Reference
52 terms
Plain definitions
Glossary of binaural beats and brainwave audio.
Most of the confusion in this subject is vocabulary. “Entrainment” describes a mechanism but is sold as an outcome; “carrier” and “beat” are routinely swapped; and a band name like alpha describes a measured rhythm, not a state you can be put into on request. These are the 52 terms this site uses, defined plainly — including the ones where the honest definition is “this is a tradition, not a finding.”
On this page
§ 01 Mechanism
How the sound works
- Binaural beatalso: binaural beats
- A rhythm you perceive when each ear receives a steady tone of a slightly different frequency. It is not present in the air: the brainstem computes it from the timing difference between the two ears, which is why it requires headphones and disappears on a speaker. The perceived rhythm equals the difference between the two tones — 200 Hz and 210 Hz produce a 10 Hz beat. In depth →
- Monaural beat
- A beat produced by mixing two tones before they reach the ear, so the interference happens acoustically rather than neurally. Because the rhythm is already in the air it works on speakers, and it is physically a different phenomenon from a binaural beat despite the similar name. In depth →
- Isochronic tonealso: isochronic tones
- A single tone switched on and off at a steady rate, producing a pulse rather than a beat. The rhythm exists in the signal itself, so no stereo separation is needed. The evidence base for isochronic tones is smaller than for binaural beats, not stronger. In depth →
- Carrier frequencyalso: carrier
- The pitch you actually hear, as distinct from the beat. In a binaural setup the carrier is the midpoint of the two ear tones. It mostly affects comfort: 100–200 Hz is easy to listen to for a long session, and the beat effect is thought to weaken as the carrier rises past roughly 1000 Hz. In depth →
- Beat frequency
- The difference between the two ear tones, and the number that the brainwave-band labels refer to. A 4 Hz beat is a delta-band beat regardless of whether it sits on a 100 Hz or a 400 Hz carrier. In depth →
- Pure tonealso: sine tone
- A single sine wave at one frequency, with no beat and no modulation. Setting a beat frequency of zero produces one. It is the simplest thing an oscillator can make and the reference signal most hearing measurements are built on. In depth →
- Frequency-following responsealso: FFR
- The tendency of neural activity to synchronise to a periodic stimulus, measurable in EEG. That the response exists for binaural beats is well documented; how far it translates into a felt change in mood, sleep or attention is a separate and much weaker claim. In depth →
- Brainwave entrainmentalso: neural entrainment, auditory entrainment
- The general idea that rhythmic stimulation can pull brain rhythms toward the stimulus frequency. It is an umbrella term covering binaural beats, isochronic tones, photic (light) stimulation and tactile methods. Used loosely in marketing to imply an outcome; used precisely it describes a mechanism, not a benefit. In depth →
- Superior olivary complexalso: SOC, medial superior olive, MSO
- The first place in the auditory pathway that receives input from both ears, in the brainstem. It compares the timing of the two signals — the job it evolved for is locating sound in space — and that comparison is where a binaural beat is generated. In depth →
- Phase locking
- The ability of auditory neurons to fire in step with individual cycles of a sound wave. It degrades as frequency rises and largely fails above roughly 1000 Hz, which is the accepted explanation for why binaural beats fade with high carriers. In depth →
- Amplitude modulationalso: AM
- Varying the loudness of a signal over time. An isochronic tone is amplitude modulation applied to a single tone; the depth of the modulation determines how pronounced the pulse feels. In depth →
- Stereo separationalso: channel separation
- The degree to which the left and right channels stay independent on the way to your ears. It is the one equipment property binaural beats actually depend on, which is why bone-conduction headphones and single earbuds break the effect while cheap wired headphones do not. In depth →
§ 02 Bands
The brainwave bands
- EEGalso: electroencephalography
- Electroencephalography — recording electrical activity from the scalp. The band names below are conventional divisions of the EEG spectrum. They describe measured rhythms, not states you can be put into on request. In depth →
- Deltaalso: delta waves
- Roughly 0.5–4 Hz. The dominant rhythm of deep, slow-wave sleep. Sleep presets target this band, which is also why a twenty-minute nap deliberately does not. In depth →
- Thetaalso: theta waves
- Roughly 4–8 Hz. Associated with drowsiness, the transition into sleep, deep relaxation and meditation. In depth →
- Alphaalso: alpha waves
- Roughly 8–12 Hz. The characteristic rhythm of relaxed, eyes-closed wakefulness. The most common default for a first session. In depth →
- Betaalso: beta waves
- Roughly 12–30 Hz. Associated with alert, active, externally directed thinking. Sustained high beta is also associated with anxiety, which is why more is not better. In depth →
- Gammaalso: gamma waves
- Roughly 30 Hz and above. Associated with demanding cognitive work and with binding separate features into one percept. The most over-claimed band in consumer marketing. In depth →
- SMRalso: sensorimotor rhythm
