Filter
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FUNCTION REFERENCE 5 - 35
FILTER
Description:
The FILTER function is a waveform MATH function. It is a post- acquisition
algorithm which can be used to simulate the effect of a low-pass filter process on
a trace. The cut-off frequency of the low-pass filter can be adjusted and the result
trace is stored as a new trace in a separate register. This implies that the original
waveform or trace is never disturbed by the process, allowing you to "experiment"
with different filter factors.
A typical use of this digital low pass filter is to suppress noise even after a signal
acquisition. Since the FILTER function is a post acquisition process, it can also be
used on single event waveforms.
Any newly acquired trace or previously stored trace can be used as the source for
the filter process.
The result trace is automatically written in memory location m1 for MATH1 and m2
for MATH2 and instantly displayed on the screen.
For each sample point of the trace, a (1 - cos X) weighted sum is calculated over
a window of N samples (convolution). N is adjusted with the ∆ control. The window
value is displayed in the ‘MATH FILTER PARAM’ menu. The resulting cut-off
frequency is the result of the sample rate set by the time base and N. The -3 dB
point is displayed in the bottom area of the screen.