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This chapter consists of four parts. First, in Section 8.1, I discuss the acoustic
properties of consonants. This includes labial flaps, implosives, labial-velar stops, and
prenasalized stops. In Section 8.2, I look at the acoustic properties of vowels. I plot the
formant values of the vowels, and look at duration and nasalization. In Section 8.3, I
provide preliminary evidence that secondary articulations are closer to mid vowels than
high vowels, and I discuss phonetic evidence that secondary articulations do not bear
tone. Finally, in Section 8.4, I summarize the findings and discuss items for future
research. Except where noted, the findings of this chapter are valid for all of the subjects.
8.1 Consonants
8.1.1 Labial flap
Because the labial flap is rare in the world’s languages, there has been little
acoustic research carried out on the sound. Three previous works discuss the acoustic
properties of the sound: Ladefoged (1968) for Margi, Thelwall (1980) for Ndogo, and
Demolin & Teston (1996, reiterating Demolin 1992) for Mangbetu. Of these, Demolin &
Teston go into the greatest detail. The present work represents the first study of the
acoustics of the labial flap in Mono.
The labial flap can be identified by virtue of a combination of four acoustic
correlates: (1) a short closure duration, (2) ascending transitions for F1, F2, and F3
immediately after release, (3) a short duration of the formant transitions immediately
after release, and (4) a slow, gradual drop in F2 before the closure.
Concerning the first correlate, Catford (1977: 130) notes that taps and flaps
typically have an oral closure duration of 10-30 ms. This duration distinguishes taps and
flaps from stops, which typically have a closure duration of at least 50-60 ms. According
to my measurements, the average closure duration of the labial flap in Mono is 23 ms
(SD=5.0, n=15). Ladefoged notes that the contact is less than 30 ms in Margi, and
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