Investigating the Utility of Surprisal from Large Language Models for Speech Synthesis Prosody

This paper investigates the use of word surprisal, a measure of the predictability of a word in a given context, as a feature to aid speech synthesis prosody. We explore how word surprisal extracted from large language models (LLMs) correlates with word prominence, a signal-based measure of the salience of a word in a given discourse. We also examine how context length and LLM size affect the results, and how a speech synthesizer conditioned with surprisal values compares with a baseline system. To evaluate these factors, we conducted experiments using a large corpus of English text and LLMs of varying sizes. Our results show that word surprisal and word prominence are moderately correlated, suggesting that they capture related but distinct aspects of language use. We find that length of context and size of the LLM impact the correlations, but not in the direction anticipated, with longer contexts and larger LLMs generally underpredicting prominent words in a nearly linear manner. We demonstrate that, in line with these findings, a speech synthesizer conditioned with surprisal values provides a minimal improvement over the baseline with the results suggesting a limited effect of using surprisal values for eliciting appropriate prominence patterns.

The Power of Prosody and Prosody of Power: An Acoustic Analysis of Finnish Parliamentary Speech

Parliamentary recordings provide a rich source of data for studying how politicians use speech to convey their messages and influence their audience. This provides a unique context for studying how politicians use speech, especially prosody, to achieve their goals. Here we analyzed a corpus of parliamentary speeches in the Finnish parliament between the years 2008-2020 and highlight methodological considerations related to the robustness of signal based features with respect to varying recording conditions and corpus design. We also present results of long term changes pertaining to speakers' status with respect to their party being in government or in opposition. Looking at large scale averages of fundamental frequency - a robust prosodic feature - we found systematic changes in speech prosody with respect opposition status and the election term. Reflecting a different level of urgency, members of the parliament have higher f0 at the beginning of the term or when they are in opposition.