A family of Microsoft word processing software products for creating web, email, and print documents.
I have same issue,
Sometimes it reads one paragraph whit once voice and next in valley girl voice then again in generic English voice.
So far what i know is changing proofing language change voice of read out loud. (PS: Canadian English voice is almost ok)
Also it seems if you let it detect language and you proofing language is one that don't have tts engine support it default to generic English voice what i usually hear and like. but sometimes it detect US English word only and then jump into valley girl voice on that sentence.
There is no generic English proofing language option so i cant force that voice to be all time what is kind of sad.