Binaural Rhythms and the Limits of Human Hearing
Humans can't hear an 8Hz brainwave frequency directly - but the brain can hear the difference between two tones that are 8Hz apart.
Human hearing runs roughly 20Hz to 20,000Hz. Brainwave activity - the alpha, beta, theta and delta bands visible on an EEG - sits far below that, around 0.5-40Hz, and is inaudible on its own.
Binaural beats work around that limit. Play two slightly different tones, one in each ear - say 136.10Hz and 144.10Hz - and the brain perceives the 8Hz difference between them as a slow pulsing rhythm, not two separate pitches. That 8Hz difference sits in the alpha range, associated with a relaxed, wakeful state.
One way to build those component tones without synthesizing them from scratch: start from a single field recording - in this case forest ambience captured on a portable Zoom H5 - and isolate the target frequencies with EQ rather than layering tones on top of the recording. The tones existed in the original material; the job was separating them out.
A related principle worth keeping in mind for panning and spatial mixing generally: humans localize a sound source far more precisely at high frequencies than at low ones. It's a useful rule of thumb whenever a mix decision comes down to where something should sit in the stereo or spatial field.
Adapted from a binaural / spatial-audio project completed during Philipp's studies at BIMM Berlin.