A technique for examining the frequency content of a signal with a fine resolution over a relatively narrow band of frequencies. The technique basically takes a band of frequencies and translates them to a lower band of frequencies (demodulation) where the signals can be decimated to reduce the sample size. A standard DFT can then be used to analyze the data.

Note that the increased resolution of this technique requires a corresponding increase in the time record length. The sample rate is decreased by decimation, to reduce the number of samples in the time window, only after demodulation.