Through the battered century of world wars and massive violence by other means, there had always been an undervoice that spoke through the cannon fire and ack-ack and that sometimes grew strong enough to merge with the battle sounds. It was the struggle between the state and secret groups of insurgents, state-born, wild-eyed—the anarchists, terrorists, assassins and revolutionaries who tried to bring about apocalyptic change.
verb
(transitive) To voice too weakly.
(transitive) To make a quieter or background sound beneath.