Instruction manual

5 Analysis 51
Notice that the filter is subject to the Nyquist limitation of frequency. The maximum frequency
in the Filter Setup dialog is exactly half of the sample frequency.
Smoothing All experimental data includes noise to varying degrees. Noise can obscure important features
like peaks, valleys, or peak widths. DataTrax2 allows you to smooth noisy signals to reveal
significant features of your data. In addition to filters, DataTrax2 also offers the ability to smooth
the data. Smoothing is used to remove noise that is uniform across all frequencies. Each
method offers different performance to best show significant aspects of your results. Filtering
allows you to eliminate noise above a specified frequency. DataTrax2 provides two kinds of
smoothing; Moving Average does wide smoothing, while Savitzky-Golay seeks to preserve
shapes of peaks.
Moving Average: Applies a user specified number of points on either side of each data point
to calculate the mean and replaces the datapoint with the calculated mean. For example, if you
set the number of data points on either side to 1, then
new data (N) = {data(N-1) + data(N) + data(N+1)}/ 3
Savitsky-Golay: The Savitzky-Golay method essentially performs a local polynomial
regression to determine the smoothed value for each data point. This method is superior to
Moving Average because it tends to preserve features of the data such as peak height and
width, which are usually 'washed out' by adjacent averaging. To use the Savitsky-Golay
smoothing type, the order of the polynomial and the number of points on each side of the data
need to be specified.
In addition to smoothing the data, DataTrax2 also provides the option to calculate the
smoothed 1st, 2nd or 3rd derivative of the data.
Power The Power function performs a Fast Fourier Transform (FFT) on data in the selected channel
and returns the average Power in the frequency band selected.
Figure 5-6: The Power dialog window.
In DataTrax2, this function works only off-line. The graphic interface in the Power dialog
window is similar to the one in the Filter Setup dialog. The band of frequencies selected from
the Power dialog window are not filtered, but they are subjected to an FFT whose output is