You know what London looks like. But have you really heard it?

The musician Dessa took a sensory tour in London with the synesthete LJ Rich. Here is how it sounded.

On the NASA website, LJ Rich’s profile lists “recreational lock picking” as a hobby. She has glossy dark hair, a compact build, a master’s degree from Oxford and synesthesia, an unusual condition that blurs and blends sense perception. A synesthete might report that the sound of the letter B tastes like mashed potatoes. Or that magenta smells like cedar wood. The incoming stimulus of one sense jumps its lane to trigger perception in another. For LJ, shapes, colors, textures and flavors set off a concert in her head.

LJ presents for the BBC in London, covering music and tech. She’s also part of a NASA program called Datanauts, where she’s working on a technique to sonify data: to communicate through melody what might be more traditionally expressed with a chart or a scatter graph. Melody has been an unrelenting part of LJ’s life; in a TEDx talk she delivered in Tokyo, she told her audience, “I hear music everywhere, whether I like it or not.”

I first met LJ in 2014, at a fancy professional conference. Accomplished lawyers, writers and business people were chatting in small groups aboard a chartered bus, waiting to depart for the evening activity. One person thought to bring a flask and was, briefly, our hero. But then LJ arrived.

She wore a glittering silver dress and a backpack from which she pulled a bag of marshmallows. As she proceeded down the aisle, she offered a marshmallow to the occupant of every seat — and these decorated adults melted into the grade-school versions of themselves, happily sinking a hand into LJ’s cellophane bag. I make my living as performing musician, so I can say authoritatively that LJ works a room with professional skill. Armed with two bucks’ worth of aerated sugar, she became the most admired member of the traveling party.

This spring, I set out on a long headlining tour. The routing looped through London, so I dropped LJ a note. We arranged to meet in the Shoreditch neighborhood for a walk down Brick Lane. I had visited the area before and remembered it as full of cafes, boutiques and street art — Brooklyn with cobblestones. This walk with LJ, however, would be unlike any other I’d taken in London, or anywhere else for that matter. We’d be doing what LJ called “glitching.” Using an iPad, special microphones, a digital amplifier and some music software, LJ would manipulate the sounds of Brick Lane — adding reverb, echoes, EQ filters and melodies — and then share this altered audio with me through earbuds. According to LJ, the experience can simulate synesthesia for a neurotypical person. Adding music to my world could make it more like the one she lives in.

We convened in the yard of St. Leonard’s Church. It was noon and it was hot; the heat wave had been making headlines. I arrived with my bandmate Matthew Santos, who’d accepted my invitation to tag along before we had to report to sound check. Like me, Matthew is almost 6 feet tall. Like LJ, he’s musically multitalented: In my band he sings, plays keyboard and guitar and often rearranges songs on the fly for acoustic performances.

The grounds of St. Leonard’s are lush. There’s a flower garden so immodestly fragrant it seems to exceed all botanical limits, crossing from horticultural into Haribo olfactory territory. In the center of the lawn are a pair of white tombstones commemorating the civilian war dead of Shoreditch. The inscription reads, “The names of the people interred in this grave are recorded on the memorial erected in another part of this cemetery” (a rather administrative tone for an engraver).

LJ carried a small black bag full of electronic equipment. She also brought a pair of 4 1/2-inch rhinestoned heels. She said they were to elevate her ears to roughly the same plane as Matthew’s and mine. After strapping them on, she announced, “That’s a little better acoustically.”

Together we set out toward Brick Lane, chatting a bit before the glitching began. LJ said she had been a “weird prodigy kid.” For her, perfect pitch had been a nightmare. The whole world seemed out of tune. But then teachers introduced her to Indian ragas, Gamelan music and compositions with quarter tones, unfamiliar modes and atonal structures. As her musical horizons expanded, her anxiety dissipated. (She remains exceedingly sensitive to pitch, though. Her refrigerator, for example, hums in A flat. Working from home, I hear my fridge running 12 hours a day. Blindfolded, I’m not sure I could pick the thing out of a lineup of three other refrigerators.)

