, an ingressive sound is one where air
flows inward. They do not occur in any of the familiar European or Asian languages, under normal conditions. In the unusual environment of singing
, I have heard examples. One is when Martha Davis
of The Motels
sings "Total Control
": in the line "I'd sell my soul for total control...", the two S's have a peculiar resonance
which is, as far as I can tell, the result of her breathing in as she sings them. No doubt part of the vowel is also ingressive, but by the nature of a vowel
, it is hard to notice the difference.
Reversing the normal process of breathing by sucking air into the lungs is almost impossible to sustain in speech*. The Martha Davis S is one example, if I am right about it. Languages that use ingressives use one of two other mechanisms to briefly interrupt the air flow and cause a pressure change: blocking the mouth either at the soft palate (the velaric sounds or clicks), or at the glottis (the implosives). See those for more detail, and the opposite term egressive.
* Since writing this I've got a book on phonetics which cites pulmonic ingressives in one single person's idiolect of a an Austronesian language in Taiwan!