Phase-Scaling Effects Using Giant FFT

Välimäki V, Salmi R, Bilbao S, Schlecht S, Zicarelli D, Clayton JK (2026)

Publication Type: Journal article

Publication year: 2026

Journal

Journal of the Audio Engineering Society Audio Engineering Society

Book Volume: 74

Pages Range: 497-512

Journal Issue: 7-8

DOI: 10.17743/jaes.2026.0280

Abstract

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 zerophase 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 overlapadd 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.

Authors with CRIS profile

Sebastian Schlecht Lehrstuhl für Audiocodierung (AudioLabs)

Involved external institutions

Aalto University Espoo FI Finland (FI) Sorbonne Université FR France (FR) Cycling ’74 US United States (USA) (US)

How to cite

APA:

Välimäki, V., Salmi, R., Bilbao, S., Schlecht, S., Zicarelli, D., & Clayton, J.K. (2026). Phase-Scaling Effects Using Giant FFT. Journal of the Audio Engineering Society, 74(7-8), 497-512. https://doi.org/10.17743/jaes.2026.0280

MLA:

Välimäki, Vesa, et al. "Phase-Scaling Effects Using Giant FFT." Journal of the Audio Engineering Society 74.7-8 (2026): 497-512.

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