How does the brain interpret loudness of a sound?

The brain interprets the loudness of a sound primarily through the amplitude of sound waves. Amplitude refers to the height of the sound wave, which correlates with the amount of energy the wave carries. When the amplitude of the sound wave is greater, the sound is perceived as louder. This relationship is fundamental to how sound is processed; larger amplitudes create more vigorous vibrations in the air, which translates into a higher loudness perception.

In contrast, frequency, which is related to the pitch of a sound, does not directly affect loudness, nor does the duration of the sound waves. While the type of sound wave can influence timbre, it does not fundamentally alter the perceived loudness. Thus, amplitude is the key factor in determining how loud a sound is perceived by our auditory system.