffy (but very whistle-like… I don’t find allegations that they are recorder-like to be accurate)
Loud
Strong tone
Takes a lot of wind
Big finger holes (especially on the one)
Tacky-looking (okay, this is a subjective matter 
… I’m just kidding, Mike… don’t get angry)
I can describe what I mean by these terms with susatos, copelands, and burkes (the only whistles I’ve played on your list)
Backpressure: This is how much “resistance” a whistle has to your blowing..Susato has a bit..copeland and burke don’t have much.
Chiff: This has two definitions, depending on who you ask: Some folks (like me) subscribe to the original organ-pipe definition: the hissy chirp at the biginning of a note. Others use it to describe the “white noise” or “windiness” during the entire note duration.
Attack Chiff: Burke the least with almost none, Susato low has a bit if you hit it right, Copeland can have some depending on how hard you hit it. A good example of this kind of chiff is the Clarke original
Tone Chiff: None of these three are very windy, though they have differing degress of “purity” of sound, which is a different thing entirely. I think a really good example of tone chiff would be the Clarke original also, or a shaw.
Purity vs Complexity. I think this has to do with the harmonics the instrument produces. Pure instruments are very singular-note sounding, like Burkes and Hoovers..they have a focused quality. Richer instruments (Susato and Copeland, for instance) I think have different types of harmonics that make the notes sound more complex. This can be good or bad..for instance, the Susato can sound harsh in the 2nd octave. Cheapo whistles usually are a lot less pure than expensive ones. But many expensive whistles are chosen for a specific “non-pure” sound..my Silkstone alloys had a very satisfying complexity to them.