Noisy Pulse Analyzed with a Median Filter

One of the conditions the Pulse Parameters VI imposes is that the expected peak amplitude of the noise portion of the signal be less than or equal to 50% of the expected pulse amplitude. This condition is necessary because after the VI completes the modal analysis to determine the baseline and the top, it is difficult to discriminate between noise and signal without more information. In some practical applications, this kind of pulse-to-noise ratio is difficult to achieve, and you must do some preprocessing to extract pulse information.

If the pulse is buried in noise whose expected peak amplitude exceeds 50% of the expected pulse amplitude, using a lowpass filter removes some of the unwanted noise. However, the filter also shifts the signal in time and smears the edges of the pulse because these transition edges contain high frequency information.

A median filter can extract the pulse more effectively. A median filter is a nonlinear filter that removes high frequency noise while preserving edge information.

The following block diagram demonstrates how to use the Median Filter VI to successfully analyze a noisy pulse whose expected peak noise amplitude is greater than 100% of the expected pulse amplitude.

The following multiplot graph shows how you can easily track the pulse signal with the aid of a median filter in spite of the fact that the pulse is deeply buried in noise.

By removing the high frequency noise with the Median Filter VI, you can attain the condition for the Pulse Parameters VI and complete the analysis correctly. The results shown in the following illustration correspond to the analyzed pulse in the previous multiplot graph.

The ideal pulse values when the signal was generated were as follows: