Had th same issues everyone else has with the original GS12 internal and factory issued external microphone, had to hear and bad sound overall.
Puchase this adapter from Dasaita and coupled it with a microphone I bouth from
https://shop.enfigcarstereo.com/product/enfig-mic-uni2-universal-headliner-microphone/
All my problems have gone away with this microphone, people are now able to hear me perfectly I can actually carry on a conversation hands free for once.