Stephen Karam thinks his elderly neighbor is losing her marbles. Like, really losing them.  “I still have no idea whether the wonderful woman who lives above me has grandchildren who visit,” said Mr. Karam, a playwright who lives on the sixth floor of a seven-story tenement in Manhattan’s Chinatown section. “There are inexplicable thumps, like she’s dropping marbles.”  The mystery of what’s happening above Mr. Karam is more than just a nuisance of city life: It helped inspire the moody sound design of his acclaimed new play, “The Humans.”  Set in a rough-around-the-edges duplex apartment in Chinatown, the show features a soundscape of what Mr. Karam describes as “mysterious and inexplicable” noise that becomes its own character in the drama, which unfolds during a family’s emotionally fraught Thanksgiving dinner.  To match the sense of dread, which intensifies as the show progresses, Fitz Patton, the show’s sound designer, uses about 80 sound cues. That’s actually a modest number for a play — some shows can have north of 500 cues — but many of his sounds are imposing, like the monstrous thumps that appear to come from a giant stomping across the roof. Other everyday sounds, like a cellphone ring and a trash compactor, work in aggregate to amp up the anxiety.  Like Mr. Karam, Mr. Patton is inspired by his own surroundings. Most of the sounds he uses in the show were recorded at various locales across New York, including his own apartment.  He recently spoke about how he devised five cues in “The Humans,” which is moving to Broadway in January after finishing its current Off Broadway run at the Laura Pels Theater of the Roundabout Theater Company. Following are edited excerpts from the conversation. Audio clips are at nytimes.com/theater.  At the beginning of the play, the actor Reed Birney hears a singular bump overhead, as he stands alone on the second floor of the apartment. Mr. Patton said he created this sound by putting a hand-held recorder near his foot that he set to “double the resolution of human hearing” and then stomping on the wooden floor of his daughter’s bedroom in their home on the Upper West Side.  “The audience hears a physical impact,” he explained. “But what’s happening is that the speaker is moving air a very short distance to hit the plaster of the ceiling above Reed. The ceiling, in a physical sense, becomes the speaker.” (Interesting detail: Mr. Patton made the recording without clothes on to avoid the rustle of fabric.)  Mr. Karam said this sound — which recurs with increasing severity in the play — comes across like “a dead body being dropped,” adding, “At the end of the day, I don’t know if I want to know what’s going on up there.”  Mr. Patton described this sound, which comes near the end of the show in almost total darkness, as “a heart beating at an abnormally low speed.” Mr. Birney is onstage alone with just a flashlight and his nerves, hearing “at a level that’s almost supernatural,” Mr. Patton said.  The sound was created by recording a slow pulse, “like flexing a muscle,” as Mr. Patton put it, that he had discovered near a boiler in the laundry room of his apartment building. “Hovering over the middle was a tone that had a pitch to it,” he said. “I wasn’t able to hear it in the basement with my ears, but through the recorder, it was loud. It was unnerving.”  This sound comes from a woman pushing a laundry cart past an open apartment door.  It was taken from the high-resolution sound design library Sonopedia, which features some 40,000 sounds organized by category. To create the sound of a passing object requires more than just making it soft, then loud, then soft again, Mr. Patton said. “To represent the sound of a thing being far away and then near, I took away the lower and high frequencies,” he said. “As it approaches, I add them back. At the door you hear the sound in full, and then, as she goes away, you subtract the volume, and also the high and low frequencies at a sharper rate. It’s all about modulating intensity.”  Mr. Patton obtained this sound by waiting in the basement of his apartment building for 45 minutes before the trash compactor finally compressed. The sound runs twice in the show, including at a strikingly surreal moment at the end when it’s played at four times the normal volume.  “I stood close and recorded it at a high resolution,” he said. “It’s a piston that’s taking all this trash and smooshing it so it can be stuck in a bag. It gets harder to smash, so there’s this arc of a machine that goes from an easy place of work to a harder place.”  This low-humming city soundscape, heard through a window, is an example of the “natural and textural” sounds requested by the show’s director, Joe Mantello, Mr. Patton said.  “You have to learn how to love that in Manhattan,” he said. “The whole city vibrates like a machine. It’s what everyone who lives in Brooklyn is happy they don’t have to deal with anymore, and it’s what Manhattanites defend.”  Mr. Patton’s recording is about 20 minutes long, but it’s repeated five times in the play to make it seem continuous.  A version of this article appears in print on December 3, 2015, on page C6 of the New York edition with the headline: A Master of the Hum and Creak. Order Reprints| Today's Paper|Subscribe
The designer Fitz Patton explains how he created the sounds for this warmly reviewed play, from a dull roar to jangling metal.