Timbre Lab: hearing sound structure
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timbre synthesiser
click a harmonic card to mute or unmute it · drag its slider to adjust the volume
This synthesiser runs entirely in your browser. It generates six sine wave oscillators simultaneously: one for the fundamental frequency and one for each of the first five overtones. You can adjust the volume of each overtone independently in real time, mute and unmute them, and watch the composite waveform change shape on the oscilloscope as you do. The attack and release controls shape how the sound fades in and out. Pink noise can be layered over the harmonic tones.
Timbre lab
Written by Jordan Elias, MT-BC
What makes a flute sound like a flute or a violin like a violin, even when they play the same note at the same volume? The unique timbre of a note is the result of the harmonic overtones an instrument generates. Experiment yourself with adding overtones to a pure sine wave and shaping its timbre.
What is timbre?
Every pitched sound is a composite. When a string vibrates at 110 Hz, it simultaneously vibrates at 220 Hz, 330 Hz, 440 Hz, and beyond. All this layering is still heard as a single note. These higher frequencies are called harmonics or overtones. The lowest is the fundamental, which gives you the perceived pitch. The overtones determine its warmth, brightness, roughness, or sharpness.
At the physics level, timbre is simply the structure of a sound wave; the relationship between a fundamental frequency and its overtones, including their relative volumes. At the perceptual level, it is the thing that allows us to instantly recognise an instrument, a voice, an environment, without consciously analysing anything. Note that these presets may not sounds exactly like the acoustic instruments they are trying to emulate. But synths build sounds exactly like this, they are just usually much more complex.
The brain does not hear individual frequencies. It hears relationships between frequencies. Timbre is encoded as spectral patterns in the distribution of energy across the frequency spectrum. These patterns are processed not only in the auditory cortex but across emotional and embodied networks: the limbic system, particularly the amygdala, is involved in evaluating whether a sound signals safety or threat before it even reaches conscious perception. The sensorimotor cortex creates embodied resonance, the felt physical quality of a sound in the body rather than just the ears, which is why certain timbres register as grounding or activating at a somatic level. The default mode network and particularly the prefrontal cortex are involved in the higher-order work of meaning-making and conceptual labelling. This is the point at which a sound becomes something that feels like it belongs to an instrument or a feeling. And this network connects these sounds to your memory and identity. These systems operate in parallel, and often the emotional and embodied response to sound arrives before the cognitive one.
Experiments
1. the pure sine
Select pure sine and press play. You're hearing a single frequency oscillating air pressure, with nothing added on top of it. Notice what it lacks: warmth, color, instrument character. Watch the clean, simple arc on the oscilloscope. This is a pure sound wave.
2. introduce one harmonic at a time
Stay on pure sine. Now click H2's card to unmute it, and slowly drag its slider up from zero. Listen for the moment warmth appears, and watch the waveform shift on the oscilloscope. Then bring in H3 and hear it become rounder and fuller. H4 adds brightness; H5 and H6 push toward edge and intensity. Each harmonic is a distinct physical layer with a distinct pitch and character. Notice which arrivals feel most dramatic, and whether the changes register in your body as well as your ears.
3. sculpt in reverse
Load brass. Now click cards to mute harmonics one at a time, starting from H6 and working downward. Track when it stops feeling like brass. At what point does it cross from bright to warm? From metallic to something rounder? The line between "brass" and "not-brass" is perceptual.
4. the bell
Load bell. This preset is different from all the others. Instead of integer harmonic ratios (2:1, 3:1, 4:1), the upper partials use inharmonic ratios: 2.7×, 5.8×, 8.9×. These don't belong to any harmonic series. The result is a sound that feels metallic, unstable, and not-quite-pitched. These frequencies don't fuse into a unified note the way true harmonics do. This is why struck metal objects have that characteristic. The overtones are not in resonance.
5. the hollow clarinet sound
Load hollow. This preset uses only odd-numbered harmonics (H1, H3, H5) with H2, H4, and H6 muted. The physical reason clarinets have this sort of quality is that the body of the instrument itself suppresses these harmonics, producing a spectrum built only from odd partials. Try toggling H2 in and out slowly and listen to the even-odd distinction.
Attack, release
Timbre is not a static property. It unfolds through time. The attack slider controls how quickly the sound fades into full volume when you press play. The release controls how quickly it fades out when you stop.
