White noise is a random signal (or process) with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency. White noise draws its name from white light in which the power spectral density of the light is distributed over the visible band in such a way that the eye's three color receptors (cones) are rather equally stimulated.

One aspect of music perception which is not invariant under amplitude scaling is that our level of enjoyment of music that we like is increased when that music is played more loudly. A common consequence of this preference is deafness caused by listening to over-loud music. Other emotional impact can also be effected by volume; haunting music, for example, may be perceived differently at a louder volume.

It has been shown that the right auditory cortex is the primary component for perceiving pitch, and parts of harmony, melody and rhythm (Tramo 2001). One study by Petr Janata found that there are tonally sensitive areas in the medial prefrontal cortex, the cerebellum, the Superior Temporal Sulci of both hemispheres and the Superior Temporal gyri (which has a skew towards the right hemisphere). When unpleasant melodies are played, the posterior cingulate cortex activates, which indicates a sense of conflict or emotional pain (Tramo, 2001). The right hemisphere has also been found to be correlated with emotion, which can also activate areas in the cingluate in times of emotional pain, specifically social rejection (Eisenberger). This evidence, along with observations, has led many musical theorists, philosophers and neuroscientists to link emotion with tonality. This seems almost obvious because the tones in music seem like a characterization of the tones in human speech, which indicate emotional content. The vowels in the phonemes of a song are elongated for a dramatic effect, and it seems as though musical tones are simply exaggerations of the normal verbal tonality.