Abstract
Although the acoustic variability of speech is often described as a problem for phonetic recognition, there is little research examining acoustic-phonetic variability over time. We measured naturally occurring acoustic variability in speech production at nine specific time points (three per day over three days) to examine daily change in production as well as change across days for citation-form vowels. Productions of seven different vowels (/EE/, /IH/, /AH/, /UH/, /AE/, /OO/, /EH/) were recorded at 9AM, 3PM and 9PM over the course of each testing day on three different days, every other day, over a span of five days. Results indicate significant systematic change in F1 and F0 values over the course of a day for each of the seven vowels recorded, whereas F2 and F3 remained stable. Despite this systematic change within a day, however, talkers did not show significant changes in F0, F1, F2, and F3 between days, demonstrating that speakers are capable of producing vowels with great reliability over days without any extrinsic feedback besides their own auditory monitoring. The data show that in spite of substantial day-to-day variability in the specific listening and speaking experiences of these participants and thus exposure to different acoustic tokens of speech, there is a high degree of internal precision and consistency for the production of citation form vowels.
Highlights
There is an enormous amount of acoustic to phonetic variability in the speech signal that arises from many sources
We demonstrate quite the opposite: citation form vowels on a whole show incredible stability and reliability over the course of several days, with systematic changes only occurring within days, albeit slightly
The results demonstrate that citation-form speech production of isolated vowels is extremely precise and reliable
Summary
There is an enormous amount of acoustic to phonetic variability in the speech signal that arises from many sources. Peterson and Barney [1] conducted one of the first studies documenting this acoustic variability, demonstrating large, systematic between-talker acoustic variability among men, women and children as well as within-in talker acoustic variability among different tokens of vowels. They found that across talkers the same acoustic pattern could denote different phonetic categories and further that for the same talker tokens of the same vowel could be acoustically distinct from each other even when the linguistic context is held the same. This latter finding by Peterson and Barney [1], that there is notable acoustic variability from token to token even within a talker, suggests that motor execution of articulation is not substantially regular.
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