Time Domain vs. Frequency Domain

General Instructions

This spectral simulation is an interactive Java applet. You can change parameters by clicking on the vertical arrow keys. The five control buttons at the lower right are used to start (triangle) and pause (square) the simulation, to skip forward or back one section at a time (double triangles), and to change speed (+ and -).

After the simulation is complete, the start button takes you back to the beginning of the simulation. You may experience a delay at this point.

The three-dimensional plot of frequency, amplitude and time that shows the relationship between the time and frequency domains. It does so by looking at the fundamental of a sine wave -- and up to three harmonics -- as they are formed by rotating vectors. It's another way to view the construction of a complex waveform.

An oscilloscope is a device that views a waveform's voltage vs. time. It is the most general-purpose tool we have to gain insight into how a circuit or signal is performing. This plot simulates an oscilloscopes view. Look at the diagram from the lower left. What you see is an oscilloscopes view of the waveform (amplitude vs. time), which is really the vector sum of all of the sinusoidal components vs. time.

A spectrum analyzer is another visual analysis device. The spectrum analyzer works in the frequency domain. It displays the amplitude of the individual frequency components vs. frequency. If you choose "4 harmonics" and look at the 4 waveforms from a vantage point at the lower right of the drawing, you essentially see what a spectrum analyzer would display (amplitude vs. frequency). Depending upon the type of spectrum analyzer chosen, the phase relationships of the frequency components may or may not be preserved. Looking from the lower left, you get an oscilloscope's view of the waveform (amplitude vs. time).