Fundamentals of Wearable Computers and Augmented Reality, 2nd Edition

292 Fundamentals of Wearable Computers and Augmented Reality

Apparent distance of a sound source (Bronkhorst and Houtgast 1999, Moore and

King 1999) is determined mainly (Villegas and Cohen 2010) by

Overall sound level: Intensity of a point source varies as the reciprocal of

its squared distance (Mershon and King 1975). Simple models might use

this inverse-square free-eld spherical intensity attenuation, equivalent to

linear gain scaling as a simple inverse and level falling off at −6 dB/range

doubling.

Interaural level differences: Closer sources present a larger ILD (Brungart

and Rabinowitz 1999), especially exaggerated at intimate, near-eld whis-

per ranges.

Reverberation: Distance perception is affected by lateral reections (Nielsen

1992). ...