Slides that Sing

Recall that slides are, in essence, built from very many little hits in quick succession. The pattern of hits occurring inside a slide depends on the nature of the materials sliding together, and this pattern is what determines the nature of the slide’s sound. If you scrape your pencil on paper, then because the paper’s microscopic structure is fairly random, the sound resulting from the many little hits is a bit “noisy,” or like radio static, in having no particular tone to it. (The pencil scraping may also cause some ringing in the table or the pencil, but at the moment I want you to concentrate only on the sound emanating from the slide itself.)

However, now unzip your pants. You just made another slide. Unlike a pencil on paper, however, the zipper’s regularly spaced ribs create a slide sound that has a tonality to it. And the faster you unzip it, the higher the pitch of the zip. Slides can sing. That is, slides can have a ringlike quality to them, due not to the periodic vibrations of the objects, but to the periodicity in the many tiny hits that make up a slide.

Whether or not a slide sings depends on the nature of the materials involved, and that’s why the voice of a slide is an auditory feature that brains have evolved to take notice of: our brains treat singing and hissing slides as fundamentally different because these differences in slide sounds are informative as to the identity of the objects involved in the slides. Although slides can sing, it is more common that they don’t, because texture with periodicity capable of a ringlike sound is rare, compared to random texture that leads to generic friction sounds akin to white noise.

Do human languages treat singing slide sounds as different from otherwise similar nonsinging slide sounds? Yes. Languages have fricatives of both the singing and the hissing kinds, called the voiced and unvoiced fricatives, respectively. Voiced fricatives include “z,” “v,” “th” as in “the,” and the sound after the beginning of “j” (which you will recall is an affricate, discussed earlier in “Nature’s Other Phoneme”). Unvoiced fricatives include “s,” “f,” “th” as in “thick,” and “sh.” Just as singing slides will be rarer than nonsinging slides–because the former require special circumstances, namely, slides built out of many periodically repeating hits–voiced fricatives are rarer in languages than unvoiced fricatives. John L. Locke tabulated data in his excellent 1983 book, Phonological Acquisition and Change , and discovered that “s” is found in 172 of 197 languages in the Stanford Handbook[1] (87 percent) and in 102 of 317 languages in the UCLA Phonological Segment Inventory Database (32 percent), whereas “z” (the voiced version of “s”) is found in 77 of 197 languages (39 percent) and 36 of 317 languages (11 percent), respectively. Similarly, “f” is found in 106 of 197 languages (54 percent) and in 135 of 317 languages (43 percent), whereas “v” is found in 61 of 197 languages (31 percent) and in 67 of 317 languages (21 percent), respectively. These data suggest that unvoiced slides are about twice as likely as voiced slides to be found in a language. (And notice how, in English at least, one finds voiced‑fricative words with meanings related to slides that sing: rev, vroom, buzz, zoom, and fizz. One also finds unvoiced‑fricative words with meanings related to unsung slides: slash, slice, and hiss.)

Voiced and unvoiced fricatives are found in languages because they’re found in the physics of slides. Hits can also be voiced or unvoiced, but for completely different physical reasons than slides. Zip up your pants and let’s get to this.