Filters

Overview

Filters allow an operator to alter the waveform data in various ways before processing. There are a number of filters available, operating in both time and frequency.

Averaging/Median

These filters will perform a running average/median on a specified number of samples. For example, given a 10-sample filter, the 10th sample will be replaced with the median/average of the previous 10 samples, the 11th sample will be replaced with the median/average of previous 10 samples, etc. Note that the first and last n samples in the waveform are not changed, where n is the number of samples to average.

FIR Filters

a [Finite Impulse Response (FIR)] filter can be added. A dialog box is shown allowing the user to specify a simple FIR filter or load a pre-defined filter from a file. Use of this filter requires knowledge of how to generate FIR filters beyond the scope of this document.

Envelope

A filter envelope will take the root of the square of each sample and apply it to the waveform. This has the effect of rectifying all waveform data. An averaging filter of the specified number of samples is then applied to the result.

LowPass/Highpass/Bandpass/BandStop

These filters will remove certain frequencies from the waveform data. This is useful for removing constant frequency noise or otherwise isolating a desired frequency.

• Low-Pass filters will pass any signal below the specified cutoff frequency, and attenuate any signal above the cutoff frequency.

• High-Pass filters will pass any signal above the specified cutoff frequency, and attenuate any signal below the cutoff frequency.

• Band-Pass filters will pass any signal between the specified high and low frequency, and will attenuate everything else.

• Band-Stop filters will pass any signal that is not within the specified high and low frequency, and will attenuate between the high and low frequency.

Mixers

A mixer will add a waveform with the specified frequency to the current signal.

Savitzky-Golay

Runs a [Savitzky-Golay] smoothing filter. The width and polynomial order can be specified.

Slope

Performs a first derivative of the waveform data and displays the results.

Integration

Not enabled as of this writing

Activating/Deactivating Filters

To activate a filter, select the Filter Settings tab on the Digital Oscilloscope. At the left will be a list of the type of filters available. To add a filter, click on the name, make changes to the available settings (as needed), and press the Add button. This will add the filter to the Active list. The operator can add as many filters as he desires.

To remove a filter, click on the item in the Active list and press "Remove".

The order of filters can be changed using the Move Up and Move Down buttons.

Using Filters

When using filters, image processing will be done using Software peak detection.