To reduce the level of anxiety without using medications, some authors used "Binaural Beats". This simple technique , described for the first time since by Gerald Oster , include the presentation of two acoustic stimuli with similar frequencies through the two channels of stereo headphones. The interference of their waves which occurs at the level of the central nervous system, produces a composite signal with a frequency resulting from the difference of the two original frequencies. For example if you give an acoustic stimulus of 100 Hz to an ear and simultaneously administering another acoustic stimulation of 104 Hz to the opposite ,ear the person who listens to these stimuli will perceive a "Binaural Beat" of 4 Hz caused by the difference between the two frequencies.