Preface: How It Is Said Rewrites What Was Said

Note

Please read this first. This book discusses how the physical features of a voice affect listeners’ judgements, using simplified models and programs. Unless a source is given, the numbers are illustrative and are not measurements of anyone. In research, the effects of acoustic features on listeners’ judgements are mostly small to moderate effects on average; they cannot guarantee the outcome of any one speech or negotiation, and they do not replace the quality and honesty of the content. This book is about helping true content to be heard and remembered, not about manipulating listeners with vocal technique, and it does not encourage anyone to use prosody to dress up claims that are untrue. For voice discomfort, persistent hoarseness or pain when speaking, consult an ear, nose and throat doctor or a speech and language therapist.

Two people read the same business proposal. One speaks at an even pace, pauses before the key figures and lets each sentence fall naturally at the end; the other speaks fast, ends every sentence on a rise and fills the gaps with “uh” and “you know”. The listeners hear exactly the same words, yet may judge the two speakers very differently: who is more credible, who is surer, whose project is more worth backing.

This book asks where that difference comes from, how large it is, and which popular claims about it have evidence and which do not.

What the book covers

The book discusses voice and persuasion on five levels:

Paralinguistic acoustics. How fundamental frequency, formant dispersion, harmonics-to-noise ratio and speech rate affect listeners’ judgements of a speaker; and what the much-repeated “7 %–38 %–55 %” rule actually says.
The information theory of prosody. Using Shannon surprisal and the uniform information density hypothesis to show why pausing and slowing down may help listeners take in key information, and what fillers such as “uh” really do.
Pitch contours. Generating and measuring sentence-final falls and rises with the Fujisaki model, and the limits of the claim that “rising means unsure”.
Interpersonal synchrony. Brain coupling between speaker and listener, heart-rate synchrony among listeners, and how to tell “a shared acoustic drive” from “resonance between people”.
Roughness and the microphone. Why the fast amplitude modulation in screams is so alarming; how the proximity effect, signal-to-noise ratio and reverberation change a recorded voice.

Chapter 7 reads this modern research beside the Record of Music’s “all sound arises from the human heart”, the arts of “probing and sounding out” in the Guiguzi, and the Analects’ “the gentleman has three aspects”. Chapter 8 offers a four-step acoustic checklist for use before speaking or recording, and a protocol for a pre-registered double-blind randomised controlled trial.

This book complements 5D Library volume 10 (5DL-B-010), on the biomechanics of voice production and attentional focus: that book is about how a voice is produced, this one about how it is heard.

Claims corrected on checking

Several popular claims needed correction once they were checked: “7 %–38 %–55 %” applies only to the situation in Mehrabian’s experiments, where a liking or disliking was conveyed by a single word and the word and the tone contradicted each other; it is not a general law of communication. Fillers are not simply harmful: research has found that they can help listeners remember the word that follows, although they may also make a speaker seem less sure. A final rise has many functions, and in one study of a single word a rise was judged more trustworthy; “rising means seeking approval” is a social interpretation, not a physiological fact. Heart-rate synchrony among listeners mainly reflects shared attention and a shared stimulus, and cannot simply be equated with “resonance” or “presence”. Each chapter says so where it arises, and the Editor’s Notes published with the book files collect these points.

How to read the boxes

As in other 5D Library books, different kinds of statement are marked separately.

Evidence

Evidence boxes report published findings, with sources.

Calculation

Calculation boxes give formulas and short Python programs. Every program runs as printed in a standard Python 3 installation using only the standard library; its actual output is shown beneath it. All the sounds in the book are synthesised by the programs; none is a recording of a real person.

Hypothesis · not established

Hypothesis boxes hold the author’s ideas, marked “not yet established”, with a statement of what result would show them wrong.

Source text

Source boxes quote classical texts, with the author’s plain-language reading.

Note

Note boxes give cautions and explain choices.

About this edition

This is version 1.0.0, the first complete edition: a preface and eight chapters, in Chinese and English. Corrections and missing references are welcome through the 5D Library website.

Disclosure

The author runs the voice-teaching websites vocal.guru and singingasia.com, the media-production website xmediaasia.com and the influencer-marketing agency website asiainfluencerx.com, and works in voice teaching, content production and live-streaming training; he therefore has a direct commercial interest in the subject of this book. The book promotes no course or service; the Chapter 8 trial is designed to be run and analysed by researchers independent of the author’s business; all the code and the study protocol are published openly for anyone to check.

Fan, Y. (2026). Acoustic Persuasion, Prosodic Information Theory and Interpersonal Physiological Synchrony: Pitch Contours, Pause Entropy and Listener Autonomic Coupling in Public Speaking and Leadership [声音说服力、韵律信息论与人际生理同步] (Version 1.0.0). 5D Library. https://doi.org/10.5281/zenodo.23753267 · Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0).