In common use, the word noise means any unwanted sound.
Young adults can pick up frequencies ranging from as low as 20 Hz (bass) to 20 000 Hz (squeaks). But as we age, we tend to lose some of our high-frequency hearing to about 14 000 Hz or even less. For most people, peak sensitivity occurs for frequencies around 1000 to 4000 Hz.
Frequency below and above this band are called Infrasound and Ultrasound respectively, similar to the Infrared and Ulraviolet, which are below and above the visible light's frequency spectrum.
The Speed of Sound is 1236 km/h, in dry air at 20°C, depending on the temperature, consistency and the humidity of the air , while the Speed of Light is 17987547.48 km/s, or 299792.458 km/s.
In physics and analogue electronics, noise is a mostly unwanted random addition to a signal; it is called noise as a generalisation of the acoustic noise ("static") heard when listening to a weak radio transmission with significant electrical noise. Signal noise is heard as acoustic noise if the signal is converted into sound (e.g., played through a loudspeaker); it manifests as "snow" on a television or video image. High noise levels can block, distort, change or interfere with the meaning of a message in human, animal and electronic communication.
In signal processing or computing it can be considered random unwanted data without meaning; that is, data that is not being used to transmit a signal, but is simply produced as an unwanted by-product of other activities. "Signal-to-noise ratio" is sometimes used to refer to the ratio of useful to irrelevant information in an exchange.
In biology, many different forms of cellular noise exist, where a measurement displays substantial variance around its mean: for example, transcriptional noise describes the variability in gene activity between cells in a population.
In many cases, the special case of thermal noise arises, which sets a fundamental lower limit to what can be measured or signalled and is related to basic physical processes described by thermodynamics, some of which are expressible by simple formulae.
In some fields, noise means unwanted information or data that is not relevant to the hypothesis or theory being investigated or tested.
Noise pollution is excessive, displeasing human, animal, or machine-created environmental noise that disrupts the activity or balance of human or animal life. The word noise may be from the Latin word nauseas, which means disgust or discomfort. The source of most outdoor noise worldwide is mainly construction and transportation systems, including motor vehicle noise, aircraft noise, and rail noise. Poor urban planning may give rise to noise pollution, since side-by-side industrial and residential buildings can result in noise pollution in the residential area.
A pink noise study aid for those who need a break from the brain entrainment frequencies (i.e. if you exceed several hours of use, load this one up instead and experience the same benefits). This also provides an alternative for epileptics, pregnant women or people with heart trouble for whom brain entrainment is not suitable for.