The sound came across the water with a distinctness that pierced and subdued all other sounds, which were now __ to his ears.

deafening.

From the excerpt:

"A counter-swirl had caught Fahrquhar and turned him half round; he was again looking at the forest on the bank opposite the fort. The sound of a clear, high voice in a monotonous singsong now rang out behind him and came across the water with a distinctness that pierced and subdued all other sounds, even the beating of the ripples in his ears. Although no soldier, he had frequented camps enough to know the dread significance of that deliberate, drawling, aspirated chant; the lieutenant on shore was taking a part in the morning's work. How coldly and pitilessly - - with what an even, calm intonation, presaging, and enforcing tranquility in the men - - with what accurately measured interval fell those cruel words ... "

I concluded.