I only found 'dictator', but even as a non-native-speaker I guess that is overly associated with 'tyrant' or 'despot'.
In my case I need someone who speaks into a microphone for text recognition.
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Ah, but don't you want to have some fun? Just as someone who makes an allegation can be described as a allegator, can't you see the comedic opportunities in referring to this person as a dictator? :p
But seriously, as long as the context is clear, it's fine to call this person a dictator. It's common for words to have different meanings in different contexts.
I would simply suggest
because dictionary.com says
a person who speaks.
a person who speaks formally before an audience; lecturer; orator.