What defines the intensity of sound as perceived by the human ear?

The intensity of sound as perceived by the human ear is primarily defined by loudness. Loudness is the subjective perception of sound intensity, and it is influenced by the amplitude of the sound wave. The greater the amplitude, the louder the sound is perceived to be. This concept is crucial in understanding how we experience and differentiate sounds in our environment.

While frequency refers to the number of vibrations per second and is associated with the pitch of the sound, it does not directly determine how loud that sound is perceived. Pitch is the quality that allows us to distinguish sounds as high or low, but again, this relates more to frequency than to intensity. The type of sound can influence our perception based on context, but it is not a defining characteristic of sound intensity itself. Therefore, loudness is the correct response as it specifically measures how intense or strong a sound is in terms of human perception.