Approximants

Liquids and glides form the category of approximants. These sounds are made in such a way that one articulator is close to another without creating enough narrowing to result in friction. As sonorant consonants, they have formant structures but the formants are less pronounced than those of vowels because of a slight obstruction placed somewhere along the vocal tract. The shared characteristics in this group include their low F₁ and similar durations for the transitions between vowels and the consonant constrictions. Glides (or semi vowels, as they are sometimes referred to) reveal patterns very similar to, but markedly fainter than, high vowels. In /w/, we see that F₁ and F₂ are very close (as in /u/). In /j/, F₁ and F₂ are wide apart, resembling the situation of /i/ (low F₁ and high F₂). A glide starts with a vocal tract configuration simi lar to the corresponding high vowel, then changes shape for the vowel that follows it. A glide-to-vowel sequencing is rather different from a vowel-to-vowel sequencing in that the transition from a glide to a vowel is faster than from a vowel to a vowel.

Liquids have properties that are similar to both stops and glides (especially to /w/). They are quite rapid, like stops, but have resonant quality (low F₁ ) and transition speed like those of glides. Liquids differ from /w/ in frequency of the third formant; /w/ produces an F₃ that is usually so decreased in intensity that it is not visible in a spectrogram. The liquid / ɹ̣ /, on the other hand, has a third formant frequency that is relatively low (below 2,000 Hz), strong, and close to the second formant frequency. While it is relatively easy to separate / ɹ̣ / from /w/, /w/ and /l/ may appear quite similar, because they have similar formant values for the first three formants. The following two factors can be used to discriminate between the two sounds. First, the glide /w/ is formed with practically no constriction at all; the liquid /l/ is formed with a constriction of the tongue tip. As a result, the energy around F₃ for /l/ is much higher than for /w/. Second, because of different degrees of constriction, the formants in and out of /w/ are continuous, whereas for /l/, the formants at the vowel junctures show a slight discontinuity. To separate a /l/ from a / ɹ̣ /, one has to examine the F₃. In /l/, F₃ is much higher. In addition to these higher frequencies, the higher formants of the lateral are considerably reduced in intensity. The difference between the ‘clear’ and the ‘dark’ /l/ lies in the timbre of their high front/back vowel. In ‘clear /l/’, F₁ and F₂ are farther apart, as we would expect in a high front vowel, and closer and lower in ‘dark /l/’, as in a high back vowel. Postvocalic final /l/ may be like a vowel, making no contact, which results in an /u/-like formant structure. However, in American English, /l/ more commonly shows different degrees of ‘darkness’ rather than the ‘clear’ vs. ‘dark’ contrast occurring in British English.