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Delta Waves 20 min L 60 Hz - R 60.5 Hz A delta wave is a high-amplitude brainwave with a frequency of oscillation between 0.5 and 4 hertz. Delta waves, like other brain waves, are recorded with an electroencephalogram (EEG) and are usually associated with the deep stage 3 of NREM sleep, also known as slow-wave sleep (SWS), and aid in characterizing the depth of sleep.