Nervousness is a speed demon. Most people speak 20–30% faster when they are anxious, which makes them harder to understand.
A two-second pause after a major point makes you look confident and gives the audience time to process what you said. Voice and Speaking Skills For Dummies
Most people "chest breathe," which leads to a thin, shaky voice. To get a rich, resonant sound, you need to use your diaphragm. Nervousness is a speed demon