If I try to do a frequency sweep while whistling, I find that there are certain frequencies where I’m unable to whistle. For example, using this online tone generator as a reference, I find that there’s a gap between 1507 Hz and 1930 Hz. Despite changing the shape of my mouth and lips as gradually and subtly as possible, the tone I produce just fades from one frequency to the other without hitting any of the intermediate frequencies. There are several other gaps like this in my whistle range, particularly at higher frequencies.
I used the tone generator you referenced, and was easily able to match pitches in that range. I have not noticed any pitches in the middle of my range at which I cannot whistle. There is a top end and a bottom end to my overall range, but no gaps in between. I do notice that the manner in which I whistle changes at the higher pitches - I have to use a modified/tightened embouchure and blow harder. You might yet discover a technique that lets you whistle in that range.
Just being silly, perhaps your frequency gap is a safety feature to prevent you from whistling at the resonant frequency of your skull. It would be terrible if someone could whistle at the right pitch and make their head explode, like Ella Fitzgerald shattering a wine glass.
Interesting question. I’ve ben fascinated by how pure a tone whistling seems to generate – if you whistle into a microphone hooked up to an oscilloscope you seem to be generating almost pure sine waves. It would be interesting to hook it up to a frequency analyzer and see the results.
I used a search engine, and this is the first paper that showed up, trying to answer the question about exactly how the fundamental tone of the whistle is generated. In their tests they appear to cover the whole audio range with no obvious gaps, and it’s clear they recorded whistling i the range 1500-1930 Hz. I myself don’t recall encountering gaps when I whistled into the oscilloscope. Possibly this is a problem unique to yourself
Azola, Alba, Jeffrey Palmer, Rachel Mulheren, Riccardo Hofer, Florian Fischmeister, and W. Tecumseh Fitch. “The physiology of oral whistling: a combined radiographic and MRI analysis.” Journal of Applied Physiology 124, no. 1 (2018): 34-39.