There is no question that zombies have excellent hearing. Not only can they detect sound--they can determine its direction. The basic range appears to be the same as that for humans. Experiments with extreme high and low frequencies have yielded negative results. Tests have also shown that zombies are attracted by any sounds, not just those made by living creatures. it has been recorded that ghouls will notice sounds ignored by living humans. The most likely, if unproven, explanation is that zombies depend on all their senses equally. Humans are sight-oriented from birth, depending on other senses only if the primary one is lost. Perhaps this is not a handicap shared by the walking dead. If so, it would explain their ability to hunt, fight, and feed in total darkness.