White noise has flat power across the 20 to 20,000 Hz hearing range

Evidence

White noise is a very specific type of noise, which is random in nature and has a constant power spectral density. Essentially, this means that when the power spectrum of white noise is plotted, it looks flat across frequency. Within the human hearing sciences, we generally assume that the frequencies contained within the white noise roughly correspond to the range of human hearing, or 20 to 20,000 Hz. … We can see large random amplitude fluctuations over time in the waveform represented in Figure 3–1. The spectrum also contains a representation of those fluctuations, but the fluctuations are relatively small and we generally treat the spectrum of white noise as being flat across frequency, particularly for long-duration white noise. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 408

Categorization

• DEFINE: Defines white noise by its flat power spectral density and assumed hearing-range bandwidth.