FFT Implementation of the Phase Vocoder

In the 1970s, the phase vocoder was reimplemented using the FFT for increased computational efficiency [212]. The FFT window (analysis lowpass filter) was also improved to yield exact reconstruction of the original signal when synthesizing without modifications. Shortly thereafter, the FFT-based phase-vocoder became the basis for additive synthesis in computer music [187,62]. A generic diagram of phase-vocoder (or vocoder) processing is given in Fig.G.4. Since then, numerous variations and improvements of the phase vocoder have appeared, e.g., [99,215,140,138,143,142,139]. A summary of vocoder research from the 1930s to the 60s appears in a review article by Manfred Schroeder [245]. The phase vocoder and its descendants (STFT modification/resynthesis, sinusoidal modeling) have been used for many audio applications, such as speech coding and transmission, data compression, noise reduction, reverberation suppression, cross-synthesis (§10.2), time scale modification (§10.5), frequency shifting, and much more.