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A hum has a particular timbre (or sound quality), usually a monotone or with slightly varying tones. There are other similar sounds not produced by human singing that are also called hums, such as a sound produced by machinery in operation or by an insect in flight. The hummingbird was named for the sound that bird makes in flight.
A 'hum' or 'humming' by humans is created by the resonance of air in various parts of passages in the head and throat, in the act of breathing. The 'hum' that a hummingbird creates is also created by resonance: in this case by the passage of air against wings in the actions of flying, especially of hovering.
Humming in human evolution
Joseph Jordania suggested that humming could have played an important role in the early human (hominid) evolution as contact calls. Many social animals produce seemingly haphazard and indistinct sounds (like chicken cluck) when they are going about their everyday business (foraging, feeding). These sounds have two functions: (1) to let group members know that they are among kin and there is no danger, and (2) in case of the appearance of any signs of danger (suspicious sounds, movements in a forest), the animal that notices danger first, stops moving, stops producing sounds, remains silent and looks in the direction of the danger sign. Other animals quickly follow suit and very soon all the group is silent and is scanning the environment for the possible danger. Charles Darwin was the first to notice this phenomenon on the example of the wild horses and the cattle (Darwin, Descent of Men, 2004:123). Jordania suggested that for humans, as for many social animals, silence can be a sign of danger, and that's why gentle humming and musical sounds relax humans (see the use of gentle music in music therapy, lullabies).
Humming is often used in music of genres, from classical to jazz to R&B.
- The Hum - an apparently widespread phenomenon involving a low-frequency hum of unknown origin, inaudible to most people
- Mains hum - an electric or electromagnetic phenomenon that causes a low frequency (50 or 60 Hz) audible signal
- Jordania, J. (2009). Times to Fight and Times to Relax: Singing and Humming at the Beginnings of Human Evolutionary History. Kadmos, 1, 272–277
- Jordania, Joseph (2010). Music and Emotions: humming in Human Prehistory (proceedings of the International Symposium on Traditional Polyphony, held in Tbilisi, Georgia in 2008
The dictionary definition of hum at Wiktionary