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chapter 6
CHAPTER 6BAD CHANNEL
REPLACEMENT
Concepts
T
he Bad Channel Replacement tool is designed to operate on any Net Station
Native file that has been operated on by the Artifact Detection tool. The results are
output to a file that has the same format as the input file.
The Bad Channel Replacement tool replaces the bad channels detected by the
Artifact Detection tool with data interpolated from the remaining channels and
inactivates the “bad channel” status. For more information about detecting artifacts,
see Chapter 4, "Artifact Detection.”
Theory
Caution!: If Bad Channel Replacement is run on a file that has undergone
Montage Operations with a bipolar montage, the file may crash.
Because of electrical volume conduction, scalp locations in proximity to each other
have similar voltage values. It has been shown that by using spherical splines, you can
accurately interpolate the voltage at a given scalp location from the voltage values at
many other locations. Assuming that the locations that you are interpolating from are
evenly distributed across the scalp, your ability to interpolate the voltage at any
location accurately depends on
• the spatial frequency of voltages across the scalp (the rate at which voltages
change as you move from one scalp location to another)
• the number of locations from which you are interpolating
In bad channel replacement, you replace the data in bad channels with data
interpolated from the remaining channels, using spherical splines. This
approximation increases in validity as channel count increases.
Net Station Waveform Tools Technical Manual S-MAN-200-WFTR-001 • December 21, 2006
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