DFT / FFT Software for the Macintosh

Introduction

DFT_FFT is a Macintosh utility that reads either real or complex series and computes either the DFT or FFT. It is designed as a data exploratory/investigation tool rather than a total analysis package.

Saving At any stage the current series can be saved to a text file in one of the following formats, chosen from the "Save" in the "File" menu. In all cases the file will contain two columns, the interpretation of the index is left up to the operator.

Graphing

The time series is displayed as follows, note that in this example the file contained two columns and was opened as real/imaginary even though the imaginary term is 0. Note also that no assumptions are made as to the meaning of the index, it could be a time series, frequency, spatial, etc.

By default the real and imaginary data will be plotted, various other graphs can be chosen from the "Graph Options" in the "Analysis" menu. The graphing are minimal, for more professional and publication graphs the operator is expected to save the data and create graphs using their favorite graphing package.

For example the magnitude/phase graph is shown below. The form of this shouldn't be a surprise since the input series above looks like a sinusoid plus noise, there aren't an integer number of cycles in the series so there is spectral leakage. The first N/2 samples are the positive frequencies from DC to Nyquist, the second N/2-1 samples are the negative frequencies.

Or the power/phase

Or the polar plot

At any time information on the series in either domain can be obtained from the "Get Info" in the "Analysis" menu.