LJ walked with the careful steps of someone wearing very high heels, in sharp contrast to Matthew’s unusual gait. He’s got a bouncing, long-limbed stride that swings both arms in large, pendular arcs. I happen to know this springiness was drilled into him by a basketball coach, to keep him on the balls of the feet. But it’s become a signature feature, and it suits him.

Matthew seems to live quite comfortably in his body — takes the time to stretch and run on tour, delights in a nice perfume worn by someone walking by, happily pays cocktail prices for Whole Foods juices. Meanwhile, my body sometimes feels like the spacesuit I use to chauffeur my mind from room to room. I’ve done enough science writing to know that kind of mind-body dualism is garbage; there’s no clean partition. All of our systems work in a dynamic concert; even perception isn’t just the passive reception of information. Our brains and bodies work together to make meaning from the hurricane of sensory input that whirls around us night and day.

Synesthesia is so fascinating because it underscores the fact that people experience the world in profoundly different ways — and some might be living in richer, more interesting hurricanes. When I learned that goldfish could see infrared radiation I had a pang of FOMO, a flash of anxiety that this creature was somehow getting more of the world than me. A creature, mind you, that lived in a bowl.

LJ routed us through Arnold Circus, a tiny park set in a roundabout. Arnold Circus is tiered like a wedding cake (if you were inclined to make a cake out of asphalt and frost the sides with wood chips and leafy perennials) and topped with a bandstand.

LJ led us to the center of the bandstand, which had green railings and a low wooden ceiling beneath a peaked roof. “Clap your hands,” she instructed. Matthew and I complied, setting off a shimmer of quick echoes that collided with one another as they bounced off the ceiling and the floor and back and again in a strange, rubbery effect. “Oh my God,” Matthew said. I stamped. Cool. Matthew noted there was a tremolo to the sound; something about the space made the pitch of the echoes wobble up and down as they repeated.

In a tour-guide voice, LJ announced, “The acoustically interesting spaces of London!” Despite the jokey tone, she made an interesting point: It’s remarkable how few sonic experiences we seek while traveling. We lean into our adventures with wide eyes and open mouths, hunting for photographic vistas and authentic local meals. It’s a rare story that leads with another sense. (I do remember an Indian acquaintance saying that when she stepped off the plane into the U.S., she was startled by the report of her nose: “It smelled like nothing. Nothing!”) But we could travel as sonic tourists if we were so inclined. In a 2016 report called “City of London Noise Strategy,” I found a ranked list of London’s iconic sounds. Attractions included St. Paul’s bells, open outcry trading and boats on the Thames.

In the acoustic funhouse of the bandstand, Matthew and I let out little vocal yelps, listening to the how the bass in his voice resonated more dramatically than mine. None of the strange reflections were audible outside the railings, so to the people sunning on the grass nearby, we were just easily delighted idiots.

“OK, would you like to plug in?” LJ pulled the iPad out of her bag and wrestled with a knot of wires, getting all her digital equipment in order. Matthew and I handed over the jacks for our earbuds. Connected, we had to stay close, effectively leashed together by the ears.

LJ warned that we might feel disoriented at first. She snapped her fingers near her right ear and I heard it in mine. The sounds around us began to echo in tight repetitions; every chirping bird triggered a treble cascade, like ripples of a stone thrown into still water. A little girl kicked a bottle cap through the bandstand; the metal skittering across the asphalt became an extended iridescent tinkle.

LJ pressed play on a soft prerecorded musical track she’d composed. I hadn’t expected that; I thought we’d be working only with environmental sounds. The music layered with the echoes coming from all directions made it difficult to speak at a normal rate. Deliberately, LJ said simply, “Sound … changes.” The rolling delays felt like a cinematic representation of intoxication, I thought. Like a sober mushroom trip.

The three of us stepped out of the bandstand and went glitching into the sunlight. LJ cued up another composition, specifically inspired by Brick Lane.

