Phase Vocoder

At the heart of the phase vocoder is the STFT (short-time Fourier transform), typically coded using fast Fourier transforms. The STFT converts a time domain representation of sound into a time-frequency representation (the "analysis" phase), allowing modifications to the amplitudes or phases of specific frequency components of the sound, before resynthesis of the frequency domain representation into the time domain by the inverse STFT. The time scale of the resynthesis does not have to be the same as the time scale of the analysis, allowing for high-quality time-scale modification of the original sound file.