described are methods and a device for determining a valid intrinsic alpha frequency . described herein are methods and a device for determining the appropriate intrinsic alpha frequency to be applied for neuro - eeg synchronization therapy using alternating magnetic fields to gently “ tune ” the brain and affect the mood , focus and cognition of subjects . methods and a device described herein use an algorithm to quantitatively analyze eeg recordings to determine if recorded eeg frequencies are valid , and if necessary , requiring additional recordings and analysis until a valid eeg is found . methods and devices described herein can be utilized to calculate the intrinsic frequency of other eeg bands , including the theta , beta gamma and delta bands .