- Sensorimotor rhythm, roughly 12–15 Hz over the sensorimotor cortex, associated with calm, still alertness. Most SMR evidence comes from neurofeedback, where people train their own rhythm — that is a different intervention from listening to a matching tone, and the transfer is not established. In depth →
- Hypnagogiaalso: hypnagogic
- The transitional state between waking and sleep, often with drifting imagery. Associated with theta activity, and the state theta presets are usually aimed at. In depth →
- Cross-frequency couplingalso: theta-gamma coupling
- When the rhythm of one frequency band organises the timing of another — gamma bursts nested inside a theta cycle is the best-studied example, and it is a real and active area of memory research. Whether an audio track can reproduce it in a listener is a much larger claim than the underlying neuroscience supports. In depth →
§ 03 Sound
Noise and sound
- White noise
- Noise with equal energy at every frequency. Because human hearing is not flat, it is perceived as bright and hissy rather than neutral. In depth →
- Pink noise
- Noise that falls off at about 3 dB per octave, which compensates for the ear’s own response and is why it sounds “flat” and rain-like. The usual general-purpose default. In depth →
- Brown noisealso: red noise, brownian noise
- Noise falling off at about 6 dB per octave — deep and rumbling, like a waterfall. The best choice for masking low-frequency intrusion such as snoring or traffic. In depth →
- Green noise
- Noise concentrated in the midrange, near 500 Hz, which reads as moving water. Chosen for how it sounds rather than for any particular masking property. In depth →
- Violet noisealso: purple noise
- Noise rising at about 6 dB per octave — the mirror of brown, bright and airy. Sometimes used in tinnitus masking because tinnitus is often perceived as a high tone. In depth →
- Maskingalso: sound masking
- Making one sound harder to hear by adding another. It works through spectral overlap, which is the practical reason brown noise beats white noise against snoring: the energy has to be where the intrusion is. In depth →
- Spectral tilt
- How energy is distributed across frequency, usually quoted in decibels per octave. It is the only real difference between the noise colours — they all start as the same randomness. In depth →
- Sample rate
- How many times per second digital audio is measured, in Hz. The free web tool synthesises at whatever rate your device runs at; the mobile app synthesises at 48 kHz. For a sine wave in the audible range this makes very little audible difference. In depth →
- Audible rangealso: hearing range
- Conventionally about 20 Hz to 20 kHz for a young, undamaged ear. Sensitivity is far from even across it, peaking between roughly 2 and 5 kHz, and the top narrows gradually with age for everyone. In depth →
§ 04 Sleep
Sleep and timing
- Slow-wave sleepalso: deep sleep, N3
- The deepest stage of non-REM sleep, dominated by delta activity. Being woken out of it is what produces the heaviest grogginess, which is the entire reason a power nap is kept short. In depth →
- Sleep inertia
- The measurable impairment in alertness, reaction time and mood in the first minutes after waking. Worst when woken from slow-wave sleep. Light and movement shorten it; deciding whether to get up does not. In depth →
- Sleep pressurealso: homeostatic sleep drive
- The drive to sleep that accumulates the longer you are awake. A nap discharges some of it, which is why a late-afternoon nap and trouble falling asleep that night are connected. In depth →
- Sleep latency
- How long it takes to fall asleep. One of the few sleep outcomes that small audio trials can measure reasonably, and where the honest evidence for sound is strongest — largely through masking. In depth →
- Circadian rhythm
- The roughly 24-hour internal clock that governs alertness, temperature and hormone timing. It is why the early-afternoon dip is real rather than caused by lunch, and why jet lag and shift work resist being fixed with audio. In depth →
- Cortisol awakening responsealso: CAR
- The sharp rise in cortisol in the first half hour after waking. Normal physiology, and part of why some people feel most anxious in the morning. In depth →
§ 05 Evidence
Reading the evidence
- Randomised controlled trialalso: RCT
- A study in which participants are assigned to conditions by chance. It carries more weight than an open-label pilot because it controls for who ends up in which group. Most of the strongest binaural-beats findings are RCTs, and most of the trials are small. In depth →
- Sham controlalso: sham audio
- A control condition that sounds like the real thing but lacks the active ingredient — matched audio with no beat, rather than silence. Without it, expectancy cannot be separated from effect, and a good deal of this literature lacks it. In depth →
- Effect sizealso: Cohen's d
- How large a difference is, as opposed to how confident we are that it is not zero. Reported as Cohen’s d or Hedges’ g. Roughly: 0.2 small, 0.5 moderate, 0.8 large. The pooled binaural-beats effect on state anxiety sits around d ≈ 0.45. In depth →
- Meta-analysis
- A study that pools the results of other studies to estimate a combined effect. Garcia-Argibay and colleagues (2019) pooled 22 binaural-beats studies and is the single most useful reference on this topic. In depth →
- State anxietyalso: trait anxiety
