The word ‘stereo’ comes from a Greek word meaning ‘solid’. ‘Stereoscopic vision’ means perceiving things as being solid when viewed with two eyes. Although the term ‘3D’ has become the standard (easier to spell!), ‘stereoscopy’ is still basically correct. From there it was but a small step to extend the ‘stereo’ part to sound and hence we have ‘stereophony’, or ‘stereo’ for short.
There is a sort of solidity, in a sense, when sound images are spread out in front of the listener. Here we shall deal with the usual form where there are two loudspeakers, two tracks on a tape, and so on. Actually, stereo sound could have any number of such channels – there are good reasons for saying the more the merrier – but practicalities such ...