* Instrumental music
* Any soft / classical music
* Sounds of the nature. For e.g.: Birds chirping, Sounds of the wind, rain, any water body - seas / oceans, etc.
* Motzart classics
* Yanni classics
* Your mom's voice - Does not matter what she says!!!
* Any sound / music / voice that you love, that relaxes you and makes you happy!!!
Note: Above note is compiled purely on my personal experiences and advice from friends and family.