The perceptual intensity of sound. Loudness depends importantly on the physical intensity of sound, increasing when physical intensity increases and decreasing when physical intensity decreases. But loudness also depends on other physical properties of sound, such as frequency and duration. Sound waves with frequencies between 1000 and 5000 Hz are louder than sound waves that have the same intensity but lower or higher frequencies. Very brief bursts of sound are less loud than are longer bursts, loudness increasing regularly as duration increases up to about 0.1–0.2 s, beyond which point in time, loudness no longer increases with increasing duration.