This is accomplished by the use of monaural and binaural cues. There are a couple of important factors involved in deciphering spatial properties of sounds from monaural cues.
Individuals utilize the intensity of a stimulus to judge the distance of a sound source.
For example, if two sounds are presented simultaneously, the louder one is perceived to be closer. The change in pitch emitted by an object moving horizontally in space, in relation to a stationary observer, is termed the Doppler shift. The basis for this shift in pitch is that as a sound producing body moves toward you, each of its successive sound waves is emitted slightly farther ahead in its path. On the other hand, the sound waves following the object tend to be more stretched-out, and the frequency of that sound is perceived as lower.