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the peculiar high-pitched, often unintelligible speech sounds produced when one breathes a mixture of up to 80% helium and 20% oxygen.
The altered voice produced by inhaling helium and then speaking as the helium is exhaled. The very low density of the helium causes the alteration. The intelligibility of helium speech is important, esp. to deep-water divers who transmit and unscramble oral information using helium as a speech-enhancement medium.
See also: speech