IntuiLink Waveform Editor

This article appeared on the Test & Measurement World web site at www.tmworld.com.
Filter your data in software
Werner Haussmann, Agilent Technologies, Loveland, CO -- 4/1/2002
Test & Measurement World
When you capture waveform data, you often want to process the data to extract information about
the signal or to extract a particular wave shape. Filters—analog or digital—often provide the
signal processing you need. Analog filters process signals before you digitize them. Digital filters,
which apply software algorithms to digitized waveforms, can work in digital signal processors for
"real-time" filtering. You can also use digital filters that run on a PC to process data you've
already captured.
Filters act on specific frequency components. With a filter, you can isolate wanted frequencies
(pass band) from unwanted frequencies (stop band). Digital filters isolate frequencies by applying
mathematical formulas called transfer functions to data points. The characteristics of a transfer
function define a filter's frequency response.
While working on a recent project, I needed to capture a signal, remove unwanted high-frequency
noise, and store the "clean" signal in a file. Then, I needed to load the clean signal data into a
waveform generator.
To filter the data, I developed a digital filter
in Visual Basic 6.0 that runs under Windows
98 or 2000 (I haven't tested it under XP).
The filter works on data I've already
captured, plots raw and filtered data, and
displays a filter's frequency response.
Figure 1 shows how well the filter removes
noise from a sine wave.
You can download a free copy of the filter,
which resides in an ActiveX control, and
use it in your own programs or in an
application program I wrote. ("Using the
filter," below.) You also can download the
complete source code for the filter control
and the accompanying application.
Figure 1. A digital filter removes unwanted
frequency components such as noise from the
upper trace to produce the filtered lower trace.