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SAMPLING RATE
The MLD allows selection of a tracking sampling rate via the "Sampling rate" control in
the real-time screen. The maximum recommended sampling rate is determined by the
size of the tracking area and is dependent on room geometry. Generally, lower
sampling rates result in more stable positioning readings (although one can trade this off
somewhat by changing the number of samples averaged to stabilize readings at higher
sampling rates). The MLD rule is that the maximum sampling rate is given by
max sampling rate = 300 / diagonal
where "diagonal" is the distance from one speaker to the floor below the speaker in the
opposite corner, which is given by the formula
diagonal = square root (depth
2
+ width
2
+ height
2
)
where depth, width and height correspond to the 3D box defined by the ultrasonic
speakers, measured in centimeters.
It is possible for users to enter sampling rates higher than the maximum but positioning
anomalies such as sudden shifts in apparent position may occur when using these higher
sampling rates. Users must experiment to find what tradeoff of sampling rate, number
of samples averaged, and tracking area is best for their application.
Side note: if the configuration of the speakers is not regular then the maximum sampling rate
can be calculated by using the 3D diagonal from the farthest speaker to the diametrically
opposite point in the interactive area floor.
It should be noted that the MLD is NOT a reliable system for generating completely
stable data rates which can serve as a clock or "sync" signal for other systems. Due to
the nature of the PC clone computer architecture and the processing involved, timing
jitter of a few milliseconds can occur. Also, the processing speed of the particular PC
being used may have an effect on the system timing. Because of these factors, the
"Sampling rate" parameter should be regarded as approximate and should be fine tuned
using an accurate timing reference to time the output of serial or MIDI position data
until the desired rate is achieved.
MLD manual 1.1
Page 81
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