about some details in Audio Record tutorial

I learn about record with microphone in godot docs.
But it seems There are some details that the tutorial didn't write.
I spend some time to Find why my code can't record Audio and play correctly.
when I play it ,it sounds like electronic sound!
I want to add some details to the tutorial to help people who meet my problems.
I haven't use red the docs. I may try to learn how to use it.
I really like godot .
Maybe My English is not so good .
It's 22:17 in my city. I will go to sleep .
Tomorrow MayBe I will try to do the thing.