Speech earthquakes: scaling and universality in human voice

TL;DR

This study reveals universal power-law statistics and criticality in human speech production, suggesting that speech operates near a critical point and is governed by physiological mechanisms rather than cognitive processes.

Contribution

It uncovers universal scaling laws and critical phenomena in speech, contrasting with chaos-based models and providing insights for future speech synthesis improvements.

Findings

Speech energy release follows a power-law distribution.

Interevent times in speech are power-law distributed and scale-invariant.

Speech generation operates near a critical point, independent of language or speaker.

Abstract

Speech is a distinctive complex feature of human capabilities. In order to understand the physics underlying speech production, in this work we empirically analyse the statistics of large human speech datasets ranging several languages. We first show that during speech the energy is unevenly released and power-law distributed, reporting a universal robust Gutenberg-Richter-like law in speech. We further show that such earthquakes in speech show temporal correlations, as the interevent statistics are again power-law distributed. Since this feature takes place in the intra-phoneme range, we conjecture that the responsible for this complex phenomenon is not cognitive, but it resides on the physiological speech production mechanism. Moreover, we show that these waiting time distributions are scale invariant under a renormalisation group transformation, suggesting that the process of speech generation is indeed operating close to a critical point. These results are put in contrast with current paradigms in speech processing, which point towards low dimensional deterministic chaos as the origin of nonlinear traits in speech fluctuations. As these latter fluctuations are indeed the aspects that humanize synthetic speech, these findings may have an impact in future speech synthesis technologies. Results are robust and independent of the communication language or the number of speakers, pointing towards an universal pattern and yet another hint of complexity in human speech.