Robin Pecknold’s voice was big enough to fill Constitution Hall, but his band needed help filling some dead air. (All photos by Astrid Riecken/FTWP)

That’d be frontman Robin Pecknold, a man with a lithe and limber voice whose stage persona is as winning and humble as his songs — heavy with invocations of trees and mountains and snowflakes — would suggest. During the show’s most indelible moments — his solo-acoustic encore of “Oliver James,” the epic ballad “The Shrine/An Argument” — Peck­nold’s supple pipes transcended the many patches of dead air.