Character Animator lip sync with Mp3

you can use swap set for expression change. (if you wanna put a little more effort into this) and you can trigger that expression with your key
here's example.

also a description of this part is included in this guide link (5.1. Triggers in Character Animator)

https://graphicmama.com/blog/beginners-guide-to-adobe-character-animator/

It's not completely clear from the screenshot, but it looks like your netural mouth shape might be the happy one. The lip sync alone can't determine whether shapes should be "happy" or "sad." Do you mean that when you use the webcam your character can have a neutral mouth or a bit of a frown? If so, those shapes are being chosen via facial tracking and not lip sync. You can right-click on any of the visemes in the timeline and change them to be something else if you want.