The Zoom-FFT is a process where an input signal is mixed down to baseband and then decimated, prior to passing it into a standard FFT. The advantage is for example that if you have a sample rate of 10 MHz and require at least 10Hz resolution over a small frequency band (say 1 KHz) then you do not need a 1 Mega point FFT, just decimate by a factor of 4096 and use a 256 point FFT which is obviously quicker. Advantages of the Zoom FFT are : Increased frequency domain resolution Reduced hardware cost and complexity Wider spectral range Applications of the Zoom FFT include : Ultrasonic blood flow analysis R.F. communications Mechanical stress analysis Doppler radar The following diagram shows the zoom process :