- How anxious someone feels right now, as opposed to trait anxiety, which is their general disposition. The distinction matters here: the evidence supports a modest effect on state anxiety, and says essentially nothing about trait anxiety. In depth →
- Within-subject designalso: cross-over
- Every participant experiences every condition, so each person is their own control. Efficient with small samples, but vulnerable to order and practice effects. In depth →
- Null result
- A study that found no effect. They are as informative as positive findings and are routinely left out of marketing pages, which is how a mixed literature comes to look conclusive. In depth →
- Expectancy effectalso: placebo
- Improvement that follows from believing something will help. It is real, it is not nothing, and it is the main thing sham control exists to separate out. A tool that works partly through expectancy still works — it just does not work for the stated reason. In depth →
§ 06 Claims
Adjacent claims, honestly labelled
- Solfeggio frequenciesalso: 528 Hz, 963 Hz
- A set of nine tones — 174, 285, 396, 417, 528, 639, 741, 852 and 963 Hz — drawn from a medieval hymn and given specific properties by twentieth-century writers. The cultural tradition is real and worth describing. No controlled research has tested the specific tones for the effects attributed to them, and we say so on every page that covers them. In depth →
- 432 Hz
- An alternative concert pitch, against the standard 440 Hz. The difference is real and audible as a slight lowering; the claims that it is more natural or more healing are not supported by controlled evidence. In depth →
- Schumann resonancealso: 7.83 Hz
- The fundamental electromagnetic resonance of the cavity between the Earth’s surface and the ionosphere, about 7.83 Hz. A genuine geophysical phenomenon. That playing an audio tone at the same number confers its properties is a leap the physics does not license. In depth →
- 40 Hz GENUSalso: gamma sensory stimulation
- Gamma ENtrainment Using Sensory stimulus — the MIT line of work in which 40 Hz light and sound reduced amyloid-beta pathology in mice. Widely cited in consumer marketing without the species. Human trials are ongoing and early. In depth →
- Bilateral stimulationalso: EMDR
- Alternating input between left and right, used in EMDR therapy alongside a structured protocol delivered by a clinician. Audio that pans between ears is not EMDR, and the site is explicit about that. In depth →
- Heart rate variabilityalso: HRV
- The variation in time between heartbeats, often used as an index of autonomic balance. Slow breathing at around 5.5 breaths per minute raises it reliably — that is one of the better-supported mechanisms anywhere near this topic, and it belongs to the breathing, not the audio. In depth →
- Vagus nervealso: vagal tone
- The main nerve of the parasympathetic nervous system. Slow exhalation and humming engage it, which is a real and citable mechanism. “Vagus nerve activation” used as a marketing phrase for any calming sound is not. In depth →
- Flow state
- Csikszentmihalyi’s term for absorbed, effortless engagement in a task that matches your skill. Repetitive lyric-free audio can protect the conditions for it by removing interruptions; no sound induces it. In depth →
§ 07 Questions
Things people reasonably ask.
What is the difference between carrier frequency and beat frequency?
The carrier is the pitch you hear; the beat is the difference between the two ear tones and is the number the band names refer to. A 10 Hz beat on a 200 Hz carrier means 195 Hz in one ear and 205 Hz in the other. See carrier frequency and beat frequency.
Are binaural, monaural and isochronic the same thing?
No. A binaural beat is produced in your auditory system from two tones and needs headphones. A monaural beat is produced by mixing the tones before they reach you. An isochronic tone is one tone pulsed on and off. The last two work on speakers.
Does an alpha beat put my brain into alpha?
That is the claim, and it is weaker than the vocabulary implies. A frequency-following response to binaural beats is well documented in EEG; whether it produces a felt change is small, variable between people and inconsistent across trials. The band name describes a measured rhythm, not a guaranteed state.
Which noise colour should I use?
What does effect size mean and why does it matter more than significance?
Significance says a result is unlikely if nothing were happening; effect size says how big the something is. A tiny effect can be statistically significant in a large enough sample. For this topic the pooled effect on state anxiety sits around d ≈ 0.45 — small to moderate.
Are solfeggio frequencies and the Schumann resonance evidence-based?
They are described accurately on this site as what they are. Solfeggio is a twentieth-century tradition attached to a medieval hymn, and no controlled research has tested the specific tones for the effects claimed. The Schumann resonance is a genuine geophysical phenomenon; that playing a tone at the same number transfers its properties is not something the physics supports.
→ Continue reading
What are binaural beats The long-form explanation, with citations.
Research hub 26 studies with sample sizes, null findings included.
Brainwave frequencies explained The five bands, and what each actually describes.
Noise colours guide White through violet, and which masks what.
Beat calculator Turn the vocabulary into two ear tones you can play.
Beginner’s guide Where to start if none of these words were familiar.