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Question
Why the Frequency Domain?
Solution Suppose we wish to do modal analysis on solid rocket motor during a test fire. Or we might be trying to detect the particular audible frequencies in a noisy test chamber. In each case, we are trying to detect a small periodic wave in the presence of large signals. In the picture below we see a time domain waveform which seems to be single sine wave.



The following image shows in the frequency domain that the same signal is composed of a large sine wave and significant other sine wave components (distortion components). When these components are separated in the frequency domain, the small components are easy to see because they are not masked by larger ones. The frequency domain’s usefulness is not restricted to electronics or mechanics. All fields of science and engineering have measurements like these where large signals mask others in the time domain. The frequency domain provides a useful tool in analyzing these small but important effects.