Transform Data

The Transform Data dialog is opened by chosing the corresponding item in the pop-up menu 'Preprocess' in the ident window.

This function tranforms the Working Data between the frequency and time domains and may also provide a frequency function (IDFRD) data set.

Transformations
Frequencies
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Transformations

The Transform to popup-menu controls the transformation.

A time domain data set (indicated by a white background color) can be transformed to
Frequency domain data (using FFT)
A Frequency function (IDFRD) data set (using SPAFDR)
A frequency domain data set (indicated by a slightly green background color) can be transformed to
Time domain data (using IFFT)
A Frequency function (IDFRD) data set (using SPAFDR)
A frequency function data set (indicated by a light brown background color) can be transformed to
Another Frequency function (IDFRD) data set (using SPAFDR), typically corresponding to a courser resolution
A Frequency Domain data set (IDDATA) by setting the input to ones, and the outputs to the frequency function.

Frequencies

When transforming to the Frequency function format, you may determine for which frequencies the frequency function should be computed/estimated. These are determined by the popup-menu 'Frequency Spacing' and the edit box 'Number of Frequencies'. The frequencies are always in rad/s.

Choose linear or logarithmic spacing by the popup-menu, and enter the disired number of frequency values in the box Number of Frequencies. Then a frequency vector vector with this number of points and this spacing is formed. The frequency span, for a time domain data set is from 0 (excluded) to the Nyquist frequency. For frequency domain data it is between the smallest and largest frequencies in the data set.

The frequency resolution in this calculation is adjusted to the frequency spacing. This means that the default resolution in SPAFDR is used. (See HELP SPAFDR.)

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(file trf.htm)