The Little Vulgar Book of Mechanics (v0.17.3) - Sound I - Space I
Last updated: March 22nd 2023
Just updated this section of the book: Sound I - Space I
Sound I - Space I #
Interaural time differences (ITDs) are one of the primary cues available to the auditory system for determining the spatial location of sound sources. ITDs come about due to the separation of the two ears in space, and the resulting differences in path length that a sound must travel to reach the two ears. – Virginia Best and Jayaganesh Swaminathan. "Revisiting the detection of interaural time differences in listeners with hearing loss." 2019. Journal of the Acoustical Society of America.
Imagine there's a sound source producing disturbances in a medium. Your brain, conceptualizing it as a single agent, analyzes, for example, the differences in time and intensity of said disturbances on each of our ears. This is one of main factors that influence your perception of spatial content in sound.
So you have these factors:
- Interaural Time Differences (ITD).
- Interaural Level Differences (ILD).
According to a 1986 study by Blauert and Lindemann, your brain needs ITDs of around 650 microseconds and ILDs of approximately 12 decibels for accurate localization of a sound source.
If you're an engineer mixing music, this should ring bells (in stereo!)
When mixing, you are often trying to make things sound "wide." As in "stereo" vs. "mono." And usually, the reason your "double-tracked" metal guitars (to give an example) don't sound "as wide" as those in someone else's mix that you admire, is that the left and right sound content is too similar.
The point is: The perception of spatial content in sound emerges from, among other things, the differences in time and intensity of the disturbances, caused by anything we consider a single agent, on each of our ears.
External resources #
- (Text/HTML) How Well Do Dogs and Other Animals Hear?
- (Text/HTML) 1883 eruption of Krakatoa @ Wikipedia
- (Text/HTML) Interaural time difference @ Wikipedia
- (Text/HTML) Audio Spatial Representation Around the Body
See current full book's WIP here.