What are binaural beats?

Binaural beats are a listening illusion. Play one steady tone in your left ear and a slightly different tone in your right, and you’ll often hear a soft, slow pulse that isn’t in either recording. Here’s how that works, why headphones matter, and what research has and hasn’t found.

How a binaural beat works

When two tones of slightly different frequencies reach each ear separately, the listener hears a third, pulsing sound at the difference between them. For example, 400 Hz in the right ear and 420 Hz in the left produces a 20 Hz binaural beat. People often describe it as located inside the head, or between the ears (Ingendoh et al., 2023).

The pulse isn’t a sound wave in the air. It’s created by your auditory system as it combines the signals from both ears. The superior olivary complex in the brainstem, the first stage of hearing to receive input from both ears, is considered the main structure involved (Ingendoh et al., 2023).

Binaural vs. monaural beats

If both tones play through the same speaker, or reach the same ear, the sound waves physically interfere. That produces a real rise and fall in loudness called a monaural beat, at the same difference rate (Beat (acoustics)). Musicians use these beats every day to check tuning: as two strings get closer to the same note, the beating slows down and disappears. A binaural beat needs each ear to receive only its own tone.

Why headphones matter

Research on binaural beats almost always uses headphones, so that each frequency reaches only one ear (Ingendoh et al., 2023). On speakers, both tones reach both ears, so you mostly hear an ordinary monaural beat instead. Any comfortable stereo headphones or earbuds will do. Make sure left and right are the right way round and that “mono audio” is switched off in your device’s accessibility settings.

The limits of the effect

Not every pair of tones produces a binaural beat. Classic hearing research found that:

• the two tones need to be below about 1,000 Hz, and the beat is heard best with tones around 400 Hz;
• the difference between them needs to be under about 30 Hz. Beyond that, people hear two separate tones;
• very slow differences, under about 3 Hz, can sound like a tone slowly rotating from ear to ear;
• these thresholds are approximate and vary from person to person.

All of these points are summarised in Ingendoh et al., 2023, citing Licklider et al. (1950) and Perrott & Nelson (1969).

A brief history

The German physicist Heinrich Wilhelm Dove first described binaural beats in 1839. For more than a century they were treated as a curiosity. Interest returned after Gerald Oster pulled together the early research in a 1973 Scientific American article, “Auditory beats in the brain” (Oster, 1973; Ingendoh et al., 2023).

Brainwave bands and “delta,” “theta” and “alpha”

Binaural beats can be heard from about 1 to 30 Hz, a range that overlaps the main rhythms recorded by electroencephalography (EEG) (Ingendoh et al., 2023). That’s why tracks are often labelled by EEG band. One common classification (Delta wave) is:

• Delta: up to about 4 Hz. Associated with deep, slow-wave (stage N3) sleep.
• Theta: about 4–7 Hz.
• Alpha: about 8–12 Hz.
• Beta: about 16–31 Hz.

Exact boundaries differ between sources. A label like “delta” on a track tells you the beat rate. It doesn’t guarantee anything about the listener’s brain activity.

What does the research say?

The idea that a binaural beat can pull brain rhythms toward its own rate is called the brainwave entrainment hypothesis. A 2023 systematic review in PLOS ONE looked at 14 EEG studies that tested it directly. Five reported results consistent with entrainment, eight reported contradictory results, and one was mixed. The studies used very different methods, so the authors concluded that the question can’t be settled yet and called for more standardised research (Ingendoh et al., 2023). In short, binaural beats are a well-documented hearing effect, but their effects on the brain and mood are still an open research question.

How Whole Hum uses them

In our sessions, binaural beats are a quiet texture mixed well below the music, never a harsh, isolated tone. For example, our 432Hz Deep Sleep session puts 96 Hz in the left ear and 99 Hz in the right, for a gentle 3 Hz pulse. Keep the volume comfortable: the World Health Organization suggests no more than 60% of maximum on personal audio devices (WHO).

Sources

1. Ingendoh RM, Posny ES, 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.
2. Oster G (1973). Auditory beats in the brain. Scientific American 229(4):94–102.
3. Wikipedia. Beat (acoustics).
4. Wikipedia. Delta wave.
5. World Health Organization. Deafness and hearing loss: Safe listening.

Related: What is 432Hz?