Downdrift
Downdrift, where the absolute pitch (not tones) of the speaker's voice is gradually decreased as the sentence continues (often resulting in initial low tones being pronounced at a higher pitch than final high tones), is a feature during natural speech. Basically, a high tone immediately following a low tone is pronounced at a slightly lower frequency than a previous high tone.
Additionally, a slightly more dramatic lowering of pitch (a downstep) may occur between certain syllables. In Sesotho, the downstep (indicated with a !) naturally occurs between words (being less noticeable if the first word has no low tones) though there is at least one instances (in rule 1 of the plain copulative) where the lack of downstep (as well as other tonal factors) changes the utterance's meaning. In the following example, a grave accent (à) indicates a low tone and an acute accent (á) indicates a high tone.
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| I need you to go look where she has gone to |
This downdrift is greatly attenuated when the sentence is a question not using the interrogative adverb na?.
Read more about this topic: Sotho Tonology