4.1 Java1482-spectrum analysis using java, sampling frequency,  (Page 8/24)

That's it for dsp029

That's about it for the program named Dsp029 . If you understand this program, you are well ahead of the game. The overall structurefor the programs named Dsp028 and Dsp030 are very similar to the structure for Dsp029 . The big difference is the manner in which they populate the array objects with the data that is to beplotted. Instead of simply plotting sinusoids, they perform spectral analysis on sinusoids and provide the results of the spectral analysis to be plotted.

Using the interface named graphintfc01

As you learned earlier, this is a very simple interface. However, because the class named Dsp029 implements the interface, the interface definition file must be in the same directory as the source file for Dsp029 in order to successfully compile Dsp029 . Therefore, I have provided a complete listing of GraphIntfc01 in Listing 17 near the end of the module.

The program named Graph06

A complete listing of the program named Graph06 is provided in Listing 18 near the end of the module. This is simply a newer version of graphics display programs that I explained in the earlier module titled Plotting Engineering and Scientific Data using Java . Therefore, I won't repeat that explanation here. The comments at the beginning and spreadthroughout the program provide considerable information about it.

Operational aspects of graph06

However, an explanation of the operational aspects of the program will be useful here. You can use this program to display the output produced by Dsp029 by entering the following at the command line prompt:

As you saw in Figure 3 and other previous figures, this program provides the following text fields for user input, along with a button labeled Graph :

• xMin = minimum x-axis value
• xMax = maximum x-axis value
• yMin = minimum y-axis value
• yMax = maximum y-axis value
• xTicInt = tic interval on x-axis
• yTicInt = tic interval on y-axis
• xCalcInc = calculation interval

These text fields make it possible for you to adjust the plotting parameters and to re-plot the graphs as many times as needed.

You can modify any of these parameters and then click the Graph button to cause the five functions to be re-plotted according to the newplotting parameters.

Spectral Analysis using a DFT Algorithm

Now that you have a good idea where we are heading, it's time to start doing some spectral analysis.

Let's begin by looking at some output obtained by performing a spectral analysis on the same five sinusoids shown in Figure 3 . The parameters used to perform this spectral analysis are shown in Figure 8 . (I will explain each of these parameters as we go along.)

Although more parameters are required to perform spectral analysis than are required to simply generate and plot the sinusoids, the number of sinusoids, thefrequencies of the sinusoids, and the amplitudes of the sinusoids in Figure 8 are the same as in Figure 2 .