Real FFT and Complex FFT

Most real-world signals are real-valued. Therefore, you can use the real fast Fourier transform (FFT) for most applications. You also can use the complex FFT by setting the imaginary part of the signal to zero. An example of an application where you use complex FFT is when the signal consists of both a real and an imaginary component. A signal consisting of a real and an imaginary component occurs frequently in the field of telecommunications, where you modulate a waveform by a complex exponential. The process of modulation by a complex exponential results in a complex signal, as shown in the following figure.