  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.
