Whistles, or duct flutes, have a device to channel the player's breath, so a narrow air stream hits a sharpened edge, causing the necessary turbulence to vibrate the air column without the player using any special embouchure. Usually this duct is created by inserting a block, known as a fipple, into the end of the tube, with one side shaved. This allows a narrow air stream that emerges into a usually rectangular or 'D'-shaped window cut in the tube to hit the sharpened tone-producing edge on its far side.
It is possible to make a whistle by sliding the bark off a sappy willow stick, cutting a notch in the bark tube, and reinserting a short length of the stick with one side shaved as a fipple to direct air at the notch. Blowing progressively harder produces an ascending series of harmonics. Alternating opening and partially closing the lower end with a finger allows the gaps between those harmonics to be bridged by intermediate whole steps and half steps.
No-holed whistles like this, and less ephemeral ones of wood or other more robust material, have been made for millennia, often as a pastime by animal herders. In Norway, for example, this type of whistle known as seljefløyte, in Sweden a sälgpipa (both meaning 'sallow flute'), elsewhere vilepill (Estonia), svilpas (Lithuania), koncovka (Slovakia, tilinca (Romania), and among the Hutsulsof the Carpathians, tylynka or telenka.
Drilling finger holes in the tube produces an instrument that can play a range of modes and keys. Generally no attempt is made to make a single instrument cope with all possible key signatures (though it is possible – the recorder). A six-hole whistle, for example, copes easily with complete diatonic scales in two keys, plus their related minors; for others, the player simply swaps to a different-sized whistle. Thus the well known European tin whistle (not necessarily made of tin) much used in 'Celtic' music comes in a range of sizes down to the C or D of the low whistle.
While tin whistles and recorders have a beak-shaped mouthpiece, many of the world's duct flutes are flat-ended. In some, such as the Javanese suling, rather than the breath passing inside the tube to the tone-edge, it is channelled via a short external duct formed by tying a loop of palm-leaf, bamboo, or other material around the tube just above the rectangular edge-aperture.
In another external-duct flute, the Native American courting flute, the air passes out of a hole into an external duct formed by a small piece of wood tied to the flute body, which directs it against the edge of a second aperture.
Many duct flutes have the edge-window on the back. If it is sufficiently near the top, this makes it possible to affect the air stream with the lower lip or chin. This creates a breathier tone, emphasizing the low octave and lowering the pitch slightly. A further timbral change can be wrought by vocalizing while playing; the voice and blown tone intermodulate to produce a grainy multiphonic effect.
Slovakia is particularly rich in duct flutes, and the home of of of the largest, the fujara, a pastoral flute normally about 180 cm (71 in) long. A blowing tube, tied parallel to the main pipe, conducts the breath to the fipple, which is some distance above the player's head. A similar air-tube arrangement is found in the Andean moxeñ.
A fujara has just three finger holes, but it can play a full diatonic scale by overblowing into higher octaves. The same method is used on smaller whistles, such as the three-holes Basque txistu, smaller txirula, and larger silbote, old English tabor-pipe, Portuguese pifaro, and the Provençal galoubet. These are played with one hand while the other beats a drum. The Catalan flabiol uses keys to allow control of up to eight holes with one hand.
In the Balkans and surrounding regions, pairs of whistles bound together or bored from the same piece of wood are common. One bore has enough finger holes – usually six – to make a diatonic scale of at least two octaves, while the other either has three or more finger holes for playing in harmony or has none and provides drones. Names include dvojnice (Croatia, Serbia, Montenegro), dvojnica (Poland), dvojacka (Slovakia, Czech Republic), dvodentsivka (Ukraine), dvoyanka (Bulgaria), and further afield xeremia bessonia (Balerarics), satara (Rajasthan), and the Kurdish doozela.
Some duct flutes are not in fact tubes, but rather closed vessels. The ocarina (Italian for 'little goose') is a vessel – usually ceramic – of varying globular shapes, that produces a rounded, plummy flue tone. It is known throughout Europe, and there are similar instruments with a long history in South America, and among the Maoris of New Zealand (where it is called a nguru).