in regards to psychoacoustics, do a search on HRTF. (head related transfer functions) we studied the effects of speaker placement and sonic perception at the army research lab (no, i'm not a soldier...) along with the 'effects' created by headphones. if you really want to get into all that stuff, you have to study transfer functions (fft and ifft among others) and be willing to read through A LOT of literature. we used matlab and a tucker davis machine (basically a rack full of dsp units connected to the p.c. via fiber optic cables to eliminate line noise) to design a digital filter (software based and programmed in pascal and m) which would (in conjunction with the td machines) accurately recreate a desired waveform. basically we would set up a bose speaker and a microphone and program the td to send out 10 pink noise bursts. (churps actually...) the td (capable of full duplex... i.e. play and record at the same time) and matlab would know exactly what was projected thro!
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ugh the speaker and compare that signal with what was recorded through the microphone. matlab would instruct the programmable dsp units of the td to 'adjust' the churps until what was recorded matched the desired waveform we programmed in matlab. lots of pole / zero plotting and z-transform analysis which, to my belief, was only truly understood by the scientist i was working with. (smartest man i've EVER met) 'folding' imaginary Xs (poles) back into a circle representing real and imaginary numbers in a three dimensional plane can be a bit, um, confusing. (like this message...hehe) in short, it's an 'inverse' filter used to remove the 'distortion' of soundwaves caused by surface structures. (floors, ceilings, etc) oh yeah, whenever you listen to music through a speaker, you're hearing a distorted signal regardless of how good your speakers are... (yes, we actually used bone conducting transducers to vibrate the inner bones of the ear to compare with the sound of headphone!
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s. kinda fun actually)
many of the effects regarding headphones (the research lab has lots of life sized 'dummies' used to study the long term effects of gun fire on soldiers hearing / performance) involves the fact that the sound coming out of the headphones actually resonates in the ear canal and 'bounces' off the diaphragm of the headphones. (this is the equivalent of an infinite impulse response filter which isn't phase linear or stable...) before i left, we were working on a filter (matlab and td again) which would cause the headphones to be 'transparent' to the listener. (3D audio is a big area of research for pilots in the military... helicopters in particluar) i had to leave for college before i could hear / see the final results but i'm hoping to sneak a peak over the break.
glad to say that i've never worked with weapons,
christian.adam.hresko.
: the research lab had the facilities to make some INCREDIBLE sounds... enough equipment and software to make any electronic music 'fan' grin in envy
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