Painting with Frequencies: How Bell Tones Are Becoming the New Medium for Cross-Sensory Design

There is a particular tone — a sustained, mid-register bell strike with a slow decay — that sound designer Mara Voss describes as "the color of unripe copper." She cannot point to it on a Pantone swatch. It does not exist in the visible spectrum. Yet when she plays it for a room of listeners, a surprising number of them nod, as if they recognize something they have never seen.

This is the territory that synesthetic sound design occupies: the deliberate construction of audio experiences that activate perception beyond the auditory cortex. It is a discipline that has moved from neurological curiosity to studio practice with remarkable speed, and it is reshaping how experimental audio creators approach everything from immersive media installations to the sonic branding of premium consumer products.

What Synesthesia Actually Is — And What It Isn't

Clinical synesthesia is an involuntary neurological phenomenon in which stimulation of one sensory pathway automatically triggers an experience in another. Roughly four percent of the population perceives letters as inherently colored, or tastes words, or — most relevant to sound designers — sees music as moving shapes and hues. This variant, known as chromesthesia, has been documented in figures ranging from Nikola Tesla to Pharrell Williams.

But the synesthetic design movement emerging from studios across New York, Los Angeles, and Chicago is not waiting for that four percent. It is working from a more expansive premise: that the human brain, regardless of clinical diagnosis, is wired to process sound in multisensory terms. Neuroimaging research from institutions including MIT's McGovern Institute for Brain Research has demonstrated that auditory stimuli reliably activate regions of the visual cortex in non-synesthetic subjects. The cross-sensory wiring is present in most listeners. The question, for a new generation of sound artists, is how precisely it can be addressed.

"We stopped thinking of tone as something that lives exclusively in the ear around 2019," says audio artist and researcher Dominic Farrell, whose studio in Brooklyn has consulted on VR experiences for several major entertainment platforms. "Once you understand that a frequency can reliably activate a visual or tactile response, you start treating the frequency as a brushstroke. The canvas just happens to be inside someone's nervous system."

The Bell as a Synesthetic Instrument

Bell tones occupy a privileged position in this emerging practice. Unlike synthesized waveforms, which can be engineered to near-mathematical precision, bell sounds carry what acousticians call a complex inharmonic spectrum — a dense cluster of overtones that do not resolve into clean harmonic ratios. This sonic complexity is, paradoxically, what makes them so effective as cross-sensory triggers.

"An inharmonic overtone series creates perceptual ambiguity," explains Dr. Renata Sousa, a cognitive neuroscientist who has collaborated with sound artists on several cross-sensory design projects. "The brain is searching for a category that fits what it's hearing, and when it can't find one cleanly in the auditory domain, it reaches into other sensory domains for context. That's the opening that synesthetic designers are exploiting."

In practical terms, this means that specific bell tones can be engineered — through careful control of strike point, material resonance, and digital post-processing — to reliably evoke particular visual or textural impressions across a broad population of listeners. A tone struck near the rim of a large bronze casting, processed with a gentle high-frequency roll-off, tends to register as something cool and blue in informal perceptual tests. A smaller, harder-struck bell with prominent upper partials often reads as sharp, angular, and yellow-adjacent. These are not universal laws, but they are statistically consistent enough to be operationally useful.

From Neuroscience to the Studio Floor

The practical application of these principles is already visible — or rather, audible — across multiple industries. In the VR and immersive media space, sound designers are using synesthetic tones to reinforce the spatial and material qualities of virtual environments without relying solely on visual rendering. A digital space constructed to feel vast and cold can be anchored perceptually by bell tones engineered to evoke gray, receding distances. A virtual material that is meant to read as warm and tactile can be introduced with a tone whose overtone structure maps, for most listeners, to amber and soft resistance.

"The visual rendering can only do so much before it starts taxing the hardware," says Farrell. "But if the sound design is doing genuine cross-sensory work, the brain fills in the rest. You're not just hearing the space — you're constructing it."

High-end product design has arrived at similar conclusions from a different direction. Several luxury brands — primarily in the fragrance and automotive sectors — have commissioned bespoke sonic identities built around synesthetic principles. The goal is not merely a memorable chime but a tone that communicates material quality, sensory refinement, and brand character through the activation of non-auditory perception. A fragrance house, for instance, might commission a bell tone whose frequency profile evokes the olfactory impression of cedar and cold air — not through any literal encoding, but through the statistical tendencies of cross-sensory response.

The Limits and the Ethics

The discipline is not without its complications. The reliability of cross-sensory mapping varies significantly across demographic groups, cultural backgrounds, and individual neurological profiles. What reads as blue-gray stillness to one listener may register as something entirely different to another, and the research base for population-level synesthetic mapping remains relatively thin.

There is also a question of manipulation. If a tone can be engineered to reliably trigger specific emotional or sensory states without the listener's awareness, the ethical framework governing its use becomes important. Dr. Sousa is direct on this point. "The same principles that make synesthetic design useful for creating genuinely beautiful, immersive experiences can be used to engineer subliminal influence. The field needs to develop an ethics alongside its technique."

For most of the designers currently working in this space, the motivation is less commercial than it is genuinely artistic. The appeal of crafting a sound that arrives in the listener's mind as a color that has no name — a hue that exists only in the interaction between a carefully tuned frequency and a particular nervous system — is, by most accounts, difficult to resist.

"I'm not painting pictures," says Voss, who is currently developing a solo installation for a gallery in Chicago that will feature exclusively bell-derived tones mapped to a visual vocabulary she describes as existing "between silver and the idea of distance." "I'm giving people access to perceptions they didn't know they were capable of having. That feels like the most honest thing I can do with a studio."

The canvas, as it turns out, was always larger than the speaker.