| ■ | The FFT tool uses a fixed window size of 30 seconds. |
| ■ | This dialog box lets the whole record be scanned on the selected channel for FFT. |
The figure presents a Graphical User Interface (GUI) provided in Polysmith for setting up the FFT analysis. An important point is that the DFT operates on only a single channel of data. Additional channels can also be transformed, but I do not know of any quantitative techniques that combine multiple channels other than those used for brain mapping. The GUI enables the user to select the signal channel for analysis and the DFT is then calculated for each epoch in the PSG. The purpose of the “Advanced” button is explained next as is the reason for restricting the FFT analysis to thirty second epochs. “FFT Multi-Trend” button is used to display the results of FFT analysis as a trend plot (shown in page 9).