** INTERACTIVE SIGNAL DEMO **

** **

** You are seeing discrete samples of a periodic waveform (above) and the **

** absolute value of its discrete Fourier transform (DFT), obtained using **

** a fast Fourier transform ( FFT ) algorithm (below). **

** In the lower plot, frequencies from 0 to 100 Hertz are displayed. **

** The DFT at negative frequencies is a mirror image of the DFT at positive **

** frequencies. The sampling rate is 200 Hertz which means the "Nyquist **

** frequency" is 100 Hertz. The DFT at frequencies above the Nyquist **

** frequency is the same as the DFT at lower (negative) frequencies. **

** **

** **

** Click and drag a point on the waveform displayed in the upper plot **

** to move that point to a new location, thereby setting a new fundamental **

** frequency and amplitude. **

** **

** **

** Use the pop-up menu in the bottom left of the figure window to change **

** the shape of the waveform. The possible wave shapes are sinusoidal, **

** square, and sawtooth. **

** **

** **

** The fundamental frequency of the waveform is given in the editable **

** text box in the middle of the bottom row. You can change this **

** fundamental frequency by clicking in the text box and editing **

** the number there, and then pressing RETURN . The fundamental is also **

** changed when the waveform is altered by clicking and dragging. **

** **

** **

** If the Signal Processing Toolbox is installed, then the menu entitled **

** "Window" allows you to select a window function. This window is **

** multiplied by the time waveform prior to taking the DFT. To display **

** the current window function in another figure window, select the menu **

** item "Show window...". **

** **