In tonal languages how does the pitch of a person voice affect speaking it? Does it cause everyone to speak in the same tone to be understood?
No. There is a tonal “context” if you will, which varies from person to person. A person with a high squeaky voice will send her voice even higher on the rising tone, establishing (after a native speaker hears her speak for a few words) what her normal “steady” tone is. There are other ways the speaker can place stress on certain words if it is needed, without changing the critically important tone.
This is my experience with Vietnamese, which has six different tones… I would think it holds true for all tonal languages.