The time waveform is a plot of time vs. amplitude, and is referred to as the time domain. The time domain signal can be converted into a frequency domain representation, which is in fact the spectrum. The spectrum is a plot of frequency vs. amplitude. The FFT for the time waveform from Figure 6 is plotted in Figure7. We can clearly read from this plot that the frequency content of the signal is 10 Hz, and that its amplitude at 10 Hz is 5 mm.
What now, if our time waveform has more than one frequency present? Let’s take a look at another example. Consider the waveforms in Figure 8. In the top graph we have our 10 Hz waveform, called S1. The second waveform is a 25 Hz waveform with amplitude 2 mm, which we can call S2. The third waveform, plotted at the bottom, is S1+S2, which yields a much more complex waveform.
Let us examine the FFT for S1+S2, depicted in Figure 9. We can clearly observe two peaks in spectrum, namely a 5 mm peak at 10 Hz, and a 2 mm peak at 25 Hz. Thus, by only looking at the spectrum, we can characterize our S1+S2 waveform much better than by examining the waveform from Figure 8. The frequency spectrum is hence much easier to interpret and gives us information that is often impossible to observe by just looking at the time waveform.
The time waveform is a plot of time vs. amplitude, and is referred to as the time domain. The time domain signal can be converted into a frequency domain representation, which is in fact the spectrum. The spectrum is a plot of frequency vs. amplitude. The FFT for the time waveform from Figure 6 is plotted in Figure7. We can clearly read from this plot that the frequency content of the signal is 10 Hz, and that its amplitude at 10 Hz is 5 mm. What now, if our time waveform has more than one frequency present? Let’s take a look at another example. Consider the waveforms in Figure 8. In the top graph we have our 10 Hz waveform, called S1. The second waveform is a 25 Hz waveform with amplitude 2 mm, which we can call S2. The third waveform, plotted at the bottom, is S1+S2, which yields a much more complex waveform. Let us examine the FFT for S1+S2, depicted in Figure 9. We can clearly observe two peaks in spectrum, namely a 5 mm peak at 10 Hz, and a 2 mm peak at 25 Hz. Thus, by only looking at the spectrum, we can characterize our S1+S2 waveform much better than by examining the waveform from Figure 8. The frequency spectrum is hence much easier to interpret and gives us information that is often impossible to observe by just looking at the time waveform.
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