Brown Noise

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What Is This Sound?

This is brown noise (also called Brownian noise or red noise) — a deep, rumbling noise signal with strong low-frequency emphasis. It sounds like a distant thunderstorm, a powerful waterfall, or heavy wind rushing past your ears. Of the three common noise colors, brown noise has the deepest, most bass-heavy character.

Despite its name, brown noise has nothing to do with the color brown. It is named after Robert Brown, the botanist who first described Brownian motion in 1827. The signal is generated using a random walk process — each sample is derived from the previous one plus a small random step — which is the audio equivalent of a particle undergoing Brownian motion.

How Is Brown Noise Created with Code?

Tone.js provides brown noise as a built-in noise type, making generation effortless.

The Complete Signal Chain

import * as Tone from "tone";

// Create a brown noise source
const noise = new Tone.Noise("brown");

// Brown noise has heavy low-frequency energy,
// so we set gain to 0.3 for comfortable listening
const gain = new Tone.Gain(0.3);

// Connect: Noise → Gain → Output
noise.connect(gain);
gain.toDestination();

// Start the noise
noise.start();

The Random Walk Algorithm

Under the hood, brown noise is generated by integrating (accumulating) white noise samples. Each output sample is the previous output plus a small random value, clamped to prevent runaway:

let lastOut = 0.0;

for (let i = 0; i < bufferSize; i++) {
  const white = Math.random() * 2 - 1;
  // Integrate with a leaky integrator
  lastOut = (lastOut + (0.02 * white)) / 1.02;
  output[i] = lastOut * 3.5; // Compensate for volume loss
}

The division by 1.02 acts as a gentle leak that prevents the signal from drifting too far from zero. The multiplication by 3.5 compensates for the significant volume reduction caused by the integration process.

The Science Behind Brown Noise

The 1/f² Spectrum

Brown noise has a power spectral density proportional to 1/f², which means its energy drops by 6 decibels for every doubling of frequency. Compared to pink noise (−3dB/octave) and white noise (0dB/octave), brown noise is dramatically tilted toward the bass end. By the time you reach the upper midrange, there is very little energy left.

This steep rolloff is a direct mathematical consequence of integrating white noise. Integration in the time domain corresponds to division by frequency in the frequency domain, and since we start with a flat spectrum (white noise), dividing by f gives 1/f per amplitude, or 1/f² per power.

Brownian Motion and Random Walks

The signal is called Brownian noise because its waveform traces a random walk — exactly the path a microscopic particle takes when buffeted by molecular collisions in a fluid. If you plot the waveform of brown noise, you see a slow, wandering line that drifts up and down unpredictably. This is fundamentally different from white noise, which looks like static, or pink noise, which falls somewhere in between.

The Deep Rumble Quality

The strong bass emphasis gives brown noise its characteristic rumbling quality. Human perception is less sensitive to very low frequencies (as described by the Fletcher-Munson equal-loudness contours), so brown noise needs to be played at moderate volume for the low-frequency content to be fully appreciated. When it is, the effect is immersive and almost physical — you feel it as much as hear it.

Common Uses

• Deep Sleep — The heavy low-frequency content is particularly effective at masking bass-heavy disturbances like traffic rumble, HVAC systems, and neighbor noise
• ADHD Focus — Brown noise has gained significant popularity in the ADHD community, with many reporting improved concentration and reduced mental restlessness
• Relaxation & Stress Relief — The deep, enveloping quality creates a cocoon-like sensation that many find deeply calming
• Sound Design — Serves as raw material for thunder, wind, engine rumble, and other low-frequency sound effects
• Tinnitus Masking — Particularly useful for low-frequency tinnitus that white noise does not adequately cover
• Creative Writing & Reading — The unobtrusive, low-frequency backdrop helps maintain flow states without demanding attention

Technical Details

Frequently Asked Questions

What is the difference between brown noise and pink noise?

Brown noise rolls off at −6dB per octave, while pink noise rolls off at −3dB per octave. This means brown noise has significantly more bass and significantly less treble. Brown noise sounds like a deep rumble; pink noise sounds like balanced static. The difference is immediately obvious when you hear them side by side.

Is brown noise safe to listen to?

Yes. Brown noise is no more dangerous than any other audio signal. As with all sound, keep the volume at a comfortable level — prolonged exposure to loud sound of any type can cause hearing damage.

Why has brown noise become popular for ADHD?

While scientific research is still catching up, many people with ADHD report that brown noise helps quiet internal mental chatter and improve focus. The theory is that the deep, consistent sound provides just enough stimulation to occupy the part of the brain that seeks novelty, allowing the rest to concentrate on the task at hand.

Can I loop this seamlessly?

Brown noise is random, so any two segments join together without an audible click or gap. Simply set your player to loop the downloaded WAV file. For extra-smooth results, apply a very short crossfade (5–10ms) at the loop boundary.