Brick Lane is a narrow one-way lined with cafes, vintage shops, curry houses, bars and salons. Most walls are blond brick, although some have been coated with so many layers of thick, glossy paint that they shine as if perpetually wet. I imagine that a core sample taken from one of these painted walls — a little cylinder the width of mechanical pencil lead, say — could be analyzed like tree rings. There’d be a complete history in the tiny stack of colored wafers: the coats of paint applied when London-born daughters took over from their immigrant fathers, when the first wave of Bangladeshi arrived, the Jews before them, the French — all the way down to the brick itself, made by masons whose factories on the lane gave it its name.

The three of us walked slowly, on account of both the wires and the sensory bombardment. An old man, leaning drunkenly on a stoop, heard me mutter “Oh my God” and mimicked me. LJ’s microphones picked him up and his voice ricocheted with mine in our ears. After we’d passed, I couldn’t tell if he continued to parrot me or if the echoes were generated by the software. I wondered if LJ sometimes found it difficult to discern raw signal from synesthetic effects in her daily life.

Matthew, LJ and I hummed, making chords. Both of them are more musical than me, and I felt embarrassed to always offer up the most predictable note, the vanilla pop chord; never finding an exotic minor triad like they did. Glitching seemed to offer a portal into LJ’s musicality — her facility with improvisation and her attraction to found sounds — but I wasn’t sure if I was getting a better understanding of her synesthesia. What features of a particular road or roundabout determined the sounds she heard while traveling it? The lines, the colors, the shapes? When I asked her later, even LJ wasn’t totally sure.

We left Brick Lane for a tranquil path, lawn on one side and elevated train tracks on the other. LJ stopped. She wanted to hear the train come by — one of her favorite sounds. A train and a plane passed over at the same moment, the engine noises rising like a slow ocean. It felt lucky.

It was midafternoon; soon Matthew and I would have to leave for our show. The three of us disconnected and the world went regular again, although I found myself still sensitized to sound of people’s footsteps. LJ took us to a place we could debrief before parting ways.

We followed her beneath an overpass where every inch of concrete was covered with full-color spray-painted murals. We passed through a small gate and the Nomadic Community Gardens opened around us: a rush of art and anarchy. Tiny wooden lean-tos were arranged in ragged rows, strewn with silk flowers, strands of lights, hand-painted signs. Some held small groups of chatting drinkers. One had a wooden piano missing two black keys, like it lost them in a fistfight. One housed a healthy-looking, butterscotch-colored dog. Sun-bleached boards were lashed together to serve as planters for unruly flowers that climbed over one another, trying to escape. In one corner, a wooden boat had been converted into a jungle gym, an aluminum slide rammed through its hull. The Nomadic Community Garden closes at night, but if permanent residents were permitted, Jack Sparrow would be their mayor.

LJ and I bought cups of tea from a woman running a cafe out of a three-wheeled vehicle. I told LJ truthfully that I’d enjoyed glitching. But I was still keen to home in on the particulars and parameters of her synesthesia. Did she hear specific notes when she ate? I asked.

“Sushi tastes like power chords on acoustic guitar,” she answered.

Excellent! This was exactly the sort of one-to-one effect I’d been hoping to learn about. But LJ went on to explain that while not all flavors had sonic resonance, her synesthesia allowed her to taste each individual ingredient in a dish and reverse-engineer the recipe. Wait, I thought, was there anything necessarily synesthetic about a discerning palate? Later, a Google search revealed synesthetes are, in fact, often hypersensitive, but in that moment LJ’s response seemed to frustrate my attempt to snap a clear picture of her synesthesia. Every time I had it framed up nicely, it darted out of the shot or something else dove in. A half-dozen questions later, I still didn’t have a satisfying portrait.

On my ride with Matthew back to our hotel, and in the following days, I came to believe my approach was flawed: It was impossible to isolate LJ’s synesthesia from the rest of her, because none of us can be disassembled into our component parts. I can’t tour London as a woman without also traveling as an American; those lenses don’t come uncoupled. The question “What would it be like not to be me?” is maddening because it’s answerable only in fragmentary secondhand reports. We use the best and only tools at our disposal — conversation, art and travel — but nobody can break into another mind. Still, we try and try to pick the lock.