Shepherd's whistle
They are also produced commercially. Simple whistles may cost less than 1 USD in bulk; expensive ones may be quite ornate. They are commonly made of plastic, aluminum, stainless steel, silver, brass, titanium, Corian, jade, buffalo horn and other materials.
Whistle register
The whistle register is the highest phonational register, that in most singers begins above the soprano "high C" (C or 1,046.5 Hz) and usually extends to about two Ds above (D or 2349.3 Hz). It is created by using only the back of the vocal folds. The lower part of the whistle register may overlap the upper parts of the modal and falsetto registers, making it possible for singers to phonate these notes in different ways. However, fundamentally the whistle register is most commonly used to produce pitches above C. As with the other vocal registers, the whistle register does not begin at the same point within every voice, and there are rare voices which can extend the whistle register much higher or lower than the range listed above. For example, most operatic coloratura sopranos can sing up to the "high" F above "high" C without entering into the whistle register. Cleo Laine of UK and Yma Sumac of Peru are two sopranos with extreme vocal ranges.