🎚️ Band mixer

Mix delta, theta, alpha, beta and gamma into one trace and watch its spectrum change.

Start from:

Background noise

The signal at one electrode (4 seconds)

Its spectrum: how much power at each frequency

How to read this

Sliders: each band adds a wobbling wave at its own speed. The trace is their sum, like the voltage one electrode records.
Spectrum: the same 4 seconds split into frequencies with a Fourier transform. Each band shows up as a hump in its own range, even when the trace looks like a mess.
Presets: rough mixes for common states. Eyes closed gives a clear alpha peak near 10 Hz; deep sleep is mostly slow delta; focus adds beta. Real recordings vary a lot from person to person.
Noise: real EEG has a "1/f" background: more power at low frequencies. Turn it up and small bands disappear into it.

Frequency band: A range of speeds: delta 0.5–4 Hz, theta 4–8, alpha 8–13, beta 13–30, gamma above 30.
Amplitude: How big the wave is, in microvolts (µV).
Power spectrum (PSD): How much signal power there is at each frequency.
Alpha peak: The hump near 10 Hz, strongest at the back of the head with the eyes closed.
1/f background: The smooth background where power falls as frequency rises.

Buzsáki G., Draguhn A. (2004). Neuronal oscillations in cortical networks. Science 304(5679): 1926–1929.
Kane N. et al. (2017). A revised glossary of terms most commonly used by clinical electroencephalographers. Clinical Neurophysiology Practice 2: 170–185 (band names and limits).
Donoghue T. et al. (2020). Parameterizing neural power spectra into periodic and aperiodic components. Nature Neuroscience 23: 1655–1665 (the 1/f background).

Used in lessons 4, 12 of EEG from zero.