This study examines phonological and phonetic properties of ATR contrasts in the vowel system of Akebu (Kwa). The sum of descriptive evidence, including vowel harmony, vowel distribution in non-harmonising contexts, vowel reduction and typological and etymological considerations, indicates a rare vowel inventory with an ATR contrast in front/back vowels but a height contrast in the three redundantly [−ATR] central vowels /ᵻ, ə, a/. This analysis was checked against four common acoustic metrics of ATR: F1 and F2 frequencies, spectral slope and F1 bandwidth size (B1). As expected, the results for the last three metrics were variable across speakers and vowel types, and are therefore inconclusive. The results for F1 were consistent but do not distinguish between ATR and vowel height. Two results nonetheless suggest the [−ATR] status of central vowels: they occupy the same belt of F1 frequencies and show the same position of observed-over-predicted B1 values as front and back [−ATR] vowels.

本研究考察了 Akebu (Kwa) 元音系统中 ATR 对比的音系和语音特性。描述性证据的总和，包括元音和谐、非和谐语境中的元音分布、元音减少以及类型学和词源学考虑，表明罕见的元音库存，前/后元音具有 ATR 对比，但三个冗余 [− ATR] 中央元音/ᵻ、ə、a/。该分析根据 ATR 的四个常见声学指标进行了检查：F1 和 F2 频率、频谱斜率和 F1 带宽大小 (B1)。正如预期的那样，最后三个指标的结果因说话者和元音类型的不同而不同，因此没有结论。F1 的结果是一致的，但没有区分 ATR 和元音高度。尽管如此，两个结果表明了中央元音的 [−ATR] 状态：它们占据相同的 F1 频率带，并且显示出与前和后 [−ATR] 元音相同的观察到过度预测的 B1 值的位置。