Noise may be continuous or intermittent. Noise may be of high frequency or of low
frequency which is undesired for a normal hearing. For example, the typical cry of a child
produces sound, which is mostly unfavorable to normal hearing. Since it is unwanted
sound, we call it noise.
The discrimination and differentiation between sound and noise also depends upon the
habit and interest of the person/species receiving it, the ambient conditions and impact of
the sound generated during that particular duration of time. There could be instances that,
excellently rendered musical concert for example, may be felt as noise and exceptional
music as well during the course of the concert!
Sounds of frequencies less than 20 HZ are called infrasonics and greater than 20,0000 HZ
are called ultrasonics. Since noise is also a sound, the terms noise and sound are
synonymously used and are followed in this module.