Phase-Scaling Effects Using Giant FFT

Välimäki V, Salmi R, Bilbao S, Schlecht SJ, Zicarelli D, Clayton JK. Phase-Scaling Effects Using Giant FFT. J Audio Eng Soc. 2026;74(7/8):497-512. doi:10.17743/jaes.2026.0280

@article{Valimaki2026_23383,
  author = {Välimäki, Vesa and Salmi, Roope and Bilbao, Stefan and Schlecht, Sebastian J. and Zicarelli, David and Clayton, Joshua Kit},
  title = {{Phase-Scaling Effects Using Giant FFT}},
  journal = {Journal of the Audio Engineering Society},
  volume = {74},
  number = {7/8},
  pages = {497--512},
  year = {2026},
  month = jul,
  publisher = {Audio Engineering Society},
  doi = {10.17743/jaes.2026.0280},
  url = {https://doi.org/10.17743/jaes.2026.0280}
}

TY  - JOUR
TI  - Phase-Scaling Effects Using Giant FFT
AU  - Välimäki, Vesa
AU  - Salmi, Roope
AU  - Bilbao, Stefan
AU  - Schlecht, Sebastian J.
AU  - Zicarelli, David
AU  - Clayton, Joshua Kit
T2  - Journal of the Audio Engineering Society
J2  - J. Audio Eng. Soc.
VL  - 74
IS  - 7/8
SP  - 497
EP  - 512
PY  - 2026
DA  - 2026/07/08
DO  - 10.17743/jaes.2026.0280
UR  - https://doi.org/10.17743/jaes.2026.0280
PB  - Audio Engineering Society
LA  - en
AB  - The fast Fourier transform (FFT) enables processing of extremely long signals quickly. This has opened up new possibilities in audio processing, generally called giant-FFT methods. This paper presents audio modification techniques using frequency-domain phase scaling. In zero-phase conversion, the signal’s phase is reset to zero, and the inverse FFT is performed. The result is a modified sound that retains the original frequency content but has a different temporal structure. Zero-phase sound is palindromic and sounds the same when played forward or backward. It makes speech sounds unintelligible, thereby serving as a method for synthesizing babble noise. A variation of the zero-phase method can produce a corresponding stereo signal. Scaling of the phase with a positive constant also leads to exciting modifications. Phase-scaling with an integer produces a time-stretching effect on wideband sounds having their energy concentrated tightly in time, whereas a factor slightly smaller than 1 leads to whisperization. The basic giant-FFT phase-scaling methods are suitable for offline processing only, but a real-time version is proposed, which processes the input signal in frames and uses overlap-add resynthesis, producing texture-like sounds with the original overall timbre. Phase-scaling effects can be applied in sound design for music, games, and film production.
ER  -