Combined with the steady inhalation and exhalation as the cat breathes, a purring noise is produced with strong harmonics.
Purring is sometimes accompanied by other sounds, though this varies between individuals.
Some may only purr, while other cats also emit low level outbursts sometimes described as "lurps" or "yowps". One study reported that domestic cats purr at average frequencies of 21.98 Hz in the egressive phase and 23.24 Hz in the ingressive phase with an overall mean of 22.6 Hz.
There are three categories: tonal sounds, pulse sounds, and broadband sounds.
Tonal sounds are further categorized into groups of harmonically structured sounds or regular tonal sounds.
Pulse vocalisations are separated into pulse bursts and hybrid pulse bursts with tonal endings.
author of The Moral Animal, Nonzero, The Evolution of God; editor for Time, Slate, The New Republic, The Wilson Quarterly; has written for The Atlantic Monthly, The New Yorker, The Huffington Post, and The New York Times Magazine; runs websites and Meaningof Robert Wright (born January 15, 1957) is an American journalist who writes about science, history and religion, including The Evolution of God, Nonzero: The Logic of Human Destiny, The Moral Animal, Why Buddhism is True, and Three Scientists and Their Gods: Looking for Meaning in an Age of Information. He is a Senior Fellow at New America, His professors at college included author John Mc Phee, whose style influenced Wright's first book, Three Scientists and Their Gods: Looking for Meaning in an Age of Information.
In early 2000, Wright began teaching at Princeton University and the University of Pennsylvania, teaching a graduate seminar called "Religion and Human Nature" and an undergraduate course called "The Evolution of Religion." At Princeton, Wright was a Laurence S.