Stick electrodes on a scalp and the recording you get isn't a single signal — it's a layered hum of oscillations at different frequencies, all happening at once. Those oscillations are brainwaves. The convention is to bin them by frequency band: delta, theta, alpha, beta, gamma. Each band corresponds, loosely but reliably, to a different mental state. The whole basis of auditory entrainment — the binaural beats and isochronic tones in AmberRoom's recipes — is the hypothesis that you can nudge the dominant band by giving the brain an external rhythmic input to synchronize to.
This page is a plain-language map of the bands. We use it as the anchor point that every recipe's "BIN" value (the binaural beat frequency) links back to.
Delta · 0.5–4 Hz · the deep sleep band
Delta is the slowest, deepest, lowest-frequency band — and it dominates during slow-wave sleep, the kind of sleep where your body restores itself, memories consolidate, and growth hormone is released. You can see massive delta activity on the EEG of someone in stage 3 NREM. You almost never see it dominant during waking hours unless something is wrong (severe brain injury, certain pathologies). The Papalambros (2017) finding — that pink-noise pulses phase-locked to slow waves can amplify them — is the strongest single piece of evidence that auditory input can usefully reshape delta. AmberRoom's sleep recipe targets a delta carrier (~2.5 Hz) underneath a pink-noise floor.
Theta · 4–8 Hz · the inner band
Theta sits just above delta. It's the band of hypnagogia (the half-asleep state when you start drifting), of deep meditation, of REM-related dreaming activity, and of certain emotionally absorbed states. Experienced meditators show elevated theta during practice; so do people in flow on creative work. Theta is also where the binaural-beat anxiety-reduction effect is strongest — the Garcia-Argibay meta-analysis (2019) found theta-band exposure produced the largest anti-anxiety effect across 14 trials. AmberRoom's calm recipe targets 6.0 Hz theta; the grief recipe sits a touch lower at 5.0 Hz; meditation targets 6.5 Hz.
Theta is the most commonly targeted band for sound therapy because it sits at the boundary between the body's rest state and the deeper sleep states — the transition zone where most stress-related interventions actually do their work.
Alpha · 8–13 Hz · the relaxed-alert band
Alpha shows up when you close your eyes, take a breath, and stop directing your attention outward — but you're still awake and aware. It's the surface layer of meditation, the resting state of the visual cortex, the "reading mode" band. Some neurofeedback work on attention training operates on alpha. AmberRoom's focus recipe targets the high end of the alpha band (~10 Hz) plus a brown-noise floor; the goal is relaxed-alert sustained attention, which is what alpha-band activity correlates with.
Beta · 13–30 Hz · the engaged-thinking band
Beta dominates when you're actively thinking, problem-solving, in conversation, or alert to your environment. Low beta (13–18 Hz) is engaged calm; high beta (24–30 Hz) is closer to anxious vigilance. Most of waking adult cognition runs in beta. AmberRoom's energy recipe targets low beta (~13 Hz) — engagement without the cortisol-spike of high-beta hypervigilance. We deliberately don't target high beta; nudging the brain toward more vigilance is rarely what you want.
Gamma · 30–100 Hz · the binding band
Gamma is the highest-frequency band routinely studied. Its functional role is the most contested: leading hypothesis is that gamma reflects the brain's "binding" of disparate signals into a unified percept — what makes the red and the round of an apple feel like one thing. Gamma is also where the most interesting recent therapeutic work lives: 40 Hz auditory and visual stimulation has shown some preliminary effect on chronic pain, attention, and even Alzheimer's biomarkers in mouse models and small human pilots. The evidence is preliminary; the mechanism is plausible. AmberRoom's pain recipe targets 40 Hz gamma directly, paired with low gong tones and a brown-noise floor — auditory-only, so the full vibroacoustic effect (which uses body transducers) isn't replicated, but the auditory half is delivered.
What "entrainment" actually means
When you play a binaural beat — two pure tones in each ear, slightly detuned — the brain perceives a phantom third tone at the difference frequency. If the difference is, say, 6 Hz, the auditory cortex fires in a 6 Hz rhythm to track that phantom. The claim of entrainment is that this rhythmic firing nudges nearby frequency-coupled neural populations toward the same rhythm — that the dominant EEG band can be coaxed toward the target.
This claim is real but partial. The auditory cortex follows binaural beats reliably; whether broader brain regions follow, and how strongly, depends on the listener, the duration, the band, and a dozen variables we don't fully understand. Effect sizes in the published literature are modest. Treat AmberRoom's recipes as well-calibrated nudges, not as switches.
Each session in AmberRoom shows the active band in the recipe inspector — the BIN value. Click any band on this page, or the BIN value during a session, to come back here.