Additive synthesis parameters in a discrete-time implementation can be determined using the Fast Fourier Transform (FFT).
The analyzed time-domain signal is split into blocks or “frames”, each of which is processed using the FFT (referred to as the Short-Time Fourier Transform (STFT).
The STFT provides a means for joint time-frequency analysis.
As well, a time-domain signal can be resynthesized using the Inverse Fast Fourier Transform (IFFT). The resulting IFFT frames are “assembled” using overlap-add techniques.
With improvements in computer processing speed, it is now possible to perform IFFT resynthesis in real time.
FFT/IFFT synthesis lends itself well to sound transformations, such as time-stretching and pitch scaling.