Every brainwave band, audio term, and physiology concept used across the site, defined in plain language. Each entry leads with what the term is; the longer note adds the evidence base or the AmberRoom-specific use. If a term is missing, tell us and we'll add it.
Brainwaves
Delta band
0.5–4 Hz. The slowest brainwave band, dominant during deep, non-REM sleep.
AmberRoom's sleep recipe carries a delta-band binaural carrier. Direct delta-entrainment evidence for sleep is preliminary; the recipe relies primarily on the better-evidenced pink-noise floor.
Theta band
4–8 Hz. Associated with deep relaxation, hypnagogic states, absorbed visualization, and parasympathetic activation.
Strongest sound-therapy evidence sits here. Garcia-Argibay et al (2019) meta-analysis found theta-band binaural beats produced the largest measured anxiety-reduction effect. AmberRoom's calm, grief, meditation, and visualization recipes all target theta sub-bands.
Alpha band
8–13 Hz. Associated with relaxed alertness — the surface where you're aware but not directing attention outward.
Target band for the focus recipe. Mid-alpha (~10 Hz) is the relaxed-alert sweet spot for sustained cognitive work. Sits between deep relaxation (theta) and active attention (beta).
Beta band
13–30 Hz. Associated with active, focused attention and alertness.
AmberRoom's energy recipe targets low-beta (13 Hz) — the alert-but-not-anxious edge of the band. Higher beta correlates with stress and rumination, which is why the recipe stays at the lower end.
Gamma band
30–100 Hz. Fastest band, associated with cross-modal binding and certain meditative states.
40 Hz gamma stimulation has shown analgesic and Alzheimer's-related effects in early research. Not currently a target band in AmberRoom's recipes; on the research-watch list.
Audio
Auditory entrainment
The hypothesis that brainwave activity can be nudged toward a target frequency by giving the auditory cortex a steady rhythmic stimulus to lock onto.
Mechanism behind binaural beats and isochronic tones. Evidence is strongest for state-anxiety reduction (theta band) and weakest for direct sleep induction (delta band). The brain doesn't always follow — entrainment is a probabilistic shift, not a guarantee.
Binaural beat
A perceived third tone the brain generates when each ear receives a slightly different pure-tone frequency. Pulses at the difference between the two.
First described by H.W. Dove in 1839. A 200 Hz tone in the left ear and a 206 Hz tone in the right ear produce a perceived 6 Hz beat. Requires headphones — speakers cancel the effect. AmberRoom uses isochronic tones as a fallback when headphones aren't detected.
Isochronic tone
A single tone pulsed on and off at a target rate, used as a speaker-compatible alternative to binaural beats.
Doesn't require ear separation. Less subtle than a binaural beat but more reliably audible. Used in AmberRoom's mono fallback path.
White noise
Random sound with equal energy at every frequency. Bright and hissy, like static.
The flat reference for noise-color comparisons. Less commonly used in sound therapy because the high-frequency emphasis can feel harsh; pink and brown are usually preferred. A narrow-notch variant is used to mask tinnitus.
Pink noise
Random sound with energy that rolls off at higher frequencies (1/f spectrum). Steady, like rain. Best-evidenced color for sleep.
Anchor citation: Papalambros et al (2017) used phase-locked pink-noise pulses to enhance slow-wave sleep activity in older adults. Continuous pink noise is also supported as a sleep-onset masking layer.
Brown noise
Random sound with energy that rolls off twice as steeply as pink (1/f² spectrum). Deep and rumbly, like distant surf. Common choice for focus.
Less harsh than white, deeper than pink. AmberRoom's focus and grief recipes use brown as the noise floor; calm uses brown for the same reason — the warmth doesn't pull attention.
Physiology
Resonant breathing
Breathing at approximately six breaths per minute — the rate at which heart rate and blood pressure oscillations align with respiration, maximizing heart rate variability.
Strongest research evidence in the entire sound-therapy adjacent literature (Lehrer & Gevirtz, 2014). Five seconds in, five seconds out. AmberRoom's reset recipe is built on this mechanism; every other recipe carries a slow rhythmic pulse near this rate.
Heart rate variability (HRV)
The variation in time between consecutive heartbeats. Higher HRV generally indicates greater parasympathetic (rest-and-digest) tone.
Useful biomarker for tracking nervous-system regulation. Resonant breathing measurably raises HRV; theta-range audio appears to as well, though the evidence is thinner. AmberRoom's wearable integration (planned) will use HRV to bias recipe selection.
Slow-wave sleep (SWS)
The deepest stage of non-REM sleep, characterized by high-amplitude delta-band EEG activity. Where most physical restoration happens.
Target outcome for sleep-related sound therapy. Papalambros et al (2017) demonstrated that closed-loop pink-noise pulses can enhance slow-wave activity. Open-loop consumer headphone listening doesn't replicate that mechanism, but masking benefits remain.
Practice
Solfeggio frequencies
A set of tones (174, 285, 396, 417, 528, 639, 741, 852, 963 Hz) drawn from medieval Gregorian chant tunings, popularized in the 1970s.
Cultural tradition, not a clinical claim. There is no peer-reviewed evidence that specific solfeggio frequencies produce specific physiological effects. AmberRoom uses 528 Hz and 396 Hz crystal-bowl tunings because the harmonic stack sounds resonant and listeners coming from contemplative traditions expect them — we don't make health claims about the frequencies themselves.
Tinnitus masking
The use of broadband or notch-filtered noise to reduce the subjective loudness or salience of tinnitus.
Effective when the masking signal is matched to the user's tinnitus frequency profile (calibration is non-negotiable for clinical effect). AmberRoom's tinnitus mode uses notch-filtered audio rather than the standard pink-noise floor, which can worsen some tinnitus presentations.
AmberRoom
Recipe
AmberRoom's term for the layered audio composition tied to a single intent (sleep, calm, focus, etc.). One default recipe per intent on free; up to three variants per intent on Pro.
Each recipe specifies a frequency band, a noise color, a bowl/instrument layer, an ambient pad, a pacing curve, and a target session length. Generated live each session — same recipe, never the same audio twice.
Pacing curve
The shape of a session's intensity over time — arrival, descent, ground, return. Different intents get different curves.
Sleep curves descend and fade to silence by minute 24 of a 30-minute session. Focus curves are nearly flat, holding steady-state for the whole session. Reset is short and symmetrical. The pacing curve is what makes a recipe feel like a session, not a track.