Filtering is the operation which removes or changes specific frequency components from the
signal. In SIGVIEW, you can simply apply a filter to the signal by defining frequency segment to
be removed, or the segment you want to leave in the signal. That way, you can create bandstop,
bandpass, highpass and lowpass filters.
When you choose Signal tools/Filters option from the main menu or press
toolbar button, a
dialog will appear where you can enter segment boundaries (in Hz) and determine if you want to
remove that frequency segment (bandstop), leave only that frequency segment (bandpass) or
you want to remove all frequencies up to (highpass) or above some frequency (lowpass).
For Bandstop and Bandpass filter types, you can also include all higher harmonics of defined
frequency segment. If the defined segment is [x,y], it will also include all segments [N*x, N*y],
There is also an option to use custom filter curves for signal filtering. For details, please see Custom filter curves section.
After pressing OK, a new window with filtered signal will appear. You can change filter’s
frequency boundaries later by choosing Edit/Properties on filtered signal window from the menu.
You will be able to see instantly how these changes affect the filtered signal.
SIGVIEW uses FFT-based filtering algorithm. It is a combination of the FFT calculation,
modifications in the FFT result (filling some frequency bands with zeros or applying custom filter
curve) and the inverse FFT calculation. This method is relatively slow compared to other filtering
methods, but is usually very accurate.