palmer@tybalt.caltech.edu (David Palmer) (07/18/87)
In article <802@aurora.UUCP> jbm@aurora.UUCP (Jeffrey Mulligan) writes: > >Let v represent the speed of sound. >Let h represent the interaural distance (width of head) > >v =~ 1000 feet/second (within a factor of 2, anyway) >h =~ 0.5 feet (also within a factor of 2) > >The delay (d) for a sound source at some angle theta from the observer >(theta=0 == straight ahead) is ( h sin( theta ) ) / v . >"Worst case" occurs when theta = +- 90 degrees, so >d = h / v = 0.5 MILLIseconds. > >Interaural phase differences are only useful for wavelengths less than >2h, i.e. frequencies less that 1kHz. For higher frequencies, delays >of transients as well as intensity differences ("acoustical shadow" >effects) are probably important. > Recently, neurobiologists discovered a structure in the brain of a species of owl which is used for echolocation. It consists of two tapped delay lines of neurons coming from the ears in opposite directions, and coincidence detectors at the taps viz: +<-O<-+<-O<-+<-O<-+<-O<---From right ear | | | | @ @ @ @ | | | | From left--->O->+->O->+->O->+->O->+ Ear Where '+'s are taps, 'O's are delay elements, and '@'s are coincidence detectors (neurobiologists probably have different names for these wetware components). The location of the coincidence detector which is most strongly activated indicates the time difference of the signals from the two ears. David Palmer palmer@tybalt.caltech.edu "We must learn from the future if we are to pass on a better world to our ancestors"