12.6 Distance cues

There are two main cues available that allow us to judge the distance to a sound source. The first of these is the sound pressure level. Sound pressure level drops by 6 dB each time the distance that a sound travels doubles. In other words, if the sound pressure level of a sound is 60 dB SPL when its source is 1 m from you, then it will be 54 dB SPL if you move back another metre so that you are now 2 m away from its source. Therefore lower sound pressure levels indicate a greater distance. A second cue relates to the frequency of a sound. When a sound travels over a distance, the high-frequency components attenuate to a greater extent than the low-frequency components. This means that sounds that are further away tend to be richer in low frequencies and therefore have a lower pitch.