Daniel Friedrichs

Vowel recognition at fundamental frequencies up to 1 kHz reveals point vowels as acoustic landmarks

The phonological function of vowels can be maintained at fundamental frequencies (fo) up to 880 Hz [Friedrichs, Maurer, and Dellwo (2015). J. Acoust. Soc. Am. 138, EL36-EL42]. Here, the influence of talker variability and multiple response options on vowel recognition at high fos is assessed. The stimuli (n = 264) consisted of eight isolated vowels (/i y e ø ε a o u/) produced by three female native German talkers at 11 fos within a range of 220-1046 Hz. In a closed-set identification task, 21 listeners were presented excised 700-ms vowel nuclei with quasi-flat fo contours and resonance trajectories. The results show that listeners can identify the point vowels /i a u/ at fos up to almost 1 kHz, with a significant decrease for the vowels /y ε/ and a drop to chance level for the vowels /e ø o/ toward the upper fos. Auditory excitation patterns reveal highly differentiable representations for /i a u/ that can be used as landmarks for vowel category perception at high fos. These results suggest that theories of vowel perception based on overall spectral shape will provide a fuller account of vowel perception than those based solely on formant frequency patterns.

Mapping vowel categories at high fundamental frequencies using multidimensional scaling of cochlea-scaled spectra

Recent studies have shown that accurate vowel category perception can be maintained at fundamental frequencies (f o) up to at least 880 Hz. In such cases, the typical first formant frequency (F 1) of most vowels is exceeded by f o and the vocal tract transfer function is to a high degree undersampled. It seems therefore unlikely that common formant patterns are the main acoustic features used by listeners to recognize vowels at high f os. Here, we present results from multidimensional scaling (MDS) analyses calculated by averaging cochlea-scaled spectra across multiple steady-state vowels (N = 324; all 250 ms) produced by a female native German speaker at nine f os within a range of 220-880 Hz. All vowels (/i, y, e, o, ɛ, a, o, u/) were recognized accurately by listeners (N = 20) in a previous study [Friedrichs et al., The phonological function of vowels is maintained at fundamental frequencies up to 880 Hz, J. Acoust. Soc. Am. 138, EL36-EL42 (2015)]. MDS reveals that with increasing f o, the vowel height...

Gender and age differences in vowel-related formant patterns: What happens if men, women, and children produce vowels on different and on similar F0?

There is a broad consensus in the literature that vowel-specific formant patterns differ as a function of gender (men/women) or age (adults/children) due to different average vocal tract sizes. Although an additional influence of fundamental frequency F0 is discussed in corresponding normalization approaches, formant patterns relating to sounds of adults and children that exhibit the same F0, to sounds of adults with higher F0 than sounds of children, and to sounds of men with higher F0 than sounds of women are barely compared. Investigating vowels of men, women, and children producing sounds with varying F0, we observed (1) a possible decrease or even a disappearance of the expected speaker-group differences in the formant frequencies 1.5 kHz was found. These observations call for a further examination of the role of F0 when interpreting speaker-group related differences in formant patterns.

Vowel discrimination at high fundamental frequencies in real speech

Previous research showed that, in singing, vowel qualities of isolated vowel sounds can be discriminated up to a fundamental frequency (F0) of about 500 Hz. However, indications are reported in literature for vowel discrimination on F0 > 500 Hz for singing (raised larynx condition, CVC context) as well as for speech-like sounds. In this study, we tested vowel discrimination at a high F0 in speech using minimal pairs build from eight long German vowels. Words were produced in speech mode at F0 of about 650 Hz by two female speakers. For all samples except the words including /a/ and /ɛ/, F0 exceeded F1 values as given in vowel statistics for Standard German. In a listening test, stimuli were played back in random order to 14 listeners (7f, 7m) for identification. The results showed that vowel discrimination can be preserved at such high fundamental frequencies. This could mean that, for our speakers and the high fundamental frequency examined, (1) source-filter-characteristics were effective up to 650 Hz, or (2) transitions played a crucial role, or (3) other spectral characteristics than formants have to be taken into account in order to explain these results.