Most people find a gentle melody to be calming, while some people need background sounds to concentrate. White and pink noise are colors of the noise spectrum that have different audio signals that sound different to yoru ears. White or pink noise generators are inexpensive and easy to find for iPhones, Androids and on the web. Another use of sound for calming or aiding with focus is binaural beats, which are paired frequency tones that are slightly different in each ear. This produces a frequency "Beat" that is perceived by the brain and may induce a neural frequency that occurs in the states of sleep, rest, or alertness. Two resources for white noise and binaural beats are White & Pink Noise (iOS, Android, web) and Binaural Beats (iOS, Android, web).