Loudness of sound is measured in decibels or dB. It refers to a ratio of two sound levels. The ratio between the loudest sound human brains can detect without damage to the sense of hearing and the softest sound detecible is a million to one. The range of loudness the human ear can detect is called the dynamic range. The threshold of human hearing is zero dB; jet engine is 135 dB. Even minute changes in loudness can have a powerful impact on the emotions communicated through music. (Sternberg, Barbara, PhD. Music & the Brain. p 9-10. CA: Institute for Natural Resources, Home-Study #2320, 2009).