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.
Two-Hit Wonder
Each day, more than a billion people wake to the sound of a ringing alarm, reach over, and hit the alarm clock, thereby terminating the ring and giving themselves another five minutes of sleep. In these billion cases a hit stops a ring, rather than starting one as we talked about earlier. Of course, the hit on the clock does cause periodic vibrations of the clock (and of the sleeper’s hand), but the sound of these vibrations is likely drowned out by the sound of the alarm still ringing in one’s ears.
Although hitting the snooze button of an alarm clock is not a genuine case of a hit stopping a ring, there are such genuine cases. Imagine a large bell that has been struck and is ringing. If you now suddenly place your hand on it, and keep it there, the ringing will suddenly stop. Such a sudden hand placement amounts to a hit—a hit that sticks its landing. And it is, in this case, by virtue of dampening, a hit that leads to the termination of a ring. Some dampening will occur even if your hand doesn’t stick the landing, so long as you hit the bell much less energetically than it is currently ringing; the temporary contact will “smother” some of the periodic vibrations occurring in the bell.
Although in such cases it can sound as if the bell’s ringing has terminated, in reality one can leave the bell with a residual ring. A hit on a quiet bell would sound like an explosive hit, because in contrast to the bell’s stillness, the hit is a sudden discontinuous rise in the ringing magnitude. But that same hit on an already very loudly ringing bell causes a sudden discontinuous drop in the ringing magnitude. In contrast to the loud ringing before the hit, the hit will sound like the sudden ceasing of a ring, even if there is residual ringing.
Hits, therefore, have two voices, not just the one we discussed earlier in the section called “Nature’s Phonemes.” Hits not only can create the sudden appearance of a wide range of frequencies, but can also sometimes quite suddenly dampen out a wide range of frequencies. These two sounds of hits are, in a sense, opposites, and yet both are possible consequences of one and the same kind of hit. This second voice is rarer, however, because it depends on there already being a higher-energy ring before the hit, which is uncommon because rings typically decay quickly. That is, the explosive voice of hits is more common than the dampening voice, because most objects are not already ringing when they are hit.
If languages have harnessed our brain’s competencies for natural events, then we might expect languages to utilize both of these hit sounds. And indeed they do. The plosives we discussed earlier consisted of an explosive release of air, after having momentarily stopped the airflow and let pressure build. But plosives also occur when the air is momentarily stopped, but not released. This happens most commonly when plosives are at the ends of words. For example, when you utter “what” in the sentence “What book is this?” your mouth goes to the anatomical position for a “t,” but does not ever release the “t” (unless, say, you are angry and slowly enunciating the sentence). Such instances of plosive stop sounds are quite common in language, but less so than released plosive sounds—there are many languages that do not allow unreleased plosives, but none that do not allow released plosives. John Locke tabulated from the Stanford Handbook that, in 32 languages that possessed word-position information, no plosives were off limits at word starts (where they would be released), but 79 plosives were impermissible at word-final position (where they are typically unreleased). Also, among the words we collected from 18 languages, 16,130 of a total of 18,927 plosives, or 85 percent, were directly followed by a sonorant (and thus were released), and therefore only 2,797 plosives, or 15 percent, were unreleased. And even in languages (like English) that allow both kinds of plosive sounds, plosives are more commonly employed in their explosive form, something we will talk about in a later section (“In the Beginning”). This fits with the pattern in nature, where explosive hits are more common than dampening hits.