White noise, black noise, brown noise, green noise, and pink noise are terms used to describe different types of sound signals or frequency distributions. Each type of noise has distinct characteristics and spectral properties.
White noise: White noise is a signal that contains equal energy at all frequencies within a given range. It has a flat power spectral density, meaning that the energy is distributed uniformly across the entire frequency spectrum. In simple terms, white noise sounds like a random hiss with no particular emphasis on any frequency range.
Black noise: Black noise is a term that can have different interpretations depending on the context. In some cases, it refers to a signal with no sound or silence. In other contexts, black noise may refer to an idealized noise signal that absorbs all frequencies, reflecting none. It is essentially the opposite of white noise.
Brown noise: Brown noise, also known as Brownian noise or red noise, has a power spectral density that decreases by 6 dB per octave as the frequency increases. It is often described as having a "rumbling" or "thunder-like" quality. Brown noise is characterized by more energy in the lower frequencies, giving it a deeper and more bass-heavy sound compared to white noise.
Green noise: Green noise is not a well-defined term and is not commonly used to describe specific types of noise. It does not have a standard spectral characteristic or recognized meaning in the context of audio or sound signals.
Pink noise: Pink noise, also known as 1/f noise, has a power spectral density that decreases by 3 dB per octave as the frequency increases. It is named "pink" because it is analogous to the color spectrum, where different colors have different energy distributions. Pink noise is characterized by having equal energy in each octave or logarithmic bandwidth. It sounds similar to white noise but has a more balanced and less harsh sound, with a greater emphasis on lower frequencies.
It's important to note that the terms "black noise" and "green noise" are less commonly used and may not have widely accepted definitions in the field of audio or signal processing. White noise, brown noise, and pink noise, however, are well-established concepts used to describe specific types of noise signals based on their spectral properties.