Binaural Sound Part 2

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And that, the "Time/Distance/Phase Effect" is where stereo falls down and binaural sound reigns supreme. If our marching band - even if it's standing still - is fifty feet long, from the first row of musicians to the last; our microphones are eight feet apart, centered on the band; and our ears are six inches apart, also centered on the band, both the two mics and our ears will hear all of the whole fifty feet of band  -- meaning that the two eardrums or the two mic diaphragms will both be moved by the sound of it, with the total net movement of any diaphragm determined by the relative amplitude of all of the sounds and all of their frequencies  at all of their distances. (Remember that this is music, so instead of just a single tone, it will be a complex waveform constituted of the algebraic sum of all of the frequencies comprising it, each at a degree of phase determined by the distance of the source of each tone from the hearing or recording diaphragm.)  That's why stereo can never really sound like what we hear; it's actually "hearing" something different from what we would hear: 

AR-binu2a.jpgWith both the ears and the mics exactly centered on the band (and presumably the same distance away from it), and with the mics 7 ½ feet farther apart than the ears [8'-6"=7 ½'] each of the microphones will be 3.75 feet [7.5'÷ 2 = 3.75'] farther to the left or to the right of the center line than the corresponding ear.  That means that there will be 3 ¾ feet (1.143m) more distance (and therefore more time and more phase) between the right-end-of-the-band sound heard by the left microphone and the right-end-of-the-band sound heard by the left ear, and that same will hold true for the left-end-of-the-band sound heard by the right mic and the right ear and, for both ears and both mics, for all of the sound originating in-between. In short, the pressure wave components summing algebraically to determine the position of the mic diaphragms and the eardrums at any instant will be different , and therefore can' t possibly result in the same perceived or recorded sound. 

AR-stereolabel1.jpgWith binaural recording, though, the recording is made with two small microphones mounted in a dummy head, with the mics positioned to, as much as possible, mimic the positioning of the eardrums and the spacing of the ears on either side of a real human head. Also, the head, itself, is positioned just where a listener's head might be if listening "live" to the same thing, so that binaural, which, unlike stereo, does "hear" just the way we do and is played-back only through headphones, can provide time-perfect and phase-perfect recordings. 

More next time; see you then!

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