My first encounter with binaural beats came in the early 1990s through CoolEdit, a Windows audio editor with a purpose-built binaural plugin. I was in high school, starting to explore natural, meditative altered states, and it made the experimentation easy: dial in a frequency, set a session length, put on headphones.

Getting back into it recently sent me down two paths. The Monroe Institute's Hemi-Sync recordings are the most credible work in this space; their research goes back to the 1970s and the recordings themselves are genuinely good. But they're opaque, expensive, and fixed. Everything else I found was consumer wellness: streamed playlists, AI-generated focus music, glossy branding with nothing configurable. What I wanted was something that let you design a session.

Sympatheia (συμπάθεια, the Stoic concept of cosmic interconnection) is what I built. It runs entirely in the browser using the Web Audio API. Put on headphones and press play.

Open Sympatheia →

What binaural beats are

Binaural beats are a psychoacoustic phenomenon. Your left ear hears one tone; your right ear hears a slightly different one. Your brain resolves the difference into a phantom pulse with no physical existence. The auditory system constructs it, through a structure called the superior olivary nucleus.[1]

The theory: sustained exposure to that pulse nudges the brain's electrical activity toward the beat frequency. Alpha (8–12 Hz) produces relaxed, diffuse awareness. Theta (4–7 Hz) sits at the hypnagogic edge between waking and sleep, which is where I spend most of my time. The research is genuinely inconsistent on whether this entrainment works reliably.[2] It works for me, and differently on different days. Open-minded skepticism is the right posture: bring some intention and see what happens.

Because the mechanism requires each ear to receive an isolated signal, the binaural channel requires headphones. Earbuds are fine.

What's in the tool

The binaural channel is the core. Beat frequency is the entrainment target; carrier is the base pitch of the oscillators. The preset strip gives one-tap access to the standard targets: Delta, Theta, Alpha, Beta, Gamma, Schumann. Drift options let the frequencies wander slowly, which keeps the brain from habituating to a fixed pitch over longer sessions.

Background layers fill the acoustic space around the entrainment signal. A lone sine tone is technically correct but fatiguing over time; the mind has nothing to settle into. Noise (white, pink, or brown), a procedurally generated ocean, and a sub-bass oscillator each address a different part of this. The ocean is where I spend most sessions. Something about irregular wave rhythm releases attention in a way that steady noise doesn't.

Sacred frequency tones offer eleven named frequencies drawn from the solfeggio tradition, plus a custom input. Three character modes change the timbre: Pure runs two slightly detuned sine oscillators for a clean, wide pitch; Warm adds harmonic overtones; Bowl models the inharmonic vibrational modes of a Tibetan singing bowl. Tones fire manually or on random intervals during a session. The mythology around these frequencies is murky and contested; I include them because some sound genuinely interesting and that is reason enough.

The pads channel adds sustained harmonic chord progressions: nine options drawn from Western modal, church, and Eastern traditions, with configurable voice leading, reverb, and filtering. A tremolo synced to the beat frequency turns the pads into an additional entrainment signal that works over speakers, without the binaural mechanism.

The sequencer lets you build a full session arc: stages with ramps between beat frequencies, tone cues timed to fire at specific moments, per-step layer changes. The Chakra Bowl is a built-in example that moves through seven steps over 28 minutes, descending to theta at the heart step and returning to close at a slight elevation from where it started.

Play to find out

You won't know what works for you until you try it. Responses to different frequencies vary widely: some people drop easily into theta; others find it disorienting and do better at alpha or Schumann. The ocean layer lands differently for different people. The sacred tones may feel significant or inert depending on what you bring to them.

Start with the defaults. Put on headphones, press play, and sit with it for twenty minutes before assessing. Notice what happens to the body and the quality of thought. Adjust one thing at a time.

The tool is configurable specifically because a single preset can't account for your particular nervous system, the time of day, or what you're trying to do. Play to find out what happens.

Further reading

  1. Oster, G. (1973). "Auditory Beats in the Brain." Scientific American, 229(4), 94–102. ↩︎

  2. Ingendoh, R.M., Posny, E.S., & Heine, A. (2023). "Binaural beats to entrain the brain? A systematic review of the effects of binaural beat stimulation on brain oscillatory activity, and the implications for psychological research and intervention." PLOS ONE, 18(5), e0286023. https://doi.org/10.1371/journal.pone.0286023 ↩︎