Whereas part I and part II of this series have explored vocal inflection in English — and what makes it so hard for machines to get right — this final post in our series on vocal inflection explores tone in a radically different way.

Linguists describe Chinese, Vietnamese and a great many other southeast Asian and also west African languages as tonal. This use of “tonal” contrasts with our use of “intonation” and “inflection” in our exploration of text-to-speech. Whereas we explored the emotive and discourse meanings behind “up” (pronounced with a rising tone), “up” (pronounced with a falling tone), and “up” (pronounced with a compound falling-then-rising tone) in English, speakers of tone languages use tones to distinguish different lexical words. One Googleable example in (Mandarin) Chinese runs through the four different tones speakers may place on the syllable “ma”. The resulting words denote “mother”, “scold”, “hemp” or “horse”. These four words distinguish purely on the basis of tone and have nothing otherwise to do with each other. A very different situation than what we find in English.

This much you’ve likely encountered already somewhere.

What’s less widely known about the tone languages that serve the mostly emerging markets of literally billions of people, however, are these three facts:

First, most of the world’s approximately 6000 languages are, in fact, tonal like Chinese rather than nontonal like English. Chinese has an enormous number of speakers, of course. But note that certain other tone languages, such as many of the tone languages of Africa, have considerably fewer speakers.

Second, while you’ll have much better results getting the correct word-tone out of a text-to-speech system for Chinese (because word-tone is so well studied and understood for Chinese, by linguists, by everyday users of the language, and by developers), you’re still going to run into the same problem with sentence-tone in Chinese that we’ve explored in our last two posts here for English. Yes, Chinese has both word-tone and sentence-tone. Try modelling that correctly in a synthesis system.

Third — and this one’s astounding — researchers at the University of Edinburgh reported last year in the Proceedings of the National Academy of Sciences that populations of speakers of tonal languages possess special varieties (alleles) of two genes. This is especially surprising given the almost complete lack of known associations between genetic variation and high-level language characteristics in humans (at least at this point in time). The findings were reported last year in the Economist in an article which closes with the equally spectacular fact that the genes correlating with tone languages appear to be both “highly beneficial” to the groups involved and very recent in the evolution of humans (developing only some 5,800 and 37,000 years ago).

Tone in languages like Chinese and vocal inflection (or intonation) in languages like English are spectacularly complex phenomena. We’ll have an opportunity to come back to these and other findings when we consider the special things that voice gives us a developers and consultants and problem-solvers that written words do not.

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2. Vocal Inflection, Part II In part I of this post we looked at the...