I'm currently reading TEACHER MAN, by Frank McCourt, the author of ANGELA'S ASHES. First of all, if you're ever not quite sure about voice? Read Frank McCourt's books. The man's writing voice is a lovely thing.
But something else leapt out at me, something I wasn't expecting at all, and I quote:
"Any playwright will tell you that when the actor sits down the play sits down."
When the actor sits down, the play sits down.
In my head, that immediately turned into:
When your characters sit down, the pace of your story slows down.
As somebody who writes a lot of dialogue, I try to keep my characters from being mere "talking heads," but I've never seen the "why" of that put so succinctly or so memorably.
To be sure, there are probably exceptions (there always are in writing), like, say a lot of quick, bantering-type dialogue while your characters are driving somewhere. That's going to read "fast."
But this line will remind me of something to avoid that could lead to "talking head syndrome" and sluggish pacing.
And here I thought I was just taking a break....