Since I began writing, I've heard the term, "writer's voice." I've finally stopped trying to define it. I can't tell you why I recognize the physical voice of my wife, or son, or daughter, while I can't tell you what is unique about each one. I've about decided that "voice" is like a giraffe--I can't exactly describe it, but you know it when you see it.
I'm reading a book written by another author chosen to carry on the tradition of one of my favorite writers, the late Robert B. Parker. I've read two other books by writers Parker's widow chose to keep the line of novels alive, and frankly, wasn't impressed. They didn't have Parker's "voice." The one I'm now reading, a western, is better, although there are places where it's obvious that the writer has chosen to show off how much research he's done--something of which Parker was never guilty. The book may be pretty good, but it's not a Robert B. Parker.
I've just completed responding to an extensive set of edits of my novel that will be released this fall, Heart Failure. The line editor did a very thorough job of suggesting areas where the novel could be tightened, the wording improved. The edits were valuable, but at almost every juncture I ended up changing her words to mine. Why? The insertions weren't in my "voice."
Do your favorite authors have a unique "voice?" Can you define it? Or is it, like a giraffe, something you can't describe?