Fortunately for the 50 million Americans who experience hearing loss, hearing aids have improved since the cumbersome, hand-held trumpets of the late 18th century. Back then, mechanically amplifying any and every sound frequency was the only option.
Today, audiologists know that loss of sensitivity to sound first becomes measureable at frequencies around 4000–8000 Hz—much higher than the dominant frequencies in normal speech, which range from around 100–1000 Hz. Most modern hearing aids work by providing frequency-dependent amplification based on the severity of an individual’s loss at each frequency. That approach works well in quiet settings.
However, in noisy settings, listeners also need to distinguish competing talkers and interpret speech based on a few heard fragments—a problem that extends beyond amplification alone. (See the article by Emily Myers, Physics Today, April 2017, page 34.) Even for people with normal hearing, understanding a conversation in a noisy train station or...