jhs@MITRE-BEDFORD.ARPA (12/18/87)
Rodney Peck's description of the audio haircut sounds like an old-fashioned "binaural" recording, which has nothing whatever to do with "holograms". Binaural recordings which you listened to with headphones were in vogue in the 1950s, before "stereo" with loudspeakers took over. Such recordings do indeed sound impressive, especially if the original was done with a dummy head, complete with realistic ears, and the microphones mounted inside the ears just where the transducer in a human ear is mounted. In that case, the phase-versus-frequency-versus-location function of the recording closely matches that of the live sound, so the brain evidently can dig the location information out surprisingly accurately. Someone once told me about some experiments in which this was carried a step further--the playback transducers were somehow installed inside the listener's ears so that there was no additional phase shift due to the path from the transducer to the eardrum. They said the sound was so real it was indistinguishable from hearing the live sound. Nowadays the same result could probably be done with a digital computer to compute the inverse function of the path from a normal headphone driver to the inner ear. The fake head would still probably be the cheapest way to compute the function at the recording microphones. -John Sangster / jhs@mitre-bedford.arpa