Page 62 - Summer2020

SPEECH ACOUSTICS
sounds like fricatives, stops, and affricates), many languages useothersources,referredtoas“airstreammechanisms.”
Just over 10%, or 230, of the languages in the PHOIBLE sample contain ejective sounds (Moran and McCloy, 2019). Ejectives, illustrated in Figure 7A, are made using the laryngeal airstream mechanism as the source. It is first important to understand how these sounds are pro- duced, and then we describe the acoustic characteristics of these sounds. Ejectives are made by first making a closure somewhere in the oral tract, like at the alveolar ridge (the hard ridge behind the upper teeth; Figure 4A).
The speaker also closes the vocal folds and quickly raises the entire laryngeal system. The air trapped in the oral tract is compressed, increasing the air pressure in the oral tract. The tip of the tongue is lowered, opening the oral tract, and releasing the compressed air, creating an extreme popping sound. The waveform and spectrogram in Figure 7B are the same word recorded by Goddard in 1912 (Figure 3), [tɬ’i:ze], “a (horse) fly,” by a speaker of Dene Sųłiné in 2020 (see Multimedia9 at acousticstoday.org/tuckermedia). This word contains an ejectivized alveolar lateral affricate, which is an ejective that is released at the side of the tongue followed by a fricative. It can be seen in the spectrogram that the ejective release (between 0 and 50 ms) is the loudest part of the speech in the word, with strong transients in the waveform (e.g., Wright et al., 2002).
Another airstream mechanism used is velaric. Sounds produced using this airstream mechanism are com- monly known as clicks. By way of example, we describe the process of producing an alveolar click; this process is illustrated in Figure 8. First, the speaker raises the tongue and creates a closure both at the alveolar ridge with the tip of the tongue and at the velum with the back part of the tongue. The tongue is then pulled down while maintaining the closure at the alveolar ridge and velum. This creates an area of low pressure (a vacuum) within the cavity between the tongue and the roof of the mouth. Finally, the tip of the tongue is released from the alveolar ridge, creating a very loud popping sound as air fills the area of low pressure.
Clicks, like ejectives, are also extremely loud speech sounds. The high-intensity release of the click can clearly be seen in the four different realizations of the alveo- lar click in Ju|'hoan in Figure 9. These recordings come from the University of California, Los Angeles (UCLA) Phonetics Lab Archive dataset. Ju|'hoan, a Kx’a language, is spoken in Namibia and Botswana, with a population of about 44,000 speakers (Eberhard et al., 2019). Clicks represent just 1% or 29 of the languages spoken in the PHOIBLE sample (Moran and McCloy, 2019). One of the interesting things about clicks is that they can be combined with other sounds so that they are produced in many dif- ferent ways. Figure 9, A and B, illustrates the plain alveolar click in the words [!ābē], “to be crinkled” (see Multime- dia10 at acousticstoday.org/tuckermedia), and [!āá], “to run” (see Multimedia11 at acousticstoday.org/tuckermedia), respectively. The remaining examples illustrate the clicks occurring with different combinations of sounds. The example in Figure 9C illustrates a prenasalized alveo- lar click [ŋ!áā], “type of acacia” (see Multimedia12 at acousticstoday.org/tuckermedia), and in Figure 9D is the voiced alveolar click from the word [ɡ!āà], “to dry something” (see Multimedia13 at acousticstoday.org/tuckermedia).
As seen from the examples in this section, there is a wide variety of sounds in human language that are worthy of closer acoustic study. Some of the more interesting sounds are found in only a handful of languages, so one would need a very broad sample not to miss them.
Language Endangerment
We often hear about the tragedy of the loss of biological diversity, which is a major loss to the planet’s ecosystem. Less often, we hear about cultural and linguistic diversity
Figure 8. Midsagittal view of the vocal tract illustrating the process of click production. Dotted line, closure both at the alveolar ridge with the tip of the tongue and at the velum with the back part of the tongue. Arrow, direction of the tongue movement to create the low-pressure area before release.
62 Acoustics Today • Summer 2020