There are supplementary differences of lexical choice, as well as many types of phonological reduction and change which mark the various 'levels' of discourse. [...] There are still other features, not normally included in a phonemic statement but meaningful in the socio-linguistic context: preciseness of articulation, speed of utterance, 'voice color' (serious, happy, non- committal, etc.). [...] environments that are connotatively distinct.
- Nida (1948), a pag.433