BILOCATION - TRANSAURAL PROCESSING

Binaural recordings can be uncannily realistic - but only when played back on headphones. With playback on speakers, the stereo imaging can sometimes be quite poor. This is because the headphones ensure that each ear only hears what was recorded by the mic on that side of the head. The speakers produce crosstalk, so that some of the sound from the left speaker can be heard by the right ear, and vice versa; and this muddies the spatial imaging.

A solution to this problem has been around since the 1960's. If some of the left channel is mixed with the right, but out-of-phase, the unwanted crosstalk will be cancelled out. (The same must be done with the other channel.) Also, the out-of-phase signals should be delayed, by however long it takes for the sound to travel from one ear to the other - about half a millisecond.

This method can work very well, but only in a rather small 'sweet spot' which can be only inches across sometimes. The two speakers and the listener must form an exactly equilateral triangle, so movements of the listener's head will disturb the spatial imaging.

Bilocation uses a simple and obvious way around this problem - one that no-one else seems to have thought of! By coupling the front and rear speakers at each side of the 5.1 system together, the sweet spot will be made very much bigger - up to several feet. The listener is in effect wearing 'virtual headphones', so can move around quite a bit and still hear detailed surround sound. The binaural soundfield is actually much easier to listen to with this method than with headphones: less listening fatigue and more of an impression of space.

There is much more detailed information about all of this in the Sound on Sound article about the making of Bilocation.

Copyright © 2005 Steve Marshall.