語音降階
From Phonology
在語音學上，語音降階(downstep-phonetics) 用以表示在聲調語言之音節與字詞之間，其聲調上之音位、或語音的向下轉移之特性。西非的語言上語音降階是廣為人所知曉的，但是日語(一種非聲調的語言)的音調重音現象是非常類似於非洲語言裡的語音降階特性。語音降階是對比於一般比較少出現的語音升階之語音特徵。在國際音標裡語音降階的符號是用一個向下指的上標箭頭來表示，不過目前Unicode還沒有支援這種符號。一般我們可以看到是用一個感嘆號 ! 的上標來替代它。
Phonetic downstep may occur between sequences of the same phonemic tone. 舉例來說, when two mid tones occur together in 加納的多威語, the second is at a lower pitch than the first. Thus downshift plays a vital role in downdrift and tone terracing.
Phonemic downstep may occur when a low tone is elided, or occurs as a floating tone, and leaves a following tone at a lower level than it would otherwise be. An example occurs in 班巴拉語. In this language, the 定冠詞 is a floating low tone. With a noun in isolation, it docks to the preceding vowel, turning a high tone into a falling tone: [bá] river; [bâ] the river. However, when it occurs between two high tones, it downsteps the following tone: [bá tɛ́] it's not a river; [bá ↓ tɛ́] it's not the river.
Japanese pitch accent is similar. About 80% of Japanese words have an evenly rising pitch, something like French, which carries over onto following unstressed grammatical particles. However, a word may have a drop in pitch between moras, or before the grammatical particle. 範例如下：
| /ka↓ki/ | /kaki↓/ | /kaki/ |
| [kákì] | [kàkí] | [kàkí] |
| 牡蠣 | 籬笆 | 柿子 |
In isolation like this, the first word has a high-low pitch, whereas the second and third are homonyms with a low-high pitch. However, all three are distinct when followed by the so-called "subject" particle ga:
| /ka↓kiga/ | /kaki↓ga/ | /kakiga/ |
| [kákìgà] | [kàkígà] | [kàkīgá] |
| 牡蠣 | 籬笆 | 柿子 |
