<P> The auditory system uses these clues to estimate the distance to a sound source: </P> <Ul> <Li> Direct / Reflection ratio: In enclosed rooms, two types of sound are arriving at a listener: The direct sound arrives at the listener's ears without being reflected at a wall . Reflected sound has been reflected at least one time at a wall before arriving at the listener . The ratio between direct sound and reflected sound can give an indication about the distance of the sound source . </Li> <Li> Loudness: Distant sound sources have a lower loudness than close ones . This aspect can be evaluated especially for well - known sound sources . </Li> <Li> Sound spectrum: High frequencies are more quickly damped by the air than low frequencies . Therefore, a distant sound source sounds more muffled than a close one, because the high frequencies are attenuated . For sound with a known spectrum (e.g. speech) the distance can be estimated roughly with the help of the perceived sound . </Li> <Li> ITDG: The Initial Time Delay Gap describes the time difference between arrival of the direct wave and first strong reflection at the listener . Nearby sources create a relatively large ITDG, with the first reflections having a longer path to take, possibly many times longer . When the source is far away, the direct and the reflected sound waves have similar path lengths . </Li> <Li> Movement: Similar to the visual system there is also the phenomenon of motion parallax in acoustical perception . For a moving listener nearby sound sources are passing faster than distant sound sources . </Li> <Li> Level Difference: Very close sound sources cause a different level between the ears . </Li> </Ul> <Li> Direct / Reflection ratio: In enclosed rooms, two types of sound are arriving at a listener: The direct sound arrives at the listener's ears without being reflected at a wall . Reflected sound has been reflected at least one time at a wall before arriving at the listener . The ratio between direct sound and reflected sound can give an indication about the distance of the sound source . </Li> <Li> Loudness: Distant sound sources have a lower loudness than close ones . This aspect can be evaluated especially for well - known sound sources . </Li>

Sense of pitch relies on which signal(s) from the cochlea