Life is difficult, simple ways usually don't work in real life.
------Prof C.C.Ko(NUS)
In signal processing, both time domain and frequency domain analysis are important. The frequency domain plot is usually called the spectrum of a signal. In theory, a signal's spectrum can be calculated by using Fourier transform which is in a form of integration from minus infinity to infinity in time domain.
However, this way only works theoretically. It can't be applied in real practices. The reason is very simple. It is not possible to get a infinite time range. For example, if we use the theoretical way to estimate a patient's heart signal spectrum. we can only calculate it after the patient dies. Because if he or she doesn't die, the signal doesn't end and we can't get the point "infinity". Obviously it is not practical.
The practical way is to get the signal in certain time range which is called window. Then the spectrum is estimated by the information within this window. The estimated spectrum may be different from the theoretical spectrum. This difference is called the windowing effect.
Things in real life are complicated. We usually can’t get the perfect solution. Practical approach is a necessary extend of theories.
However, this way only works theoretically. It can't be applied in real practices. The reason is very simple. It is not possible to get a infinite time range. For example, if we use the theoretical way to estimate a patient's heart signal spectrum. we can only calculate it after the patient dies. Because if he or she doesn't die, the signal doesn't end and we can't get the point "infinity". Obviously it is not practical.
The practical way is to get the signal in certain time range which is called window. Then the spectrum is estimated by the information within this window. The estimated spectrum may be different from the theoretical spectrum. This difference is called the windowing effect.
Things in real life are complicated. We usually can’t get the perfect solution. Practical approach is a necessary extend of theories.
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