Black noise is noise that has a frequency spectrum of predominantly zero power level over all frequencies except for a few narrow bands or spikes. An example of black noise in a facsimile transmission system is the spectrum that might be obtained when scanning a black area in which there are a few random white spots. Thus, in the time domain, a few random pulses occur while scanning. [1]Black noise, or silent noise, has several different definitions:1. Silence
2. Noise with a 1/fß spectrum, where ß 2 (Manfred Schroeder, "Fractals, chaos, power laws"). Used in modeling various environmental processes. Is said to be a characteristic of "natural and unnatural catastrophes like floods, droughts, bear markets, and various outrageous outages, such as those of electrical power." Further, "because of their black spectra, such disasters often come in clusters."
3. Noise that has a frequency spectrum of predominately zero power level over all frequencies except for a few narrow bands or spikes.
4. Whatever comes out of an active noise control system and cancels an existing noise, leaving the world noise free. The comic book character Iron Man used to have a "black light beam" that could darken a room like this, and popular sci-fi has a tendency to portray active noise control in this light.
5. As seen in the sales literature for an ultrasonic vermin repeller, black noise with a power density that is constant for a finite frequency range above 20 kHz. More accurately, ultrasonic white noise. This black noise is like the so-called black light with frequencies too high to be sensed, but still capable of affecting the environment.
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