This special sound is used in many Silva Mental Exercises. Play it while meditating with the Silva techniques or simply to relax in the alpha state of mind.
The Theta to Alpha sound consists of two similar sounds. The Theta sound ticks at 5 beats per second whereas the Alpha sound ticks at 10 beats per second. It is used to help your brain frequency slow down towards a passive, deep and calm inner state associated with the theta frequency. At theta, the thinking is inductive. At this deep inner state old memories and experiences can be triggered as well as intuitive impressions and hypnagogic dreams.
Theta meditations are very deep and often result in sleep. This is the reason why the Theta to Alpha sound is used. The rapid shift from 5 ticks per second to 10 ticks per second helps the brain frequency speed up into the higher alpha frequency making it easy to exit the meditation.