Documentation

This is machine translation

Translated by
Mouseover text to see original. Click the button below to return to the English version of the page.

Note: This page has been translated by MathWorks. Please click here
To view all translated materials including this page, select Japan from the country navigator on the bottom of this page.

Remove Spikes from a Signal

Sometimes data exhibit unwanted transients, or spikes. Median filtering is a natural way to eliminate them.

Consider the open-loop voltage across the input of an analog instrument in the presence of 60 Hz power-line noise. The sampling rate is 1 kHz.

```load openloop60hertz fs = 1000; t = (0:numel(openLoopVoltage) - 1)/fs;```

Corrupt the signal by adding transients with random signs at random points. Reset the random number generator for reproducibility.

```rng default spikeSignal = zeros(size(openLoopVoltage)); spks = 10:100:1990; spikeSignal(spks+round(2*randn(size(spks)))) = sign(randn(size(spks))); noisyLoopVoltage = openLoopVoltage + spikeSignal; plot(t,noisyLoopVoltage) xlabel('Time (s)') ylabel('Voltage (V)') title('Open-Loop Voltage with Added Spikes')```

`yax = ylim;`

The function `medfilt1` replaces every point of a signal by the median of that point and a specified number of neighboring points. Accordingly, median filtering discards points that differ considerably from their surroundings. Filter the signal, using sets of three neighboring points to compute the medians. Note how the spikes vanish.

```medfiltLoopVoltage = medfilt1(noisyLoopVoltage,3); plot(t,medfiltLoopVoltage) xlabel('Time (s)') ylabel('Voltage (V)') title('Open-Loop Voltage After Median Filtering') ylim(yax) grid```

Related Topics

Was this topic helpful?

Download ebook