Acoustic Cues and Formants

Acoustic cues are the measurable properties of the speech signal that distinguish speech sounds, with vowel formants and the timing of voicing among the most studied.

Definition

The measurable acoustic properties—including formants, formant transitions, spectral shape, and voice onset time—that listeners use to identify speech sounds.

Scope

This topic surveys the principal acoustic correlates of speech sounds: the formant frequencies (especially the first and second formants) that characterize vowels, formant transitions that cue place of articulation in consonants, the spectral shape of fricatives, and temporal cues such as voice onset time that distinguish voiced from voiceless stops. It treats how multiple cues combine and trade off, and how they are measured from spectrograms and acoustic analysis. The treatment is descriptive and grounded in measurement.

Core questions

• What are formants and how do they distinguish vowels?
• How do formant transitions cue consonant place of articulation?
• What temporal cues distinguish voiced from voiceless stops?
• How do multiple acoustic cues combine and trade off in perception?

Key theories

Voice onset time as a voicing cue

Lisker and Abramson's cross-language demonstration that the timing between a stop release and the onset of voicing systematically distinguishes voicing categories, providing a robust temporal acoustic cue.

History

Systematic identification of acoustic cues followed the development of the spectrograph and the speech-synthesis experiments at Haskins Laboratories in the 1950s, which isolated the cues responsible for perceiving particular sounds. Lisker and Abramson's 1964 study established voice onset time as a key dimension across languages.

Debates

Cue weighting and trading relations

Researchers debate how listeners weight and combine multiple, partly redundant acoustic cues, and how cue trading relations vary across listeners, languages, and contexts.

Key figures

• Kenneth Stevens
• Leigh Lisker
• Arthur Abramson
• Keith Johnson

Seminal works

• stevens1998
• lisker1964

Frequently asked questions

What is a formant?

A formant is a concentration of acoustic energy at a particular frequency, corresponding to a resonance of the vocal tract. The pattern of the lowest formants is the main acoustic property that distinguishes one vowel from another.

What is voice onset time?

Voice onset time is the interval between the release of a stop consonant and the start of vocal-fold vibration. Differences in this timing distinguish sounds such as the [p] and [b] of many languages.