Trans:space

In trying to understand some the questions from ‘Medway Tabla’ further reading has led me here….I think it helps to answer some of them.

Sound localization is the process of determining the location of a sound source. The brain utilizes subtle differences in intensity, spectral, and timing cues to allow us to localize sound sources.[7] Localization can be described in terms of three-dimensional position: the azimuth or horizontal angle, the zenith or vertical angle, and the distance (for static sounds) or velocity (for moving sounds).[8] The basis of localization is based on the slight difference in loudness, tone and timing between the two ears. Humans as most four legged animals are adept at detecting direction in the horizontal, but less so in the vertical due to the ears being placed symmetrically. Some species of owls have their ears placed asymmetrically, and can detect sound in all three planes, an adaption to hunt small mammals in the dark.[9]

http://en.wikipedia.org/wiki/Psychoacoustics

Evaluation for low frequencies
For frequencies below 800 Hz, the dimensions of the head (ear distance 21.5 cm, corresponding to an interaural time delay of 625 µs), are smaller than the half wavelength of the sound waves. So the auditory system can determine phase delays between both ears without confusion. Interaural level differences are very low in this frequency range, especially below about 200 Hz, so a precise evaluation of the input direction is nearly impossible on the basis of level differences alone. As the frequency drops below 80 Hz it becomes difficult or impossible to use either time difference or level difference to determine a sound’s lateral source, because the phase difference between the ears becomes too small for a directional evaluation.[citation needed]
Evaluation for high frequencies
For frequencies above 1600 Hz the dimensions of the head are greater than the length of the sound waves. An unambiguous determination of the input direction based on interaural phase alone is not possible at these frequencies. However, the interaural level differences become larger, and these level differences are evaluated by the auditory system. Also, group delays between the ears can be evaluated, and is more pronounced at higher frequencies; that is, if there is a sound onset, the delay of this onset between the ears can be used to determine the input direction of the corresponding sound source. This mechanism becomes especially important in reverberant environment. After a sound onset there is a short time frame where the direct sound reaches the ears, but not yet the reflected sound. The auditory system uses this short time frame for evaluating the sound source direction, and keeps this detected direction as long as reflections and reverberation prevent an unambiguous direction estimation.[7]
The mechanisms described above cannot be used to differentiate between a sound source ahead of the hearer or behind the hearer; therefore additional cues have to be evaluated.[8]

http://en.wikipedia.org/wiki/Sound_localization

One Response to “In trying to understand some the questions from ‘Medway Tabla’ further reading has led me here….I think it helps to answer some of them.”

  1. Sian Thomas Says:

    Reading the above post bought something to mind that I had not considered in terms of this project, however the memory having been triggered by this post it may be that it has some relevance. This is very personal and i hope it’s OK to put on here. I have, in my life, had two ‘pschycotic episodes’ bought on by stress. In both cases the main disturbance was aural. I simply hear too much! I think I lost my ability to edit and separate degrees and direction of sound. As such, it was very disturbing for me to go out into a public urban space as I suffered from a complete overload of aural information coming in from the environment. To be clear, this was not about hearing voices. This was simply sound overload. Vehicles, conversations of people nearby and far away, bird sounds, the sea, music from a distant radio.. all coming in at the smae level all jumbled up.