If the same signal if sent to both speakers (and if the speakers are
wired "in phase" and if the listener is more or less midway between
the speakers and if the room is not too acoustically irregular), a "phantom
source" will appear to originate from a point midway between the two
loudspeakers. By "crossfading" the signal from one speaker to
the other, one can create the impression of the source moving continuously
between the two louspeaker positions. However, simple crossfading will never
create the impression of a source outside of the line segment between the
two speakers. As we shall see, that can be done with crosstalk-cancelled
stereo.
In fact, one can also shift the location of the phantom source by exploiting
the precedence effect. If
the sound on, say, the left is delayed by 10 or 15 ms relative to the sound
on the right, the listener will localize the sound on the right side, even
if the sound that comes on the left is as loud or somewhat louder. Of course,
with too much delay, the listener will eventually become aware of the sound
on the left as an annoying echo.
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