The phonetics of NCh in Tumbuka and its implications for diachronic change

The phonetic motivation for the synchronic and diachronic development of post-nasal voicing (*NT > ND) is well understood. Less well understood is the phonetic motivation for other common synchronic and diachronic developments from *NT, widely attested in Bantu languages, such as aspiration of the voiceless plosive and subsequent loss of either the nasal or the plosive portion of the sequence: *NT > NTh > Th, Nh. In this paper we first review the existing (scarce) phonetic literature on these developments. Then we present the results of a phonetic study of NC sequences in Tumbuka, a Bantu language where NT > NTh, as a way of exploring how the acoustic and perceptual properties of NTh sequences could motivate the development, found in other Bantu languages, of Th or Nɦ from NTh. We conclude by proposing that a perceptual cue approach, rather than a gestural or other articulatory approach, provides the most persuasive phonetic account, not only of the motivation for post-nasal aspiration of voiceless stops, but also for the instability of nasals and of voiceless stops in the NTh context which leads to other sound changes.