A
data processing method is provided to enable a calculation based
signal analyzer, such as an FFT based
spectrum analyzer, to produce results corresponding to a swept
spectrum analyzer employing a video bandwidth (VBW) filter. Once a spectrum is produced the
frequency axis is replace by a corresponding time axis, so that a
time domain filter, such as a video bandwidth (VBW) filter can be applied. In a first example, the filter characteristics are applied by performing an FFT on display spectrum data, which has had its
frequency axis replaced by a corresponding time axis, produce
frequency domain data, multiplying by the
frequency response to produce a filtered version, performing an
inverse FFT and replacing the time axis with the original
frequency axis to produce a filtered version of the display spectrum data. In another example, a
filter impulse response is computed based upon the desired filter characteristics, a
convolution integral of the display spectrum data, which has had its frequency axis replaced by a corresponding time axis, and the
filter impulse response is conducted, and the time axis is replace by the original frequency axis to produce filtered display spectrum data.