Loudness - Explanation

Explanation

The perception of loudness is related to both the sound pressure level and duration of a sound. The human auditory system integrates (averages) the effects of sound pressure level (SPL) over a 600–1,000 ms window. For example, a sound of constant SPL will be perceived to increase in loudness as 20, 50, 100, 200 ms samples are played, up to a maximum of approximately 1 second at which point the perception of loudness will stabilize. For long duration sounds (greater than 1 second), the moment by moment perception of loudness will be based on the integration of the preceding 600–1,000 ms.

In terms of the relationship between SPL and loudness for sounds longer than 1 second, this can be approximated by a power function with an exponent of 0.6 when plotted against sound pressure or 0.3 when plotted against sound intensity (Stevens' power law). More precise measures have been subsequently made that show that loudness grows more rapidly (with a higher exponent) at low and high levels and less rapidly (with a lower exponent) at moderate levels.

Units used to measure loudness:

  • Sone (loudness N)
  • Phon (loudness level L)

The sensitivity of the human ear changes as a function of frequency, as shown in the equal-loudness graph. Each line on this graph shows the SPL required for frequencies to be perceived as equally loud. It also shows that humans with good hearing are most sensitive to sounds around 2–4 kHz, with sensitivity declining to either side of this region. A complete model of the perception of loudness will include the integration of SPL by frequency and the duration of each.

Read more about this topic:  Loudness

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