We do not perceive all frequencies as equally loud even at equal physical amplitude

Loudness is perceptual, not purely physical: two sounds at the same physical amplitude are not heard as equally loud if their pitch differs. The ear gives more precedence to higher-pitched sounds — which is why white noise, whose amplitude is equal across all frequencies, still sounds distinctly high-pitched, and why bass tends to be heard as comparatively quiet relative to higher frequencies. This is the core reason a DJ or engineer must EQ by ear rather than by meters alone: a spectrally ‘flat’ balance does not sound balanced. It also explains why cutting bass frees up a lot of headroom while barely changing perceived level, and why boosting highs can make a track feel louder without more energy.

Examples

White noise contains equal amplitude at every frequency yet is perceived as bright/high-pitched. A bassline swap can remove a huge share of a track’s energy while the crowd barely registers a volume drop, because low frequencies read as quieter.

Assessment

Why does white noise sound high-pitched despite having equal amplitude at all frequencies? What does frequency-dependent loudness imply for how a DJ should judge an EQ move?