White noise refers to noise whose power spectral density is evenly distributed throughout the frequency domain. Random noise with the same energy at all frequencies is called white noise. From the frequency response of our ears it sounds like a very bright "hiss" sound (the frequency doubles every octave higher. So the energy in the high frequency area is also significantly enhanced).

White noise or white noise is a random signal or random process with a constant power spectrum density. In other words, the power of this signal is the same in each frequency band. Since white light is a mixture of monochromatic light of various frequencies (colors), the property of this signal with a flat power spectrum is called "White", this signal is also called white noise. In contrast, other noise signals that do not have this property are called colored noise.

Ideal white noise has infinite bandwidth, so its energy is infinite, which is impossible to exist in the real world. In fact, we often regard flat signals with limited bandwidth as white noise because it makes mathematical analysis more convenient. However, white noise is more convenient for mathematical processing, so it is a powerful tool for system analysis. Generally, as long as the spectral width of a noise process is much larger than the bandwidth of the system it acts on, and its spectral density can basically be considered as a constant in this bandwidth, it can be treated as white noise. For example, thermal noise and shot noise have uniform power spectral density over a wide frequency range and can generally be considered white noise.

When you need to concentrate on your work and there are always complicated sounds around you, you can choose these two sounds to block them. Generally speaking, you can choose white noise under normal circumstances, while pink noise is a masking material specifically for speech sounds.

Pink noise is also called inverse frequency (1/f) noise because its energy distribution is inversely proportional to frequency, or the energy decreases by 3 dB for every octave (Octave).

A band-limited analog white noise generator is composed of an analog white noise generating circuit and a filter circuit, and is characterized in that the analog white noise generating circuit is connected to and provided with the filter circuit, and the The analog white noise generating circuit generates a white noise signal, which is further transmitted to the filter circuit for signal filtering, and then the signal is amplified and output by the amplifier circuit.

White noise analysis

It is the infinite-dimensional Schwartz extensive function theory newly created internationally in the mid-1970s. Researcher Yan Ji'an from the Institute of Applications is the main contributor to establishing and improving the mathematical framework of this theory. One of the frameworks he proposed with Professor Meyer, a corresponding member of the French Academy of Sciences, is called Meyer-Yan space. The recently published paper by him and Kondratiev et al. established a complete mathematical framework for infinite-dimensional non-Gaussian analysis. Pioneering research is planned to be conducted in this area in the future. Since white noise analysis has a profound physical background, it has increasingly profound applications in quantum physics.

Application

One of the application fields of white noise is architectural acoustics. In order to reduce the distracting and undesirable noise in the internal space (such as human conversation), continuous noise is used. low-intensity noise as background sound. Some emergency vehicle sirens also use white noise, which is more likely to attract people's attention because it can pass through background noise such as traffic noise in cities without causing reflections.

White noise is also used in electronic music. It is used directly or as the input signal of a filter to generate other types of noise signals, especially in audio synthesis, where it is often used to reproduce sounds similar to cymbals. This is a percussion instrument with a very high noise component in the frequency domain.

White noise is also used to generate impulse responses. In order to ensure a balanced effect for concerts or other performances at a performance location, a momentary white noise or pink noise is emitted from the PA system, and the noise signal is monitored in different places, so that engineers can automatically amplify the acoustic effect of the building Or cut certain frequencies, so you can adjust the overall equalization effect to get a balanced harmony.

White noise can be used for frequency response testing of amplifiers or electronic filters, sometimes with flat-response microphones or with automatic equalizers. The idea of ??this design is that the system will generate white noise, the microphone will receive the white noise generated by the speaker, and then automatically equalize in each frequency band to obtain a flat response. This type of system is used in professional-grade equipment, high-end home stereo systems, or some high-end car radios.

White noise is also used as the basis for some random number generators.

White noise can also be used to disorient people before interrogation, and may be used as part of sensory deprivation techniques. White noise machine products on the market include privacy enhancers, sleep aids, and tinnitus masking products.

There are diverse vibrations in complex physical systems

In daily life, noise is considered a harmful physical phenomenon. But physics believes that noise, as a complex system, can also play an important role in certain circumstances.

For example, in the case of random noise vibration, within a certain range, as the noise increases, the system's sensitivity to external effects gradually increases.

In the past, physics studied complex systems composed of identical "components." Spanish researchers made some changes to the system, studying a large number of interconnected components rather than a single component. It was found that if one of the components is transformed by external effects, the others are also "jointly" transformed. When a large number of components undergo transformation, it means that the entire system responds to external influences.

The researchers also found that a system composed of the same components has a very small response to external effects, and a system composed of widely different components also has a very small response to external effects. But if there are small differences between the "components", the system becomes a complex system of optimized diversity. When periodic weak external forces act on the system, the system's sensitivity to the outside world increases by 10 times. Researchers call this phenomenon the diversity boom.

Researchers pointed out that the phenomenon of system optimization diversity oscillation may be the biggest response to the weak influence of biological diversity on the outside world during the evolution of nature. They believe that for more than 20 years, the noise random vibration theory has been widely used in medicine and other fields. There is no doubt that the newly discovered diversity vibration phenomenon will also be widely used in many fields.