Localization Accuracy
Our ability to detect changes in localization or lateralization is not absolute. Experimentally, it is measured as the minimum audible angle, but is also called localization blur. The minimum audible angle can be determined for both horizontal and vertical directions. Spatially, our most acute sense of localization is directly in front (0° azimuth). In fact, in that position we have a maximum accuracy of 1 degree. Localization blur does vary with signal parameters, and more typical frontal accuracy is within 5 degrees. The minimum audible angle increases as sounds are moved towards the axis of the ears, where it reaches an overall maximum of +/-10 degrees.
Visual localisation is just as accurate, but not nearly as efficient and not possible in low or reduced light situations, or when the source of the sound cannot be visualized.
Horizontal source location:- Low Frequencies / Timing Cues Dominate
- High Frequencies / Intensity Cues Dominate
- Determined from pinna cues
- Listener’s intimate knowledge of complex geometry of pinna helps pinpoint elevation
- For frequencies above 5000Hz
- Shoulder reflection causes changes in signal in 2000-3000Hz range
- Less understood
- Spectral balance = primary cue
- Hi freq sounds boosted by pinna when they arrive from the front; attenuated when from behind
- Most common localization error
- Feasible for sources up to ~6m
- Listener must be able to turn head, and source must be repeated or be continuous for sufficient time to allow multiple head orientations
- Provides info re: front vs. back & distance
- Cues are found in variance in ITD’s and ILD’s as listener moves head
- Visual cues
- Source familiarity
- Once head reaches final size and distance between ears, nothing will change these stored patterns except ear disease, trauma, or hearing changes
- Can adapt to stable unilateral hearing loss, assuming sound remains audible on both sides.
Effect of hearing loss on sound localisation
- Horizontal localization ability decreases with increasing low freq. hearing loss (below 1500 Hz)
- Sounds must be audible (at least 10 dB above threshold)
- Vertical localization ability decreases with increasing high freq. hearing loss
- Severely disrupts horizontal localization ability
- Front to back localization remains intact (other studies dispute this)
- Vertical localization only slightly affected provided the other ear is adequate
- May be possible, but not as accurate as binaural localization
- Time delay between direct and pinna-reflected sound is the dominant cue for monaural localization
- Greatest decrease in accuracy found in judgment of front/back differences
- Up/down errors occur with less frequency
- Least influence on left/right judgments
- Accuracy decreases as S/N decreases
See also: Binaural, Interaural Cross-Correlation Coefficient, Interaural Level Difference.
Subjects: Audio Noise & Vibration
- Weblinks:
- Introduction to Computer Music: An Acoustics Primer An introduction to acoustics for musicians - a well written clear introduction.