Lexicon LXP-15 Owner's Manual page 43

Creating Sounds and Effects
A sound source can be located along two dimensions in the stereo field: lateral
Localization
(left–right) and frontal (near–far). Lateral perception of a sound is affected by
relative differences between left ear and right ear perception of loudness and
the arrival time of sound from a single source. For lateral localization effects, you
can control the left-right loudness of both the dry and wet signal with Dry Pan and
Wet Pan. You can also create lateral localization effects by setting up a relative
delay between the left and right signals. The sound will be perceived as comming
from the undelayed side. Increasing the delay will increase the lateral shift.
(Since the maximum distance between the ears and any path a sound might take
to the ears is less than one foot, the maximum delay used for lateral localization
is less than one millisecond.)
Frontal perception of sound is affected by such factors as relative loudness,
high-frequency content and the relative mix of direct and reflected sound. As the
sound source moves away, it grows softer, its high-frequency content decreases
and more reflected sound is heard. If the source is moving relatively quickly, a
pitch shift is heard as well. The pitch increases as the source approaches and
decreases as it moves away. You can create frontal localization effects by
controlling input/output levels, high-frequency roll-off, dry/wet mix, and pitch.
A useful localization effect for sound reproduction is to use delays to eliminate
echoes and increase the intelligibility of sound systems.
Time delay can't eliminate refelections from walls or boundaries, but it can be
used to eliminate the confusion that results when sound arrives at the listener
from different loudspeakers at different times.
Ideally, the sound should arrive at the listener first from the main speakers and
then about 20 milliseconds later from the auxiliary speaker (like the delay towers
near the middle of the audience at a large rock concert). The LXP-15 can provide
two delay paths for two zones of auxiliary speakers by using the stereo delay in
the Pitch/Delay algorithm.
The correct amount of delay can be approximated by using the formula:
(d x .885) + 20
where d = the difference in the path length to the listener from the main and the
auxiliary speaker.
The result is the approximate number of milliseconds of delay required for the
auxiliary speaker.
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