Typology and acoustic strategies of whistled languages: Phonetic comparison and perceptual cues of whistled vowels

Whistled speech is a complementary natural style of speech to be found in more than thirty languages of the world. This phenomenon, also called 'whistled language', enables distant communication amid the background noise of rural environments. Whistling is used as a sound source instead of vocal fold vibration. The resulting acoustic signal is characterised by a narrow band of frequencies encoding the words. Such a strong reduction of the frequency spectrum of the voice explains why whistled speech is language-specific, relying on selected salient key features of a given language. However, for a fluent whistler, a spoken sentence transposed into whistles remains highly intelligible in several languages, and whistled languages therefore represent a valuable source of information for phoneticians. This study is based on original data collected in seven different Cultural communities or gathered during perceptual experiments which are described here. Whistling is first found to extend the strategy at play in shouted voice. Various whistled speech practices are then described using a new typology. A statistical analysis of whistled vowels in non-tonal languages is presented, as well as their categorisation by non-whistlers. The final discussion proposes that whistled vowels in non-tonal languages are a reflection of the perceptual integration of formant proximities in the spoken voice.