What is the amplitude of a DFT?

In a normal DFT, each harmonic amplitude is the result of N complex multiplies with N different complex exponentials – giving a total of N2 multiplies for all N harmonics. When N is a power of 2, many of these multiplies concern identical numerical multiplicands and many of the complex exponentials are zero or 1.

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What is a spectrogram used for?

A spectrogram is a visual way of representing the signal strength, or “loudness”, of a signal over time at various frequencies present in a particular waveform . Not only can one see whether there is more or less energy at, for example, 2 Hz vs 10 Hz, but one can also see how energy levels vary over time.

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