Noise is unwanted or unpleasant sound. The classification of sound as noise is subjective; what may count as sound to one person or culture may count as noise to another person or culture. Sound may be classified as noise based on its magnitude, characteristics, duration and time of occurrence.
The magnitude of sound may make it undesirable if it disturbs people. Music at an acceptable volume might be pleasant, but raising the volume of the music too high causes it to become a nuisance.
The subjective desirability of sounds may also classify them as noises. Several people conversing in a room may classify all conversations other than their own as noise.
The setting of occurrence also differentiates between sounds and noises. Loud sounds occurring in a socially acceptable setting such as a rock concert may be acceptable, whereas even whispering conversation is classified as noise in a library or religious sermon.
Time of occurrence also differentiates between sound and noise. The sound of midday traffic may be acceptable, whereas this same magnitude is intolerable in the middle of the night.
The duration of occurrence is the subjective time after which listening to a repetitive sound becomes annoying. Listening to a song a single time may be pleasant, whereas listening to this song several times becomes an annoyance, leading to its classification as noise.