What "subtle changes" does Scout notice in her father?

From the text:

I was beginning to notice a subtle change in my father these days, that came out when he talked with Aunt Alexandra. It was a quiet digging in, never outright irritation. There was a faint starchiness in his voice when he said, “Anything fit to say at the table’s fit to say in front of Calpurnia. She knows what she means to this family.”