6. envelope as instrument character
Try string with a 1.5 second attack. Press play. The sound blooms from silence, gaining body as it arrives, similar to a bow across a string, pulling the tone out of nothing. Then try brass with a 10 ms attack and a 50 ms release. The same harmonic richness becomes percussive.
Long attacks don't trigger the startle reflex; they arrive as gradual presence. Short attacks register as arrival and punctuation. Notice what each does in your body.
Pink noise
Toggle on pink noise using the button above. What you're hearing is noise with equal energy per octave. The same total energy exists between 20–40 Hz as between 2,000–4,000 Hz. This differs from white noise, which distributes equal energy at every individual frequency and consequently sounds harsh and artificial to the ear.
Pink noise is structurally abundant in the natural world: rainfall, rivers, wind through foliage, the ocean heard from a distance. It has no perceptible pitch. But perceptually distinctive in that the nervous system experiences it as a bit unremarkable.
7. noise layer
Load the flute preset with harmonics playing. Now activate pink noise and notice what it does to the sound wave.
Try the same addition with voice, then with brass. Does the noise feel more or less natural against different timbres?
The priming effect: hearing what you expect to hear
With only pink noise active and harmonics fully muted, try this. Read the word waterfall slowly, hold an image of a waterfall in your mind, and listen for thirty seconds. Then read the words air conditioner and listen to the same sound again.
When a sound is acoustically ambiguous, the auditory cortex actively draws on prior expectation to construct the percept. Research on exactly this stimulus has found physiological differences in response to identical acoustic information depending solely on the label applied to it.
The 2018 phenomenon known as the Laurel/Yanny effect exemplified this. A single recorded word that listeners would clearly hear as either name, depending on what they expected to hear and, as turned out to matter considerably, which frequency ranges their hearing happened to be most sensitive to. What made this so disorienting was that it demonstrated that two people listening to the exact same sound could be having completely different experiences with no objective way to determine which was "correct."
Perception is an active process shaped by expectation, context, memory, and language. Listening is something the brain does to sound, not just something sound does to the brain.
Imagining
This set of exercises draws on the top-down capacity of auditory perception: the ability to impose interpretive frames on sound and have those frames reshape the experience from the inside. How does deliberately shifting that interpretation change what you hear?
preset: flute
Imagine a wooden flute in a large stone cathedral. Where does the sound seem to originate? Is it close or distant, above or in front of you? Now imagine the player is outside. Where are they? Does anything change about how the sound feels?
preset: hollow
Imagine you're seated at the back of a recital hall, the performer far away. Listen to the drone. Now imagine you are the performer. What changes about how the sound feels in your chest?
build your own
Build a timbre from scratch using the sliders. Give it a name. What does it remind you of? What sense of space does it evoke? What emotion does it evoke?
These prompts engage what researchers call auditory scene analysis: the brain's capacity to place sounds in space, reconstruct source characteristics, and build coherent perceptual environments from raw acoustic data. What Pauline Oliveros called deep listening is in part the practice of attending to this process directly: noticing not just what you hear, but how you are hearing it, and what you are bringing to the act. If the indeterminacy post was about expanding attention outward, this is about attending to the physics underneath the experience.
Music as therapy, sound as nervous system data
Every spectral structure carries a physiological signal. Warm timbres with strong fundamentals and soft upper harmonics tend to activate parasympathetic responses. Bright, strong upper partials are activating. Inharmonic sounds like the bell create a dissonance that the nervous system notices.
There's also agency in the act of construction itself. When a person shapes a sound, there is a relationship between the person and the sonic material. Exploring this play between the sound imposing itself on the listener, and the listener imposing their own thoughts, memories, and embodied feelings onto the sound I think reveals something about the nature of listening.
Try the experiments. Note which timbres feel soothing and which feel activating, and whether those responses are consistent or vary with context and mood.
If you're curious about working with sound perception, embodied listening, or the therapeutic dimensions of creative sound-making in the context of music therapy, please feel free to request an intro call via the contact page. I work with musicians, neurodivergent individuals, and people navigating trauma, illness, and significant life transitions. Music experience is not required.
Further reading:
- This Is Your Brain on Music — Daniel J. Levitin
- Musicophilia: Tales of Music and the Brain — Oliver Sacks