Physical properties vs perceptual attributes

There is a certain correspondence between the attributes of sound perceived by the listener and the properties of the physical wave, however each perceptual attribute usually depends on more than one physical property. The loudness of a sound event is related to its level and is measured in phons. Not all frequencies are perceived as equally loud, however. The phon scale is coincident with the SPL scale at 1kHz (loudness of n phones is equivalent to the loudness of a sine wave of 1kHz at n dB SPL), but at other frequencies it is different. The loudness of pure sinusoidal tones has been determined experimentally by Fletcher and Munson as compared to 1kHz tone at given level.

In general, the loudness of a complex sound not only depends on its intensity, but is also related to its periodicity, frequency, duration and structure. For example, the perceived loudness of a short (below 200ms) impulse or a tone burst almost linearly decreases with duration, which suggests an existence of a bandpass filter in the inner ear, with long impulse response and consequently long rise (or settle) time (the theory of auditory filters is based on this observation). Also, for broadband signals (signals with bandwidth wider than so called critical bandwidth, like white noise), their loudness is apparently higher than narrowband signals of the same intensity.