"Give this Mii a voice! You can select a preset or random setting or customize it yourself."
— Tutorial, Tomodachi LifeVoice is an adjustable setting that determines a Mii's manner of speech. There are 6 preset voices: male child, female child, male adult, female adult, elderly male, and elderly female. Voice can also be randomized, and can be customized using the 6 different settings: Pitch, Speed, Quality, Tone, Accent and Intonation.

Here are all of the settings and what they do:

Pitch: Overall, how high or low your Mii's voice is.

Speed: How quickly your Mii talks.

Quality: How clear/understandable your Mii's speech is.

Tone: How high-pitched the Mii starts a sentence.

Accent: How low-pitched the Mii ends a sentence.

Intonation: The tone of voice used during a sentence. 1 is normally. 2 ends higher, like with a good attitude or as if asking a question. 3 is a explaining-like voice. Going high to low. 4 is normally the same throughout the whole sentence.